72 STUDIES IN COMPARATIVE ANATOMY. 



We have traced the arteries tkroughout the body, but the 

 details of distribution offer few significant features. 



Anterior Vence Cavce. — Dr Watson observes that " each was 

 formed by the junction of three large trunks a short distance in 

 front of the arch of the subclavian artery. Of these, one came 

 from the outside, a second came from the direction of the middle 

 line, whilst an intermediate one passed directly backwards. 

 The vena cava of each side, thus formed, passed directly back- 

 wards, receiving in its course several smaller veins, one of which 

 was the trunk formed by the union of the companion veins of 

 the mammary artery, and finally opened into the right auricle. 

 In addition to these, the right anterior cava received the azygos 

 vein immediately before piercing the pericardium. There was 

 no trace of a small or left azygos vein : the posterior cava, 

 immediately after piercing the diaphragm, opened into the 

 auricle." 



Veins and Venous Plexuses. 



The most striking peculiarity of the veins lies in the plexuses 

 and free anastomoses which occur in nearly all sheltered parts 

 of the body. We find extensive plexuses in the superficial and 

 deep temporal, pharyngeal, pectoral, anterior and internal femo- 

 ral, popliteal, axillary, and brachial regions, besides less impor- 

 tant communications elsewhere. The veins are in general large 

 and capacious. In some cases, at least, valves are wanting in 

 the plexuses, but we were unable to test the freedom of com- 

 munication in different directions by a general venous injection. 



Su;perficial Temporal Plexus. — This lies above the zygoma and 

 behind the eye, beneath the temporal gland and superficial to 

 the temporal muscle. Its communications are with the tem- 

 poral vein by means of a superficial branch which crosses the 

 posterior end of the zygoma, with the internal maxillary and 

 facial veins, and with the deep temporal plexus. The temporal 

 artery crosses the zygoma immediately behind the vein noticed 

 above, and gives branches, which do not inosculate, to the area 

 of the venous plexus.^ 



^ Neugebaur has described a temporal venous plexus in the goose [Nova Acta, 

 vol. xxi. p. 521. 1845). In Froriep's Notizen, Oct. 1832, p. 39, Otto has de- 



