The extent and dimensions of the thoracic cavity are not apparent on inspection of the live animal.
Features such as the narrowness of the cranial part of the thorax or the part of the abdomen enclosed by the rib cage are not appreciated from the external viewpoint (Fig. 27.1).
Certain features of the limb skeleton provide helpful guides to the location of deeper parts: the point of the shoulder projects a few centimeters in front of the lower part of the first rib, the caudal angle of the scapula lies over the vertebrae dorsal to the sixth rib, and the point of the elbow lies over the fifth intercostal space, just above the costochondral joints, and just a short way cranial to the vertex of the diaphragm (Fig. 27.2A and B).The thoracic wall of cattle, unlike that of sheep or goats, is mainly remarkable for the great breadth of the ribs that hampers access to the thoracic cavity through the intercostal space for any rarely indicated thoracic surgery. The intercostal vessels follow both margins in the ventral parts of the spaces, which is a point relevant to pleurocentesis, which is best performed by puncture of the 6th or 7th space directly above the level of the costochondral joints. The ribs from the 5th to the 13th may generally be identified with ease, though possibly not palpated along their entire lengths. The ribs become more oblique and bowed while the cartilages gain more forward slope as the series is followed caudally. The cartilages of the last five (asternal) ribs combine to form the costal arch that defines the cranial limit of the flank. The sternal ribs join the sternum via their cartilages. Compared to the rigid cranial part of the chest wall, the wider caudal part makes more contributions to the respiratory movements; but the activity of the diaphragm still predominates. Despite this, cattle survive diaphragmatic paralysis; however, they suffer greater distress than is usual in smaller species.