256 Anatomy of the Rabbit. 



from the second to the sixth, at the junctions of the bone ribs with 

 the costal cartilages. 



The artery passing along the ventral wall between the foregoing muscle and 

 the internal intercostals is the internal mammary (p. 257). 



For the general relations of heart and lungs, see pp. 84 and 87. 



2. Dissection of structures in the superior thoracic aperture. 



The nerves and bloodvessels of this region are concealed by the 

 thymus gland, a large triangular flattened structure of fatty 

 consistence, extending forward from the base of the heart to the 

 anterior end of the thorax. The thymus should be carefully 

 scraped away, all vessels except those of the gland itself being kept 

 intact. 



The following structures, including the aortic arch and the 

 arteries arising from it, the superior caval veins, and the vagus, 

 phrenic, and sympathetic nerves, cannot be dissected exactly in the 

 order given below, but must be separated from one another and 

 identified as they appear. The left superior caval vein is superficial, 

 crossing the ventral surface of the aortic arch. Care should be 

 taken not to injure the nerves (c-f) in exposing the branches of the 

 subclavian artery. 



(a) The arch of the aorta (arcus aortae). Beginning at the 

 base of the heart, the aorta passes at first forward, and then 

 describing a curve, in the course of which it lies slightly to 

 left of the median plane, turns backward, along the ventral 

 surfaces of the bodies of the thoracic vertebrae. With the 

 exception of the coronary arteries (p. 260) the first branches 

 are the large paired vessels arising from the anterior wall. 

 They comprise the common carotid and subclavian 

 arteries. On the right side the carotid and subclavian 

 arise from a short common trunk, the innominate artery 

 (a. anonyma). The left common carotid arises immediately 

 to the left of this vessel or from its base. 

 The subclavian artery (a. subclavia) is the first portion of 

 the artery of the anterior limb. It passes from its point of 

 origin laterad to the anterior margin of the first rib, where it 

 is replaced by the axillary artery. Near its point of origin 

 it gives off several branches, the relations of which are 

 subject to considerable variation. They include: 



