344 THE MUSCLES AND FASCIAE OF THE TRUNK. 



in front of the anus, and the posterior fibres similarly join with those of the other side to be 

 attached to the front of the coccyx. The hinder part of the muscle (the iscJiio-coccygeus of 

 Henle, obturato-coccygeus of Savage) proceeds from the pelvic fascia and the ischial spine, and 

 its fasciculi converge to be inserted into the lateral margin of the coccyx and the median 

 aponeurosis. (C. Roux, " Beitrage zur Kenntniss der Aftermuskulatur des Menschen," Arch. 

 f. mikrosk. Anat., 1881.) 



Relations. The upper or pelvic surface of the levator ani is in contact with the recto- 

 vesical fascia, which intervenes between the muscle and the rectum and prostate. The lower 

 or perinea! surface, invested by the thin anal fascia, is covered by the fat which occupies the 

 ischio-rectal fossa. The posterior border is adjacent to, and often continuous with, the 

 coccygeus. Between the anterior borders of the right and left muscles the membranous part 

 of the urethra passes downwards as it issues from the prostate. 



The coccygeus or levator coccygis muscle is composed of fleshy and tendi- 

 nous fibres, forming a thin, flat, and triangular sheet, which arises by its apex from 

 the spine of the ischium, and from the inner surface of the obturator fascia above 

 the spine, and is inserted by its base into the border of the coccyx and the lower 

 part of the sacrum. 



Relations. The internal or pelvic surface of this muscle assists in supporting the rectum : 

 its external surface is intimately united to the small sacro-sciatic ligament. 



The levatores ani and coccygei muscles together have been appropriately named by Meyer 

 the pelvic diaphragm. 



Varieties. The coccygeus is sometimes inserted wholly into the side of the sacrum. A 

 few fleshy and tendinous fibres are occasionally seen passing from the lower part of the anterior 

 surface of the sacrum to the coccyx, constituting the sacro-coccygeus anticus or curvator 

 coccygis muscle. 



~b. GENITOURINARY MUSCLES. These are three muscles on each side, placed 

 immediately beneath the superficial perineal fascia, viz., the transversus perinei, the 

 ischio-cavernosus, and the bulbo-cavernosus, and one single muscle more deeply 

 placed, between the layers of the triangular ligament, viz., the constrictor urethras. 



The transversus perinei muscle arises from the inner side of the ischial 

 tuberosity, immediately above (deeper than) the origin of the ischio-cavernosus, and 

 is directed obliquely forwards and inwards to unite with the muscle of the opposite 

 side, as well as with the external sphincter and bulbo-cavernosus, at the central 

 point of the perineum. Behind this muscle the superficial perineal fascia turns 

 upwards to join the base of the triangular ligament. 



Varieties. The transverse muscle is exceedingly variable in its arrangement. It is some- 

 times absent, and at other times one or more small muscular slips are found lying superficial 

 to or on the same plane with it, in front or behind. It may also be inserted wholly or in great 

 part into the bulbo-cavernosus or external sphincter. A muscular slip is occasionally found 

 springing from the fascia at the lower border of the gluteus maximus, and running into the 

 transversus perinei or being inserted into the triangular ligament M. gluteo-perinealis, 

 Krause. 



The ischio-cavernosus or erector penis muscle, embracing the crus penis, 

 arises from the inner part of the tuberosity and ramus of the ischium behind and on 

 each side of the attachment of the crus. From this origin the fleshy fibres are 

 directed forwards to a tendinous expansion which is spread over the surface of 

 the crus, and is inserted into the outer and under sides of that body towards its fore 

 part. 



Variety. Houston has described (' ; Dublin Hosp. Reports," v. 458), under the name of 

 compressor ve,nce dorsalis penis, a muscular slip separated from the outer part of the erector 

 penis by an interval, though apparently belonging to that muscle. It arises from the pubic 

 ramus, in front of the origin of the erector muscle and the crus of the penis, and, passing up- 

 wards and forwards, is inserted by joining its fellow in a median aponeurosis above the dorsal 

 vein. This muscle, which is well developed in the dog and several other animals, is by no 

 means constant in the human subject. 



