480 THE ORGANS 



the splanchnic (branchial) striated voluntary muscles, on the other 

 hand, follows the same law as obtains for the somatic striated volun- 

 tary muscles, i.e., neurone bodies in the central nervous system send 

 their efferent root fibres uninterrupted to the muscle. These dis- 

 tinctions are shown centrally by differences in grouping of the neu- 

 rone bodies which supply respectively the somatic muscles, the 

 splanchnic voluntary muscles, and the smooth muscles and glands via 

 the sympathetic ganglia 



The higher coordinating apparatus or suprasegmental structures 

 (p. 426) of the brain are essentially expansions of the dorsal walls of 

 parts of the brain, each expansion having manifold afferent and 

 efferent connections with the rest of the nervous system and having 

 the endings and beginnings in it of its afferent and efferent paths 

 complexly interrelated by enormous numbers of association neurones. 

 The presence of these latter has probably necessitated the extensive 

 layers of externally placed neurone bodies (cortex) characteristic 

 of suprasegmental structures. 



The structure of the basal part of the brain, connected with the 

 cranial nerves (segmental brain, p. 426), is affected by both the pecu- 

 liarities of peripheral structures mentioned above and by the presence 

 of bundles of fibres and masses of gray forming portions of paths to 

 and from suprasegmental structures (see below) . 



The following summary embodies the resulting general structural 

 features of the brain: 



Segmental Brain and Nerves 



Afferent Peripheral (Segmental) Neurones. — (i) Splanchnic 

 Group comprising nerves VII (geniculate ganglion), IX (superior and 

 petrosal ganglia) and X (jugular and nodose ganglia). The nerves 

 of taste probably belong entirely to this group. The peripheral 

 arms of these ganglia innervate visceral receptors and the central 

 arms form a descending tract in the medulla, the fasciculus solitarius, 

 which has its terminal nucleus giving rise to secondary tracts. 



(2) General Somatic Group (common or general sensibihty). — 

 Semilunar ganglion of V. The peripheral arms of the semilunar 

 ganglion cells pass to the skin of the anterior part of the head, to the 

 mouth and meninges. The central arms of the ganglion cells form a 

 descending tract in the medulla, the radix spinalis V. The terminal 

 nucleus of this tract is the continuation in the medulla of the dorsal 



