758 NEUROLOGY 





the anterior nerve roots, by which they are carried to the sympathetic nerves: 

 they constitute the white rami and are sympathetic or visceral efferent fibers; they 

 are also known as preganglionic fibers of the sympathetic system; the axons of others 

 pass into the anterior and lateral funiculi, where they become longitudinal. 



Nerve Cells in the Posterior Column. 1. The dorsal nucleus (nucleus dorsalis; col- 

 umn of Clarke) occupies the medial part of the base of the posterior column, and 

 appears on the transverse section as a well-defined oval area. It begins below 

 at the level of the second or third lumbar nerve, and reaches its maximum size 

 opposite the twelfth thoracic nerve. Above the level of the ninth thoracic nerve 

 its size diminishes, and the column ends opposite the last cervical or first thoracic 

 nerve. It is represented, however, in the other regions by scattered cells, which 

 become aggregated to form a cervical nucleus opposite the third cervical nerve, 

 and a sacral nucleus in the middle and lower part of the sacral region. Its cells 

 are of medium size, and of an oval or pyrif orm shape ; their axons pass into the 

 peripheral part of the lateral funiculus of the same side, and there ascend, prob- 

 ably in dorsal spinocerebellar (direct cerebellar) fasciculus. 2. The nerve cells in the 

 substantia gelatinosa of Rolando are arranged in three zones : a posterior or margi- 

 nal, of large angular or fusiform cells; an intermediate, of small fusiform cells; and 

 an anterior, of star-shaped cells. The axons of these cells pass into the lateral 

 and posterior funiculi, and there assume a vertical course. In the anterior zone 

 some Golgi cells are found whose short axons ramify in the gray substance. 3. 

 Solitary cells of varying form and size are scattered throughout the posterior 

 column. Some of these are grouped to form the posterior basal column in the base 

 of the posterior column, lateral to the dorsal nucleus ; the posterior basal column 

 is well-marked in the gorilla (Waldeyer), but is ill-defined in man. The axons of 

 its cells pass partly to the posterior and lateral funiculi of the same side, and 

 partly through the anterior white commissure to the lateral funiculus of the 

 opposite side. Golgi cells, type II, located in this region send axons to the lateral 

 and ventral columns. 



A few star-shaped or fusiform nerve cells of varying size are found in the sub- 

 stantia gelatinosa centralis. Their axons pass into the lateral funiculus of the 

 same, or of the opposite side. 



The nerve fibers in the gray substance form a dense interlacement of minute 

 fibrils among the nerve cells. This interlacement is formed partly of axons which 

 pass from the cells in the gray substance to enter the white funiculi or nerve roots; 

 partly of the axons of Golgi's cells which ramify only in the gray substance; and 

 partly of collaterals from the nerve fibers in the white funiculi which, as already 

 stated, enter the gray substance and ramify within it. 



White Substance (substantia alba). The white substance of the medulla spinalis 

 consists of medullated nerve fibers imbedded in a spongelike net-work of neuroglia, 

 and is arranged in three funiculi : anterior, lateral, and posterior. The anterior 

 funiculus lies between the anterior median fissure and the most lateral of the ante- 

 rior nerve roots : the lateral funiculus between these nerve roots and the postero- 

 lateral sulcus; and the posterior funiculus between the postero-lateral and the pos- 

 terior median sulci (Fig. 672). The fibers vary greatly in thickness, the smallest 

 being found in the fasciculus gracilis, the tract of Lissauer, and inner part of the 

 lateral funiculus; while the largest are situated in the anterior funiculus, and in the 

 peripheral part of the lateral funiculus. Some of the nerve fibers assume a more 

 or less transverse direction, as for example those which cross from side to side 

 in the anterior white commissure, but the majority pursue a longitudinal course 

 and are divisible into (1) those connecting the medulla spinalis with the brain and 

 conveying impulses to or from the latter, and (2) those which are confined to the 

 medulla spinalis and link together its different segments, i. e., intersegmental or 

 association fibers. 



