One of the most important clinical problems in cattle is lameness. Lameness can be caused by several factors, including infections of soft tissue in the foot (e.g., interdigital fat pad) and by structural and bone malformations. Most clinical work on ruminant limbs involves the distal limb (carpus and below). You should focus most of your attention on the study of forelimb structures from the elbow distally. Some of the most common conditions causing lameness include: Consult a textbook on bovine medicine to learn more about these conditions (a list of clinical and anatomical books is provided in Appendix C). You will learn more about these conditions in your clinical years. Goal: Identify the major bones of the thoracic limb and their features. Compare with bones of the thoracic limb of the horse and other small animals (e.g., dog). Use the bovine skeleton and the figures provided here to study the bones of the thoracic limb (Figure 5.1). The bones of the goat and sheep thoracic limb are like those of the bovine. The scapula is a flat, roughly triangular bone of the shoulder region. It is very similar to that of the horse except for one feature. The acromion is present in the scapula of ruminants but is absent in the scapula of the horse and pig. The lateral surface of the scapula has a large infraspinous fossa and relatively small supraspinous fossa (Figure 5.2). The “shoulder blade” is a common name for the scapula that you may hear in the clinic. The scapula has three borders (dorsal, cranial, and caudal), three angles (cranial, caudal, and ventral), and two surfaces (medial and lateral). The lateral surface has the spine of the scapula that separates the supra‐ and infraspinous fossae. A prominence in the middle of the spine is the tuber of the spine of the scapula: the tuber spinae scapulae. Figure 5.1 Bones of the bovine thoracic limb: left lateral view. Forelimb regions are the shoulder (scapula), brachium (humerus), antebrachium (radius and ulna), and manus (carpus, metacarpals, and digits). Figure 5.2 The left bovine scapula: medial and lateral views * Supraglenoid tubercle. The depression on the distal end (ventral angle) of the scapula is the glenoid cavity. The glenoid cavity articulates with the head of the humerus to form the shoulder joint. Use Figure 5.2 to study the main features of the scapula. On the medial surface of the scapula, identify the subscapular fossa and the serrated face. The supra‐ and infraspinous fossae are for attachment of the supra‐ and infraspinatus muscles, respectively. The subscapular fossa is for attachment of the subscapularis muscle, and the serrated face is for attachment of the serratus ventralis muscle. In the live animal or fresh specimen, the dorsal border of the scapula has a large scapular cartilage that extends its length dorsally. The humerus forms the bone of the arm or brachium. It is a very strong and robust bone in both cattle and horses. There are minor differences in the shape of the humerus between small and large ruminants that will not be discussed. In the proximal part of the humerus, note that the greater tubercle (point of the shoulder) is well‐developed and deviates toward the medial side (Figure 5.3). It is larger than the lesser tubercle located on the medial side. The greater tubercle is located at a higher level than the head of the humerus (see Box 5.1). The round head of the humerus articulates with the glenoid cavity to form the shoulder joint. Both the greater and lesser tubercles are divided into cranial and caudal parts. In the horse, the greater and lesser tubercles are mostly equal in size. In addition, the horse has an intermediate tubercle. No intermediate tubercle is present in ruminants. The deltoid tuberosity on the lateral surface of the humerus is well developed in both the cow and horse. It is the site for attachment of the deltoideus muscle. Use Figure 5.3 to study the major bony prominences on the proximal and distal parts of the humerus. On the proximal humerus, identify the greater and lesser tubercles and intertubercular groove. The tendon of biceps brachii muscle passes in this groove. Identify the brachialis groove, the attachment site for the brachialis muscle. The humeral crest forms the cranial border of this groove. The body (shaft) of the humerus is the part between the proximal head and distal humeral condyle. On the distal humerus, identify the palpable medial and lateral epicondyles. The radial fossa is the shallow depression on the cranial surface of the humeral condyle. The relatively deep depression on the opposite caudal side of the humeral condyle is the olecranon fossa. The condyle of the humerus articulates distally with the radius and ulna to form the elbow joint. Figure 5.3 Left humerus of the ox: cranial, caudal, and lateral views. The radius and ulna are the bones of the antebrachium or forearm. Note that the ulna is complete in ruminants compared with that of the horse. The ulna in the bovine is fused to the radius except for proximal and distal interosseous spaces (Figure 5.4). In the horse, the ulna ends in the middle of the antebrachium. On the proximal ulna, and with the help of Figure 5.4, identify the olecranon tuber or (tuberosity), the palpable point of the elbow in the live animal, the trochlear notch, and the anconeal process. The olecranon tuberosity and anconeal process form the olecranon. The olecranon tuberosity is the attachment site for the extensor muscles of the elbow (e.g., triceps brachii and tensor fasciae antebrachii). See Box 5.2 for clinical application. The distal extremity of the ulna is called the lateral styloid process or styloid process of the ulna. In the horse, the styloid process of the ulna is developmentally fused to the radius. The radius is shorter and thicker than the ulna. Near the proximal extremity (head), identify the radial tuberosity on the medial side. The head of the radius and the trochlear notch of the ulna articulate with the humeral condyle to form the elbow joint. Figure 5.4 Left bovine radius and ulna: lateral, cranial, and caudal views. The distal medial end of the radius is the styloid process of the radius (Figure 5.4). The distal articular ends of the radius (trochlea) and ulna articulate with the proximal row of carpal bones to form the radiocarpal joint. The bones of the carpus, metacarpus, and phalanges are known as the manus. At the end of this