THE VASCULAR SYSTEM 209 



branches which anastomose frequently, forming a fine vascular net- 

 work, amounting almost to a 'rete mirabile'. 



Besides giving off the posterior oviducal arteries their common 

 stem also gives rise to one or both superficial renal arteries, and to a 

 pair of mesial do acal 3.rtenes (Figs. 64 and 64a) (a.cl.m.). These are 

 essentially vessels of the male sex although also present in the female. 

 In the male, these vessels, together with the superficial renal arteries, 

 are the principal branches of the common stem, while the only 

 vessels which may be considered the homologues of the oviducal 

 branches of the female are two very small twigs arising from the 

 superficial renals to the ureters and Miiller's duct. In the female 

 it is the cloacal branch which is vestigial. 



In the male (Fig. 64a) after giving off the renal vessels, the cloacal 

 artery proceeds dorso-posteriorly to the edge of the M. caudali- 

 femoralis, to which it sends a branch, and it also gives a branch to the 

 muscles of the back. The artery then turns sharply ventralwards 

 along the anterior aspect of the cloacal gland, giving off two large 

 branches which enter the gland mesially. A small continuation of 

 the vessel finally anastomoses with a cloacal branch of the vesicular 

 artery (q.v.). 



The drawings (Figs. 64 and 64a) have been carefully made from 

 a single specimen of each sex. Small individual variations from them 

 may therefore be expected. 



(b) The middle oviducal arteries (a.od.2) usually arise from the 

 same section of the aorta as the posterior mesenteric vessels, but 

 their exact point of origin varies considerably. They are usually 

 asymmetrical, but either side may be the more anterior. From what- 

 ever level they may arise, however, they always run parallel with the 

 aorta for a greater or shorter distance before turning lateralwards, 

 dorsal to the kidneys, to pass via the mesentery to the oviduct 

 at approximately the same level. Their branching commences within 

 the mesentery before reaching the oviduct. Although they are vessels 

 of considerable size they appear to supply only a comparatively short 

 section of the latter organ, namely, just anterior to the vascular net- 

 work of the posterior arteries. Renal arteries are given off by these 

 vessels from the section which runs parallel with the dorsal aorta. 

 It is probable that the posterior and middle oviducal arteries are 

 together equivalent to Osawa's AA. uterinae. 



{c) The anterior oviducal 2Lrtene.s {?A. oviductus — Osawa) (a.od.i) 

 frequently arise in conjunction with a dorso-lumbar vessel, but they 

 may come off independently from the dorsal aorta, or from the sub- 

 clavian arteries, or even from the vertebral artery without any direct 



