564 



HUMAN ANATOMY. 



subcutaneus. The sphincter superficialis is that portion of the muscle which hes above and to 

 the outer side of the sphincter subcutaneus, while more deeply still, and formmg a rmg-hke 

 mass of fibres closely encircling the rectal wall, is the sphincter profundus. It is from the 

 sphincter subcutaneus that the retractor scroti, when present, is derived, and fibres from the 

 sphincter superficialis are frequently prolonged in front of the anus to various insertions, as, for 

 instance, to the tuber ischii, the lower layer of the trigonum urogenitale, or even the sheath of 

 the corpora cavernosa. This layering of the external sphincter is probably a relic of the separa- 

 tion of the sphincter cloacae into two layers, the subcutaneous and superficial sphincters repre- 

 senting a portion of the superficial layer, while the deeper one is responsible for the sphincter 

 profundus. 



2. Transversus Perin.bi Superficialis (Fig. 554). 



Attachments. — The superficial transverse perineal muscle is an exceedingly- 

 variable sheet of muscle-fibres situated in the posterior portion of the superficial 

 perineal interspace. In its typical form it may be described as a band of fibres which 



Fig. 554. 



Bulbo-cavernosus 



Ischio-cavernosus 



Trans. pennset,± 

 superficialis 



Obturator 

 internus 



White line 

 Levator ani 



Coccygeus ^i;, 



Triangular liga- 

 ment, inf. layer 



Tendinous 

 perineal centre 



Tuberosity of 

 ischium 



_ Anus 



. Obturator fascia 



_ Sphincter 

 externus 

 _ Levator ani 



Gluteus 



maximus (cut) 



Greater sacro-sciatic 

 ligament 



Tip of coccy 



Muscles of male perineum and pelvic floor, seen from below. 



arises from the medial surface of the ischial tuberosity and passes directly medially 

 to be inserted into the central tendon of the perineum. 



Nerve-Supply. — From the perineal branches of the pudic nerve. 



Action.— To assist in fixing the central tendon of the perineum during the 

 contraction of the bulbo-cavernosi. 



Variations. — The muscle may occasionally be entirely absent. It frequently receives fibres 

 from the anterior (pubo-rectal) portion of the levator ani and from the external sphincter ani 

 and makes connections with the bulbo-cavernosi. 



3. Ischio-Cavernosus (Fig. 554). 



Attachments. — The ischio-cavernosus, also named the erector penis {erector 

 clitoridis), represents the lateral portion of the sphincter cloacae. The two muscles 

 occupy the lateral parts of the superficial perineal interspace, each arising from the 

 base of the tuberosity of the ischium, enclosing the base of the crus penis (clito- 

 ridis) as in a sheath, and passing forward to be inserted into the corpus cavernosum. 

 The muscle in the female differs from that of the male only in size. 



Nerve-Supply. — From the perineal branches of the pudic nerve 