unit, watch Video 21. As in the horse, the carpus in ruminants is composed of two rows (Figure 5.5a). The proximal row is like that of the horse and contains four bones. From lateral to medial, these are the accessory carpal, ulnar, intermediate, and radial carpal bones (Figure 5.5a). The accessory carpal is a palpable landmark on the lateral surface of the carpus. It provides an attachment point for the ulnaris lateralis and flexor carpi ulnaris muscles. Figure 5.5 (a) The left bovine carpus and proximal metacarpal region: dorsal and palmar views. The carpus has two rows. The proximal row contains four carpal bones: accessory carpal (AC), ulnar (U), intermediate (I), and radial (R), from lateral (L) to medial (M). On the dorsal view, the AC bone is obscured but can be seen on the palmar view palmar to the ulnar carpal bone. The distal row contains two bones, the fourth carpal and fused second and third carpal bones. The distal row articulates with fused metacarpals III and IV (large metacarpal bone). Rudimentary metacarpal V is shown in (b). (b) Lateral (left) and laterocaudal (right) views of bovine left carpus showing metacarpal V bone. 1, radiocarpal joint; 2, midcarpal joint; 3, carpometacarpal joint. The distal row is composed of two bones in ruminants. From lateral to medial, these are the fourth carpal and fused second and third carpal bones (Figure 5.5a). Carpal one is not present. The horse has three or four bones in the distal row including the fourth, third, second, and first carpal bones from lateral to medial, respectively. The first carpal bone in the horse may be absent, as in ruminants. Articulation between the proximal and distal rows of carpal bones forms the midcarpal joint. The articulation between the distal row of carpal bones and the large metacarpal bone (fused III and IV metacarpals) forms the carpometacarpal joint. Metacarpals 3, 4, and 5 (Mc III, Mc IV, and Mc V) are present in ruminants. Mc III and Mc IV are fused forming a single large metacarpal bone (Figures 5.5 and 5.6). Identify the metacarpal tuberosity on the proximal dorsomedial surface of the large metacarpal bone. This is the attachment site for the tendon of the extensor carpi radialis muscle. In the horse, only the Mc III (cannon bone) is present. Because of the presence of two weight‐bearing digits in ruminants, the distal end of the large metacarpal bone has two parts with an articulating trochlea at each end. The space formed by this separation is the intertrochlear notch. Each trochlea articulates with the proximal phalanx (P1) of the corresponding digit. The term cannon bone is a common name used for the third metacarpal (Mc III) bone in horses but also for the large metacarpal or fused Mc III and Mc IV bone in ruminants. Figure 5.6 Bovine left manus (carpus, metacarpals, and digits): dorsal view. The image on the left shows the articulation of the large metacarpal bone with the carpus proximally, and digits III and IV distally. The image on the right shows an isolated bovine large metacarpal bone. Each digit has a proximal (P1), middle (P2), and distal phalanx (P3). In ruminants, a small metacarpal 5 (Mc V) is present as a rudimentary bone on the proximolateral aspect of fused Mc III and Mc IV (Figure 5.5b). You should not confuse Mc V with a fracture or bone growth when examining an X‐ray of ruminant carpal–metacarpal regions. The axial line of fusion of Mc III and Mc IV forms the dorsal and palmar axial longitudinal grooves (Figure 5.6). In the live animal, blood vessels occupy the dorsal and palmar metacarpal longitudinal grooves. The dorsal longitudinal groove is more distinct than the palmar groove. Note the proximal and distal metacarpal canals (openings) at the proximal and distal ends of the longitudinal grooves (Figure 5.6). These canals allow for the passage of blood vessels between the dorsal and palmar sides of the large metacarpal bone. See Box 5.3 for the clinical relevance of the axial dorsal and palmar longitudinal grooves. Limbs of domestic ruminants have two digits. The medial digit (digit III) and lateral digit (digit IV) are weight‐bearing (Figure 5.6). The medial and lateral dewclaws form digit II and digit V, respectively. They are non‐weight‐bearing in cattle and may not have any bony skeleton. Skeletal elements of these digits are present in some ruminants. The weight‐bearing third and fourth digits have three phalanges each. From proximal to distal, these are proximal (P1), middle (P2), and distal (P3) phalanges (Figure 5.6). Each phalanx is divided into base, body, and head, from proximal to distal. The P1 and P2 are similar in shape but the length of P1 is twice as long as P2. The shape of P3 (coffin bone) is different from P1 and P2 (Figure 5.7). Identify the extensor process on the proximodorsal surface of P3. This is the site for attachment of the axial extensor tendons from the common digital extensor muscle. A similar arrangement occurs with the axial extensor tendons of the long digital extensor tendons in the hind limb. The common name for the distal phalanx (P3) is the coffin bone because it is embedded inside the hoof capsule, analogous to a coffin. Each digit has two proximal sesamoid bones (at the palmar surface of the fetlock joint) and a single distal sesamoid bone (at the palmar surface of the coffin joint). Overall, a total of four proximal sesamoid bones and two distal sesamoid bones are present in the two weight‐bearing digits of each limb (Figure 5.7). The navicular bone (analogous to a boat) is a common name for the distal sesamoid bone. Figure 5.7 The left bovine digits: (a) palmar and (b) lateral views. In the live animal, digit IV (lateral) and digit III (medial) are interconnected by proximal and distal interdigital ligaments. The nomenclature and general shape of the bones in the single digit of the horse is generally like a single digit (III or IV) in ruminants. Bones of the hind limb digits are like those of the forelimb. The articulation between fused Mc III and Mc IV and P1 on each digit forms the metacarpophalangeal joint (MCP) or the fetlock joint. Distal to the fetlock joint is the proximal interphalangeal joint (PIP) or pastern joint formed by the articulation of P1 with P2. More distally, articulation of P2 and P3 forms the distal interphalangeal (DIP) or the coffin joint. See Box 5.4 for clinical application. Goal: Identify the extrinsic and intrinsic muscles of the