THORAX AND ABDOMEN OF THE HORSE 45 



A. SUBCLAVIA DEXTRA. — The right subclavian artery continues the 

 curve that has been begun by the brachio-cephalic, and, like the left 

 artery of the same name, terminates at the border of the first rib, where 

 it becomes the axillary artery. The right subclavian is at a slightly 

 more ventral level than the left artery. 



From the right subclavian arise the vertebral artery, internal 

 thoracic artery, omo-cervical trunk and external thoracic artery of the 

 right side of the body. Each of these pursues a course similar to that 

 of its counterpart on the other side of the thorax. 



Lymph glands. — A considerable number of lymph glands have 

 been encountered during the dissection of the large vessels in the pre- 

 cardial mediastinum. Numerous glands (lymphoglandulae mediastinals 

 craniales), variable in size but generally small, lie along the course 

 of the common brachio-cephalic trunk and its branches. On the right 

 side of the body they are in contact with the trachea ; on the left side, 

 with the oesophagus also. Some of them will be found between the 

 trachea on the one hand, and the cranial vena cava and the right 

 atrium on the other, and these are generally continuous with the 

 bronchial lymph glands that have already been examined in connection 

 with the roots of the lungs. It is possible also that a few small glands 

 may be found on the dorsal surface of the trachea. 



The caudal cervical lymph glands (lymphoglandulae cervicales 



caudales) form a large group continuous with the foregoing, ventral to 



the trachea at the entrance to the chest. They fill the various chinks 



between the large vessels and muscles in this region, and extend for 



some distance into the neck. 



Dissection. — Cut through the costo-cervical, deep cervical and 

 vertebral arteries close to their origins on both sides of the body. In 

 doing this, every care must be taken not to injure neighbouring 

 structures. The thoracic duct is most liable to injury, and should be 

 secured before the arteries are severed. If a careful search be made 

 on the left side of the chest in the angle formed by the divergence of 

 the aorta and the common brachio-cephalic trunk, the duct will be 

 found as a very thin-walled vessel crossing the left face of the trachea 

 and the oesophagus. 



The trachea and bronchi. — The trachea ^ or tube by which air 



passes to and from the lungs begins in the neck, traverses the thoracic 



inlet and the precardial mediastinum, comes into contact with the base 



of the heart, and terminates in the two bronchi on a level with the fifth 



rib or the fifth intercostal space, some 10 or 12 cm. from the vertebral 



column. The thoracic portion of the trachea is not precisely in the 



median plane except at its termination. The presence of the 



oesophagus causes it to incline a little to the right. 



1 rpaxeia (tracheia) [Gr.], rough (artery). 



