MUSCLES OF THE UPPER EXTREMITY. 223 



The Constrictor vagina is analogous to the accelerators urinae ; it is 

 continuous, posteriorly, with the sphincter ani, interlacing with its fibres, 

 and is inserted, anteriorly, into the sides of the corpora cavernosa, and 

 fascia of the clitoris. 



The Transversus perinei is inserted into the side of the constrictor vagi- 

 ?ise, and the levator ani into the side of the vagina. 



The other muscles are precisely similar in their attachments to those in 

 flie male. 



Actions. The acceleratores urinaB being continuous at the middle line, 

 and attached on each side to the bone, by means of their posterior fibres, 

 will support the bulbous portion of the urethra, and acting suddenly, will 

 propel the semen, or the last drops of urine, from the canal. The poste- 

 rior and middle fibres, according to Krause,* contribute towards the erec- 

 tion of the corpus spongiosum, by producing compression upon the venous 

 structure of the bulb ; and the anterior fibres, according to Tyrrell, f assist 

 in the erection of the entire organ by compressing the vena dorsalis, by 

 means of their insertion into the fascia penis. The erector penis becomes 

 entitled to its name from spreading out upon the dorsum of the organ, 

 into a membranous expansion, (fascia penis,) which, according to Krause, 

 compresses the dorsal vein during the action of the muscle, and especially 

 after the erection of the organ has commenced. The transverse muscles 

 serve to steady the tendinous centre, that the muscles attached to it may 

 obtain a firm point of support. According to Cruveilhier, they draw the 

 anus backwards during the expulsion of the faeces, and antagonize the 

 levatores ani, which carry the anus forwards. The compressor urethras, 

 taking its fixed point from the ramus of the ischium at each side, can, 

 says Mr. Guthrie, " compress the urethra so as to close it ; I conceive 

 completely, after the manner of a sphincter." The transverse portion will 

 also have a tendency to draw the urethra downwards, whilst the perpen- 

 dicular portion will draw it upwards towards the os pubis. The inferior 

 fasciculus of the transverse muscle, enclosing Cowper's glands, will assist 

 those bodies in evacuating their secretion. The external sphincter, being 

 a cutaneous muscle, contracts the integument around the anus, and by its 

 attachment to the tendinous centre, and to the point of the coccyx, assists 

 the levator ani in giving support to the opening during expulsive efforts. 

 The internal sphincter contracts the extremity of the cylinder of the intes- 

 tine. The use of the levator ani is exp/essed in its name. It is the an- 

 tagonist of the diaphragm and the rest of the expulsory muscles, and 

 series to support the rectum and vagina during their expulsive efforts. 

 The levator ani acts in unison with the diaphragm, and rises and falls like 

 that muscle in forcible respiration. Yielding to the propulsive action of 

 the abdominal muscles, it enables the outlet of the pelvis to bear a greatej 

 force than a resisting structure, and on the remission of such action it re- 

 stores the perineum to its original form. The coccygei muscles restore 

 the coccyx to its natural position, after it has been pressed backwards 

 during defecation or during parturition. 



MUSCLES OF THE UPPER EXTREMITY. 



The muscles of the upper extremity may be arranged into groups cor 

 responding with the different regions of the limb, thus : 



* Miiller, Archiv. fttr Anatornie, Physiologie, &c. 1837 

 j- Lectures in the College of Surgeons. 1839. 