thoracic limb and know the general area of origin and insertion for each muscle. Emphasis will be placed on the musculoskeletal structures of the distal limb. Use a goat or cow thoracic limb skeleton to help you visualize the location of each muscle by identifying points of origin and insertion. Use a bovine or caprine limb to dissect muscles of the thoracic limb depending on what is available to you (there are no differences between the two). In this guide, the extrinsic muscles of the thoracic limb, which attach the limb to the axial skeleton, are dissected on a goat cadaver while the intrinsic muscles (attached to appendicular bones of the thoracic limb) are dissected on both goat and cow limbs. Use the text description below and any prosections prepared by your instructor to help you identify muscles and tendons. Follow the dissection plan in Appendix A to remove goat forelimbs. Alternatively, your instructor may provide you with isolated bovine or caprine limbs. It will be convenient to study the cutaneous and extrinsic muscles on a goat cadaver with the limbs attached (Figure 5.8). Figure 5.8 The cutaneous trunci and cutaneous omobrachialis muscles in the goat: left lateral view. The dotted line denotes the location of the clavicular intersection. Use a new scalpel blade to carefully skin the entire limb. Clean the fat and connective tissue off the regions of the limb and identify the muscles. Ask your instructor if you should preserve the blood vessels and nerves. We recommend that you use one limb (left) for dissection of muscles and a second limb (right) for dissection of blood vessels and nerves, but you can always have a mixture of both. Pay attention to the carpal fascia (carpal extensor retinaculum) and deep antebrachial fascia when skinning the limb. When dissecting the blood vessels and nerves of the forelimb, preserve the superficial vessels (dorsal common digital vein III, cephalic, and accessory cephalic veins) and nerves (branches of the superficial branch of the radial nerve) on the antebrachium and the dorsal surface of the large metacarpal bone. If you started your work with the whole cadaver and opted to preserve the cutaneous muscles, identify the cutaneus omobrachialis muscle on the lateral surface of the shoulder and caudal scapula (Figure 5.8). Identify the cutaneus trunci muscle located further caudally from the cutaneus omobrachialis (Figure 5.8). The cutaneus trunci does not cover the dorsal part of the flank region. It is thicker in two places: the area cranial to the stifle forming the fold of the flank, and close to the axilla. In small animals (dogs and cats), the cutaneous trunci reflex (twitching of the muscle upon pinching the skin) is used for localization of thoracolumbar spinal cord injuries. We will focus on the anatomy of the distal limb, but we will also attempt to give some information on the proximal muscles. Ask your instructor which muscles you need to identify. Your laboratory identification (ID) list for the forelimb (combined with the lab ID list for the hind limb in Chapter 6) has a few of the extrinsic muscles listed. However, all the distal intrinsic muscles (from the elbow and below) warrant your attention and are part of your ID list. Goal: Identify the major extrinsic muscles of the thoracic limb. Make sure you identify the brachiocephalicus (an extrinsic muscle of the thoracic limb) and sternocephalicus (sternomandibularis and sternomastoideus) muscles that form the dorsal and ventral boundaries for the external jugular groove, respectively. The muscles of the thoracic limb are divided into two groups: extrinsic and intrinsic muscles. Extrinsic muscles attach the limb to the axial skeleton. The axial skeleton comprises the skull, vertebrae, ribs, and the sternum. The extrinsic muscles of the forelimb include nine muscles (see the following list). Although the sternocephalicus muscle (specifically, the sternomandibularis part) forms the ventral boundary for the external jugular groove in cattle and goats, the muscle is not included with the extrinsic muscles of the forelimb. This is because it does not have an attachment on the limb. The extrinsic muscles must be severed to remove the thoracic limb. The extrinsic muscles are generally similar in different domestic animals with minor variations. In ruminants, they include the following muscles: There follows a detailed description of the extrinsic muscles. Some of these muscles are described in Chapter 1 (head and neck). Ask your instructor which muscles you need to identify. Stumps of several extrinsic muscles can be identified on an isolated limb. The trapezius muscle is a thin triangular muscle. The base of the triangle lies toward the vertebral column along the dorsal border of the scapula and caudal cervical region. The apex courses distally on the lateral surface of the scapula and inserts by an aponeurosis (flat shiny connective tissue sheet) on the spine of the scapula. The trapezius muscle has cervical and thoracic parts (Figures 5.8 and 5.9). The rhomboideus muscle is located deep to the trapezius muscle. As in the horse, the rhomboideus in ruminants has two parts: cervical and thoracic. In the dog, a third part, called the rhomboideus capitis, is present. Reflect the cervical and thoracic parts of the trapezius dorsally to identify the two parts of the rhomboideus muscle. The hump present in some breeds of cattle is an enlargement of the rhomboideus muscle. A hump is present in zebu cattle (Bos indicus) in Africa, and in Brahman (Bos taurus indicus) or Brahman crosses from Bos indicus cattle. Bos taurus cattle (European breeds) do not have a hump. The brachiocephalicus muscle is a compound muscle that extends craniodorsally from the distal cranial surface of the humerus to the dorsal lateral surface of the skull. In ruminants, it has three parts: the cleidobrachialis, cleidooccipitalis, and cleidomastoideus muscles. The cleidooccipitalis and cleidomastoideus form the cleidocephalicus muscle. The prefix cleido‐ in the names of the divisions of the brachiocephalicus means clavicle. No bony clavicle is present in ruminants. The divisions of the brachiocephalicus originate from the clavicular intersection cranial to the shoulder region and course to the brachium (cleidobrachialis division) or to the head (cleidocephalicus division that itself has cleido‐occipitalis and cleidomastoideus parts) (Figure 5.9). Consult