460 



THE TISSUES. 



that the white substance of the cord constantly increases from be- 

 low upwards, and that the enlargements of the cord depend mainly 

 upon the gray substance, has an important bearing on this question. 

 Moreover, no connection has been discovered between the nerve- 

 fibres in the cord, and the processes of the cells of its gray matter. 

 Still, it by no means follows that these cells may not act on the 

 fibres sent among them; and experimental physiology at present 

 demands the admission that they do impart motor impulses to them, 



at least in the production of reflex or diastaltic motions. 



QWj2vfc* 5 '4&S-6 



it ... "t 



II. STRUCTURE OF THE ENCEPHALON. 

 \ 1. The Medulla Oblongata and Pons Yarolii. 



The medulla oblongata and pons Varolii constitute a very import- 

 ant part of the encephalon, since ten of the twelve pairs of encepha- 



Fig. 305. 



Transverse section of the medulla oblongata through, the lower third of the olivary bodies. (From 

 Stilling.) a. Anterior fissure. &. Fissure of the calamus scriptorius. c. Raph6. d. Anterior co- 

 lumns, e. Lateral columns. /. Posterior columns, g. Nucleus of the hypoglossal nerve, contain- 

 ing large nerve-cells, h. Nucleus of the vagus nerve, i, i. Gelatinous substance, k, It. Roots of 

 the vagus nerve. I. Roots of the hypoglossal or ninth nerve, m. A white bundle of longitudinal 

 fibres connected with the root of the vagus, n. Soft column. (Zartstrang, Stilling.) o. Wedge-like 

 column. (Keelstrang, Stilling.) p. Transverse and arciform fibres, q. Nucleus of the olivary bodies. 

 r. The large nucleus of the pyramid, s, s, 8. The small nuclei of the pyramid, u. A mass of gray 

 substance near the nucleus of the olives (Oliven-Nebenkern), u, q, r, are traversed by numerous 

 fibres passing in a transverse semicircular direction, v, w. Arciform fibres, x. Gray fibres. (4 diam.) 



