DISSECTION OF THE ABDOMEN. 291 



The External Pudic Vein is propoi-tionally smaller than the ai-tery, 

 which it accompanies. 



The Inguinal Nerves are derived from the 2nd and 3rd lumbar nerves, 

 and are distributed to the prepuce, the scrotum, and the adjacent skin. 



Directions. — Incise the external oblique tendon, from the external 

 angle of the ilium to the edge of the prepubic tendon. Reflect Poupart's 

 ligament towards the thigh, and hook it up after the manner of Plate 40. 

 Then strip away the tendon of the external oblique from the subjacent 

 internal oblique. This Avill be found easy in the region of the flank, 

 Avhere the tendon is related to the muscular part of the internal oblique ; 

 but over the inferior part of the abdomen, and especially in front, where 

 the tendons of the two muscles are applied to each Other, the opera- 

 tion is difiicult, and in some parts impossible. In this proceeding the 

 dissector has to guard against removing the thin tendon of the inner 

 muscle along with the outer, and this he will best do by observing that 

 the fibres of the inner tendon cross these of the outer at right angles, 

 being directed downwards and forwards. Observe that anteriorly the two 

 tendons are not simply in apposition, but actually interwoven — a disposi- 

 tion of tendons which is unique, and one which greatly increases the 

 strength of the abdominal floor. The muscular portion of the external 

 oblique should be raised as far as the lower extremities of the ribs. A 

 better view of the inguinal canal and its contents will now be obtained. 



The Obliquus Abdominis Internus (Plate 40) consists of a fan-shaped 

 fleshy portion situated in the flank, and an aponeurotic tendon spread 

 over the abdominal floor. It arises from the external angle of the ilium, 

 and from the adjacent part of Poupart's ligament. It is inserted into 

 the prepubic tendon and the linea alba by the inferior edge of its tendon, 

 and by tendinous slips into the four or five last costal cartilages. In 

 front of the loAver end of the fourth last intercostal space, the aponeurotic 

 tendon has a free edge which ordinarily lies under concealment of the 

 line of overlapping costal cartilages. When the abdomen is tym- 

 panitic, however, this edge is thrust outwards, and the transversalis 

 muscle is exposed as in Plate 40. The jDOsterior edge of the fixn-like 

 muscular portion lies in contact with Poupart's ligament ; and the 

 inguinal canal, as already seen, passes between the two structures. 

 The highest fibres of its muscular part are parallel to the edge of a 

 small muscle — the retractor costoe — inserted into the last rib, under 

 cover of the most posterior slip of the serratus posticus. This is 

 described with the muscles of the back (page 96). 



Action. — Similar to that of the external oblique. 



Directions. — The internal oblique covers the transversalis and rectus 

 abdominis muscles. The outer edge of the last may be seen through 

 the thin tendon of the internal oblique, and through the same 

 tendon the posterior abdominal artery may be seen if well injected 



