532 DISSECTION OF THE PELVIS. 



this is best marked for a short distance in front of the bulb, and assists in 

 dividing that part into two lobes. The trabecular bands are much finer, 

 and more uniform in size than in the corpora cavernosa. 



Bloodvessels. The arrangement of the bloodvessels in the erectile 

 structure of the corpus spongiosum is similar in the bulb to that in the 

 corpora cavernosa; but in the rest of the spongy substance the arteries 

 are said to end in capillaries in the usual way. The helicine terminations 

 of the arteries are absent from the glans penis, where the veins form a 

 very close and regular plexus. 



The arteries are derived from the pudic on each side : one, arteries of 

 the bulb, enters the bulb behind ; and several in front, offsets of the dorsal 

 artery, penetrate into the glans. Kobelt describes another branch to the 

 bulb at the upper aspect. 



Most of the veins, including those of the glans, end in the large dorsal 

 vein of the penis, some communicating with veins of the cavernous body ; 

 others issue from the bulb, and terminate in the pudic vein. 



Nerves and lymphatics. The nerves of the penis are large and are 

 supplied by both the spinal and sympathetic nerves : on the glans penis 

 they are furnished with Pacinian bodies. The superficial lymphatics of 

 the integuments, and those beneath the mucous membrane of the urethra, 

 join the inguinal glands; the deep accompany the veins beneath the arcli 

 of the pubes, to end in the lymphatic glands in the pelvis. 



THE RECTUM. 



Dissection. The rectum is to be washed out, and then distended with 

 tow ; and the peritoneum and the loose fat are to be removed from it. 



The lower end of the large intestine, which is contained in the pelvis, 

 is not sacculated like the colon, but is smooth on the surface, the longitudi- 

 nal bands of the colon being absent from it. 



It is about eight inches in length ; and its average diameter is that of 

 the sigmoid flexure of the colon. Its size is uniform as far as the lower 

 extremity, where it is dilated, particularly in old people ; but at the aper- 

 ture of termination in the anus the gut is smaller than elsewhere. 



Structure. The rectum contains in its wall a peritoneal, a muscular, a 

 mucous, and a submucous stratum ; and the muscular and mucous layers 

 have certain characters which distinguish this part of the intestinal tube. 



The peritoneum forms but an incomplete covering, and its arrangement 

 is referred to in the description of the connections of the pelvic viscera 

 (p. 505). 



The muscular coat consists of two planes of pale or unstriated fibres, 

 viz., a superficial or longitudinal, and a deep or circular. The longitudi- 

 nal, continuous with those in the bands on the colon, are here diffused to 

 form a stratum around the gut. The circular describe arches around the 

 intestine, and become thicker and stronger towards the anus, where they 

 are collected in the band of the internal sphincter muscle. 



The mucous coat is more movable than in the colon, and resembles in 

 this respect the lining of the oasophagus ; it is also thicker and more vas- 

 cular than in the rest of the large intestine. 



When the bowel is contracted the mucous lining is thrown into numer- 

 ous accidental folds ; but some near the anus are longitudinal, inclosing 

 submucous muscular fibres, and form the columns of Morgagni. There 

 are other three permanent folds (Houston) which are half an inch or less 



