THE SPINAL CORD. 



295 



fig. 138. 



The spinal cord. 



Fig. 139. 



ments, the investitures of the cord, blood-vessels, and a 

 liquid. 



Fig. 138, A, A, shows the front view of the spinal 

 cord, with the medulla oblongata ; B, B, the posterior 

 view % ; and C, C, the decussation of its strands, from 

 which it appears that the organ is composed of two equi- 

 lateral portions. They are united by an interior com- 

 missure, but separated in front by the anterior, and be- 

 hind by the posterior fissure. Of these the posterior 

 fissure is the deeper, the anterior being wider. Besides 

 these regional divisions, the cord also presents longi- 

 tudinal furrows, two for each side, dividing it into the 

 anterior, the middle or lateral, and posterior columns or 

 tracts, as shown in the figures. 



With respect to the interior constitution of the cord, 

 it has already been stated that it is composed exteriorly 

 of white, and interiorly of gray material. The relative 

 quantities of these, and the particular form and distribu- 

 tion of the gray substance, may, perhaps, be best understood from the 



sections given in Fig. 139, 

 from one to nineteen, 1 show- 

 ing a transverse section as 

 high as the cerebral pedun- 

 cles ; 2, through the medulla 

 oblongata; and the remaining 

 figures, to 19, at lower and 

 lower points. 



In the first of these sec- 

 tions, 1 is the interpeduncu- 

 lar space ; 2, 2, inferior tract ; 

 o 9 3, 3, middle tract ; 4, 4, locus 



^H^l &* %. y/rf^WVr^ ^S^iJ^V J ---*" rr TT'*w 



dl n &i & 10 $$ m& niger ; 5, 5, superior tract ; 6, 



section of the aqueduct of 

 Sylvius ; 7, 7, section of the 

 superior peduncles of the cer- 

 ebellum ; 8, 8, section of the 

 two tubercula quadrigemina. 

 In the second section: 1, 1, 

 the pyramidal bodies; 2, 2, 

 olivary bodies ; 3, 3, resti- 

 form ; 4, 4, section of middle strands ; 5, floor of fourth ventricle. 



In the fourth of these sections : 1, the right half of the cord ; 2, left 

 half; 3, anterior median fissure; 4, posterior median fissure; 5, 5, pos- 



16 



17 



18 



Sections of the spinal cord. 



