326 ANATOMY OF THE RABBIT 



passes backward to the internal surface of the thoracic 

 wall, giving off the first three (or four) intercostal 

 arteries in the intercostal spaces, and also small 

 branches to the oesophagus, the trachea, and the 

 bronchi. 



(5) The internal mammary artery (a. mammaria interna), 

 the first portion of which runs along the inner surface 

 of the ventral wall of the thorax and has been removed 

 with it, passes backward to the ventral abdominal 

 wall as the superior epigastric artery (a. epigastrica 

 superior) anastomosing with the inferior epigastric 

 (p. 223). 



{b) The superior caval vein (v. cava superior) is formed at the 

 base of the neck by the union of the internal and external 

 jugular veins, the latter vessel receiving at this point the 

 subclavian vein (v. subclavia). The right superior caval 

 passes almost directly backward, crossing the ventral 

 surface of the right subclavian artery, and enters the an- 

 terior portion of the right atrium. The left vessel crosses 

 both the left subclavian artery and the arch of the aorta 

 and turns mediad over the dorsal surface of the heart to reach 

 the posteromedial part of the right atrium (Fig. 62, p. 111). 

 The transverse terminal portion of the left superior caval 

 vein constitutes the coronary sinus and is retained in 

 reduced size in species, such as man, where the rest of the 

 left superior caval vessel degenerates during development. 



(c) The vagus nerve on the right side crosses the ventral surface 

 of the subclavian artery, passing dorsad over the dorsal 

 surface of the bronchus to the wall of the oesophagus. It 

 gives off the recurrent nerve (n. recurrens), which curves 

 round the subclavian artery and passes forward dorsal to 

 the latter and then along the side of the trachea to the 

 muscles of the larynx (except the cricothyreoideus). On 

 the left side the vagus descends dorsal to the superior 

 vena cava, crosses the ventral surface of the arch of the 

 aorta to the point of connection of the arterial ligament 

 (p. 330), where it gives rise to the recurrent branch, and 



