MUSCLES OF THE UPPER EXTREMITY. 201 



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. Accord- 

 ing to Cruveilhier, they draw the anus backwards during the expul- 

 sion of the faeces, and antagonise 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, " com- 

 press 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 sp/tincter 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 mus- 

 cle in forcible respiration. Yielding to the propulsive action of the 

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

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

 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 defaecation or during parturition. 



MUSCLES OF THE UPPER EXTREMITY. 



The muscles of the upper extremity may be arranged into groups 

 corresponding with the different regions of the limb thus: 



Anterior thoracic region. Lateral thoracic region. 



Pectoralis major, Serratus magnUs. 



Pectoralis minor, 

 Subclavius. 



Anterior scapular region. Posterior scapular region. 



Subscapularis. Supra-spinatus, 



Infra-spinatus, 

 Teres minor, 

 Teres major. 



Acromial region. 



Deltoid. 

 26 



