Goal: Study the bones of the ruminant hind limb and their palpable features. Compare and contrast with the hind limb bones of the horse. Study the hind limb bones using a caprine or bovine skeleton (Figure 6.1). From proximal to distal, the bones of the hind limb include the os coxae (hip region), femur (thigh region), tibia and fibula (crus), tarsal bones (hock or tarsal region), fused III and IV metatarsals (cannon or large metatarsal bone) forming the (metatarsal region), and digits (each weight‐bearing digit is supported by three phalanges: proximal, middle, and distal). The term pes is used for the bones of the hock, metatarsals, and digits. The bones of the metatarsal and digital regions are similar in shape to those of the front foot. Using Figure 6.2, take time to quickly review the bones of the os coxae and compare them with the hip bone in the horse. The bones of the os coxae are discussed in more detail in Chapter 4. Compare the femur in ruminants with that of the horse and note some of the major differences. The femur is the bone of the thigh region. The head of the femur articulates with the acetabulum (socket) to form the hip joint. Distally, the femoral condyles articulate with the tibial condyles to form the stifle joint. Note the slanted or oblique orientation of the femur on the skeleton. This helps you build a mental picture of its location in the live animal. With the help of Figure 6.3, identify the features of the femur. Proximally, identify the round head of the femur. The head has a small non‐articular depression in the middle called the fovea capitis femoris. The ligament of the head of the femur originates here and extends from the fovea capitis to the acetabular fossa, the deep depression within the acetabular cavity. The greater trochanter (or major trochanter) and lesser trochanter (also called minor trochanter) are the bony eminences on the proximal lateral and medial parts of the femur, respectively. The greater trochanter in the horse is divided into cranial (low) and caudal (high) parts but not in ruminants. A large third trochanter is present on the lateral proximal surface of the horse femur, but this feature is absent in ruminants. Figure 6.1 (a) Articulated bones of the left bovine pelvic limb: medial and lateral views; (b) bones of the bovine hind limb. Articulation of the femur with the hip bone (os coxae). Mt, metatarsal bone. Identify the trochanteric fossa bounded laterally and caudally by the intertrochanteric crest (Figure 6.3). On the distal extremity of the femur, identify the medial and lateral femoral condyles and the depression between them called the intercondylar fossa (Figure 6.3). The rough surfaces on the lateral sides of the femoral condyles are the medial and lateral epicondyles. Figure 6.2 The bovine os coxae (hip bone): lateral view. (a) Greater ischiatic notch; (b) lesser ischiatic notch. Figure 6.3 The bovine femur: cranial (left) and caudal (right) views. The trochlea of the femur is the gliding surface where the patella articulates with the femur. It is situated cranial and proximal to the femoral condyles. The depressed area between the lateral and medial trochlear ridges is a sliding surface for the patella. The medial ridge is generally more prominent and thicker than the lateral trochlear ridge. The patella is a large diamond‐shaped sesamoid bone intercalated in the tendon of insertion of the quadriceps muscle. The patella has a proximal base and distal apex. Note the large depression on the caudolateral aspect of the distal part of the femur above the lateral condyle. This is the supracondylar fossa. The superficial digital flexor (SDF) muscle originates from the supracondylar fossa. Note the small depression between the lateral trochlear ridge and lateral epicondyle of the femur. This is the extensor fossa. Later, you will see that the combined tendon of the long digital extensor and fibular (peroneus) tertius muscles originates from the extensor fossa. The crus (leg) is formed by the tibia and fibula but the tibia is the only weight‐bearing bone of the crus (Figure 6.4). The fibula is vastly reduced except for small proximal and distal parts. The proximal part is fused with the lateral tibial condyle. The distal part is a separate bone located on the most distal lateral surface of the tibia, forming what is known as the lateral malleolus (Figure 6.4). The lateral malleolus remains a separate bone and should be differentiated from a fracture in X‐ray images of the ruminant tarsus. Note the angulation of the tibia and how it relates to the standing animal (Figure 6.1). Identify the medial and large condyles on the proximal aspect of the tibia. The medial and lateral tibial condyles articulate with corresponding femoral condyles to form the stifle joint. Figure 6.4 The