PERINEAL MUSCLES IX THE FE5LVLE. 



331 



of the urethra : these are continuous behind with the circuhir fibres of 

 the prostate, and are referred to in the description of that body. (See 

 Structure of the Prostate.) 



Fm. 230. 



Fig. 230. — PosTERioii YiKw OF tiiePckes 



■WITH PART OP THK ]jLAL>1)ER ANI> 



Uretiika attached (from Santorini). 4 



], boily ; 2, rami of the i^ubes ; 3, 

 obturator interuus muscle ; 5, jjoi-tion of 

 the fundus and neck of the bladder laid 

 open ; 6, the i^rostate gland ; 7, trans- 

 verse fibres of the compressor urethrro 

 muscle, passing above the urethra ; S, 

 similar fibres passing beneath that canal. 



Yar'u'tics. — A piiho-iirvfliral muscle 

 was describedby James Wilson (Mcdico- 

 Chirurgical Trans.. London, vol. i. p. 

 176). and is sometimes referred to as 

 Wilson's muscle, but has not been re- 

 cognised as a separate muscle by suc- 

 ceeding anatomists. An unstriped 

 piibo-rr.sicul band has been described, 

 descending from the back of the 

 s_^anphysis to the neck of the bladder 

 (Luschka). 



I^erves.— The muscles of the urethra and penis are supplied by the inferior 

 ha3morrhoidal branch of the pudic ner^■e ; the levator and sphincter ani by the 

 inferior hajmorrhoidal and by the fourth and fifth sacral and by the coccygeal 

 nerv-es ; and the coccygeus muscle by the three last-named nerves. 



Actions. — The xj) hi net em of the anus cause by their contraction occlusion of 

 that aperture. The contraction of the external is usually maintained involun- 

 tarily, though it may be rendered firmer by an act of the will ; that of the 

 internal is wholly involuntary. 



The Ici-ator ani and eoccijgcm elevate the lower part of the rectum and inv.crt 

 its anal border, after the protrusion and eversion which accompany defecation. 



The n-ini.srrr.si acting together draw backwards and fix the central point of the 

 perineum, thus assisting to give a base of support to the ejaculator muscle. 



The erector 2>c nix serves to compress the cms penis and thus assist in producing 

 or at least in maintaining the erection of the penis. 



The ejaeulafor uriiue compresses the bulb and the adjoining part of the corpus 

 spongiosum of the urethra, so as to eject forcibly any fluid lodged in the canal. 

 It comes into action near the end of the process of micturition, when its con- 

 traction is mainly a ^-oluntary act, and in the emission of the semen when it is 

 involuntary. 



The constrictor vrethr.-r and the circi/Iitr involuntary muscles diminish the 

 calibre of the urethra and expel its contents ; their fibres contract near the end 

 of micturition, so as to assist the ejaculator in clearing the canal. 



B. — In the femai.e. — In the female the anterior fibres of th.o 

 levator ani embrace the vaiiina as they do the prostate in the male. 



The transversus perinsei and the sphincter ani are arranged 

 nearly in the same manner as in the male. 



The erector clitoridis differs from the erector penis of the male by 

 its smaller size alone. 



The sphincter vaginae is attached behind to the central point of 

 the perina?nm, in common with the sphincter ani and transversus pei'inrei 

 muscles ; its fibres open out to surround the vaginal orifice and vesti- 

 bule, closelv embracing on the outer side the two bulbs of the vesti- 