Box 5.5 for clinical application. Figure 5.9 Superficial muscles of the goat showing several of the superficially located extrinsic muscles of the thoracic limb: left lateral view. Dotted line (white arrow) denotes the location of the clavicular intersection. * Omotransversarius muscle. The cleidooccipitalis is absent in the horse. The cleidooccipitalis and cleidobrachialis, the respective cranial and caudal divisions of the brachiocephalicus muscle, are immediately visible when you remove the skin and clean the superficial fascia from the neck and brachium regions (Figure 5.9). The cleidomastoideus forms the ventral part of cleidocephalicus and is not readily visible. It directly forms the dorsal boundary of the external jugular groove and is located ventral and medial to the cleido‐occipitalis muscle. Identify the clavicular intersection, cleido‐occipitalis, cleidomastoideus, and cleidobrachialis divisions. Note that the cleido‐occipitalis division is much larger and broader than the cleidomastoideus division and covers most of the dorsal neck region (Figure 5.9). The omotransversarius muscle extends between the spine of the scapula (acromion) and the atlas, the first cervical vertebra (C1). It is a flat, strap‐like muscle. The caudal portion of the omotransversarius muscle can be viewed close to the cranial border of the scapula between the cervical part of the trapezius and the cleido‐occipitalis muscles (Figures 5.8 and 5.9). The cranial part of the omotransversarius is covered by the cleido‐occipitalis muscle (Figure 5.9). Transect the cleido‐occipitalis muscle in the middle and reflect the two ends to uncover the cranial part of the omotransversarius muscle coursing toward the wing of the atlas. Transect the omotransversarius in the middle of the neck and reflect both ends. Preserve the superficial cervical lymph nodes that are located deep to the omotransversarius and directly cranial to the cranial border of the scapula. Consult Box 5.6 for clinical application related to superficial cervical lymph nodes. The latissimus dorsi (L. dorsi) is a large triangular muscle that lies dorsally caudal to the scapula and courses cranially medial to the proximal part of the humerus. The broad part of the muscle courses from the thoracolumbar region caudally, to the axilla (armpit) cranially (Figure 5.9). It inserts on the proximal medial surface of the humerus in conjunction with the teres major muscle (Figure 5.9). Depending on whether the forelimb is free or fixed (weight‐bearing), the L. dorsi flexes the shoulder joint and draws the trunk forward, respectively. The superficial pectoral muscle is located ventrally between the forelimbs and courses between the cranial part of the sternum and the proximomedial aspects of the humerus and the antebrachium region (radius and ulna) (Figure 5.10). The superficial pectoral muscle has two parts: descending and transverse pectoral muscles. The actions of the superficial pectoral muscles include limb adduction when not bearing weight or prevention of limb abduction when weight is placed on the body. The horse has well‐developed superficial pectoral muscles when compared with cattle. Figure 5.10 The superficial (descending and transverse pectorals) and deep pectoral muscles (goat): ventral view. The deep pectoral muscle is located ventrally behind the transverse pectoral muscle. It is thicker than the superficial pectoral muscle (Figure 5.10). The serratus ventralis muscle is a fan‐shaped muscle located deep (medial) to the scapula. It has a critical role, along with other extrinsic muscles, in attaching the forelimb to the axial skeleton (ribs and cervical vertebrae). This type of attachment (bone–muscle–bone) is different from a conventional joint and is called synsarcosis. The left and right muscles act as a sling system to carry the weight of the body between the limbs as do the pectoral muscles mentioned earlier. The thoracic limb covers much of the serratus ventralis muscle except for the cranial and caudal parts. The muscle fibers of the serratus ventralis muscle extend from the middle parts of the ribs and transverse cervical vertebrae to attach on the medial (deep) surface of the scapula along the serrated face. Remove the thoracic limb to uncover the full extent of the serratus ventralis muscle (Figure 5.11). Detach the insertion from the serrated face of the scapula. To completely remove the limb, transect the remaining extrinsic muscles at the cranial, dorsal, and caudal borders. Following removal of the thoracic limb, note the fan‐shaped appearance of the serratus ventralis (Figure 5.11). On the ribs, note that the fibers of the serratus ventralis interdigitate in a serrated manner with those of the external abdominal oblique muscle, hence the name serratus. Identify the cervical and thoracic parts of the muscle. Figure 5.11 Dissection of serratus ventralis muscle (goat: left lateral view; the left forelimb has been removed). Note the fan‐shaped cervical and thoracic parts of the serratus ventralis muscle (insertion of the muscle cut along the dotted line). The long thoracic nerve (from the brachial plexus) supplies the serratus ventralis muscle. The subclavius muscle courses along the cranial border of the scapula and supraspinatus muscle. It is well developed in goats, pigs, and horses but is absent in dogs. Do not look for it. Goal: Identify the major intrinsic muscles from proximal to distal. Emphasis will be placed on muscles and tendons in the distal limb (elbow and below). Study muscle actions on the joints. Skin the entire limb and clean the superficial fascia and fat. To keep your specimen looking fresh between labs, make sure that you keep it moistened by regularly spraying it as needed with water or InfuTrace solution (neutralizes and reduces formaldehyde in embalmed specimens). We suggest dissecting muscles and vessels on separate limbs. Muscles in proximal limb (shoulder and brachium): Muscles and structures of the distal limb (antebrachium, and manus [carpus, metacarpus and digits]). Depending on their location, the muscles of the antebrachium are broadly divided into two groups: caudolateral and caudomedial (Figures 5.12 and 5.13). Figure 5.12 (a) Overview of the lateral intrinsic muscles of the left thoracic limb (goat); (b) overview of the medial intrinsic muscles of the left thoracic limb (goat). Figure 5.13 (a) Overview of the lateral intrinsic