THE INTESTINES. 4S5 



destitute of hair, it is rich in sebaceous follicles. "We will only notice the 



The Sphincter of the Anus (sphincter ani) is formed of circular fibres, 

 some of which are fixed above, under the base of the tail, and are mixed, below, 

 with the muscles of the perineal region, especially the posterior constrictor of the 

 vulva in the female ; in the male, these fibres are lost on the surface of the 

 perineal aponeurosis. Comprised between the skin and the prolongation of 

 the muscular layer of the rectum, this muscle is (during life), owing to its 

 tonicity and natural shape, in a state of almost permanent contraction, in order 

 to keep the anal aperture closed ; it is only relaxed during the expulsion of 

 faecal matters or intestinal gases. 



The Retractor of the Anus, or Ischio-anal muscle {retractor ani), is a 

 wide band, attached to the internal surface of the sacro-sciatic ligament, and even 

 to the supra-cotyloid crest, by aponeurotic fibres. The fasciculi composing this 

 band are all parallel to each other, while their posterior extremities are insinnated 

 beneath the sphincter, and are mixed wdth its fibres. This arrangement of the 

 retractor ani clearly indicates that it pulls the anus forwards, re-establishing it in 

 its normal position after expulsion of the f feces — an act that always results in 

 canying the posterior extremity of the rectum backwards. 



These two muscles are of a red colour, and belong to those of animal life. 

 Their vessels are derived from the same sources as those of the rectum. The 

 Jmmorrhoidal nerve supplies them both with filaments. 



Differential Characters of the Intestines in the other Animals. 



In the domesticated auimals, the intestines vary as much in their dimensions, length, and 

 diametei-, as in their general arrangement. 



1. The Intestines of the Rabbit (Fig. 286). 



As for the stomach, so for the intestine we place the Ritbhit immediately after Solipeds, 

 'because the analogies are more marked in them than in the other animals. 



The small intestine does not show any dilatation at its commencement, but it has an 

 enormous one at its termination in the caecum, and which has in its interior a fine Fever's patch ; 

 for this reason it is named the glandular pouch. The other agminated glands are equally 

 very developed, and are remarkable for their thickness, thougli they are not numerous — being 

 •only seven or eight. They are easily seen through the thin wall of the intestine, when this 

 has been washed and inflated. This intestine reaches the caecum in passing before the first 

 portion of the colon. 



The cseciim is also proportionately more voluminous than in Solipeds. As in them, it has 

 the sliape of a cone suddenly attenuated towards its summit, and forming an arch or crook at 

 its upper part; but this crook is not very distinctly separated from the colon, and is continuous 

 witli it, without showing any constriction. Its internal surface is very curious, as it is 

 traversed by a spiral ridge of mucous membrane, which describes about twenty turns on the 

 wall of the intestine, and ceases about 4 inches from the point. This layer — the presence of 

 whicli is marked by a depression externally, that corresponds to its fixed border — may be about 

 \ of an inch or more in depth. The inferior cul-de-sac of tlie viscus, into which this fold does 

 not enter, forms, like the termination of the small intestine, a veritable glandular pouch. The 

 orifice of this latter intestine does not project into the interior of the caecum ; Bauhin's valve is 

 a disc, pierced like the iris, and fixed by its larger circumference around the margin of that 

 opening. 



The colon also shows the division into two portions — the first, dilated and sacculated, and 

 even provided with rudimentary longitudinal bands on its external surface — is covered inter- 

 nally by round and regularly arranged prominences which resemble tliick villi, or traces of 

 tlie valvulae conniventes; the second, narrower and uniformly cylindrical, lies alongside tlie 

 duodenum, ascends into the diaphragmatic region in company with that intestine, and termi- 

 nates in the rectum, after describing several floating convolutions. On the sides of the rectum 

 nre two elongated glands which open into the perineal region. 



