20 



THE SPINAL CORD. 



the mesial group of cells of the anterior cornu, and others to the other side of the 

 cord through the anterior commissure, there perhaps to become connected with the 

 corresponding cells. The outwardly directed fibres of the root are connected with 

 the cells which form the lateral groups of the anterior horn, and partly with some 

 of the cells of the intermediate cell-column. The middle fibres are partly con- 

 nected to the cells of the anterior horn, and partly pass on to the posterior 

 horn, where they are probably continued into some of the cells there present. 



In the cervical region of the cord, from the sixth nerve upwards, the root-fibres of the 

 spinal part of the spinal accessory nerve may also be seen passing out of the anterior horn 

 through the lateral column (fig. 31, p. 40). They arise from a group of somewhat large cells, 

 which in the uppermost region of the cord lies in the antero-lateral part of the horn, close to 



Pig. 17. TRANSVERSE SECTION OF THE SPINAL CORD OF A CHICK ON THE 9in DAY OF INCUBATION, 

 PREPARED BY GOLGI'S METHOD (Ramon y Cajal). 



A , axis-cylinders of anterior root-fibres issuing from large cells of the anterior horn, C. 



B, Posterior root-fibres passing from the bipolar cells of the spinal ganglion, into the posterior column 

 of the spinal cord, D, where they bifurcate, d, and become longitudinal ; e, f, y, collaterals from these 

 fibres, passing into the grey matter. 



its ventral edge, but in the middle and lower cervical regions tends gradually to occupy a 

 position nearer the base of the horn (see p. 16). This group of cells is the direct continuation 

 downwards of the accessory nucleus which will be seen in the lower part of the medulla 

 oblongata. 



The posterior roots at their entrance into the cord are seen to separate into 

 two sets. Of these the lateral, which contains most of the smallest fibres of the 

 root, enters opposite the tip of the posterior horn and joins a bundle of fine longitu- 

 dinal fibres which lies close to the periphery of the cord in this situation. This bundle 

 is known as the marginal bundle or column of Lissamr. Its fibres, which are 

 evidently different from most of those which enter with the posterior root, for they 

 acquire their medullary sheath considerably later (Bechterew), appear, as they pass 

 vertically, gradually to lose themselves in the adjacent gelatinous substance. The mesial 

 set containing the larger and some smaller fibres of the posterior root passes into the 



