152 TOPOGRAPHICAL ANATOMY OF THE 



the psoas major and iliacus muscles. Thickest and densest in the 

 neighbourhood of the pelvic inlet, where it is continuous with the 

 pelvic fascia, it becomes thinner towards the diaphragm. Medially it is 

 attached to the lateral border of the psoas minor muscle. Other 

 connections and attachments are to the inguinal ligament and the coxal 

 tuber of the ilium. The iliac fascia affords origin to the sartorius and 

 cremaster muscles and the transverse muscle of the abdominal wall. 



Dissection.— The iliac fascia must be removed. In doing this, 

 preserve the nerves and blood vessels related to it. The psoas minor 

 and iliopsoas muscles are now to be examined. 



M. PSOAS MINOR. — The lesser psoas' muscle is elongated and 

 flattened, and lies alongside the median plane. Its origin is from the 

 bodies of the last three thoracic and the first four or five lumbar 

 vertebrae, and from the vertebral end of the last two or three ribs. 

 Some of its fibres arise from the tendinous origin of the diaphragmatic 

 crura. It is inserted by a flattened tendon to the psoas tubercle of the 

 ilium. 



M. ILIO-PSOAS. — The powerful and fleshy ilio-psoas muscle lies 

 lateral to, and partly covered by, the preceding. It is divisible into two 

 parts — m. psoas major and m. iliacus — which quickly merge into a 

 single structure inserted into the lesser trochanter of the femur. 



M. 2)Soas major. — The greater psoas begins as a broad, flat muscle 

 that gradually becomes more compact and rounded. Its origin is from 

 the internal surface of the last two ribs near their vertebral end, and 

 from the transverse processes and bodies of the lumbar vertebrae. The 

 terminal part of the muscle is received into a deep groove on the 

 surface of the m. iliacus. 



M. iliacus. — The iliac muscle is of triangular outline and of con- 

 siderable extent. It covers the whole of the ventral surface of the 

 ilium and projects for some distance beyond the lateral border of this 

 bone. The origin of the iliacus is from the entire ventral surface of the 

 ilium, the ventral sacro-iliac ligament, and the adjacent part of the 

 sacrum. 



Dissection. — Some of the luml)ar spinal nerves should be examined 

 at this stage of the dissection. Certain derivatives of these are visible 

 without further dissection. From the lateral margin of the greater 

 psoas muscle the ilio-hypogastric and ilio-inguinal nerves emerge ; and 

 between the psoas minor and psoas major the lateral cutaneous nerve of 

 the thigh appears. A small nerve, the genitofemoral (external 

 spermatic), pierces the psoas minor ; and along the medial border of the 

 same muscle the lumbar part of the gangliated cord of the sympathetic 

 should be found. 



' i/'o'a (psoa) [Gr.], the loins. 



