The thoracic cavity is relatively small; it is especially short
dorsally, and is diminished laterally by the mode of attachment of the
diaphragm to the ribs (_vide_ Myology). The endothoracic fascia is
better developed than in the horse, and is distinctly elastic. The
pleura is also thick, and there are no perforations of the mediastinum.
The pleural sacs are more unequal in extent than in the horse, and the
ventral part of the mediastinum is further to the left; in front of the
pericardium it lies for the most part on the left wall of the chest.
[Illustration:
FIG. 366.—CROSS-SECTION OF THORAX OF SHEEP, PASSING THROUGH MIDDLE OF
FIFTH PAIR OF RIBS, POSTERIOR VIEW.
_1_, _1′_, Lungs; _2_, _2′_, bronchi; _3_, _3′_, pulmonary arteries;
_4_, thoracic aorta; _5_, œsophagus; _6_, lymph gland; _7_, vena
hemiazygos; _8_, posterior vena cava; _9_, large pulmonary vein;
_10_, left atrium, _11_, vena hemiazygos; _12_, left ventricle;
_13_, right ventricle; _14_, sternum; _15_, internal thoracic
vessels; _16_, sixth thoracic vertebra.
]