338 



AVES. 



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 

 distributed 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 meta- 

 tarsal bone, left for the purpose, when the 

 original parts of this bone were united by ossi- 

 fication. In this situation the artery might 

 receive the name of the plantar. It has 

 scarcely passed through the bone, when it di- 

 vides 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 with the descending 

 branches of the peroneal artery ; the fourth 

 branch supplies the pollex, and also sends a 

 branch from the metatarsus. The remaining 

 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 ar- 

 teries send off numerous branches, which, ra- 

 mifying in the membrane between the toes, 

 establish a communication with each other. 

 The present description has been taken from 

 birds which possess three principal toes, and 

 the back toe or pollex ; but no material diffe- 

 rence can be expected in those with a greater 

 number of toes. 



" After the trunk of the aorta has detached 

 the ischiadic arteries, it is continued along the 

 spine as the arteria sacra media (29, Jig. 170), 

 sending off small branches analogous to the 

 lumbar arteries, one of which ascends upon 

 the rectum, supplies the place of the inferior 

 rnesenteric (30, Jig. 170), and unites with the 

 superior rnesenteric as already mentioned. The 

 aorta separates above the coccygeal vertebrae 

 into three branches ; two of these, (the hypo- 

 gaatric arteries, 31, Jig. 170,) proceed laterally, 

 and are distributed to the neighbouring parts, 

 and to the kidneys and oviduct; the third 

 branch (the coccygeal artery, 32, Jig. 170) de- 

 scends 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, dif- 

 fers from that of mammals chiefly in the fre- 

 quent anastomoses, which exist more especially 

 amongst the arteries of the head and the 

 viscera. Similar communications occur between 

 the veins, which are even in some instances 

 more singular and unaccountable, as will be 

 perceived by the following description, which 

 has been taken principally from the Goose, 

 Duck, and Common Fowl." 



Besides the remarkable arterial plexuses men- 

 tioned in the general description, as the orbital, 

 the temporal, the spermatic plexuses, &c., that 

 which Barkow has described under the name of 



the plexus of the organ of incubation (Brut* 

 organe) deservese special notice. It is repre- 

 sented at 17, 18, fg. 170, and is composed 

 of branches coming from the posterior thoracic, 

 abdominal, cutaneous, and ischiadic arteries, 

 which ramify beneath the integument of the 

 abdomen, and form, by their unions, a rich net- 

 work of vessels which becomes truly extraordi- 

 nary in the time of hatching. At this period 

 many birds pluck off the feathers from the seat 

 of incubation, probably thereto impelled by the 

 great degree of heat caused by the influx of 

 blood into the incubating plexus. 



Fig. 171. 



Veins of a Fowl. 



" Veins. The venous system returns the 

 blood to the heart by means of three trunks; two 

 of these, for the convenience of description, we 

 shall call the subclavian veins (a a, fig. 166), 

 although they do not correspond in every respect 

 with the veins of this name in mammalia ; the 

 other trunk is analogous to the inferiorvena cava. 



" The subclavian vein (a, fg. 171) is com- 

 posed of the jugular and vertebral, and the 

 veins which belong to the superior extremity or 

 wing. 



" The vertebral vein is lodged in the same 

 canal with the vertebral artery; it anastomoses 

 between the vertebrae with the veins upon the 