muscles of the left bovine thoracic limb. The bovine intrinsic thoracic limb muscles are like those of the goat (Figure 5.12a). IV, lateral digit; (b) overview of the medial intrinsic muscles of the left bovine thoracic limb. The bovine intrinsic thoracic limb muscles are like those of the goat (Figure 5.12b). III, medial digit. Craniolateral group: Use the acronym “ECLU” to remember the first four of the following extensor muscles. Caudomedial group: Retinacula: Ligaments of the digits: Hoof: The supraspinatus muscle is a lateral shoulder muscle that occupies the supraspinous fossa of the scapula (Figures 5.13a and 5.14). Note that the supraspinatus muscle wraps around the cranial border of the scapula and is visible on the medial cranial side of the scapula (Figure 5.14). The main function of the supraspinatus muscle is to stabilize the shoulder joint. Other actions of the muscle are of minor significance. It inserts on the cranial surface of the greater and lesser tubercle. The infraspinatus muscle is a lateral shoulder muscle that occupies the infraspinous fossa on the lateral surface of the scapula. It is partly covered by the deltoideus muscle (Figures 5.13a and 5.14). Figure 5.14 Bovine proximal muscles of the shoulder, brachium, and antebrachium: close‐up left lateral view. The infraspinatus muscle has two insertion tendons: long superficial tendon and relatively short deep tendon. Like the supraspinatus, the infraspinatus muscle stabilizes the shoulder joint. An infraspinatus subtendinous bursa is present deep to the superficial tendon in ruminants and other most domestic animals (dog and horse). The bursa may, however, be absent in small ruminants. Reflect the scapular and acromial parts of the deltoideus muscle to uncover the distal part of the infraspinatus muscle on a cow forelimb. Transect the infraspinatus belly midway between its proximal and distal ends. Reflect the distal half from the infraspinous fossa to its insertion on the humerus. Verify the presence of the subtendinous bursa. The deltoideus muscle covers the lateral surface of the infraspinatus muscle (Figure 5.14). In ruminants, it has scapular and acromial parts. It originates from the spine of the scapula and acromion and inserts on the deltoideus tuberosity on the lateral surface of the humerus. In the horse, the deltoideus muscle lacks the acromial part. The dog, like ruminants, has both the scapular and acromial parts. The teres minor muscle is a relatively small muscle located deep to the distal end of the scapular part of the deltoideus muscle. It lies directly over the lateral surface of the shoulder joint. Reflect the scapular part of the deltoideus muscle to uncover the teres minor muscle. The teres major muscle is located along the caudomedial border of the scapula caudal to the subscapularis muscle. The teres major muscle flexes the shoulder joint. Look for the teres major on the medial surface of the shoulder region (Figure 5.15). Note that the deltoideus, teres major, and teres minor all flex the shoulder joint. The names of these muscles can be memorized by the acronym “DTT,” which stands for deltoideus, teres major, and teres minor. The subscapularis muscle occupies the subscapular fossa on the medial surface of the scapula (Figure 5.15). The muscle has several parallel parts covered by strong white deep fascia (multipennate type muscle). Ask your instructor for explanation of the terms pennate, bipennate, and multipennate muscles. The subscapularis muscle stabilizes the shoulder joint on the medial side in concert with the stabilizing actions of the supra and infraspinatus muscles on the lateral side of the shoulder joint. The subscapularis muscle inserts on the lesser tubercle of the humerus. The triceps brachii muscle occupies the triangular space cranial to an imaginary line from the caudal border of the scapula to the olecranon tuber of the ulna (Figure 5.14). The triceps brachii muscle has four heads in ruminants and dogs: long, lateral, accessory, and medial. The accessory head is small in ruminants and may sometimes be absent. Figure 5.15 Medial bovine intrinsic muscles of the thoracic limb in the shoulder, brachium, and proximal antebrachium regions: close‐up view. In the horse, the triceps brachii muscle fits its descriptive name as it has only three heads: long, lateral, and medial. The accessory head is absent. In all domestic animals, the heads of the triceps brachii join distally to insert on the olecranon tuber. A subtendinous bursa (subtendinous bursa of the triceps brachii) is located between the olecranon tuber and the combined tendon of the triceps brachii muscle. Keep in mind that the long head is the only division of the triceps brachii that originates from the caudal border of the scapula with actions on two joints: the shoulder and elbow joints. The remaining heads originate from the proximal humerus. The triceps brachii is a major extensor of the elbow joint. Other minor extensors of the elbow (anconeus and tensor fasciae antebrachii) are of negligible significance. The anconeus muscle is located on the lateral surface of the elbow joint deep to the lateral head of the triceps brachii muscle. Injections through the anconeus muscles reach the elbow joint capsule. The tensor fasciae antebrachii muscle is located on the caudal and part of the medial side of the antebrachium (Figure 5.15). In ruminants, the muscle covers the caudal border of the long head of the triceps brachii. In the horse and dog, it covers a more substantial area of the medial surface of the long head of the triceps brachii muscle. The coracobrachialis muscle is located on the medial side of the shoulder joint and proximal brachium region. The tendon of origin obliquely crosses the shoulder joint. The muscle belly lies behind the biceps brachii superficial to the distal insertion of the teres major (Figure 5.15). It has several functions, including stabilization of the shoulder joint, adduction of the brachium, and flexion of the shoulder joint. The biceps brachii muscle is located on the cranial and medial surfaces of the humerus (Figure 5.15). It originates from the supraglenoid tubercle of the scapula and inserts on the medial–proximal surface of the radius. It is a major flexor of the elbow joint. The following two features are associated with the biceps brachii: The brachialis muscle is located on the lateral surface of the humerus (in