THE ABDOMINAL AORTA 253 



tissue attaching the organs to the pelvis and the base of the tail, 

 the urinogenital tube and the rectum may be dissected out in a 

 single piece, their blood-vessels and the attaching peritoneum being 

 the only other parts divided. The rectum should then be separated 

 from the urinogenital organs. 



The middle haemorrhoidal artery (a. haemorrhoidalis media), a branch 

 of the hypogastric (p. 255), supplies the lateral walls of the rectum and the 

 vestibulum. The internal pudendal artery, accompanied by the corresponding 

 vein and nerve, passes over the side of the distal part of the vestibulum to the 

 clitoris after giving off the inferior haemorrhoidal artery to the terminal 

 portion of the rectum and to the rectal or anal gland, This gland is an elongated, 

 paired organ, the pair almost surrounding the rectum a short distance in front of 

 the anus and pouring into it an oily secretion. The rectum is connected with 

 the base of the tail by the rectocaudal muscle, a somewhat spindle-shaped 

 involuntary muscle originating on the body of the second caudal vertebra and 

 inserted a little further forward on the dorsal side of the rectum. The external 

 and internal anal sphincters are closely related thin muscles enclosing the rectum 

 and the vestibulum, the former having its origin on the dorsum of the tail. 



At each side of the external opening of the vestibulum, just under the skin, 

 lie the paired inguinal glands. As in the male, each of these comprises a larger, 

 medial, dark portion and a smaller lateral, white portion, the latter sebaceous, 

 the former a modified sweat-gland secreting an odoriferous liquid. Ducts from 

 both empty upon the hairless inguinal spaces. 



In the urinogenital ducts, examine the extent of the vagina 

 backward and its connection with the canal of the bladder (female 

 urethra) to form the common vestibulum. The canal and the 

 vestibulum together correspond with the male urethra (cf. Fig. 68, 

 p. 121). The bulbourethral gland (gl. bulbourethralis) situated 

 in the dorsal wall of the vestibulum, is similar to that of the male 

 (cf. p. 250). 



If the vestibulum be slit open and the incision be extended into 

 the bladder and also forward into the left uterus the apertures of 

 these structures may be examined from the interior. There is a 

 separate external uterine aperture (orficium externum uteri) open- 

 ing from each uterus into the vagina. 



VII. THE ABDOMINAL AORTA, INFERIOR CAYAL 

 VEIN, AND SYMPATHETIC TRUNKS 



The dissection and removal of the intestines and urinogenital 

 organs clear the dorsal body-wall for an examination of the 