bovine tibia: lateral (left) and proximal (right) views. On the proximal articular surface of the tibia, observe the intercondylar eminence separating the medial and lateral tibial condyles. The areas cranial and caudal to the intercondylar eminence are attachment sites for the cranial and caudal cruciate ligaments, respectively. The cruciate ligaments are more clinically relevant in small animals and are not shown here. The proximocranial eminence on the tibia is the tibial tuberosity. Several thigh muscles, including the quadriceps femoris, biceps femoris, and sartorius, attach on the tibial tuberosity. Identify the extensor groove, the vertical notch between the lateral tibial condyle and tibial tuberosity. The combined tendon of the long digital extensor and fibularis (peroneus) tertius muscles passes from the extensor fossa of the femur through the extensor groove of the tibia. Identify the distal depression of the tibia, called the cochlea. The cochlea articulates with the proximal trochlea of the talus to form the tibiotarsal (or tarsocrural) joint. The bony prominence on the distal medial aspect of the tibia is the medial malleolus. On the lateral distal part of the tibia, recall the presence of the lateral malleolus as the remnant of the fibula in the distal crus. The tarsus (hock) in ruminants is formed by five tarsal bones organized in three tiers (rows). With the help of Figure 6.5, study the bones of the hock and compare them with those of the horse. The proximal row or tier has two bones: the calcaneus (C) and talus (T). The middle row contains one bone that represents the combined central and fourth tarsal bones (C+4, called the centroquartal bone). The distal row consists of two bones, fused second (T2) and third (T3) tarsal bones, and singular first (T1) tarsal bone (Figure 6.5). The proximal enlargement of the calcaneus is the tuber calcaneus. The tuber calcaneus forms the point of the hock that serves as attachment point of the common calcanean (Achilles) tendon. By this arrangement, the calcaneus acts as a short lever arm facilitating extension of the tibiotarsal joint. The common calcanean tendon comprises several tendons that include the gastrocnemius and SDF muscles (the largest and most significant contributors). Identify the sustentaculum tali on the medial surface of the calcaneus. This projection serves as a sliding surface for the deep digital flexor (DDF) muscle tendon as it passes distally past the tarsus. Figure 6.5 Bovine tarsus (hock): dorsal (left) and plantar (right) views. The centroquartal bone (C+4) is formed by fusion of central and fourth tarsal bones. Note the presence of proximal and distal trochleae in the talus. The small first tarsal bone is located on the plantar aspect of the distal row. Identify the talus bone lying medial to the calcaneus on the proximal row. The talus in ruminants has a proximal and distal trochlea and is more slender in shape than that of the horse. The talus bone in the horse has only one trochlea located proximally. The distal part is flat and articulates with a similarly flat central tarsal bone. The proximal trochlea of the talus in ruminants is more slanted than that of the horse. The distal trochlea of the talus in ruminants articulates the centroquartal bone (fused central and fourth tarsal bone). Its presence in ruminants is described as a characteristic for the order Artiodactyla. The proximal and distal trochleae of the ruminant talus allow for greater movements at both the tarsocrural and proximal intertarsal joints. A tarsal canal is formed between three sets of fused tarsal bones that include fused T2+T3 tarsal bones, fused C+ 4 tarsal bones (centroquartal bone), and fused III and IV metatarsal bones. The perforating tarsal artery courses through this canal from the dorsal to the plantar aspect of the hock. A similar canal is present in the horse between the central, third, and fourth tarsal bones. Identify the tarsal canal on articulated bovine hock. The large metatarsal bone (Figure 6.6) is formed by fusion of the third and fourth metatarsal bones (Mt III and Mt IV). This bone is similar in shape to the large metacarpal bone in the forelimb except that it is slightly longer and slimmer. The large metatarsal bone has a proximal base (articulates with the distal row of tarsal bones) and distal heads (capita) that are separated by the intercapital notch (Figure 6.6). The left and right heads articulate with the proximal phalanx of the corresponding digits (digits III or IV). Identify the axial dorsal and plantar longitudinal grooves on the large metatarsal bone. The dorsal longitudinal groove on the dorsal surface is more distinct than the plantar longitudinal groove on the plantar surface. Note the presence of proximal and distal metatarsal canals that allow for