386 



MORPHOLOGY OF NEKVHS. 



to be in series with the anterior and internal cell-columns of the anterior cornu of the spinal 

 cord. These nerves also, with the exception of the fourth, emerge from the axis in a line 

 which forms a continuation of that of the anterior roots of the spinal nerves, and like those 

 they consist mainly of large fibres (not so large in the hypoglossal however as in the others), 

 which are distributed to voluntary muscles. In this group therefore are comprised the menial- 

 .to 111 (i tic efferent fibres of the cranial nerves. 1 



It has already been seen that in the upper cervical region the lateral somatie ejjereni jihrex 

 are separated from the anterior roots, and form the spinal accessory nerve, which arises from 

 the outer group of cells of the anterior horn. Proceeding upwards in the brain-stum, the 

 following nuclei form a lateral series from which the fibres of this group arise the bulbar 

 portion of the accessory nucleus in part, the accessory vago-glosso-pharyngeal nucleus (nucleus 

 ainbiguus), the facial nucleus, and the nuclei of the motor root of the fifth nerve, ventricular 

 and mesencephalic. The cells of the facial and accessory vago-glosso-pharyngeal nuclei are of 

 moderate size, but they are larger in the motor nuclei of the fifth nerve and in the nucleus of 

 the spinal accessory nerve. The fibres of the nerves arising from these nuclei are mostly of 

 medium size, but the spinal part of the spinal accessory consists of large fibres. 



Sfilanehn'u' eft'ere/// ///;/r.v, characterized by their small size, are present in the bulbar 

 portion of the spinal accessory nerve, in the vagus nerve of which they form a large part, in 



SPLANCHNIC AFFERENT 

 SPLANCHNIC EFFERENT 



LATERAL SOW. EFFT. 



MESIAL SOMATIC EFFERENT 



Fig. 241. PLAN OP THE ARRANGEMENT OP THE CONSTTTUENT PIBRES OK TIII; CKANIAI, NKKVK.S IN TIIK 

 BULB. (Based on Gaskell, with modifications.) (GK D. T.) 



the glosso-pharyngeal nerve (small superficial petrosal branch), in the facial nerve (J:irgi> 

 superficial petrosal branch and the efferent part of the chorda tympani), and in the third 

 nerve (ciliary portion). The origin of the splanchnic efferent fibres in the spinal cord has not, 

 been determined, but in the brain-stem there are special nuclei from which the fibres of this 

 group arise. These are the bulbar portion of the accessory nucleus (in part), the small-celled 

 vago-glosso-pharyngeal nucleus, from which not only the splanchnic efferent fibrefc of t he 

 vagus and glosso-pharyngeal proceed, but according to Duval also those of the facial through 

 the portio intermedia, and the groups of smaller cells at the upper end of the oculomotor 

 nucleus (see Part 1 of this Volume, p. 99). 



Somatic afferent film's constitute the greater part of the large root of the fifth nerve and 

 the auditory nerve ; and a small group of these fibres occurs also in the vagus, composing its 

 auricular branch. S/)laneli i<- afferent Jibnx are contained in the facial (afferent part of the 

 chorda tympani), glosso-pharyngeal and vagus nerves, probably also in the sensory purl, of tin- 

 fifth nerve. With regard to the central connections of these fibres it is to be remarked that 

 many of them descend in the bulb and upper part of the spinal cord, forming the so-called 

 " ascending roots " the funiculus solitarius for the vagus and glosso-pharyngeal, perhaps also 

 for the portio intermedia, and the bulbar root of the fifth nerve. A great number of the fibres 

 enter the auditory nuclei, the sensory nucleus of the fifth nerve and the siibstant ia grlatinosa, 

 which may be looked upon as derivatives of the posterior horn of the grey substance of the 

 cord, just as the nerves at their attachment to the brain-stem form a series continuing the 



1 According to Hatschek there are also ventral roots to the glosso-pharyngeal and vagus nerves in 

 Ammoctt'tes, anil the same have been described in the embryo of man and the rabbit by Zimmermann. 