the brachialis groove) and is partially covered by the lateral head of the triceps brachii muscle (Figures 5.14 and 5.15). It flexes the elbow joint. The muscles located on the antebrachium are divided into craniolateral and caudomedial groups. The craniolateral group are general extensors of the carpus and digits and the caudomedial group have the opposite effect (flexors of the carpus and digits). To identify the extensor group of carpus and digits, turn the limb so the lateral side is facing up. From cranial to caudal, these muscles include extensor carpi radialis, extensor carpi obliquus, common digital extensor, lateral digital extensor, and ulanris lateralis muscles (Figure 5.16). The muscles on the craniolateral group of the antebrachium muscles share common characteristics that help you memorize several of their characteristics: Remove the superficial and deep antebrachial fascia to uncover the muscles of the crus or antebrachium. There follows a summary of the antebrachium muscles on craniolateral aspect of the leg (crus). The extensor carpi radialis is the most cranial muscle of the craniolateral group of the antebrachium region (Figure 5.16). It originates from the lateral supracondylar crest and radial fossa and inserts on the metacarpal tuberosity of the large metacarpal bone (fused Mc III and Mc IV). It extends the carpus. Figure 5.16 Craniolateral muscles of the antebrachium and digits (left bovine forelimb). IV‐lateral digit. The superficial and deep antebrachial fascia have been removed except for the carpal extensor retinaculum. The common digital extensor in ruminants has two bellies or heads (medial and lateral) and three insertion tendons. It is located caudal to the extensor carpi radialis muscle and cranial to the lateral digital extensor muscle (Figure 5.16). The lateral head of the common digital extensor also has superficial and deep heads. It is not necessary to dissect these heads but follow their tendons to the digits. The common digital extensor muscle has one belly in the horse. The tendon of the medial head of the common digital extensor is sometimes called the medial digital extensor tendon or proper extensor tendon of digit III. The tendon of the lateral head is called the common extensor tendon of digits III and IV. Follow the medial and lateral (middle) tendons of the common digital extensor coursing distally on the dorsal surface of the metacarpal region. The relatively large medial tendon inserts on the medial digit (digit III). The lateral (or middle) relatively thin tendon splits into two tendons that course to the interdigital space to insert on the extensor processes of P3 of digits III and IV. The lateral digital extensor muscle lies caudal to the common digital extensor (Figure 5.16). Like the common digital extensor muscle, it originates from the lateral epicondyle of the humerus. The tendon of the lateral digital extensor inserts on the lateral digit (digit IV) in the same manner as the insertion of the medial (proper) tendon of the common digital extensor on the medial digit (digit III). Note that the tendon of the lateral digital extensor muscle to the lateral (IV) digit and the medial tendon of the common digital extensor muscle to the medial (III) digit are wider in size than the extensor tendons that course to the interdigital space. They are known as the “proper” digital extensor tendons of digits IV and III, respectively (Figures 5.16 and 5.17). Figure 5.17 (a,b) Distal extensor tendons of the left bovine forelimb. Extensor tendons originate proximally from the common and lateral digital extensor muscles in the forearm region (a); (c) distal insertion of extensor tendons of the lateral and common digital extensor muscles, and axial and abaxial extensor branches of the interosseus III and IV muscles. Goat right forelimb: dorsal view. Source: Garrett P.D. (1988), Iowa State University Press. The ulnaris lateralis muscle is the most caudal muscle of the craniolateral group (Figure 5.16). It inserts on the AC bone and on metacarpal IV and/or V by short and long tendons, respectively. The ulnaris lateralis muscle flexes carpal joints and extends the elbow joint. The belly of the extensor carpi obliquus muscle is located deep to the muscles of the craniolateral antebrachium group. It is known as the abductor pollicis longus or abductor digiti I longus in the dog. Its tendon of insertion courses obliquely over that of the extensor carpi radialis muscle to insert on the proximal medial surface of the large metacarpal bone (Figure 5.16). Goal: Identify the flexors of the carpus and digits and know their general area of origins and insertions especially that of the distal digital flexor tendons (SDF and DDF). To identify muscles in this group, turn the limb so the medial side is facing up (Figure 5.18). Clean the muscles and tendons by removing the overlying fascia and fat. The flexor carpi ulnaris muscle lies next (caudal) to the ulnaris lateralis muscle on the caudomedial side of the antebrachium. It has a small ulnar head and a large humeral head. It is one of two muscles that insert on the AC bone (Figure 5.18). The other muscle is ulnaris lateralis previously discussed with extensors of the carpus. Identify the flexor carpi radialis and ulnaris lateral on a caudal view of the forelimb (Figure 5.19b). Figure 5.18 Bovine left forelimb. Caudomedial flexor muscles of the antebrachium and digits. The flexor carpi ulnaris flexes the carpus and extends the elbow. Figure 5.19 (a) Bovine left forelimb. Figure shows caudomedial flexor tendons of the distal forelimb. Tendons are separated apart to demonstrate the heads of the superficial digital flexor (SDF) and a band analogous to accessory (check) ligament coursing from the interosseus muscle to the SDF tendon. Proximally, the flexor retinaculum is incised and removed to open the carpal canal. (b) Bovine left forelimb: caudal view. The figure shows the caudal view of flexors of the carpus and digits. The flexor retinaculum is incised. The flexor carpi radialis muscle has one belly and is located on the medial surface of the antebrachium directly caudal to the radius (Figure 5.19a). It originates from the medial epicondyle and inserts on the lateral surface of the proximal end of the large metacarpal bone (fused Mc III and Mc IV). As you will see later, this muscle must be reflected to uncover the median artery and median nerve on the