150 INTRODUCTION TO NEUROLOGY 



2. Special Somatic Afferent Systems. (1) Vestibular nuclei; (2) cochlear 

 nuclei; (3) optic tectum in the colliculus superior, optic part of the thala- 

 mus (lateral geniculate body and pulvinar). 



3. General Somatic Efferent System. Not represented in the human 

 cranial nerves. 



4. Special Somatic Efferent Systems (III, IV, VI, and XII nerves). 

 A series of ventral motor nuclei in the midbrain and medulla oblongata. 



5 and 6. General and Special Visceral Afferent Systems (VII, IX, and X 

 nerves). All of the fibers concerned with general visceral sensibility and 

 taste enter a single longitudinal tract, the fasciculus solitarius, and termin- 

 ate in the nucleus which accompanies this fasciculus. (The olfactory nerve 

 and its cerebral centers probably should also be included here.) 



7. General Visceral Efferent Systems (III, VII, IX, X, and XI nerves). 

 These are preganglionic fibers of the sympathetic system and arise from 

 laterally placed nuclei (except that of the III nerve, which is joined to the 

 ventral somatic motor nucleus) . 



8. Special Visceral Efferent Systems (V, VII, IX, X, and XI nerves). 

 A series of lateral motor nuclei of the medulla oblongata. 



The spinal nerves, as we have seen, enter the spinal cord by a 

 series of segmentally arranged roots. Within the spinal cord, 



Somatic sensory column 



Dorsal funiculus 

 Visceral sensory column 



/ f^>V"\5A^---^ V~~ Dorsal column 



V menu motor column _ ^^, , ^_, 



' Lateral column 

 Somatic motor column . 



' Ventral column 



Fig. 66. Diagrammatic transverse section through the spinal cord of a 

 fish (Menidia) to illustrate the relations of the functional columns of the 

 gray matter to the nerve roots. The relations of the visceral sensory 

 component are problematical, and fibers of the visceral motor component 

 probably emerge with the dorsal root, as well as with the ventral root, 

 though only the latter are included in the diagram. 



however, their components are rearranged in longitudinal col- 

 umns which cut across and obscure the primary segmentation. 

 The sensory root-fibers and their terminal gray centers occupy 

 the dorsal part of the spinal cord and the motor roots and their 

 centers the ventral part (Figs. 66 and 67). In the brain the 

 same arrangement prevails, the sensory centers lying dorsal to 

 the motor. In the cranial nerves, moreover, the four primary 

 groups of functional systems of the peripheral nerves are more 

 clearly differentiated than in the spinal nerves, and from this 



