Fig. 5.1 Surface features of the shoulder and thorax: left lateral view. The palpable bony ‘landmarks’ and those muscles whose contours are clearly recognizable on palpation are indicated. In the normal standing posture the scapula and its associated muscles cover ribs 1 to 4 completely. The broken green lines indicate the position of structures as they are seen in subsequent dissections. It is extremely important to appreciate that these are not the normal positions in the live animal (see Fig. 1.3). In the live animal, the heart is more cranially placed and the cupola of the diaphragm may extend as far cranially as rib 6.

Fig. 5.2 Skeleton of the shoulder and thorax: left lateral view. Palpable bony features shown in the surface view are colored green for reference. In addition, the more caudal ribs and the entire length of the sternum within the median pectoral groove are palpable. Passing caudally from the small cranial thoracic aperture (thoracic inlet) between the first pair of ribs, the sternum and vertebral column diverge, and the ribs lengthen (up to rib 9) and increase in their outward curvature.

Fig. 5.3 Radiograph of the thorax: lateral view. Air within its lumen highlights the trachea. The heart is clearly visible. The lungs can be seen by virtue of their air content. The majority of other structures are soft tissue and mediastinal and so cannot be clearly distinguished from one another. The position, shape and relationship of structures may alter quite markedly according to breed type, body condition and stage of respiration.

Fig. 5.4 Radiograph of the thorax: dorsoventral view. Only the lungs and the heart can be easily appreciated in this view as other structures are mediastinal and thus superimposed on the spine and sternum.

Fig. 5.5 Radiograph of the thorax: lateral view, immediately after oral administration of barium mixed with dog food. (1), (2) & (3) A bolus of food mixed with contrast medium can be seen within the esophagus. The longitudinal mucosal folds can be seen in the distal esophagus. (4) Streaks of barium remaining within the esophagus highlight its path and the mucosal folds.

Fig. 5.6 Superficial fascia of the shoulder thorax: left lateral view. The superficial fascia is not attached to the skeleton and may be variably infiltrated with fat. The cutaneous muscle of the trunk is visible embedded in the fascial layer.

Fig. 5.7 Cutaneous muscle of the trunk and cutaneous nerves of the thorax: left lateral view. Limited cleaning of superficial fascia has exposed the cutaneous muscle. It has been cut into and reflected ventrally, revealing two series of lateral cutaneous nerves, with their accompanying small cutaneous blood vessels which originate from the intercostal vessels.

Fig. 5.8 Superficial structures of the shoulder and thorax (1) cutaneous nerves: left lateral view. The remaining superficial fascia and most of the cutaneous muscle have been cleaned. The lateral thoracic vessels and nerve emerge from between the diverging pectoral and latissimus dorsi muscles which extend from the axilla caudally onto the chest.

Fig. 5.9 Superficial structures of the shoulder and thorax (2) extrinsic forelimb muscles: left lateral view. Extrinsic muscles of the forelimb are exposed after removal of the superficial fascia and trimming of lateral cutaneous nerves. The basis of the caudal boundary of the upper arm, the tricipital margin, is clearly displayed. Deep thoracic fascia passes internal to the latissimus dorsi and pectoral muscles and medial to the upper arm, and forms the medial lining layer of the axilla (see Figs 3.43 and 5.82).

Fig. 5.10 Thoracic wall (1) after removal of the latissimus dorsi muscle: left lateral view. The latissimus dorsi and trapezius muscles have been removed to begin exposure of the thoracic wall, displaying the entire thoracic origin of the external abdominal oblique muscle from rib 13 cranially to rib 6; the caudal attachments of the thoracic ventral serrate muscle from ribs 5 to 8; the thoracic rhomboid at the dorsal end of the scapula related to its caudal angle and vertebral border. Part of the deep thoracolumbar fascia covering the epaxial musculature has been removed in order to demarcate those areas of the fascia which also act as aponeurotic attachments for the cranial and caudal dorsal serrate muscles.

Fig. 5.11 Thoracic wall (2) after removal of the forelimb: left lateral view. The forelimb was removed by severing the rhomboid muscle at its attachment to the supraspinous and nuchal ligament, and the mid dorsal tendinous raphe of the neck; cutting the ventral serrate muscle from its attachment onto the serrated face of the scapula; freeing the superficial and deep pectoral muscles from their humeral attachments and severing axillary vessels and nerves arising from the brachial plexus.

Fig. 5.12 Thoracic wall (3) dorsal serrate and scalene muscles: left lateral view. The ventral serrate muscle has been removed (bar its ventral rib attachment) exposing the cranial dorsal serrate muscle. Left pectoral musculature has been removed exposing the medial surface of the right pectoral muscles abutting onto the left pectoral muscles ventral to the sternum; the small rectus thoracis muscle; the aponeurosis of origin of the rectus abdominis muscle; and the manubrium of the sternum.

Fig. 5.13 Thoracic wall (4) external abdominal oblique muscle: left lateral view. The thoracolumbar fascia has been removed exposing the origin of the splenius muscle (see also Chapter 3), the supraspinous ligament and the spinalis and semispinalis thoracis muscles. Component parts of the scalenus muscle (dorsal and middle) which extended caudally onto ribs 2-6 have been removed leaving only the rib 1 attachment. This has exposed rib 1, parts of ribs 2-5 and the external intercostal muscles in the intervening intercostal spaces.

