THORAX AND ABDOMEN OF THE HORSE 161 



The pelvic fascia (Fascia pelvis). — The wall of the pelvis is 

 lined by a layer of fascia (parietal pelvic fascia), which is connected 

 with all the muscles and blood vessels applied to the wall, and from 

 which sheets pass into the several peritoneal folds. Wherever there is 

 a free bony surface, as, for example, on the ventral surface of the ilium, 

 the fascia fuses with the periosteum. At the outlet of the pelvis it is 

 continued on to the surface of the pelvic viscera (visceral pelvic fascia), 

 and in this way assists in the closure of the outlet. 



The fascia of the pelvis is continuous with that clothing the 

 internal surface of the transverse abdominal muscles (fascia trans- 

 versalis) and with the iliac and coccygeal fascise. 



The rectum (Intestinum rectum). — In the male, the greater part 

 of the cavity of the pelvis is occupied by the Hask-shaped rectum,^ 

 the terminal and widest part of which is known as the ampulla. In 

 length the rectum is from 20 to 30 cm. In position it occupies the 

 median plane, except at the pelvic inlet where the pelvic flexure of the 

 great colon generally pushes it towards the left. 



The first part of the rectum is provided with a mesentery (meso- 

 rectum), but this gradually narrows, and the terminal part of the tube 

 is connected with the sacrum and the coccygeal musculature by loose 

 connective tissue. 



The ventral relations of the rectum of the male are the urinary 

 bladder, the terminal parts of the ureters, the seminal vesicles, the 

 prostatic utricle, the terminal part of the ductus deferentes, the 

 prostate, the bulbo-urethral glands and the pelvic part of the urethra. 



It will be observed that the wall of the rectum is smooth and 

 reveals the presence and course of longitudinal muscular fibres. 



The last part of the rectum which surrounds its external orifice, 

 the anus, forms a projection covered with soft, thin, hairless and 

 pigmented skin, in which sebaceous and sweat glands are numerous. 

 Surrounding the anus, and lying immediately under the skin, is the 

 well-developed external sphincter^ of the anus (m. sphincter ani 

 externus). Two portions of this muscle may be distinguished. The 

 deeper and more extensive fibres form a complete ring-like invest- 

 ment to the terminal part of the rectum. Lying superficial to these 

 is a narrow band on each side with a dorsal attachment to the fascia 

 of the tail and the coccygeus muscle. Ventrally some of these fibres 

 blend with the retractor muscle of the penis, while others mix with 

 the circular fibres of the rectum. The anal canal, about 5 cm. in 



' Rectus [L.], straight. The rectum is that part of the intestine in which con- 

 volutions are absent. 



■^ ffcpiyKTrip (sphincter) [Gr.], a band, a binder. 

 11 



