THE ABDOMINAL WALLS 269 



to slip away from between the finger and thumb. If both cords 

 are examined at the same time,, the presence of an additional 

 structure on the affected side can often be determined. 



In children, the cremasteric muscle may be so strongly 

 developed that it is able to draw the testis up into the inguinal 

 canal. The sudden disappearance from the scrotum of a lump 

 which may as suddenly reappear may lead the mother to suppose 

 that the child is suffering from a rupture, whereas the swelling 

 is simply the testis. Similarly, the condition of undescended 

 testicle may be mistaken for a rupture, if the mother fails to 

 notice the absence of the testis from the scrotum on the affected 

 side. Examination of the mobility of the testis can be carried 

 out by testing the cremasteric reflex. Gentle stroking of the 

 skin over the proximal part of the front of the thigh stimulates 

 the sensory branches of the genito-femoral (genito-crural) nerve 

 and causes a reflex contraction of the cremaster, which is supplied 

 by the motor part of the same nerve. 



Posterior Abdominal Wall. The Lumbo - dorsal 

 (Lumbar) Fascia is a strong aponeurotic layer which extends 

 between the ribs and the iliac crest. Laterally it gives origin 

 to the internal oblique and the transversus. Medially it splits 

 into three lamellae. Of these, the posterior reaches the lumbar 

 spines, and the middle the tips of the transverse processes. 

 They enclose between them the large sacro-spinalis (erector 

 spinse) muscle. The anterior lamella is attached to the bases 

 of the transverse processes ; between it and the middle lamella 

 the quadratus lumborum is situated (Fig. 82). 



The posterior lamella of the lumbo-dorsal fascia is covered 

 by the latissimus dorsi, to which it partly gives origin. The 

 lateral margin of this muscle crosses the free posterior border 

 of the external oblique, and, together with a portion of the 

 iliac crest, they enclose the lumbar triangle of Petit. The roof 

 of this triangle is formed by the deep fascia of the back, and its 

 floor by the internal oblique (Fig. 74). 



The upper lumbar triangle lies under cover of the latissimus 

 dorsi, above and to the medial side of the lumbar triangle of 

 Petit. It is bounded above by the twelfth rib ; medially, by 

 the lateral margin of the sacro-spinalis ; below, by the line of 

 origin of the internal oblique from the lumbo-dorsal fascia, 

 which corresponds to the lower border of the latissimus dorsi. 

 The floor of this space is formed by the lumbo-dorsal fascia, 

 and constitutes the weakest part of the posterior abdominal wall. 



