ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. fill 



may be regarded as purely artificial ; seen only after the spinal nerves 

 are torn from the cord. 



By virtue of the median and lateral fissures the cord is divided 

 -into columns, paired and symmetrical. The portion comprised be- 

 tween the anterior median and the antero-lateral fissures is known 

 as the anterior column. That portion between the two lateral fissures 

 bears the name of lateral column. That part between the postero- 

 lateral and posterior median groove is the posterior column. 



Anatomy and physiology demonstrate that the separation of the 

 anterior from the lateral column is not complete; hence it is cus- 

 tomary to reunite these two columns under the name of antero- 

 lateral columns. 



Internal Conformation of the Spinal Cord. The texture of the 

 cord is best studied by means of transverse section. These sections 

 show that the cord is composed throughout its whole extent of two 

 substances: one, .the cortical., white substance; and the other, the 

 central, gray substance. 



The white substance is located peripherally and covers all of the 

 gray substance except at the base of the posterior median groove. It 

 forms the columns which have just been pointed out. 



The gray substance forms in each half of the cord a longitudinal 

 column whose transverse section appears in the form of a crescent 

 with its concavity directed externally. The crescent terminates in 

 two swollen extremities, the anterior one having the name of anterior 

 horn; the posterior one, that of the posterior horn. 



The two crescents are bound to one another at their convexity 

 by the aid of a transverse band of gray substance, the gray commis- 

 sure. This band is pierced centrally by a canal, the central canal of 

 the cord. It runs down the central axis of the cord and is accom- 

 panied on each side by a vein, the central veins of the cord. In all 

 actions the gray matter is vaguely represented by the letter H; per- 

 ips better by the two wings of a butterfly united by a transverse 

 ir. The column of gray matter is not exactly of the same form 

 its whole length. It is thicker in the cervical and lumbar regions 

 lan in the thoracic. The white matter is likewise thicker at the 

 >vel of the cervico-dorsal and lumbar enlargements. At the level 

 the cauda equina the white substance forms but an enveloping 

 lyer for the gray matter. 



In the cervical 'and lumbar regions the anterior cornua are 

 emarkable for their volume; toward the dorso-lumbar enlargements 

 ie posterior cornua increase in size. The anterior cornu of the 



