1266 HUMAN ANATOMY. 



Special fibres are furnished to the heart, liver, spleen, pancreas, kidneys, suprarenal 

 bodies and intestinal blood-vessels. 



It is generally admitted that the bulbar or accessory portion of the eleventh nerve forms an 

 integral part of the motor division of the vagus, and, hence, should be included with the efferent 

 fibres of the tenth. As to the ultimate distribution of these accessory fibres, and conversely of 

 the vagus motor fibres proper, much discussion and many conflicting views have existed and, 

 even at present, a consensus of opinion can scarcely be said to have been reached. After 

 reviewing the evidence, both anatomical and experimental, Van Gehuchten ' concludes that the 

 accessory fibres are distributed chiefly, if not indeed exclusively, to the larynx through the infe- 

 rior laryngeal branch of the vagus, and are continued neither to the heart nor to the stomach. 

 The efferent vagus fibres proceeding to the heart are inhibitory in function ; whether they directly 

 reach the cardiac muscle is doubtful, since, reasoning from analogy, it is probable that the vagus 

 fibres end around sympathetic neurones whose axones are the filaments coming into immediate 

 relations with the muscle-fibres. Of the efferent fibres of the vagus distributed to the stomach 

 and other parts of the digestive tract, some are secretory, while others, possibly, influence the 

 caliber of the blood-vessels, in both cases being interrupted in sympathetic ganglia before gain- 

 ing their destination. 



Deep Origin of the Motor Portion. As stated above, the efferent fibres of 

 the vagus consist of two sets, vagus fibres proper and those derived from the acces- 

 sory portion of the spinal accessory. The former have their deep origin in the nu- 

 cleus ambiguus and the dorsal motor nucleus, in series with the motor fibres of the 

 ninth nerve ; the accessory fibres arise from the nucleus ambiguus only. The 

 detailed description of these nuclei has been given (page 1260). The fibres arising 

 from the nucleus ambiguus at first pass backward toward the floor of the fourth 

 ventricle, then bend sharply outward and, condensed into compact strands that 

 receive the fibres originating from the motor cells of the dorsal nucleus, proceed, 

 ventro-laterally in company with the sensory fibres, to their superficial origin along 

 the postero-lateral groove behind the olivary eminence. 



Central Connections of the Sensory Portion. The afferent root-fibres of 

 the vagus are the axones of the neurones lying within the ganglia of the root and 

 of the trunk situated on the upper part of the nerve. The centrally directed processes 

 pass into the medulla, in company with the motor strands, and divide into two sets. 

 Those forming the larger of these end in arborizations around the cells within the 

 lower portion of the dorsal sensory nucleus ; those of the smaller set bend downward 

 and enter the fasciculus solitarius to terminate in arborizations around the cells of 

 the spinal nucleus of reception. (For details of these nuclei see page 1260). As in 

 the case of the other mixed nerves the fifth, seventh and ninth the secondary 

 paths distributing the sensory impulses include (a) fibres that pass from the recep- 

 tion-nuclei to the tract of the mesial fillet, and so on to the great brain, and 

 (b) those that pass to the cerebellum. 



Course and Distribution. The vagus, disregarding its accessory fibres 

 which at first are incorporated in a common trunk with the eleventh nerve, arises 

 from its superficial origin by a row of twelve or fifteen filaments which emerge 

 from the surface of the medulla along the postero-lateral sulcus between the olivary 

 eminence and the inferior cerebellar peduncle. These fasciculi lie in series with 

 those of the ninth nerve above and of the eleventh below (Fig. 1046). 



After leaving the surface of the brain-stem, the converging rootlets of the vagus 

 fuse to form a single flattened trunk, which passes outward beneath the flocculus of 

 the cerebellum to the jugular foramen (Fig. 1074). The trunk leaves the cranium 

 through the rear division of the middle compartment of this foramen, invested by a 

 dural sheath shared by the spinal accessory IHTYC. In this situation it presents a 

 ganglionic enlargement called fat ganglion of the root. Emerging from the jugular 

 foramen, the vagus bears a second thickening, the ganglion of ///<" trunk, and niters 

 the carotid sheath, through which it passes downward the entire length of the neck. 

 Within the carotid sheath the nerve lies at first between the internal carotid artery 

 and the internal jugular vein, and then between the common carotid artery and the 

 vein, occupying the posterior groove between these vessels. At the root of the 



1 Anatnmir <ln S\ stenie NVrveux, 1906. 



