VI. SURGICAL DISEASES OF THE POS¬ 
TERIOR 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 uterus. 
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 which contain a yellow substance. 
I.—CONGENITAL MALFORMATIONS. ABSENCE OF THE 
ANUS AND FORMATION OF CLOACiE (ATRESIA 
ANI ET RECTI, FISTULA RECTO-YAGINALIS). 
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 primae 
formationis maybe confined to the anus (fig. 152), or the posterior portion 
of the rectum may also be closed (atresia recti, fig. 158); 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 condition 
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 defecation become well marked; the little animal’s 
