448 THE MUSCULATURE 



there is an irregularly shaped space, cavum pelvis subperitoneale, bounded above by peritoneum, 

 below by the fascia covering the pelvic diaphragm and filled with connective tissue of varying 

 density. The tissue in this space in the female is continuous with that between the two per- 

 itoneal surfaces of the broad ligament. Between the viscera in the subperitoneal region and 

 about their walls the connective tissue is more or less definitely condensed into membranes 

 which constitute the endopelvic fascia, variously described by difi'erent authors. The fascia 

 covering the pelvic diaphragm, especially that on the deep surface, is fused to the endopelvic 

 fascia where the viscera pass through the pelvic diaphragm. In the connective tissue of the 

 subperitoneal space are found the hypogastric artery and vein and their chief branches, and 

 various visceral nerves. The subperitoneal space above the pelvic diaphragm is to be compared 

 with the subcutaneous space below the pelvic diaphragm known as the ischio-rectal fossa and 

 described above. 



MUSCLES 

 A. Muscles of the Pelvic Diaphragm, Coccyx, and Anus 



The coccygeus (figs. 393, 395, 397, 400). — Origin. — From the ischial spine and the neigh- 

 bouring margin of the great sciatic notch. Structure and insertion. — The fibre-bundles diverge 

 to be inserted partly directly, partly by means of an aponeurosis, into the lateral margin of the 

 fourth and fifth sacral vertebrae and of the coccyx. Usually the muscle is composed in consider- 

 able part of tendinous connective tissue, especially on the dorsal side of the cranial portion, and 

 the ventral side of the caudal portion. 



Nerve-supply. — From the pudendal plexus several small nerves enter the cranial margin 

 and pelvic surface of the muscle. They arise usually from the third and fourth sacral nerves. 

 Actio7i. — Insofar as the muscle is active it flexes and abducts the coccyx. 

 Relations. — Ventrally the muscle bounds the pelvic cavity, from which it is separated by 

 the pelvic fascia, beneath which runs the nerve to the levator ani muscle. The dorsal surface 

 is partly covered by the sacro-spinous (lesser sciatic) ligament and helps to bound the ischio- 

 rectal fossa (posterior recess) . 



Variations. — The muscle varies greatly in the extent of its fleshy development. It may be 

 doubled. It may be partially fused with the levator ani. Occasionally it is absent. 



The sacro-coccygeus anterior (fig. 393). — This inconstant muscle, when well developed, 

 arises from the sides of the fourth and fifth sacral and from the front of the first coccygeal ver- 

 tebra and from the sacro-spinous ligament. The short fibre-bundles which compose it make up 

 a somewhat irregular belly which is inserted into the anterior sacro-coccygeal ligament and into 

 the second to fourth coccygeal vertebrae dorsal to the insertion of the levator ani. The innerva- 

 tion is from the fourth and fifth sacral nerves. 



The sacrococcygeus posterior is an inconstant muscle consisting of a few muscle bundles 

 which extend from the dorsal surface of the lower sacral vertebrae or from the posterior iliac 

 spine to the dorsal surface of the coccyx. It lies beneath the superficial layer of the sacro- 

 tuberous (great sciatic) ligament. 



The levator ani (figs. 392, 394, 395, 396, 399, 401) is divisible into three portions, the ilio- 

 coccygeus, the pubo-coccygeus and the pubo-rectalis. 



The ilio-coccygeus (fig. 397) arises from the ischial portion of the arcus tendineus (white 

 line). This extends from the ischial spine and posterior part of the arcuate line to the superior 

 ramus of the pubis near the obturator canal, curving downward for a variable distance below 

 the obturator canal. The constituent fibre-bundles form a muscular sheet which is inserted 

 into the side of the coccyx and into the median raphe (ano-coccygeal) which extends from the 

 tip of the coccyx to the rectum. Many fibre-bundles cross the median line. 



The pubo-coccygcus (figs. 395, 397) arises from the inner surface of the os pubis, along 

 a line extendmg from the lower margin of the symphysis pubis to the obturator canal, and from 

 the arcus tendineus as far backward as the origin of the ilio-coccygeus. The fibre-bundles 

 form a sheet of muscle which passes backward, downward, and medialward past the urogenital 

 organs and the rectum on each side and is inserted by means of an aponeurosis into the anterior 

 sacro-coccygeal ligament. Back of the rectum some of the fibre-bundles of the muscle sheets 

 of each side interdigitate across the median line. Some of the more superficial fibres are in- 

 serted into the deep part of the ano-coccygeal raphe. Some of the fibre-bundles which arise 

 nearest the symphysis are inserted on each side into the rectum. The pubo-coccygeus lies to 

 some extent on the pelvic surface of the insertion of the ilio-coccygeus. 



The pubo-rectalis (fig. 395) arises (a) from the body and descending ramus of the pubis 

 beneath the origin of the pubo-coccygeus, (b) from the neighbouring part of the obturator fascia 

 and (c) from the fascia covering the pelvic surface of the urogenital trigone. The fibre-bundles 

 form a thick band on each side of the rectum behind which those of each side are inserted into 

 the ano-coccygeal raphe. Many fibre-bundles may be traced into the muscle of the opposite 

 side. Some of tlic more superficial fibre-bundles are reflected medialward in front of rectum 

 and may be followed into the superficial transverse perineal muscle, others may be followed into 

 the sphincter ani externus, or even to the skin. 



Nerve-supply. — By a special nerve which arises usually from the fourth sacral, runs across 

 the pelvic surface of the muscle and gives a special branch to each portion. 



Action. — To flex the coccyx, raise the anus and constri(;t the rectum. It resists the down- 

 ward pressure which the thoracio-abdomiiial diaphragm exerts on the viscera during inspiration. 

 Relations. — Between the right and left muscles in front lie the urethra and the lower part 

 of the |)rostate in the male, the urethra and vagina in the female. In the triangle between the 

 ischio-pul)ic rami of each side lies the lu'ogcnital diaphragm separatcsd from the pubo-rectal part 

 of the mu.scle by the deep layer of the trigone from which some of the fibres of the latter arise. 

 Back of the urogenital diaphragm the muscle helps to bound the ischio-rectal fossa. 



