410 Bashford Dean Meynorial Volume 



RECTUM AND RECTAL GLAND 



In most elasmobranchs the portion of the digestive tube extending from the valvular 

 intestine to the anal opening is differentiated into two parts, colon and rectum. In 

 conformity v^ith the usual practice I have distinguished two regions, colon (c.) and 

 rectum (r.), in Text-figure 72; but these parts are much aHke and there is no definite 

 boundary' between them, therefore I shall here consider the two regions, combined, under 

 the term rectum. 



The lengths, in my three specimens, are given in Table I, p. 412. It will be noticed 

 that in specimen No. II the rectum is unusually long. In each specimen, the viridth of the 

 rectum is about the same throughout its length, so that in ventral view it appears to be of 

 uniform diameter; but when \-iewed from the side, the rectum appears somewhat funnel- 

 shaped since it enlarges toward the anus. In specimen No. I the rectum is 9 mm. wide 

 and has a dorsoventral diameter of 13 mm. at its cephaHc end, 16 mm. at its middle, and 

 20 mm . at the anal end. Similar proportions are found in my other specimens. In speci- 

 men No. II the rectum is 6 mm. v.dde; its dorsoventral diameter is 10 mm. at the cephalic 

 end, and 16 mm. at the anal end. In specmien No. Ill the width is 8 mm.; the dorso- 

 ventral diameter is 10 mm. at the cephaHc end, and 18 mm. at the anal end. From these 

 dimensions it is evident that in each case the rectum is laterally compressed, and dorso- 

 ventrally enlarged to\^-^rd the anus. The anal opening faces both ventrad and caudad, 

 so that It leads directly to the exterior and also into the cloaca. The wall of the rectum 

 is from 1 to 2 mm. thick. The Kning is cast into slight longitudinal folds which are more 

 pronounced in specimen No. I. There is no mesorectum save the very small mesentery 

 supporting the rectal gland, at the extreme caudal end of the rectum. 



The rectal gland is a laterally compressed, somewhat kidney-shaped body situated 

 in the angle between the rectum and the cloaca. In Text-figure 72 the rectal gland 

 (r.g.) is shown turned tou-ard the left. The dimensions in my three specimens are: No. 

 I, 20 X 13 x 6 mm.; No. II, IS x 14 x 7 mm.; No. Ill, 17 x 12 x 9 mm. The duct leads 

 anteriorly and ventraUy to open into the dorsal side of the rectum. In all three specimens 

 the duct is 13 mm. long. The opening is distinctly \^sible on the inner surface of the 

 rectum; it is guarded by a \^lve-Hke flap and readily admits a probe which passes easily 

 into the rectal gland. In specimen No. I the opening is situated 20 mm. from the valvular 

 intestine, just midway in the length of the rectum. In specimen No. II the opening is 

 situated 40 mm. from the \^lvular intestine, also at the middle of the rectum. In speci- 

 men No. Ill the opening is situated 15 mm. from the valvular intestine and 25 mm. 

 from the anus. 



The proximity of the rectal gland to the cloaca has led to its being figured with the 

 reproductive system. Thus Garman (1885.2) shows in his Fig. 2, pi. XIX (reproduced 

 as my Text-figure 92, p. 440) an organ labeled "caecal pouch" which corresponds with 

 what I have called the rectal gland. He does not describe its duct, but in his Fig. 3, pi. 

 XIX a duct appears to open from this gland into the rectum. Giinther (1887) figures 

 a gland (my Figure 19, plate V) in the position of a rectal gland, and asserts that it opens 



