460 COMPARATIVE ANGIOLOGY. 



uny of the domesticated riiinmaiits ; some of its branches, however, lead to the 

 formation of structoren interesting to the anatomist ; these are the arterial 

 plexuses, or retia mirabilia, the largest of which is formed inside the cranium 

 by branches from the internal maxillary artery. One of these branches, the 

 spheno-spinaly en^-srs the cranium by the foramen ovale, and, as a rule, two 

 arteries of the rete enter by the anterior common foramen ; the first of these 

 inclines forwards, the two latter backwards. The three arteries anastomose by 

 forming a small and intricate plexus known as the cranial rete mirahilej it ia 

 8itua%:-d at the side of the sella' turcica of the sphenoid bone, communicating 

 with its fellow posteriorly, and giving off superiorly the encephalic artery, a 

 branch considered by Chauveau to be "completely analogous to the intra/- 

 craniftl portiou. of the internal corotid in the solipede." From this artery are 

 given off the cerebral branches, anterior, middle, and posterior ; the last 

 passing backwards, forms a convergent anastomosis with its fellow, thus 

 constituting the basilar trunk leading to the mldrlle spinal artery. Another 

 arterial plexus is found on . the ophthalmic artery just where the arteries of 

 the eye are given off. The glosso-facial artery is found only in the larger 

 ruminants. 



Veins.. 



The suheutaneous abdominal vein is very large in the ox, the subcutaneous 

 thoracic being proportionally small. The saphenic veins differ from those of 

 the horse, the external one being larger than the internal. The jugular vein 

 is large, and there is a small accessory jugular which varies much in size, 

 originating in the occipital vein, and joining the great jugular near its termi- 

 nation. The angular vein of the eye is very prominent in sma'll ruminants. 



The digital veins of the posterior limb are three in number, an anterior or 

 common one between the digits, formed by twigs from the solar plexuses of 

 both, and two lateral ones placed on the outer sides of the digits. There are 

 usually five metatarsal veins ; two anterior deep ones which accompany the 

 great metatarsal artery ; an anterior superficial one, which forms one root of 

 the external saphenic ; an internal and external posterior vein, which pass 

 upwards over the tarsus, and assist i^ forming the saphenic veins. In the 

 anterior limb there is a fourth or posterior digital vein, which accompanies the 

 common digital and internal metacarpal arteries. 



Ths Lymphatics. 

 In the large ruminants the thoracic duct not only exhibits great complexity 

 of form, but it is also extremjely variable, being sometimes double throughout 

 its extent. Some compleintj generally exists near its anterior termination. It is 

 more deeply seated than that of the horse, lying between the right upper part 

 of the aorta and the vertebral column, buried in a quantity^ of fat. It does not 

 pass through the aortic hiatus, but has an opening in the diaphragm for itsel£ 



OMNIVORA. 



In the hog the branches of the posterior £S)rta call for no remark, since they 

 resemble those of the horse, excepting the mesenteric arteries, which are distri- 

 buted somewhat like those of the ruminant. Alter giving off the gluteal and 