Fig. 5.14 Thoracic wall (5) longissimus and iliocostalis thoracis muscles: left lateral view. The rest of the ventral serrate and cranial dorsal serrate muscles and the component of the scalene muscle which attached to rib 1 have been removed. The overall extent of the ribcage is now becoming apparent with all 13 ribs at least partly exposed. Splenius and semispinalis capitis muscles have been removed from the neck (see Chapter 3) with much of the longissimus cervicis muscle. This has exposed the spinalis thoracis and semispinalis thoracis muscles, the longissimus thoracis extending cranially to cervical vertebra 6, and the iliocostalis thoracis muscle extending cranially onto cervical vertebra 7.

Fig. 5.15 Thoracic wall (6) rectus abdominis muscle and rectus sheath: left lateral view. The rib attachments of the external abdominal oblique muscle have been removed leaving that part of the ventral aponeurosis which contributes to the external lamina of the rectus sheath closely adherent to the rectus muscle surface. Caudally the contribution of the internal abdominal oblique aponeurosis to the rectus sheath remains intact. The rectus abdominis muscle is now exposed along the length of the thorax.

Fig. 5.16 Ribcage (1) external intercostal muscles: left lateral view. The rectus thoracis muscle has been removed and the rectus abdominis muscle is reflected caudally, although a fleshy attachment of the rectus abdominis muscle to the sternal portion of costal cartilage 9 prevents total reflection. Practically the entire ribcage is now exposed with the external intercostal muscles occupying much of the intercostal spaces.

Fig. 5.17 Ribcage (2) internal intercostal muscles: left lateral view. The rectus abdominis muscle is fully reflected following the severance of its fleshy attachment (see Fig. 5.16). Exposed by this procedure are the costal arch, the continuation of the rectus sheath and the cranial epigastric vessels. The external intercostal muscles have also been removed from all of the intercostal and caudal interchondral spaces exposing the internal intercostal muscles.

Fig. 5.18 Ribcage (3) transverse thoracic muscle and endothoracic fascia: left lateral view. The internal intercostal muscles and their interchondral components have been removed, bar those small portions in interchondral spaces 11 & 12 lying caudal to the costodiaphragmatic line of pleural reflection. In the last four intercostal spaces the endothoracic fascia has also been removed. In those intercostal spaces in which the fascia is intact, an intercostal artery, vein and nerve ‘triad’ lies embedded in fat against the caudal border of a rib.

Fig. 5.19 Ribcage (4) topography of the thorax: left lateral view. Intercostal spaces were cleared by removing the endothoracic fascia, transverse thoracic muscle, internal thoracic vessels, and intercostal arteries, veins and nerves. The ribs are outlined and the costal surface of the left lung is viewed through the intercostal spaces. An accurate representation of the position and extent of the lungs is sometimes difficult to obtain in embalmed material. The broken green line indicates the approximate contour of the caudal and ventral borders of the lung in a ‘resting’ position.

Fig. 5.20 Ribcage (5) topography of the thorax: right lateral view. The lung has been preserved in a fairly normal ‘resting’ condition, its outer contour conforming quite closely to the proposed borders – the broken green line on the drawing. This line passes cranioventrally from the upper end of the penultimate intercostal space at the lateral border of the iliocostalis muscle and parallels the costodiaphragmatic line of pleural reflection (broken blue line) down to the costochondral junction of rib 6 where it continues cranially parallel with the sternum.

Fig. 5.21 Thoracic viscera in situ: left lateral view. Ribs 1, 3 and 6 are left in place to show the costal relationships of the viscera. The lungs in this specimen had hardened on fixation rather than becoming ‘waterlogged’ (unlike Fig. 5.19), presenting a more ‘normal’ outer contour. The costodiaphragmatic line of pleural reflection is indicated on this, and accompanying drawings by the broken blue line. It follows the attachment of the diaphragm to the ribcage from the midpoint of rib 13, through the distal part of rib 12 and the costochondral junction of rib 11 and follows the costal cartilages of ribs 10 and 9.

Fig. 5.22 Thoracic viscera in situ: right lateral view. Removal of ribs 4 and 5 has exposed the cardiac notch in the ventral border of the lung between cranial and middle lobes. Through the notch the fat-infiltrated pericardium is exposed on the surface of the heart. The cranial extent of the pleural cavity does not show at all well in any of the dissections – it is represented on either side by a pleural pocket at the thoracic inlet medial to rib 1.

Fig. 5.23 Caudal ribs, costal arch, intercostal arteries and nerves: left lateral view. This is an enlarged view of the caudal end of Fig. 5.18. Intercostal arteries and nerves in intercostal spaces 9, 10 and 11 are displayed after removal of the endothoracic fascia. Continuations of intercostal nerves in spaces 10 and 11 penetrate between interdigitating fibers of the diaphragm and transverse abdominal muscle dorsal to the costal arch. Some internal intercostal muscles remain between the ribs caudal to the costodiaphragmatic line of pleura reflection.