GRAY MATTER OF THE CORD. 339 



It is joined to the white matter of the opposite side by the white 

 anterior commissure. The points of the crescent are directed 

 forward and backward, respectively, and form the anterior and 

 posterior columnae. A lateral projection from the center of the 

 crescent, visible only in the thoracic region, is called the lateral 

 columna; it fuses with the anterior columna in the cervical and 

 and lumbar enlargements. Together, the two crescents and the 

 gray commissure form an H-shaped column of gray matter. The 

 H-shaped column is well marked in the cervical and thoracic 

 regions; but, toward the lower end of the cord, the crescents become 

 short and thick, and the gray column is almost cylindrical. 



The H-shaped column is composed of two kinds of gray sub- 

 stance, viz.: (i) The substantia gelatinosa (Rolandi), which forms 

 (a) a cap for the head of the posterior columna and (b) an en- 

 velope for the central canal, or ventricle, of the cord. (2) The 

 substantia spongiosa. The latter forms all the H-shaped column 

 except the tips of the posterior columnae and the thick sheath of 

 the central canal. Imbedded in the neuroglia, there is a network 

 of medullated nerve fibers; and these, with the common stains, 

 give rise to a spongy appearance under the microscope. 



Gray Crescent (Fig. 101). It is made up of (i) the anterior 

 columna; (2) the center, which is joined to its fellow of the 

 opposite side by the gray commissure and which forms the lateral 

 projection, called the lateral columna; and, (3) the posterior 

 columna. The lateral border of the crescent is not everywhere 

 clear cut and definite, especially in the cervical region, but is inter- 

 mingled for a short distance with the white matter, forming the 

 formatio reticularis. The formatio reticularis is found in the 

 cervical region, elsewhere it is very feebly developed. 



(i) The anterior columna (columna anterior} (Fig. 101) as 

 seen in sections is short and thick compared with the posterior 

 columna. It is thickest in the cervical and lumbar enlargements, 

 where it swells out sharply toward the lateral surface of the cord ; 

 in the mid-thoracic region it is more slender. It does not reach 

 the surface of the cord as does the posterior columna. It ends 

 in a bulbous, serrated head, which points toward the anterior 

 root-line, and is joined to the center of the crescent by the cervix 



