500 SANGUIFEROUS SYSTEM. 



knee, the epigastric arteries being derived from these deep 

 femoral trunks on their escaping from the pelvis. After the 

 giving off of the great external iliac or crural arteries, which, 

 from their relative size, are almost bifurcations of the aortal 

 trunk, the median sacral artery sends out a few lumbar 

 branches to the surrounding parts, a small inferior mesenteric 

 to the rectum and colon, and two minute internal iliacs to 

 the urinary and genital organs, and terminates at the end of 

 the coccyx by ramifying on the muscular and cutaneous 

 parts which it supports. 



The external iliac or crural arteries, before leaving the pelvis, 

 send off some minute renal branches to the small inferior lobes 

 of the kidneys, and on leaving that cavity to become the femo- 

 rals, they distribute the circumflex and other branches to the 

 muscles of the pelvis and thighs. As popliteal artery it gives 

 articular branches to the parts around the knee-joint, and di- 

 vides behind into the anterior and posterior tibial arteries, the 

 posterior sending out a considerable peroneal or fibular branch, 

 which descends along the fibula to form articular branches 

 around the heel. The coarse of the anterior tibial 

 artery is often marked, in aquatic birds, by an enveloping 

 plexus of its smaller anastomosing branches, which surround 

 the trunk of the vessel, and reunite to it at the heel-joint, 

 resembling in form and use the brachial and crural plexuses 

 of tardigrade mammalia. The prolonged trunk perforates 

 the lower end of the metatarsal bone, to gain the sole of the 

 foot as plantar artery, where some of its branches extend 

 to the extremities of the toes, and others ascending behind 

 the metatarsus, anastomose freely with the descending twigs 

 of the fibular artery. There is thus a nearer approach to the 

 mammiferous type in the distribution of the arterial trunks, 

 as well as in the structure of the heart of birds, than is 

 met with in the inferior vertebrata, but notwithstanding the 

 remarkable unity of organization in this class, the diversities 

 observed in the distribution of the arteries in different species 

 of birds, is almost as great as in the diversified forms of 

 quadrupeds. 



The venous blood is returned from the feet and legs of 

 birds by the deep-seated fibular and tibial veins which unite 

 to form the femoral trunk, and this uniting with the ischiadic 

 from the muscular parts around the pelvis, forms the prin- 



