112 



SPINAL MARROW. 



The 

 order, 



FIG. 



origin of the nerves brings us to the part next in 

 which is the 



SPINAL MARROW. 



The primitive longitudinal filaments, al- 

 ready noticed, coming together and growing, 

 swell into the spinal cord. 



This cord, or marrow, occupies the bony 

 vertebral canal, extending from the atlas to 

 the second lumbar vetebra, where it termi- 

 nates in the cauda-equina. It is surrounded 

 by three membranes the dura-mater, tunica 

 arachnoidea, and pia mater the first a fibrous, 

 the second a serous, the third a vascular mem- 

 brane. 



The spinal marrow presents the form of 

 a cylinder having several enlargements in its 

 course, corresponding to the points where the 

 large plexuses are given off as the brachial and 

 lumbar. It is divided in front and behind, by 

 two fissures, anterior and posterior ; thus sep- 

 arating it into two equal and lateral halves. 

 These two halves are again divided by a lateral 

 line, which consequently cuts the cord into 

 four parts two anterior, and two posterior. 



These parts receive the name of nervous 

 tracts, rods or columns. Their outer surface is 

 white or medullary, while the inner is gray or 

 cineritious. 



There is still another tract placed between 

 the anterior and posterior columns, called by 



FIG. 14. Anterior view of Spinal Marrow. 



o Dots showing corpora pyramidalia. 6 Corpora olivaria. c Anterior face 

 of spinal marrow, d Anterior roots of cervical nerves, e Anterior roots of 

 dorsal nerves. /Anterior roots of lumbar nerves, g Anterior roots of sacral 

 nerves, h, t, j, k Anterior and posterior roots joined to pass out of the dura- 

 mater. I Dura-mater of spinal cord, m, n, o, p Ganglia on cervical, dorsal 

 lumbar and sacral nerves, q Cauda equina. r Sub-occipital nerve, s Liga- 

 mentum denticulatum. 



