1 674 



HUMAN ANATOMY. 



Fig. 1422. 



measure as much as 15 mm. from its upper end to the ano-rectal groove ; probably 

 this distance is usually about i cm., while what may practically be called the canal is 

 twice as much, or even more. It is longer in men than in women. In the male the 

 beginning of the anal canal is near the lower part of the prostate and the mem- 

 branous urethra, at a point from 3. 5-4 cm. in front of and somewhat lower than the 

 tip of the coccyx. Lower still, the bulb of the urethra is separated from the anal 

 canal by the pyramidal mass of connective tissue constituting the perineal body. 

 The latter is of greater importance in the female, and separates the anal canal from 

 the lower part of the vagina and from the vulva. The moist and dark skin which 

 is puckered up to form the continuation of the anal canal is at first very thin, but 

 gradually assumes the appearance of ordinary integument. The so-called anal glands 

 surrounding the anus are of two kinds, both of which have their orifices in this skin. 

 Those nearest to the boundary line are sebaceous follicles, and external to them is a 

 zone of large sweat-glands. Just at the termination of the skin apparently forming the 

 end of the canal there is, especially in the male, a considerable development of hair. 

 Structure of the Rectum. — The mucous coat is thick and vascular, and 

 corresponds in its general histological details with the mucosa of other parts of the 

 large intestine. The glands of Lieberkiihn, however, are exceptionally large, at- 

 taining a length of .7 mm. The muscularis 

 mucosae is better developed than in the colon. 

 The rectal valves (plicae transversales recti) 

 are two or three folds, exceptionally four or 

 five, projecting like transverse shelves into 

 the cavity when it is distended, and hanging 

 loose when it is not. They are semilunar 

 in shape, with the greatest breadth from the 

 attached border to the free edge, ranging 

 from I cm. to more than 3 cm. They cor- 

 respond to, or rather are the causes of, the 

 constrictions between the saccules. They 

 contain all the coats of the gut, except that, 

 chiefly on the posterior wall, some of the 

 longitudinal muscle-fibres pass outside of 

 them, thus securing the fold. In large folds 

 there is an accumulation of the circular 

 fibres. These folds tend to be effaced in 

 the isolated and opened rectum, but they 

 are unquestionable, being shown by casts 

 and frozen sections, and in both the living 

 and the dead body when placed in the 

 knee-chest position with the rectum cleared 

 of faeces and distended with air. They are placed laterally, and have in common 

 that their points cross the middle line, although not symmetrically, extending more 

 onto the front than the back. According to the usual arrangement, the lowest, 

 which is also the smallest, projects from the left ; the second, the largest, from the 

 right; and the third from the left. The first is about 2.5 cm. (i in.) above the 

 anal canal and the second about as much higher. If the first — as often happens — 

 be wanting, the second is not necessarily any lower. The third is usually at about 

 the same distance above the second, but is subject to greater variations, since the 

 tw'O may be very near together.^ The cohanns of Morgagni are a series of per- 

 manent vertical folds of mucous membrane passing from the anal canal upward into 

 the rectum. The number of these folds varies from five to considerably more than 

 ten, which latter number is perhaps about the average. The length of the folds is 

 in most cases from 1-2 cm., but some are considerably longer. They are broad 

 and highest at their anal end, or base, from which they diminish to the upper end, 

 a transverse cut near the lower end showing them to be triangular on section. The 

 valves of Morgagni are semilunar folds of the mucous membrane connecting the 

 bases of the columns of the same name, and forming with them a number of 



* Otis : Anatomische Untersuchungen am menschliclien Rectum, Leipzig, 1887. 



Folds of rectum seen ?fter dilatation. (Otis.) 