medial surface of the antebrachium region. Note that there is no muscle covering the medial surface of the radius. In ruminants, the pronator teres muscle is a small vestigial entity of little significance (Figure 5.12b). The muscle is fleshy in dogs and cats. There is no need to identify this muscle. The SDF lies deep to the flexor carpi ulnaris muscle. It originates on the medial epicondyle of the humerus and inserts by split tendons on the palmar surface of phalanx 2 (P2) of digits III and IV. The SDF has two bellies: superficial and deep (Figure 5.19). The tendon of the deep belly of SDF passes through the carpal canal deep to the deep layer of the flexor retinaculum while the tendon of the superficial belly of the SDF muscle passes between the superficial and deep layers of the flexor retinaculum. The superficial and deep tendons of the SDF muscle join in the mid‐metacarpal region to form a single tendon. Above the fetlock joint, the SDF tendon receives a band from the interosseus muscle. This band is similar to the distal check ligament of the SDF in the horse except that this band connects two muscles (SDF and interosseus) instead of bone and muscle (radius and SDF) as is the case with the check ligament of the SDF in the horse. Additionally, this band is located in the metacarpus instead of the antebrachium where the check ligament of the SDF in the horse is located. The SDF and the band from the interosseus help form the flexor manica, a sleeve for the passage of the DDF tendon to the palmar surface of P3. The SDF muscle flexes the metacarpophalangeal (MCP–fetlock) and the proximal interphalangeal (PIP or pastern) joints. In the metacarpal region, the tendon of the DDF lies cranial to that of the SDF tendon. The DDF muscle has three parts: ulnar, radial, and humeral heads. Identify the tendons of the SDF and DDF muscles (Figure 5.19a). It is not necessary to identify the individual heads of the DDF muscle. Proximal to the fetlock, each of the SDF and DDF tendons split into two tendons that pass to the lateral and medial digits (Figure 5.20). The interosseus muscle (suspensory ligament) in ruminants is fused interosseus III and IV muscles (Figures 5.20, 5.21, and 5.22). It is located on the palmar side of the large metacarpal bone (fused Mc III and Mc IV) deep to the DDF tendon. The horse has a single interosseus III muscle (suspensory ligament). The suspensory ligament is very tendinous in horse compared with relatively fleshy muscles in ruminants. In the distal palmar metacarpal region, the fused interosseus muscle in ruminants gives a band that joins the SDF (discussed previously with SDF) and splits into five branches. Four of the five branches insert on the four axial and abaxial proximal sesamoid bones at the level of the fetlock joints (Figure 5.7). The fifth tendon courses in the interdigital space between the axial sesamoids and gives two axial extensor branches that join the “proper” extensor branches of the lateral and common digital extensor muscles on digits III and IV (Figures 5.17c, 5.20, 5.21, and 5.22). Figure 5.20 Left bovine limb: palmar view. The figure shows distal tendons of the interosseus III and IV muscles, and bifurcation of the flexor tendons (SDF and DDF) to insert on each digit. Note the attachments of four of the interosseous branches to proximal axial and abaxial sesamoid bones. Figure 5.21 Left bovine distal metacarpal region: close‐up palmar view. The SDF and DDF flexor tendons are reflected down. Figure 5.22 Bovine fetlock joints (left limb): palmar view. The figure shows left and right metacarpophalangeal (fetlock) joints (opened). Note the axial extensor branch from the fused interosseus muscle coursing distally between the medial and lateral distal condyles of the large metacarpal bone. The lateral and medial abaxial branches of the interosseus muscle that insert on the abaxial proximal sesamoids give rise to abaxial extensor branches that also join the “proper” digital extensor tendons on digits IV and III, respectively (Figure 5.17c). You should recall that the proper digital extensor tendons are furnished by distal continuations of the lateral digital extensor tendon and the medial tendon of the common digital extensor muscle. Goal: Know the definition of a retinaculum (a flat sheet of connective tissue that holds tendons in place over bony prominences), and give examples (e.g., extensor or flexor retinaculum). A retinaculum is a band of flat connective tissue that wraps around and binds down muscle tendons. In the forelimb, identify the transverse humeral retinaculum over the tendon of origin of biceps brachii (Figure 5.15) and the extensor retinaculum on the dorsum of the carpus (Figure 5.16). The carpal extensor retinaculum holds down the tendons of the extensors of the carpus and digits. A subcutaneous bursa may sometimes develop in this region. When enlarged, it is known as carpal hygroma. This condition results from poor management and lack of bedding. A flexor retinaculum is located on the caudal aspect of the carpus. It defines the caudal boundary of the carpal canal. It extends from the AC bone medially, and fans over the SDF and DDF and flexor carpi radialis flexor tendons to insert on the medial surface of the carpus. Goal: Identify the dorsal, caudal, and lateral boundaries of the carpal canal, and give examples of tendons, blood vessels, and nerves that pass through it. The carpal canal is the space behind the carpal bones and medial to the AC bone. Flexor tendons, blood vessels, and nerves pass from proximal to distal through the carpal canal (from the medial side of the antebrachium region to the palmar side of the metacarpal region). The thick palmar carpal ligament lies directly on the palmar surface of carpal bones. The palmar carpal ligament is part of the carpal fibrous joint capsule that forms the dorsal boundary for the carpal canal. Other boundaries of the carpal canal include the AC bone laterally, and the flexor retinaculum caudally. The flexor retinaculum has superficial and deep layers. Vessels and flexor tendons passing through the carpal canal include the median nerve, median artery, median vein, the flexor tendons of the SDF and DDF muscle tendons, and tendon of the flexor carpi radialis muscle. The tendon of the superficial belly of the SDF passes deep to the superficial layer of the flexor retinaculum. Identify the boundaries for the carpal