THE THIGH 183 



which the femoral sheath is derived, and the manner in 

 which it is formed, must next be considered. This entails 

 the study of some of the structures concerned in the construc- 

 tion of the abdominal wall. Unfortunately it is not likely 

 that, at this period, the dissection of the abdomen is in a 

 sufficiently advanced state for their examination. A small 

 portion of the medial part of the interval between the inguinal 

 ligament and the portion of the innominate bone over which 

 it stretches is filled up by the lacunar ligament. Immediately 

 to the lateral side of this the femoral vessels, enclosed within 

 the femoral sheath, enter the thigh from the abdominal 

 cavity, whilst still more laterally the interval is occupied by 

 the ilio-psoas muscle. Three nerves also find their way into 

 the thigh through the interval, viz. the lumbo-inguinal nerve, 

 which passes distally in the femoral sheath ; the femoral 

 (O.T. anterior crural) nerve, which occupies the interval be- 

 tween the psoas and iliacus muscles ; and the lateral cutaneous 

 nerve of the thigh, which runs behind the inguinal ligament 

 close to its iliac attachment. 



The arrangement of the aponeurotic lining of the 

 abdominal cavity with reference to this interval of communi- 

 cation between abdomen and thigh also requires attention. 

 The lower part of the posterior wall of the abdomen, immedi- 

 ately above the thigh, is formed by the iliacus and psoas 

 muscles. These are covered by that part of the aponeurotic 

 lining of the abdomen which receives the name of the fascia 

 iliaca. 1 The anterior wall of the abdomen is lined in like 

 manner by a portion of the general lining, termed the fascia 

 transversalis. To the lateral side of the femoral vessels these 

 two fascial layers become continuous with each other, and at 

 the same time are attached to the back of the inguinal liga- 

 ment. It is behind this union that the ilio-psoas, the femoral 

 nerve, and the lateral cutaneous nerve of the thigh are carried 

 distally into the thigh. But the external iliac vessels (which 

 become the femoral vessels in the thigh) with the lumbo-inguinal 

 nerve lie anterior to the fascia iliaca, or, in other words, within 

 the fascial lining of the abdomen, and, as they proceed 

 distally behind the inguinal ligament, they carry with them a 



1 The dissector must bear in mind the distinction between \h& fascia iliaca 

 and the iliac portion of the fascia lata. The former is a part of the general 

 aponeurotic lining of the abdomen, and the latter is a part of the fascial invest- 

 ment of the thigh. 



