DEVELOPMENT OF THE RECTUM 3 



tion of them here. The Uterature regarding those of the adult, 

 therefore, is briefly alluded to. 



More attention, however, has been paid to the investigations 

 bearing upon the embryology and histology of the pars analis 

 recti. More complete re-views of the literature on this subject 

 have been given by Braun ('01) and Zimmermann ('04). The 

 following resume of the literature is taken up under separate 

 headings. 



LITERATURE 



Boundaries and subdivisions of the rectum 



According to Merkel, Sanson in 1817 described the rectum as 

 beginning at the pelvic brim in the region of the sacro-iliac syn- 

 chondrosis. The first of its three divisions, as described by 

 Sanson, passes obliquely downwards from left to right, in which 

 it describes a slight curve toward the right and finally reaches the 

 mid-line against the third sacral vertebra. It is completely sur- 

 rounded by a peritoneal fold called the mesorectum. The second 

 part extends along the conca\'ity of the sacrum to the end of the 

 coccyx, where the third part begins. This turns backwards and 

 ends in the anus. This description was accepted and used by 

 most of the anatomists up until 1885 when Treves (according to 

 Symington) modified it. Treves considered as the rectum only 

 that part of the large intestine which is devoid of mesentery, 

 which he says, begins at the level of the third sacral vertebra. 

 That portion of the rectum previously known as the first part of 

 the rectum he includes with the sigmoid flexure under the term 

 'sigmoid' or 'omega loop.' 



Sjanington ('88) accepted this view of Treves in regard to the 

 upper limit of the rectum, but regards only the second part of the 

 rectum of the older anatomists as the rectum proper. The third 

 part he calls the 'anal canal,' which he says, had previously been 

 incorrectly described. It difTers from the rectum in that it 

 "exists normally as a longitudinal fissure." It is about an inch 

 in length. 



Merkel ('00) also regards the termination of the mesocolon as 

 the upper Umit of the rectum, but divides it into two parts. The 



