EXTERNAL OBLIQUE MUSCLE. 



409 



columnar), winch is connected with the margin of that opening, is to be 

 preserved. Lastly the free border of the external oblique should be made 

 evident between the last rib and the iliac crest. 



MUSCLES OF THE ABDOMINAL WALL. On the side of the abdomen are 

 three large flat muscles, which are named from their position to one 

 another, and from the direction of their fibres. The most superficial mus- 

 cle is the external oblique ; the underlying one, the internal oblique ; and 

 the deepest, the transversalis. 



Along the middle line are placed other muscles which have a vertical 

 direction. In front lie the rectus and pyramidalis, and behind is the 

 quadratus luinborum : these are encased by 

 sheaths derived from the aponeuroses of the Fig. 135. 



lateral muscles. 



The EXTERNAL OBLIQUE MUSCLE (fig. 



135, A ) is fleshy on the side, and aponeurotic 

 on the fore part of the abdomen. It arises 

 by fleshy processes from the eight lower 

 ribs; the five highest pieces alternating 

 with similar parts of the serratus magnus, 

 and the lowest three with digitations of the 

 latissirnus dorsi muscle. From the attach- 

 ment to the ribs the fibres are directed over 

 the side of the abdomen in the following 

 manner: the lower ones descend almost 

 vertically to be inserted into the anterior 

 half or more of the iliac crest, at the outer 

 margin: and the upper and middle fibres 

 are continued forwards obliquely to the 

 aponeurosis on the front of the belly. 



The aponeurosis occupies the anterior 

 part of the abdomen, in front of a line from 

 the eighth rib to the fore part of the crista 

 illi ; and it is rather narrower about the 

 centre, than either above or below. Along 

 the middle line this expansion ends in the 

 linea alba the common point of union of 

 the aponeuroses of opposite sides. Above,, 

 it is thin, and is continued on the thorax to 

 the pectoralis major and the ribs. Below, 

 its fibres are stronger and more separate 

 than above, and are directed obliquely 

 downwards and inwards to the pelvis: some 

 of them are fixed to the front of the pubes; 

 and the rest are collected into a firm band B (Poupart's ligament) between 

 the pubic spine and the iliac crest. 



Connections. The muscle is subcutaneous. Its posterior border is 

 unattached between the last rib and the iliac crest, but is overlaid com- 

 monly by the edge of the latissimus dorsi, except a small part below. 

 Appearing through the aponeurosis, external to the linea alba, is a white 

 line, the linea semilunaris, marking the outer edge of the rectus muscle 

 (fig. 139); and crossing between the two are three or four whitish marks, 

 the lineoe transverse. Numerous small apertures in the tendon transmit 

 cutaneous vessels and nerves ; and near the pubes is the large opening of 



D 



DrSSECTION OF THE FIRST LATBRAL 

 MUSCLE IN THE WALL OF THE BELLY. 



A. External oblique. 



B. Poupart's ligament. 



c. External abdominal ring. 

 D. Gimbernat's ligament. 



