THE SUPERIOR CAVA. 49 



near which organ the vessels lie alongside the bronchus 

 and pulmonary artery ; these veins open into the left 

 auricle. 



116. Note the small coronary arteries and veins lying 

 on the surface of the ventricle. The arteries spring 

 from the innominate trunk, and the veins enter the 

 venous sinus. 



U7. Trace out the system of the two superior cavse ; 

 as a preparatory step, remove the skin from the dorsal 

 side of the neck and inflate the vessels from some one 

 of their smaller branches. This inflation will need to 

 be repeated from time to time as the dissection pro- 

 ceeds, as many of the branches when empty are very 

 hard to follow. 



U8. The superior cava, shading insensibly into the 

 venous sinus at one end, is composed at its other, a 

 short way from the heart, by the junction of three 

 considerable trunks. Dissect them out on the left side. 



a. The inner division (internal jug^ular) runs up 

 the side of the neck, where it is found accom- 

 panying the carotid artery and vagus nerve. 



b. The middle and largest division (subclavian) 

 may be traced to the forelimb. Near the base 

 of the neck it receives a cervical branch {ex- 

 ternal jugular) which is to be followed up the 

 neck to the neighborhood of the occiput, 

 where it is formed by the union of a branch 

 {facial vein) from the mandibular region with 

 a cross branch, which may be followed across 

 the middle line by dividing some muscles pass- 



3 



