THE ABDOMINAL WALL 207 



the abdomen and clean the aponeurosis of the external oblique 

 muscle. Near the thorax the aponeurosis of the external oblique 

 is very thin, and it is liable to injury, unless the dissection is 

 performed with care. Proceed cautiously also at the lower part 

 of the abdomen, above the medial end of the inguinal ligament. 

 There the aponeurosis is pierced by the spermatic cord in the 

 male, and by the round ligament of the uterus in the female. 

 The lips of the opening thus formed are 

 prolonged downwards upon the cord, or the 

 ligament, in the form of a thin membrane 

 called the external spermatic fascia. In de- 

 fining this, the blade of the knife must not 

 be used. Work entirely with the handle. 



Next clean the muscular part of the 

 external oblique. It may be cleaned either 

 in the ordinary way by cutting through the 

 thin deep fascia which covers the muscle 

 along the line of the fibres, and then 

 separating the fascia from the muscle by 

 sweeping the knife forwards and backwards, 

 along the surface of the muscle, parallel 

 with the fibres, or, and in many cases more 

 conveniently, by incising the fascia along a 

 line at right angles to the fibres, over the 

 posterior part of the muscle, and afterwards 

 sweeping the knife across the surface of the 

 muscle at right angles to the fibres as the 

 fascia is reflected. At the anterior part of 

 the muscle the deep fascia blends with the 

 aponeurosis of insertion, which must not be 

 injured. Finish the cleaning of the muscle 

 by carefully defining the digitations of origin 

 from the lower eight ribs. 



M. Obliquus Externus Abdominis. The 

 external oblique muscle arises, by eight 

 pointed processes or digitations, from the 

 outer surfaces and lower borders of the lower 

 eight ribs (Vol. I. p. 45). The upper three 

 digitations interdigitate with the digitations 

 of the serratus anterior, and the latissimus FlG - 93- Crest of 



, , . . -11 7 f the Ilium as seen 



dorsi mterdigitates with the lower four. from above ( semi . 

 From their origins the fibres proceed down- diagrammatic),with 

 wards and forwards, with varying degrees of Attachments of 



, ,. r^, r . J , Muscles mapped 



obliquity. Ihe posterior fibres have a nearly out 



vertical direction, and are inserted into the 



anterior half of the external lip of the crest of the ilium. 



The superior fibres are almost horizontal, and the middle 



fibres are directed obliquely downwards and forwards. All 



the superior and middle fibres end in a strong aponeurosis 



called the aponeurosis of the external oblique. 