blood vessels to course between the dorsal and plantar sides of the limb (Figure 6.6). Figure 6.6 Bovine large metatarsal bone (fused third [III] and fourth [IV] metatarsal bones): dorsal view. The dorsal metatarsal artery III courses in the dorsal longitudinal groove. Proximal and distal perforating arteries course through the proximal and distal metatarsal canals from the dorsal surface to the plantar surface of the large metatarsal bone. The proximal and distal perforating branches originate from the dorsal pedal and dorsal metatarsal artery III, respectively. The bone has a proximal base and distal head regions. In contrast to the horse, Mt I and Mt II (splint bones) are absent in ruminants. However, a small metatarsal sesamoid is located at the proximal medioplantar aspect of Mt III (see discussion of the metatarsal sesamoid bone later). Recall that the term “pes” includes the tarsal, metatarsal, and digital bones. The corresponding term in the forelimb is the “manus,” which includes the carpal, metacarpal, and digital bones. Identify the metatarsal sesamoid bone on the plantar proximal aspect of the third metatarsal bone (Mt III). The metatarsal sesamoid was once thought of as the metatarsal II bone (medial splint) found in the horse. The bone should not be mistaken for a fracture in X‐ray films of the ruminant tarsus. The digits are similar to those of the front foot. The non‐weight‐bearing rudimentary digits II (medial) and V (lateral) are referred to as dewclaws. In ruminants, they may contain small bones that do not articulate with the other bones of the skeleton. Digits III (medial) and IV (lateral) are the weight‐bearing digits. Each is formed by proximal (P1), middle (P2), and distal (P3) phalanges similar to those in the forelimb (review Figure 5.7). A pair of proximal sesamoids and a singular distal sesamoid bone are present on each digit. Goal: Identify the major pelvic limb muscles. Have a broad understanding of their origin and insertion, especially the muscles and tendons on the distal part of the hind limb. Understand muscle actions on the joints of the pelvic limb. This is a key goal and learning objective. Detailed descriptions of pelvic limb muscles (i.e., knowing the precise origin and insertion points) are unnecessary because they are of little clinical interest in ruminants. However, we will attempt to follow a systemic approach that would be of value for students who are studying pelvic limb muscles for the first time. The sublumbar muscles (psoas minor, iliopsoas [psoas major plus iliacus], and quadratus lumborum) are located medially on the ventral surface of the lumbar vertebrae and may not be available for study if the pelvic limb is disarticulated from the hip joint. The sublumbar muscles possess little movement. They form the tender part of the T‐bone steak cuts. Ask your instructor if these muscles should be identified. There follows a brief description of their locations and actions. The psoas minor is the most medial of the sublumbar muscles. It has a long distinct tendon. In ruminants, it arises from T12–L5 vertebrae and inserts on the psoas minor tubercle on the ilium. In the horse, the psoas minor arises from T16–L5 vertebrae. The iliopsoas muscle is formed by a combination of the psoas major and iliacus muscles. As a major flexor of the hip joint, it is discussed with the muscles acting on the hip joint. The quadratus lumborum muscle has no action on the hip. The sublumbar muscles can easily be identified on a mid‐sagittal section of the caudal lumbar region, hip, and medial proximal part of the pelvic limb. From medial to lateral, the psoas minor, psoas major, and quadratus lumborum run parallel to each other. Muscles in this group include flexors of the hip joint (iliopsoas and sartorius muscles) and extensors of the hip joint (gluteal and hamstring muscles). The lateral muscles of the hip and thigh are known as “rump” muscles. You can skin the entire limb or carry out your dissection in regions. With the help of Figure 6.7a,b, make similar skin incisions and remove the skin from the hip, thigh, and proximal leg. You may opt to keep the skin on your cadaver by reflecting it sideways or dorsally so you can use it to cover your specimen. Clean the fascia overlying the gluteal and thigh regions. Do not transect the fascia lata (insertion of the tensor fasciae latae muscle). The gluteal fascia (superficial, middle, and deep layers) covers the muscles in the hip and thigh regions. Cranially, it is continuous with the thoracolumbar fascia. Note the distinct fascial separation (intermuscular septa) of the hip and thigh muscles. The prime flexor of the hip joint is the iliopsoas muscle (Figure 6.7c), a sublumbar muscle that has attachment to the ventral surface of the lumbar vertebral bodies and the