Veterinary Splanchnology and Applied Anotomy

THORACIC CAVITY - OX

• The thoracic cavity is the second in size of the three body cavities. In form, it is somewhat like a truncated cone with the base cut off very obliquely and directed backwards
• It presents a roof, floor, two lateral walls, a caudal wall and an cranial aperture or inlet
• The bodies of the thoracic vertebrae form the roof. The lateral walls are formed by the ribs and intercostal muscles. The sternum forms the floor
• The caudal wall is formed by the convex face of the diaphragm
• The inlet is small, narrow and oval. It is bounded above by first dorsal vertebra below by the first segment of the sternum and laterally by the two first ribs
• It is closed in life by structures passing into and out of the thorax viz., the longus colli muscles, the trachea, the oesophagus, vessels, nerves and lymph glands
• A longitudinal septum termed the mediastinum thoracis or septum mediastinale, extends from the dorsal wall to the ventral and caudal walls, and divides the cavity into two lateral chambers termed the pleural cavity. Each of these chambers is lined by the serous membrane, called the pleura
• The mediastinum is, for the most part, not median is position, as might be inferred from its name this is correlated with the fact that the largest organ contained in it the heart, is placed more on the left side than on the right consequently the right pleural cavity and lungs are larger than the left
• Practically all the thoracic organs are in the mediastinal space between the pleurae, with the exception of the lungs, caudal vena cava and part of the right phrenic nerve
• The part in which the heart and the pericardium are situated together with that dorsal portion is usually called the middle mediastinal space; the parts before and behind this are termed respectively the cranial and caudal mediastinal spaces