202 ANATOMY OF VERTEBRATES. 



the groove along the anterior surface of the metatarsal bone, 

 and covered by the tendon of the flexor digitorum. On coming 

 near the foot it sends off an artery, which di\ddes, behind the 

 joint of the internal toe, into two branches; one goes between 

 the internal and middle toes, ramifies upon both their joints, and 

 unites with the artery in the sole of the foot ; the other is dis- 

 tributed between the internal toe, and the pollex or toe which 

 occupies the place of the great toe ; the main artery now passes 

 to the sole of the foot through a hole in the metatarsal bone, left 

 for the purpose, when the original parts of this bone were united 

 by ossification. In this situation the artery might receive the 

 name of the plantar. It has scarcely passed through the bone, 

 when it divides into six branches ; three of these are distributed 

 to the tendons and ligaments, &c., on the outside of the foot and 

 the back of the metatarsus, anastomosing -svith the descending 

 branches of the peroneal artery ; the fourth branch supplies the 

 pollex, and also sends a branch from the metatarsus. The re- 

 maining branches are designed for the three principal toes ; one 

 dips in between the internal and middle toe, unites with the 

 anterior branch of the metatarsal artery, and is distributed to the 

 sides of these toes as far as their extremity. The other divides, 

 between the external and middle toe, into two branches, which 

 run upon the opposite side of each of these toes to the end. 



' When the feet are webbed, the digital arteries send ofl* nu- 

 merous branches, which, ramifying in the membrane between the 

 toes, establish a communication with each other. The present 

 description has been taken from birds which possess three prin- 

 cipal toes, and the back toe or pollex ; but no material difference 

 can be expected in those with a greater number of toes. 



' After the trunk of the aorta has detached the ischiadic ar- 

 teries, it is continued along the spine as the arteria sacra media, 

 fig. 93, 29, sending off small branches answering to lumbar 

 arteries, one of which ascends upon the rectum, supplies the place 

 of the inferior mesenteric, ib. so, and unites mth the superior 

 mesenteric as already mentioned. The aorta separates above the 

 coccygeal vertebrae into three branches ; two of these (the hypo- 

 gastric arteries, ib. 31, proceed laterally, and are distributed to 

 the neighbouring parts, and to the kidneys and oviduct ; the 

 third branch (the coccygeal artery, ib. 32) descends to the very 

 point of the tail, upon the muscles and quills of which its branches 

 are exhausted. 



* The arterial system of Birds, besides the distinguishing 

 characters above mentioned, differs from that of Mammals chiefly 



