152 ORIGIN, INSERTION, AND USE 



name of linea transversales is given : they consist of many 

 tendinous intersections in the straight muscles. 



OBLIQUUS EXTERNUS ABDOMINUS. OBLIQUUS INTERNUS ABDOMINXJS. 



TRANSVERSALIS ABDOMINUS. RECTUS ABDOMINUS. 



These four pairs of muscles are inserted into the lines we 

 have just described ; the latter muscle is also inserted into the 

 pubes. These muscles contribute largely to the formation of 

 the under and lateral parts of the abdominal parietes, and to 

 give support to the contained viscera. They also compress 

 the bowels, and by that means assist in the evacuation of the 

 fasces and urine, and the expulsion of the foetus. 



The use of the last muscle — rectus abdominus — appears 

 to be that of strengthening the middle parts of the belly, and 

 thereby of counteracting that tendency to relaxation which 

 must exist from the constant dependence of the bowels. 



MUSCLES OF THE FORE EXTREMITY. — EXTERNAL SCAPULA 



REGION. 



ANTEA SP1NATUS. 



Origin. — The anterior and superior spinatus fills up the 

 fossa antea spinata, from which it arises, as well as from 

 the spine and anterior costa of the scapula. 



Insertion. — Into the summits of the greater and lesser tu- 

 bercles of the os humeri, and into the capsular ligament of the 

 shoulder joint. At the point of the shoulder it sends off a 

 tendinous expansion over the joint, between which and the 

 tendon of the biceps we find a bursa mucosa. 



Use. — To extend the os humeri on the scapula ; at least, 

 as far as that motion is admitted of. 



POSTERIOR SPINATUS. 



Origin. — From the fossa postea spinata, and from the 

 spine of the bone. 



Insertion. — Into the outward part of the great tubercle of 

 the os humeri. 



