82 TOPOGRAPHICAL ANATOMY OF THE 



its radicles beginning in the prepuce or mammary gland, according to 

 the sex of the subject under dissection. At first the vein is superficial 

 to the cutaneous muscle; but, on the side of the chest, it pierces the 

 muscle and enters the axilla by following the dorsal border of the 

 deep pectoral muscle. It ends by joining the axillary vein. 



Dissection. — Reflect as much of the cutaneous muscle as is necessary 

 to expose the underlying components of the abdominal wall. In 

 performing this operation, a series of small nerves, cutaneous in distri- 

 bution, will be observed to pierce the muscle. These should be 

 preserved in order that their connection with deeper nerves may be 

 demonstrated as the dissection proceeds. Small vessels are associated 

 with the perforating nerves. 



The fascia of the abdomen is continuous with that of the trunk in 

 general, and is like that of the rest of the body in being divisible into 

 superficial and deep layers. The superficial fascia is not notably different 

 from the like fascia of other regions of the trunk with which it is 

 continuous; but the deep fascia is remarkable in that it forms a yellow 

 tunic — tunica flava abdominis — of considerable thickness over the 

 abdominal muscles. 



The elastic fibres of the tunic run in a longitudinal direction, and 

 are most numerous near the pelvis in the neighbourhood of the linea 

 alba. Over the fieshy part of the external abdominal muscle, with 

 which the tunic is nearly coextensive, the fibres gradually become 

 fewer as they are followed over the ribs and underneath the deep 

 pectoral muscle. The dissector has already noted the presence of pro- 

 longations of the tunic in association with the prepuce and the mammary 

 glands. 



The important mechanical function of a stout elastic membrane 

 incorporated in the abdominal wall will be obvious. 



Dissection. — In order that the external oblique abdominal muscle 

 may be examined, it is necessary to remove the yellow abdominal tunic 

 completely. This is a tedious operation, and must be conducted with 

 considerable care. The close adhesion of the tunic to the aponeurotic 

 tendon of the external oblique muscle renders the dissection difficult ; 

 but the dissector will run little risk of damaging the underlying 

 aponeurosis if he note that the fibres of the tunic are yellow and run 

 in a longitudinal direction, while those of the tendon of the external 

 oblique muscle are white and glistening and arranged obliquel3^ 



M. OBLIQUUS EXTERNUS ABDOMINIS. — The external oblique abdom- 

 inal muscle is extensive, and covers the whole of the lateral and ventral 

 part of the abdomen as well as a certain amount of the lateral wall of 

 the thorax. A fleshy origin is connected with the outer surface of the 

 last thirteen or fourteen ribs and the intercostal muscles between them. 

 Some fibres of origin are attached to the lumbo-dorsal fascia. The 

 muscular bundles slope obliquely in a caudal and ventral direction and 