canal on a cow or goat skeleton. Goal: Identify the interdigital ligaments (especially the distal interdigital ligament), annular ligaments (palmar annular ligament and proximal and distal digital annular ligaments). There are several ligaments associated with the SDF and DDF tendons on the palmar surface of the fetlock and below. They have more clinical significance in the athletic horse than in docile ruminants. Therefore, many of these ligaments will be studied in more detail in the horse. Ligaments unique to ruminants are the proximal and distal interdigital ligaments that prevent the lateral and medial digits from splaying (spreading apart) when they bear weight. The following discussion is an overview of the ligaments on the palmar surface of the digits. Ask your instructor which ligaments you need to identify. This ligament courses horizontally between the proximal phalanges (P1) of digits III and IV. The proximal interdigital ligament is present in cattle and goats but is absent in sheep. Do not look for this ligament as it is difficult to identify. We recommend identifying only the distal interdigital ligament. This ligament courses horizontally between the proximal parts of the middle phalanges (P2) and the distal sesamoids of the opposite digits (Figure 5.23). Identify the distal interdigital ligaments in the ox or goat. The interdigital ligaments are more developed in cattle than goats. Figure 5.23 Digits of left bovine forelimb: palmar view. (a) and (b) show the proximal and distal interdigital ligaments. The proximal interdigital ligament connects the proximal parts of the proximal phalanges (P1) of digits III and IV in cattle and goats (absent in sheep). It is difficult to identify (no need to dissect it). Note that the distal interdigital ligament forms a cross (X) in the distal part of the interdigital space. Each limb of the cross courses between the distal part of the middle phalanx (P2) and the distal sesamoid (navicular bone) of the opposite digit. In sheep, the distal interdigital ligament connects the two digits transversely. Several annular ligaments support each digit. Follow the bifurcation of the SDF and DDF tendons to digits III and IV (Figure 5.20). Identify the palmar annular ligament at the palmar surface of the fetlock joint. It wraps around both the SDF and DDF tendons of each digit at the level of the proximal sesamoids. Move your probe distal to the palmar annular ligament and identify the proximal and distal digital annular ligaments on each digit. The digital annular ligaments are attached to the proximal and middle parts of the proximal phalanx (P1) on each digit. Select one digit, transect all of the annular ligaments, and reflect the SDF and DDF tendons from the channel on the palmar side of this digit. Identify the flexor manica, a sleeve from the SDF that wraps around the DDF tendon and allows for the passage of DDF tendon to its insertion on the distal phalanx (P3) (Figure 5.19a). With the help of Figure 5.24, identify the hoof wall, sole, heel bulbs, and white line on your specimen or on a dry hoof. The hood (or claw) structure is more clinically important in horses and so most of the details are discussed in the horse. The hoof wall carries most of the weight of the animal. The white line is defined as the junction between the wall and the sole. The hoof of the lateral digit (digit IV) is larger and carries more weight than the medial (digit III) hoof. This situation is reversed on the hind limb. Goal: You should be able to identify the main arterial channels on the medial and palmar sides of the limb (axillary, brachial, and median arteries). You should be able to use the correct nomenclature when describing the distribution and branching of the median artery and median nerve on the palmar surface, especially those nerves and vessels that course into the interdigital area. At the end of this unit, watch Video 22. Consult Box 5.7 for clinical application.
5
The Forelimb
5.1 Introduction
5.2 Bones of the Thoracic Limb
5.2.1 Scapula
5.2.2 Humerus
5.2.3 Radius and Ulna
5.2.4 Carpus (Proximal and Distal Rows)
5.2.5 Metacarpal Bones (Large Metacarpal or Cannon Bone)
5.2.6 Digits
5.3 Muscles and Tendons of the Thoracic Limb
5.3.1 Extrinsic Muscles of the Forelimb
5.3.1.1 Trapezius Muscle (Cervical and Thoracic Parts)
5.3.1.2 Rhomboideus Muscle (Cervical and Thoracic Parts)
5.3.1.3 Brachiocephalicus Muscle (Cleidocephalicus and Cleidobrachialis)
5.3.1.4 Omotransversarius Muscle
5.3.1.5 Latissimus Dorsi Muscle
5.3.1.6 Superficial Pectoral Muscle (Descending and Transverse Parts)
5.3.1.7 Deep (Ascending) Pectoral Muscle
5.3.1.8 Serratus Ventralis Muscle
5.3.1.9 Subclavius Muscle
5.3.2 Intrinsic Muscles of the Thoracic Limb
5.3.2.1 Muscles of the Proximal Limb (Shoulder and Brachium)
5.3.2.1.1 Supraspinatus Muscle
5.3.2.1.2 Infraspinatus Muscle
5.3.2.1.3 Deltoideus Muscle
5.3.2.1.4 Teres Minor Muscle
5.3.2.1.5 Teres Major Muscle
5.3.2.1.6 Subscapularis Muscle
5.3.2.1.7 Triceps Brachii Muscle (Long, Lateral, Accessory, and Medial Heads)
5.3.2.1.8 Anconeus Muscle
5.3.2.1.9 Tensor Fasciae Antebrachii Muscle
5.3.2.1.10 Coracobrachialis Muscle
5.3.2.1.11 Biceps Brachii Muscle
5.3.2.1.12 Brachialis Muscle
5.3.2.2 Muscles and Tendons of the Distal Limb (Antebrachium and Manus [Carpus, Metacarpus, and Digits])
5.3.2.2.1 Craniolateral Group (Located on the Cranial and Lateral Forearm)
5.3.2.2.2 Extensor Carpi Radialis Muscle
5.3.2.2.3 Common Digital Extensor Muscle (Medial and Lateral Heads and Three Tendons)
5.3.2.2.4 Lateral Digital Extensor Muscle
5.3.2.2.5 Ulnaris Lateralis Muscle
5.3.2.2.6 Extensor Carpi Obliquus Muscle
5.3.2.3 Caudomedial Muscle Group of the Antebrachium
5.3.2.3.1 Flexor Carpi Ulnaris Muscle
5.3.2.3.2 Flexor Carpi Radialis Muscle
5.3.2.3.3 Pronator Teres Muscle
5.3.2.3.4 Superficial Digital Flexor with Superficial and Deep Parts: Flexor Manica
5.3.2.3.5 Deep Digital Flexor Muscle
5.3.2.3.6 Interosseus Muscle (Suspensory Ligament) with Axial and Abaxial Extensor Branches
5.4 Retinacula
5.5 Carpal Canal
5.6 Ligaments of the Digits
5.6.1 Proximal Interdigital Ligament
5.6.2 Distal Interdigital Ligament
5.6.3 Annular Ligaments (Palmar, Proximal, and Distal Digital Annular Ligaments)
5.6.4 Digital Annular Ligaments (Proximal and Distal)
5.7 Hoof (Wall, Sole, Bulb, and White Line)
5.8 Arteries and Nerves of the Thoracic Limb
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