388 DIGESTION. 



into an external, a middle, and an internal layer. The pos- 

 terior fibres of the external layer pass away from the lower 

 portion of the rectum, are reflected backward along the con- 

 cavity of the sacrum, and are attached to the promontory. 

 These fibres, which are generally pale, Sappey proposes to 

 designate as retractors of the anus. A few of the posterior 

 fibres are attached to the aponeurosis and the parts between 

 the coccyx and the promontory. In front, the external fibres 

 are attached to the aponeurosis which covers the vesiculse 

 seminales, and laterally they are inserted into the deep pel- 

 vic fascia. The termination of the middle layer of the 

 fibres is less clearly made out. Those situated at the sides 

 of the rectum are inserted into " a very dense cellulo-fibrous 

 band, which, by its opposite surface, gives insertion to a 

 great number of fibres of the levator ani." The others are 

 many of them continuous with the fibres of the levator 

 ani as they pass along the floor of the pelvis. Some of the 

 fibres of the deep layer are attached by little tendons 

 which pass between the external and the internal sphincter 

 to the deep portions of the skin which encircle the anus. 1 

 The importance of closely studying the attachments of these 

 fibres will be appreciated when we come to treat of defecation. 

 Over the caecum and the colon, the anterior band of mus- 

 cular fibres is from one-third to one-half an inch in width. 

 The postero-external band is not more than half as wide, and 

 the postero-internal band is even narrower. The muscular 

 bands are much shorter than the canal itself, and their attach- 

 ment to the walls gives the intestine a peculiar sacculated ap- 

 pearance. That this is produced by the arrangement of the 

 muscular fibres may be demonstrated by dividing them in 

 various places or removing them entirely, when the canal may 

 be extended to double its original length. Between the bands 

 there are no longitudinal muscular fibres ; but circular or 

 transverse muscular fibres exist throughout the whole length 

 of the large intestine. In the csecum and colon, the circular 



1 SAPPEY, op. cit., pp. 226, 227. 



