ATRESIA ANI ET RECTI. 593 



STTBGICAL DISEASES OF THE POSTERIOR 

 PORTIONS OF THE RECTUM AND OF 



THE ANUS. 



In large animals the posterior end of the rectum to the extent of 

 8 to 12 inches, and in smaller ones to a correspondingly less extent, is not 

 covered by peritoneum, but attached to the surrounding structures by 

 loose connective tissue. This portion lies, therefore, beyond the peritoneal 

 cavity, and is connected above with the sacrum, and below, in males, with 

 the bladder, in females, with the vagina. 



The thin and hairless skin of the anus possesses many sebaceous and 

 sweat glands. In carnivora a small gland, about the size of a hazel-nut, 

 exists on either side of the anus, and is surrounded by the sphincter ani ; 

 it contains a greenish fatty fluid. In addition to sebaceous glands, carnivora 

 possess flask-shaped anal or perineal glands. 



I.— CONGENITAL MALFORMATIONS. ABSENCE OF THE ANUS AND 

 FORMATION OF CLOAC/E (ATRESIA ANI ET RECTI, FISTULA 

 RECTO-VAGINALIS). 



During early intra-uterine life, the anus is formed by invagination 

 of the outer coverings. In the horse and ox this happens during 

 the eighth week, in sheep, goats, and swine in the seventh, and in 

 carnivora in the fifth. In dogs and swine, less frequently in 

 ruminants and horses, the process sometimes remains incomplete, 

 and in consequence the new-born animal possesses no anal opening. 

 This vitium primce. formationis may be confined to the anus (Fig. 419) 

 or the posterior portion of the rectum may also be closed (atresia 

 recti, Fig. 420) ; less frequently the anus appears open, but a portion 

 of the rectum closed. The sphincter ani then develops regularly, 

 and a depression occurs at its middle point in place of the anal 

 opening. 



In females the rectum sometimes opens into the vagina, a con- 

 dition described as recto-vaginal fistula (anus vaginalis or cloaca 

 formation) ; Rotter saw it in a six months pig. Less frequently 

 a communication exists with the bladder (anus vesicalis). Varoldi 

 saw atresia recti with cloaca formation and open urachus in a calf. 



Symptoms. The want of an anal opening is seldom noticed in 

 animals immediately after birth ; as a rule, it is only discovered 

 when the results of suppressed defalcation become well marked ; 



R.S. Q Q 



