32 



1 7. The spinal nerves. Observe that — 



a. The hypoglossal (1st spinal nerve ■=^ XI. cranial of man), escapes 



between the first and second vertebrae to cross first the vagus arid 

 then the glossopharyngeal, it next passes beneath the mylohyoid 

 mnsele to reach the base of the tongue. Besides supplying the 

 tongue muscles, it sends small branches to the muscles of the back 

 and the floor of the mouth. Add this nerve to the sketch showing 

 the v., VII., IX., and X. 



b. The second and third spinal nerves unite immediately after escaping 



from the spinal canal to form the brachial nerve, which supplies 

 the muscles of the shoulder, and then extends along the arm to divide 

 into the radial and ulnar nerves for the forearm and hand. 



c. The fourth, fifth, and sixth spinal nerves supply the skin and muscles of 



the trunk. 



d. The seventh, eighth, and ninth spinal nerves run obliquely back- 



wards (forming the larger part of the cauda equina), to escape behind 

 their respective vertebrae, and unite to form the sciatic plexus. The 

 seventh, before uniting with the eighth, sends branches (ileohypo- 

 gastric and crural) to the walls of the abdomen, the skin and 

 muscles of the thigh. The sciatic plexus condenses to form the sciatic 

 nerve which extends along the thigh to divide above the knee into 

 the tibial and peroneal nerves for the leg and foot, 



e. The tenth nerve (coccygeal) escapes through a small aperture in the 



urostyle, and is distributed to the walls of the cloaca and bladder, 

 and the other structures in the pelvic region. 



18. Make a sketch (2 nat. size) showing the under surface of the brain and spinal 



cord, with the origin and principal branches of all the cranial and spinal 

 nerves on the one side and the sympathetic system and sense organs on 

 the other. 



*^* In preparing the above directions the Author is indebted to Mr J. T. Cunningham, B.A., 

 for much valuable assistance. 