ventral body of the ilium. The iliopsoas has two parts: the psoas major and iliacus muscles. Identify the psoas major and iliacus on the medial aspect of the pelvis. The psoas major courses from the sublumbar region and proximal ends of the last few ribs to the lesser trochanter. It joins the iliacus at an area ventral to the sacrum. The iliacus is shorter and arises from L6 vertebra, ventral sacrum, and sacroiliac surface of the ilium. Other flexors of the hip joint include the sartorius, tensor fasciae latae, and rectus femoris muscles. Identify these muscles on an isolated bovine or goat limb. The major extensors of the hip joint are the lateral muscles of the hip and thigh including the gluteal and hamstring muscles (rump muscles) (Figures 6.7a,b and 6.8). This group of hip muscles includes the superficial, middle, and deep gluteal muscles (Figure 6.7). The tensor fasciae latae (Figures 6.7a and 6.8) can be included with the gluteal group because of its position and common innervation although it has a flexor action on the hip while the gluteal muscles extend the hip. Figure 6.7 (a) Hip (gluteal) and thigh (hamstring) muscles of a goat (left pelvic limb): left lateral view. The lateral muscles of the hip and thigh are commonly known as “rump muscles.” (b) Gluteal and hamstring muscles of a goat (left pelvic limb): left caudolateral view. (c) Hip and thigh muscles of a goat: left lateral view. Dissection of the accessory gluteal muscle by transection and reflection of the middle gluteal muscle. The gluteobiceps femoris and tensor fasciae latae muscles are removed. * Deep gluteal muscle. (d) Hip and proximal thigh of a goat: close‐up left lateral view. Dissection of the deep gluteal muscle by transection and reflection of the middle and accessory gluteal muscles caudally. The gluteobiceps femoris and tensor fasciae latae muscles are removed. * Coccygeus muscle. On the lateral surface of the thigh, and with the help of Figures 6.7a and 6.8, identify the tensor fasciae latae and middle gluteal muscles. Figure 6.8 Bovine hip and thigh muscles: left lateral view. The broad gluteobiceps muscle is formed by the fusion of the biceps femoris and superficial gluteal muscles. Understand that the gluteal fascia sends connective tissue septa that separate adjacent muscles. Clinically, these septa could hinder drainage of inflammatory exudate in an inflammatory process in the lateral hip region. Keep in mind that the superficial gluteal muscle in ruminants fuses with the biceps femoris muscle to form the gluteobiceps muscle. The tensor fasciae latae is triangular. It is located laterally distal to the middle gluteal muscle and wraps around the proximal cranial thigh region (Figures 6.7a and 6.8). It inserts on the patella and cranial tibia by a broad connective tissue sheet, called the lateral femoral fascia or fascia lata (Figure 6.7a). The middle gluteal muscle lies on the proximal lateral hip region (gluteal surface of the ilium) between the tensor fasciae latae and superficial gluteal muscles (Figures 6.7a,b and 6.8). It extends the hip joint. Transect the middle gluteal muscle from the tuber coxae (hook) and wing of the ilium and reflect it caudally (Figure 6.7c,d). This should uncover the accessory gluteal muscle located on the cranioventral border of the middle gluteal muscle (Figure 6.7c). The deep caudal portion of the middle gluteal muscle in dogs, the piriformis muscle, is thought by some to be analogous to the accessory gluteal muscle in large animals. However, this comparison raises some questions that are not answered. The insertion of the accessory gluteal on the lateral distal part of the greater trochanter is cushioned by a subtendinous bursa called the trochanteric bursa. Trochanteric bursitis (inflammation) is more important in horses and can cause lameness in racehorses. Consult Box 6.1 for clinical relevance. The trochanteric bursa can be demonstrated by transection of the middle and accessory gluteal muscles and reflection of the accessory gluteal muscle to its insertion on the distal part of the greater trochanter (Figure 6.7d). The deep gluteal muscle lies deep to the middle gluteal muscle and ventral to the course of the large sciatic nerve on the lateral surface of the sacrosciatic ligament. It has a fan‐shaped appearance and is covered by a glistening aponeurosis (Figure 6.7d). Study its origin and insertion on the skeleton. The hamstring muscles include the biceps femoris, semitendinosus, and semimembranosus muscles (Figures 6.7b and 6.8). In ruminants, the superficial gluteal muscle fuses with the biceps femoris to form the gluteobiceps muscle. The development of the hamstring muscles contributes to the shape of the pelvis (croup region). Cattle have an angular (depressed) pelvis because the hamstring muscles in ruminants