596 THE NEKVOUS SYSTEM. 



the nucleus ambiguus from which it arises has thus been termed the laryngeal nucleus (Edinger) 

 but it is not certain whether it is vagal or accessory. 



Collaterals and fibres of the opposite lateral cerebro -spinal tract end in connexion with the 

 cells of origin of the accessory nerve, and thus bring its nucleus into connexion with the motor 

 area of the cerebral cortex. Fibres also from the posterior roots of the spinal nerves (afferent or 

 sensory fibres) end in the nucleus. 



Nervus Vagus, Nervus Glossopharyngeus. The vagus and glossopharyngeal 

 nerves present similar connexions with the brain, and they may therefore be 

 studied together. The greater part of both nerves is composed of afferent fibres, 

 which arise outside the brain-stem from ganglionic cells placed in relation to the 

 nerve-trunks. Both nerves possess efferent fibres also, which spring from two 

 special nuclei of origin situated within the medulla oblongata and termed re- 

 spectively the dorsal or splanchnic nucleus and the nucleus ambiguus, which is the 

 somatic nucleus. The afferent ganglionic fibres of the vagus and glossopharyngeal 

 enter the brain by a series of roots which penetrate the medulla oblongata along 

 the ventral side of the restiform body. Within the medulla oblongata they separate 

 into .two sets, viz., a series of bundles (composed chiefly of vagus fibres, i.e. afferent 

 splanchnic), which end in the dorsal nucleus of termination of the vagus and glosso- 

 pharyngeal nerves, and another series of bundles (composed chiefly of glosso- 

 pharyngeal fibres, i.e. taste fibres), which join a conspicuous longitudinal tract of 

 fibres called the tractus solitarius. 



The dorsal nucleus (Figs. 488, p. 557, and 526, p. 593) of the vagus and glosso- 

 pharyngeal nerves is mixed, and contains both motor cells which give origin to 

 efferent fibres, and cells around which afferent fibres of the vagus, and possibly also 

 of the glossopharyngeal nerve, break up into terminal arborisations. It very nearly 

 equals in length the nucleus of the hypoglossal nerve, with which it is closely 

 related. Above, it reaches as high as the striae medullares, whilst, below, its inferior 

 end falls slightly short of that of the hypoglossal nucleus. In specimens stained by 

 the Weigert-Pal method the two nuclei offer a marked contrast. The hypoglossal 

 nucleus presents a dark hue, owing to the enormous numbers of fine fibres which 

 twine in and out amidst its cells ; the vago-glossopharyngeal dorsal nucleus is pale, 

 from the scarcity of such fibres within it. Its cells, like those of all splanchnic 

 efferent nuclei, are much smaller than the somatic cells of the nucleus ambiguus. 

 In the closed part of the medulla oblongata the dorsal vago-glossopharyngeal nucleus 

 lies in the central gray matter immediately behind the hypoglossal nucleus, and 

 upon the lateral aspect of the central canal; in the open part of the medulla oblongata 

 it lies in the gray matter of the floor of the fourth ventricle, immediately to the 

 lateral side of the hypoglossal nucleus and subjacent to the surface area termed the 

 trigonum vagi or ala cinerea. 



All the fibres which arise from this dorsal or splanchnic efferent nucleus are 

 very fine, and in sections of the vagus nerve can readily be distinguished from the 

 much coarser somatic fibres, which come from the nucleus ambiguus, and also from 

 the medium-sized sensory fibres, which spring from the ganglia placed upon the nerves. 

 The fine fibres from the dorsal nucleus are distributed (probably indirectly, i.e. after 

 being interrupted in a peripheral ganglion), to the involuntary striped muscle of 

 the oesophagus and heart, and the unstriped muscle of the oesophagus, stomach and 

 respiratory system (van G-ehuchten and Molhant, La Ntvraxe, June 15, 1912, p. 55). 



The nucleus ambiguus (Figs. 488, 530, 526) gives origin to the somatic 

 motor fibres of the glossopharyngeal and vagus nerves. All the fibres from this 

 nucleus which pass into the glossopharyngeal nerve end in the stylo-pharyngeus 

 muscle ; the vagal branches are distributed to the striated muscles of the pharyi 

 and larynx. The cells of the nucleus ambiguus are large, multipolar, and simil 

 in every respect to the large cells in the anterior column of the spinal medul 

 These cells are arranged in a slender column which is fyest developed in the 

 open part of the medulla oblongata. Here the nucleus can easily be detected, in 

 transverse sections, as a small area of compact gray matter which lies in the substantia 

 reticularis grisea, midway between the dorsal accessory olive and the nucleus 

 tractus spinalis nervi trigemini. It therefore lies more deeply in the substance of 

 the medulla oblongata than the dorsal vago-glossopharyngeal nucleus. Kolliker 

 states that it can be traced downwards as low as the level of the decussation of 



