788 



THE NERVOUS SYSTEM. 



The branch to the Crureus enters the muscle on its anterior surface about 

 the middle of the thigh, and sends a filament through the muscle to the Sub- 

 crureus and the knee-joint. 



The articular branch to the hip-joint is derived from the nerve to the Rectus. 



The articular branches to the knee-joint are three in number. One, a long, 

 slender filament, is derived from the nerve to the Vastus externus ; it penetrates 

 the capsular ligament of the joint on its anterior aspect. Another is derived from 

 the nerve to the Vastus internus. It can usually be traced downward on the sur- 

 face of this muscle to near the joint; it then penetrates the muscular fibres, and 

 accompanies the deep branch of the anastomotica magna artery, pierces the capsular 

 ligament of the joint on its inner side, and supplies the synovial membrane. The 

 third branch is derived from the nerve to the Crureus. 



THE SACRAL AND COCCYGEAL NEEVES. 



The sacral nerves are five in number on each side. The four upper ones pass 

 from the sacral canal through the sacral foramina ; the fifth through the foramen 

 between the sacrum and coccyx. 



The roots of the upper sacral nerves are the largest of all the spinal nerves ; 

 while those of the lowest sacral and coccygeal nerve are the smallest. They are 

 longer than those of any of the other spinal nerves, on account of the spinal cord 

 not extending beyond the first lumbar vertebra. From their great length, and the 

 appearance they present in connection with their attachment to the spinal cord, 

 the roots of origin of these nerves are called collectively the cauda equina. 



Each sacral and coccygeal nerve separates into two divisions, posterior and 

 anterior. 



The posterior divisions of the sacral nerves (Fig. 420) are small, diminish in 



FIG. 420. The posterior sacral nerves. 



size from above downward, and emerge, except the last, from the sacral canal 

 by the posterior sacral foramina. 



