390 Journal of Comi'Akativk Neukologv. 



of sensory and motor centres especially characterized by 

 reflex action. Corresponding to its relations with the ver- 

 tebras, it is usually divided into the five regions, cervical^ 

 thoracic, lu??ibar, sacral ., and coccygeal; and the myelic nerves 

 are named from the vertebrae cephalad of which they have 

 their respective ectal origins. The lumbar and the sacral 

 nerves form open plexuses (PI. lumbalis and PI. sacralis) , 

 from which nerves are distributed to the integument and the 

 subjacent muscles. 



POSTURE. 



Ventri-cumbent, head toward dissector's left, or lateri- 

 cumbent, with the venter toward the dissector. 



exposure. 



It is not imperative that the dissection begin at any par- 

 ticular point, but most of the nerves send branches caudad 

 rather than cephalad (v. diagram), hence it is recommended 

 to begin at the thirteenth thoracic nerve and dissect caudad, 

 removing the neural arch and exposing the myel as the dis- 

 section progresses. Make a long incision through the integ- 

 ument about 3 cm. sinistrad of the dorsi-meson, from the 

 tenth thoracic vertebra to the base of the tail. From the 

 cephalic end of this incision make a second incision ventrad 

 4-6 cm., and reflect the flap of integument over the twelfth 

 and thirteenth ribs. With the arthrotome remove the dorsal 

 muscle from the sinistral side of the meson to the level of the 

 vertebral laminae of the twelfth and the thirteenth thoracic 

 vertebras. With the tracer find the thirteenth thoracic and 

 the first lumbar nerves just peripherad of the vertebrae, trace 

 them centrad to the foramina intervertebrales, separate the 

 connecting tissues from the foramina, then with the side- 

 cutting nippers remove the neural arch of the thirteenth 

 thoracic vertebra, taking the precaution to make the first 

 incision near the neurapophysis, to insure protection to the 

 myel. The dextral lamina can be removed without injury to 



