702 



THE NERVOUS SYSTEM. 



w: s. 



Gr. S. 



composed of a minute and dense network of minute fibrils, which is termed 

 " Gerlach's nerve-network," intermingled with nerves of a larger size. This 

 network is continuous with the medullated fibres of the posterior nerve-roots on 

 the one hand (Deiters), and with the branched processes of the ganglion-cells on 

 the other (Gerlach), so that the ganglion-cells are connected with the medullated 

 fibres of the posterior nerve-roots only indirectly through the nerve-network. 

 The arrangement of the fibres in the anterior horn of the gray matter appears 

 to be somewhat different : here the medullated 

 fibres of the anterior nerve-roots are for the 

 most part directly continuous with the axis-cyl- 

 inder processes of the ganglion-cells (Fig. 411). 



The nerve-cells of the gray matter are of two 

 kinds, large branched nerve-vesicles which are 

 collected into groups, and small round cells 

 which resemble free nuclei and are found scat- 

 tered throughout the whole of the gray matter. 



In the anterior horn is a constant group, 

 situated at the anterior part of the cornu, and 

 sometimes termed the vesicular column of tlie 

 anterior cornu. It consists of two groups of 



Sinus long. sup. 



FIG. 410. Transverse vertical section of the head, 

 occipital region, showing hemispheres and cerebel- 

 lum. (Gegenbaur.) 



FIG. 411. Diagram showing collator;;! fibres (C) 

 and arborizations (6). S, arborization of the branched 

 processes of a cell, whose axis-cylinder process is seen 

 prolonged as a nerve-fibre. II'. N. and Gr. S., white 

 and gray substance. (Gegenbaur.) 



cells : one mesial, near the anterior column ; the other lateral, near the lateral 

 column. At the base of the posterior horn on its inner side, and joining the 

 gray commissure, is a group of nerve-cells, which give rise to the projection men- 

 tioned above as being seen on transverse section in the upper part of the cord, 

 which is called Clarke's posterior vesicular column. 



At the junction of the anterior and posterior cornu, in the outer portion of 

 the gray matter, is a third group of cells, the tractus intermedio-lateralis. In cer- 

 tain regions of the cord these cells extend in amongst the fibres of the white 

 matter of the lateral column, and give rise to the lateral horn. In addition to 

 these groups a few large scattered cells are found in the posterior horn, extending 

 into the substantia cinerea gelatinosa. 



THE BRAIN AND ITS MEMBRANES. 



Dissection. To examine the brain with its membranes the skull-cap must be removed. In 

 order to effect this, saw through the external table, the section commencing, in front, about an 

 inch above the margin of the orbit, and extending, behind, to a level with the occipital protu- 

 berance. Then break the internal table with the chisel and hammer, to avoid injuring the invest- 

 ing membranes or brain ; loosen and forcibly detach the skull-cap, when the dura mater will be 

 exposed. The adhesion between the bone and the dura mater is very intimate, and much more 

 so in the young subject than in the adult. 



