DISSECTION OF THE ABDOMEN. 335 



The Posterior Mesenteric Plexus is formed around the root of the 

 artery of the same name. It is united in front with the aortic plexus, 

 and receives efferent branches from the lumbar ganglia. Three sets of 

 branches pass from it : — 



i. Branches following the divisions of the posterior mesenteric artery. 



2. Branches accompanying the spermatic artery, and forming the 

 spermatic plexus. 



3. Pelvic branches to join the pelvic plexus. 



The Sympathetic Gangliated Cord in the loins. This is the back- 

 ward continuation of the dorsal cord. Beginning between the psoas 

 parvus and the diaphragmatic crus, it extends backwards to the lumbo- 

 sacral articulation, where it is directly continued by the sacral division 

 of the cord. Each nerve will be found on the inner aspect of the psoas 

 parvus muscle of the same side, the left nerve being related inwardly to 

 the aorta, and the right for the greater part of its course to the vena 

 cava, but for a short distance in front to the aorta. Six fusiform, 

 greyish ganglia stud the cord, and from these proceed the various 

 branches of the cord. These branches are : — 



1. Communicating branches with the inferior primary divisions of 

 the lumbar spinal nerves. 



2. Branches to the aortic and posterior mesenteric plexus. 



Iliac Fascia. This is the name given to the aponeurotic layer which 

 covers the inferior face of the psoas magnus and iliacus muscles. It is 

 densest and most adherent at the side of the pelvic inlet, and becomes 

 more cellular as it is traced forwards and backwards. It is adherent 

 inwardly to the psoas parvus tendon, and outwardly to the bony pro- 

 minence of the haunch. Poupart's ligament is adherent to its inferior 

 face, and it gives origin to the sartorius and cremaster muscles. 



The Psoas Magnus (Plates 44 and 45). This muscle is broad and 

 flattened anteriorly, and thick and pointed behind, where it rests in 

 a depression of the iliacus. It arises from the last two dorsal vertebrae 

 and the under surfaces of the last two ribs at their upper part ; also 

 from the lumbar vertebrae except the last, covering their transverse 

 processes. It is inserted, in common with the iliacus, into the internal 

 trochanter of the femur. 



Action. — It is a flexor and an outward-rotator at the hip-joint. When 

 the hind limbs are fixed the two muscles will arch the loins, or the single 

 muscle will incline the trunk to the same side. 



The Psoas Parvus (Plate 45). This is a smaller and more tendinous 

 muscle than the preceding, to whose inner side it is placed. It arises 

 from the bodies of the last three or four dorsal and all the lumbar 

 vertebrae. It is inserted into the ilio-pectineal eminence (of the ilium) 

 at the side of the pelvic inlet. 



Action. — To flex the pelvis on the loins when both muscles act ; or to 



