646 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



d.p 



d.r 



and His 1 has followed these two portions, with a groove dividing them, 

 through the entire length of the tube. The dorsal plate (d.p.) he designates 

 as the Flugelplatte (literally, wing-plate), and the ventral plate (v. p.) as the 

 Grundplatte (literally, foundation-plate). The interest attaching to these sub- 

 divisions resides in the fact that the parts of the 

 tube thus marked off are loci for cells having 

 well-marked and different physiological func- 

 tions. The incoming neurons arriving from 

 the cells of the spinal ganglia are limited in 

 the distribution of the main branches to the 

 dorsal plate, and the cell-bodies which give 

 rise to the efferent fibres are to be found in the 

 ventral plate only. The central cells are pres- 

 ent in both plates, though grouped in the local- 

 ity where the two plates come together, and 

 being rather more abundant in the dorsal one. 

 The collaterals of the afferent fibres are distrib- 

 uted to both plates. There is thus in the cord 

 a general arrangement whereby the central cells 

 are located between the afferent neuron and the 

 efferent cell-bodies. Far more important than 

 this, however, is the relation which becomes evi- 

 dent as we pass cephalad namely, that the cerebellum, quadrigemina, and 

 almost the entire mass of the basal ganglia, together with the hemispheres, 

 are the homologues of the dorsal plates, and contain central cells only (Fig. 

 167). 



FIG. 166. Cross section in the cer- 

 vical region of a fetal human spinal 

 cord at the sixth week ; X 50 diameters 

 (Kolliker) : c, central canal ; a, a, 

 groove separating the two plates ; d.p, 

 dorsal plate ; v.p, ventral plate, in 

 which alone are located nerve-cells 

 the neurons of which leave the central 

 system ; d.r, dorsal root ; v.r, ventral 

 root. 



Sp.c\ 



. FIG. 167. Schema showing the encephalon and cord ; the unshaded portion is that derived from the 

 dorsal plate ; the shaded that from the ventral (from Minot) : C, cerebrum ; Cb, cerebellum ; F, foramen 

 of Monro ; I, infundibulum ; M, bulb ; 0, olfactory lobe ; P, pons ; Q, quadrigemina ; Sp.c, spinal cord ; 

 171, third ventricle ; IV, fourth ventricle. 



1 His : Abhandlungen d. math.-phys. Classe d. konigl. Sachs. Gesellschaft der Wissenschaften* 

 1889. 



