ARTERIES OF MAMMALIA. 541 



in the same order as in most Mammalia, with the exception of 

 the constant absence of an inferior mesenteric artery. This 

 modification probably relates to the simplicity of the mesenteric 

 attachment of the intestines above described. A more marked 

 repetition of an oviparous arterial character occurs in the mode 

 of origin of the great arteries of the posterior extremities. In 

 most Mammalia these are derived from a single trunk on each 

 side the common iliac artery ; in Birds from two primary 

 branches of the aorta, one corresponding with the external iliac 

 and femoral, the other with the internal iliac and ischiadic arteries. 

 In the Kangaroo and vnlpine Phalanger the aorta gives off, 

 opposite the interspace of the two last lumbar vertebra?, the iliac 

 arteries, fig. 422, /; but these are afterwards resolved into the 

 ordinary branches of the external iliac of the placental Mammals, 

 with the addition of the ilio-lumbar artery. The trunk of the 

 aorta, much diminished in size, maintains its usual course for a 

 very short distance, and then gives off the t\vo internal iliacs, ib. 

 h, and is continued as the ( arteria sacra media,' i, to the tail. 

 The transitional character of this part of the marsupial sangui- 

 ferous system between the oviparous and placental types, is 

 manifested in the large size of the external iliacs as compared 

 with the internal iliacs, their greater share in the supply of blood 

 to the hinder extremities, and the brevity of the aortic trunk 



tf 



between their origins. In most Birds the femorals or external 

 iliacs (vol. ii. p. 190, fig. 98, 23) are smaller than the ischiadic or 

 internal iliac (ib. 26) arteries subsequently given off. At the 

 upper part of the thigh the femoral artery divides, in the Kan- 

 garoo, into two equal branches ; the one which corresponds with 

 the radial artery in the fore leg, m, fig. 419, principally supplies 

 the foot ; it passes along the back of the tibia, between the gas- 

 trocnemius interims and tibialis posticus, and divides a little above 

 the internal malleolus. The smaller division, ib. /, which follows 

 the ordinary course of the femoral along the popliteal space, is 

 lost upon the inner and posterior part of the tarsus ; the larger 

 branch winds over the malleolus to the front of the tarsus, sends 

 off the anterior tarsal artery, and is then continued along the 

 inner and afterwards the under part of the metatarsal bone of the 

 long and strong toe. 



In fig. 422, a is the trunk of the coeliac artery ; b that of the 

 superior and inferior mesenteric arteries; c is the adrenal artery 

 of the left side ; d, d, the renal arteries ; e the spermatic artery? 

 of which the left branch is shown continued to the left ovarium, 

 </, which, with the uterus, r, vagina, $, and bladder, t, is drawn to 



