DISSECTION OF THE ABDOMEN. 



disposition 

 above and 

 below. 



Relations. 



Lines on 

 the aponeu- 

 rosis ; 



apertures 

 in it; 



abdominal 

 ring. 



Use of both 

 muscles, 

 acting from 

 pelvis, 



and thorax ; 



one muscle 

 acting ; 



influence on 



abdominal 



cavity, 



In the linea 

 alba the 

 aponeuroses 

 are united. 



External 



abdominal 



ring: 



form and 

 situation ; 



middle line of the aponeuroses of opposite sides. Above, it is thin, 

 and is continued over the thorax to the pectoralis major muscle. 

 Below, its fibres are stronger and more distinct than above, and are 

 directed obliquely downwards and inwards to the pelvis ; some of 

 them are fixed to the front of the pelvis ; and the rest are collected 

 into a firm band, Poupart's ligament, between the pubic spine and 

 the iliac crest (p. 267). 



Relations. The muscle is subcutaneous. Its posterior border is 

 unattached between the last rib and the iliac crest, but it is usually 

 overlapped by the edge of the latissimus dorsi, except for a short 

 distance below. At the outer part of the aponeurosis in the front of 

 the abdomen is a curved white line, the linea semilunaris, marking 

 the outer edge of the rectus muscle (fig. 97) ; and crossing between 

 this and the linea alba are three or four somewhat irregular lines 

 the linece transversos. Numerous small apertures in the aponeurosis 

 transmit cutaneous vessels and nerves ; and near the pubis is the 

 large opening of the external abdominal ring (fig. 97), which gives 

 passage to the spermatic cord in the male, and to the round ligament 

 in the female. 



Action. Both muscles, taking their fixed point at the pelvis, will 

 bend the trunk forwards ; but with the spine fixed, they will draw 

 down the ribs. If they act from the thorax they will elevate the pelvis. 



Should one muscle contract, it will incline the trunk to the same 

 side, or raise the pelvis, according as the upper or the lower attach- 

 ment may be movable ; or if the trunk is prevented from being 

 bent, it will turn the thorax to the opposite side. 



The external oblique also acts powerfully with the other broad 

 muscles in flattening the wall and diminishing the cavity of the 

 abdomen, and in forcing up the diaphragm during expiration by 

 means of pressure transmitted through the abdominal viscera. 



DIRECTION. Besides the general arrangement of the aponeurosis 

 over the front of the abdomen, the student is to examine more 

 minutely the linea alba in the middle line, the external abdominal 

 ring with the fascia prolonged from its margin, and the thickened 

 border named Poupart's ligament. 



Linea alba. This white band on the front of the abdomen marks 

 the place of meeting of the aponeuroses of the opposite sides. It 

 extends from the ensiform process to the pubic symphysis, and is 

 wider above than below. It is perforated here and there by small 

 apertures, which allow pellets of fat to protrude sometimes. A 

 little below the centre is the umbilicus, which now projects beyond 

 the surface, though before the skin was removed a hollow indicated 

 its position. 



External abdominal ring (tig. 97 and fig. 98, c). This opening is 

 situate near the pubes, between the diverging fibres of the aponeu- 

 rosis. It is somewhat triangular in form, with the base at the pubic 

 crest, and the apex directed upwards and outwards. The long 

 measurement of the aperture is about an inch, and the transverse 

 about half an inch. 



