CH. XLIY.] CRANIAL NERVES 629 



the cochlea of the internal ear ; the other division, called the vestibular 

 nerve, is distributed to the vestibule and semi-circular canals of the 

 internal ear. 



9. Glossopharyngeal. This is a mixed nerve ; its motor fibres pass 

 to certain of the pharyngeal muscles ; its sensory fibres are mainly 

 concerned in the sense of taste. 



10. Vagus or pneumogastric. This is a nerve with varied efferent 

 and afferent functions ; its 'branches pass to pharynx, larynx, oeso- 

 phagus, stomach, lungs, heart, intestines, liver and spleen. Most 

 of these functions we have already studied in connection with these 

 organs. 



11. Spinal accessory. The internal branch of this nerve blends 

 with the vagus, and its larger external division supplies the trapezius 

 and the sterno-mastoid muscles. 



12. HypoglossaL This is the motor nerve to the tongue muscles. 

 A mere enumeration of the nerves connected to the bulb shows 



how supremely important this small area of the brain is for carrying 

 on the organic functions of life. It contains centres which regulate 

 deglutition, vomiting, the secretion of saliva, etc., respiration, the 

 heart's movements, and the vaso-motor nerves. 



When we further consider that the various centres are connected 

 by groups of association fibres, we at once realise the reason for the 

 complexity of the structures where all this busy traffic takes place. 



In the enumeration of the cranial nerves, it will be noticed that 

 many of them are either wholly motor or wholly sensory, and that 

 some of them, like the spinal nerves, have a double function. The 

 motor nerve fibres start as axons from the groups of nerve-cells in 

 the grey matter of this region, just as the moior fibres in the spinal 

 nerves originate from the cells of the spinal grey matter. There is 

 a corresponding resemblance in the origin of the sensory fibres of 

 the cranial and spinal nerves. In the latter, it will be remembered, 

 they originate as outgrowths from the cells of the spinal ganglia, one 

 branch growing to the periphery, and the other to the spinal cord, 

 where it terminates after a more or less extended course by forming 

 synapses with the cells of the grey matter. In the cranial nerves 

 they have a corresponding origin in peripheral ganglia, and those 

 branches which grow towards the bulb terminate by arborising around 

 special groups of cells spoken of as the sensory nuclei. 



The following diagram (fig. 456) roughly indicates the position 

 of these nuclei ; the motor nuclei are coloured blue, and the sensory 

 red. It must, however, be clearly recognised that while the motor 

 nuclei are true centres of origin, that the so-called sensory nuclei are 

 groups of cells around which the entering sensory fibres arborise ; these 

 cells do not give origin to the axons of the sensory nerves. After we 

 have studied the internal structure of the bulb we shall be able to 