have only pelvic heads (the part of the muscles that originate from the ischiatic tuberosity and run distally) but have no proximal vertebral heads covering the hip bone (i.e., no part originating from caudal vertebrae). In contrast, the hamstring muscles in the horse have both vertebral and pelvic heads. Athletic horses for example have well‐developed proximal vertebral heads of the hamstring muscles. This conceals most of the bony landmarks of the pelvis. In ruminants, the bony features of the pelvis are more easily palpable than in horses. Identify the broad gluteobiceps muscle on the lateral thigh caudal to the tensor fasciae latae muscle (Figures 6.7a,b and 6.8). Study the origin and insertion of the gluteobiceps muscle on the skeleton. Note that ruminants have no separate superficial gluteal muscle. The equivalent muscle fuses with the biceps femoris muscle to form the gluteobiceps muscle (Figures 6.7a and 6.8). The semitendinosus muscle lies between the gluteobiceps muscle cranially, and semimembranosus muscle caudally (Figures 6.7b and 6.8). Its major action is to extend the hip. Additionally, it has flexor and extensor actions on the stifle and the hock joints, respectively. In ruminants, the semitendinosus has a pelvic head but the vertebral head is absent. In horses, the semitendinosus muscle has vertebral and pelvic heads that arise from caudal vertebrae and the ischiatic tuberosity, respectively. The semimembranosus muscle lies between the semitendinosus cranially, and adductor muscle on the medial aspect of the thigh (Figures 6.7b and 6.8). On the medial thigh, it is covered by the gracilis muscle (Figure 6.9). The semimembranosus muscle is shorter than the semitendinosus and its prime action is to extend the hip. Transect the gracilis muscle on the medial aspect of the thigh to visualize the full extent of the muscle belly and its insertion on the distal medial aspect of the femur. Figure 6.9 The left bovine hind limb showing adductor medial thigh muscles: medial view. The vastus medialis muscle is part of the quadriceps muscle and not the adductors. The limb is dislocated from the hip joint. The major adductors of the hind limb can be memorized by the acronym “PAGE” that stands for pectineus, adductor, gracilis, and external obturator muscles. The sartorius muscle is discussed with the medial thigh adductor group but is not a major adductor and has other actions. The sartorius muscle is a long, relatively flat muscle in the craniomedial thigh region (Figure 6.9). It has cranial and caudal heads that are separate at their origin but are fused distally. Only at its origin does it appear to have two heads. The sartorius muscle flexes the hip and helps to adduct the limb. In the dog, the sartorius muscle, much like in ruminants, is divided into cranial and caudal parts, but remains undivided in the horse. The gracilis muscle is the most superficial muscle of the PAGE muscles on the medial thigh. It is a broad flat muscle that arises from the symphysial tendon (Figure 6.10). The symphysial tendon is a condensation of connective tissue on the ventral surface of the pelvic floor (pelvic symphysis). It is a caudal extension of the prepubic tendon, the primary insertion tendon for the rectus abdominis muscle. The symphysial tendon serves as the origin for the adductor muscles and contributes to suspension of the udder in the female. Make a note of the vessels (saphenous artery, saphenous nerve, and medial saphenous vein) obliquely crossing the superficial surface of the gracilis muscle (Figure 6.10) and note the clinical significance of the saphenous artery (Box 6.2). Figure 6.10 Bovine superficial medial thigh muscles. Note that the saphenous artery and saphenous nerve obliquely cross the distal part of the gracilis muscle. The medial saphenous vein (caudal branch), which accompanies the saphenous artery and nerve, is not visible (not injected).
6
The Hind Limb
6.1 Bones of the Hind Limb
6.1.1 Os Coxae (Hip Bone)
6.1.2 Femur (Thighbone)
6.1.3 Bones of the Leg (Crus)
6.1.4 Tarsal Bones
6.1.5 Fused Metatarsals III and IV (Large Metatarsal Bone)
![Photo depicts bovine large metatarsal bone (fused third [III] and fourth [IV] metatarsal bones): dorsal view.](https://i0.wp.com/veteriankey.com/wp-content/uploads/2023/04/c06f006-2.jpg?w=960)
6.1.6 Metatarsal Sesamoid Bone
6.2 Muscles of the Pelvic Limb
6.2.1 Muscles Acting on the Hip Joint
6.2.1.1 Gluteal Muscles
6.2.1.1.1 Tensor Fasciae Latae Muscle and Fascia Lata
6.2.1.1.2 Middle Gluteal Muscle
6.2.1.1.3 Deep Gluteal Muscle
6.2.1.2 Hamstring Muscles
6.2.1.2.1 Gluteobiceps Muscle
6.2.1.2.2 Semitendinosus Muscle
6.2.1.2.3 Semimembranosus Muscle
6.2.1.3 Medial Adductor Thigh Muscles
6.2.1.3.1 Sartorius Muscle
6.2.1.3.2 Gracilis Muscle
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