MUSCLES OF PERINEUM AND ISCHIO-RECTAL REGION. 231 

 CORRUGATOR CUTIS ANI. 



Origin Subcutaneous fibres of muscular tissue, 

 largely involuntary, which wrinkle the skin around 

 the anus. 



Insertion Skin around anus. 



Nerve Perineal. 

 EXTERNAL SPHINCTER ANI. 



Origin Plane of muscular fibres subcutaneous and 

 attached to the skin; arises from tip of coccyx. 



Insertion Tendinous centre of perineum after ellip- 

 tically surrounding the anus. 



Nerve Fourth sacral. 

 INTERNAL SPHINCTER ANI. 



Origin A ring of muscle around the lower end of 

 the rectum, about one-fourth of an inch thick, three- 

 fourths to one and one-half inches wide. 



Insertion Is a mixture of voluntary and involuntary 

 fibres. 



Nerves Sacral and sympathetic plexuses. 



In the Female. 

 The special muscles in this region are : 



SPHINCTER VAGINAE. Surrounds the vaginal orifice; it is a 

 continuation of the external sphincter ani, and is in- 

 serted anteriorly into the corpora cavernosa clitoridis. 



ERECTOR CLITORIDIS. Similar in its attachments to the 

 erector penis. 



TRANSYERSUS PERIN^EL Like its attachments in the male. 



COMPRESSOR URETHRA. Like its attachments in the male. 



SPHINCTER ANI, EXTERNAL AND INTERNAL. Like their 

 attachments in the male. 



COCCYGEUS. Like its attachments in the male. 



LEVATOR ANI. Attached below to sides of rectum and 

 vagina 



