414 v///-: im.KxTivr \rr.\it.\Ti* /.v MAM.MAIJA. 



STBUCTURE.- The ncrmitt membrane does not envelop the whole of the 

 organ; that portion which traverses the bottom of tin pelvic Oftvity being 

 left uncovered by it. The muscular layer is very thick, ainl composed 

 of large, longitudinal, and slightly spiral fasciculi, beneath which are 

 annular fibres. The mucous memlirane, loosely attached to the muscular 

 tunic, shows longitudinal and transverse rugfe. The small //>< /</<//' an<l the 

 internal pudic artery (artery of the bulb) supply these membranes with blood. 

 The nerves are derived from the pelvic or Itypogatlne jili'.i //x. 



ANUS. The anus, or posterior opening of the digestive tube, is situated 

 at the posterior extremity of the rectum, under the base of the tail, where. 

 in Solipcds, it can bo seen forming a rounded prominence which diminishes 

 with age. It is the border or margin of this orifice, which is corrugated 

 like the mouth of a draw-purse, where the intestinal mucous membrane 

 meets with, and is continued by, the external skin. 



In proceeding from within outwards, there are found the following 

 elements entering into the structure of the anus : 1, The mucous membrane 

 of the rectum; 2, The prolongation of the circular and longitudinal fibres 

 of the muscular layer, forming what is named the internal H)>liiu<-trr . 

 3, A sphincter muscle, composed of red fibres, which receives the insertion of 

 a retractor ; 4, The fine, hairless, and closely-attached skin, which covers 

 the sphincter ; though destitute of hair, it is rich in sebaceous follicles. We 

 will only notice the muscles. 



The SPHINOTKB OF THE ANUS, (sphincter am') is formed of circular fibres, 

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

 below, with the muscles of the perineal region. Comprised between the 

 skin and the prolongation of the muscular layer of the rectum, this muscle 

 is (during life) in a state of almost permanent contraction to keep the anal 

 aperture closed, it being only relaxed during the expulsion of ftecal matters. 



The BETKACTOB OF THE ANUS, or iscHio-ANAL muscle (retractor ant), is a 

 wide band attached to the internal surface of the ischiatic ligament (sacro- 

 ischiatic), and even to the supercotyloid crest, by aponeurotic fibres. The 

 fasciculi composing this band are all parallel to each other, while their 

 posterior extremities are insinuated beneath the sphincter, and are confounded 

 with 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 faeces : on act which always results in carrying 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 haemorrhoidal nerve supplies them both with filaments. 



DIFFERENTIAL CHARACTERS OF THE INTESTINES IN OTHER THAN 6OUPKI> ANIMALS. 



Iii the domesticated animals, the intestines vary as much in their dimensions, length, 

 and diameter, as in their general disposition. 



1. The Intestines of Ruminants. (Fig. 208.) 



The small intestine of the Ox floats at the extremity of a broad mesenterio lamina, 

 which is narrower in front than behind, piano throughout, except at its intestinal Ix.nli-r, 

 which is of considerable length, and is folded into a multitude <>f fatuous. TNNJC iln 

 length of the small intestine of the Horse averaging alnmt 4!) yards it is ah-nit 

 one-half its diameter. The duodenum, at fintt Biihtuincil by the omentinu, \\liieh 

 attaches the small curvature of the fourth compartm nt of the fiomach t<> tin- interior 

 fissure of the liver, forms a particular loop, which in in eon tact with the suolumbai 

 region before it goes to be suspended by the large mesentery, and to be continued by the 

 convolutions of the floating portion. The ileum terminates as in the Horse. Tin, 



