212 ANATOMY IN A NUTSHELL. 



the thigh from the middle of the thigh to the knee. The posterior one of these 

 branches helps to form the subsartorial plexus which lies on the roof of Hunter's 

 canal. The other nerves in the subsartorial plexus are the long saphenous, 

 and branches from the obturator. 



The muscular branch which passes to the Rectus muscle sends an articu- 

 lar branch to the hip-joint, while the muscular branch to the Vastus internus 

 sends an articular branch to the knee-joint. The long saphenous nerve sends 

 an articular branch to the ankle-joint. 



The blood supply of the lumbar plexus comes from the ilio-lumbar arteries. 



The obturator nerve is derived from the second, third and fourth sacral 

 nerves. Its largest root is from the third nerve. After it passes from the sub- 

 si ance of the inner border of the Psoas magnus muscle at the posterior part of 

 the brim of the pelvis, the ilio-lumbar artery separates it from the lumbo-sacral 

 cord. It now crosses the internal iliac vessels and the ureter, passing in the 

 extraperitoneal fat below the obliterated umbilical (hypogastric) artery, along 

 the inner surface and upper part of the Obturator internus muscle. It now 

 passes through the obturator foramen above the obturator membrane. In the 

 pelvis it lies above the obturator artery. After passing out of the pelvis it 

 divides into two branches, an anterior and a posterior division. The anterior 

 division crosses the Obturator externus muscle and passes between the Pectineus 

 and Adductor brevis. It sends (1) an articular branch to the hip-joint. (2) a 

 branch to the femoral artery, which is an example of the gray rami. (3) Cutane- 

 ous branch to the subsartorial plexus. (4) muscular branches to the Adductor 

 longus, Adductor brevis, the Gracilis and the Pectineus muscle. The pos- 

 terior division passes between the Adductor brevis and Adductor magnus 

 after piercing the upper part of the Obturator externus. It gives off (a) muscu- 

 lar 1 'ranches to the Obturator externus and Adductor magnus, and (b) articu- 

 lar branches to the hip-joint and knee-joint. 



Obturator accessory nerve, which is present in a little more than one-fourth 

 of the cases, comes from the second and third lumbar nerves. It passes along 

 the inner border of the Psoas muscle between the roots of the anterior crural 

 and obturator nerves. It does not pass through the obturator foramen, but 

 passes in front of the brim of the pelvis beneath the Pectineus muscle. Its 

 branches are (1) a communicating branch to the obturator nerve. (2) an artic- 

 ular branch to the hip-joint, and (3) a muscular branch to the Pectineus. 



LESSON LVI1I. 

 Sacral Plexus. (Plates LXIII-LXXIII.) 



The sacral plexus is formed by the lumbo-sacral cord and the anterior 

 branches of the first, second, third, and a part of the fourth sacral nerves. 



Tin- lumbi -sacral cord is formed by a part of the fourth lumbar nerve and 

 all i f the fifth lumbar nerve. 



This plexus is situated < n the anterior surface of the Piriformis muscle 

 and behind the pelvic fascia and the branches of the internal iliac artery. It 

 gives >>^ (A) viscera] branches, (B) muscular. (C) cutaneous, (D) terminal 

 branches. (E) Greal sciatic and its branches. 



