226 MUSCLES OF THE PERINEUM. 



Actions. The acceleratores urinae 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 sud- 

 denly will propel the semen, or the last drops of urine from the canal. 

 The posterior and middle fibres, according to Krause,* contribute to- 

 wards the erection of the corpus spongiosum, by producing compres- 

 sion upon the venous structure of the bulb ; and the anterior fibres, 

 according to Tyrrell,f assist in the erection of the entire organ by com- 

 pressing 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 antagonise the levatores ani 

 which carry the anus forwards. The compressor urethrae 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 

 perpendicular 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 intestine. The use of the levator ani 

 is expressed in its name. It is the antagonist of the diaphragm and 

 the rest of the expulsory muscles, and serves 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 abdo- 

 minal muscles, it enables the outlet of the pelvis to bear a greater 

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

 it restores the perineum to its original form. The coccygei muscles 

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

 backwards during defalcation or during parturition. 



* Miiller, Archiv fiir Anatomic, Physiologic, &c. 1837. 

 t Lectures in the College of Surgeons. 183Q. 



