606 



THE FUNCTION OF THE SPINAL CORD 



three columns or funiculi, namely: (a) one situated between the anterior furrow 

 and the anterior horn of the gray matter, (6) one neighboring upon the lateral 

 surface of the gray matter and (c) one located between the posterior fissure and 

 the posterior horn of the gray matter. We shall see later on that the anterior, 

 lateral and posterior funiculi are in turn made up of several tracts or fasciculi 

 which are anatomically and functionally distinct from one another. It is also to 

 be noticed that the median fissures do not extend directly to the commissure of 

 the gray matter, but permit bridges of white matter to intervene. These are the 

 so-called anterior and posterior commissures. The fissures themselves contain 

 a process of the pia mater which invests the external surface of the cord, and, 

 together with the arachnoid and dura mater, forms a protective envelope for this 

 structure. 



The Functional Basis of the Gray Matter. The gray matter 

 consists of the supporting neuroglia in which are imbedded numerous 

 cell-bodies and the beginning portions of their processes. The former 

 appears as a felt-like network of fibers with scattered nuclei. Around 

 the central canal and in the vicinity of the entrance of the posterior 



root, these reticular spider-shaped 

 cells are especially small and nu- 

 merous, forming here the so-called 

 substantia gelatinosa of Rolando. 

 The nerve cells of the spinal cord 

 are very numerous and exhibit a 

 variety of shapes and sizes. It 

 should also be noted that they oc- 

 cupy definite areas of the gray 

 matter and extend as distinct colo- 



A NEUROGLIA-CELL, ISOLATED nies for some distance up and down 



in the cord. In the anterior horn, 

 where they are especially promi- 

 nent, they are arranged in three groups. The median group is situ- 

 ated near the middle line and its axons may be traced across to the 

 other side through the anterior commissure of the white matter. The 

 anterior group consists of large multipolar cells, the axons of which 

 pass outward in the anterior roots of the cord and are distributed 

 eventually to the different effectors of the spinal system. Some of 

 these cells, as we shall see later, send their axons into neighboring 

 sympathetic ganglia and thus form the efferent bridges between the 

 cerebrospinal and sympathetic systems. The aforesaid cells are es- 

 pecially numerous in the cervical and lumbar segments of the cord 

 which, as we have seen above, innervate the anterior and posterior 

 extremities. The posterior group of cells is present in those regions 

 of the cord in which the lateral horn is well developed. A very promi- 

 nent column of cells also extends through the dorsal and inner area 

 of the cord near the base of the posterior root. These cells begin at 

 the level of the seventh or eighth cervical nerve and reach downward 

 as far as the second or third lumbar nerve. They are most conspicuous 

 in the thoracic region, their large bodies being elongated in the longi- 



FIG. 298. 



IN 33 PER CENT. ALCOHOL. 



