460 COMPARATIVE ANGIOLOGY. 



any of the domesticated ruminants ; some of its branches, however, lead to the 

 formation of structures 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-spinal, enters 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 mirabile; it is 

 situated 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- 

 cranial portion of the internal corotid in the solipede." From this artery are 

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

 passes backwards, forms a convergent anastomosis with its fellow, thus con- 

 stituting the basilar trunk, leading to the middle spinal artery. Another 

 arterial plexus is found. 011 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 subcutaneous 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 small 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 in 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. 



THE LYMPHATICS. 



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

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

 its extent. Some complexity 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 itself. 



OMNIVORA. 



In the hog the branches of the posterior aorta 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. After giving off the gluteal and 



