THE CENTRAL NERVOUS SYSTEM 827 



impulses from the stomach. But clinical testimony is by no means 

 unanimous on this point, and experiments on animals show that 

 other factors are involved in these sensations. 



The eleventh or spinal-accessory nerve contains only efferent 

 fibres. The cells of origin of its spinal portion lie in the lateral 

 horn of the cord, from about the level of the first to the fifth or 

 sixth cervical nerves. The bulbar portion, sometimes called the 

 bulbar accessory, arises from the lower two-thirds of the dorsal 

 accessory-vagus nucleus, from about the level of the first cervical 

 nerve up to the level of the tip of the calamus scriptorius. Tho 

 accessory portion of the nucleus lies behind and to the side of i.e., 

 dorso-lateral to the central canal ; the upper or vagus portion is 

 more laterally placed in the floor of the fourth ventricle. Soon after 

 the junction of its bulbar and spinal portions, the nerve divides into 

 two branches, an internal and an external. The external branch, 

 containing the spinal fibres, passes out to supply the trapezius and 

 sterno-mastoid muscles with motor fibres. The internal branch, 

 containing the bulbar fibres, passes bodily into the vagus. 



The twelfth or hypoglossal nerve is exclusively an efferent nerve. 

 Its nucleus of origin is an elongated collection of large nerve-cells 

 extending throughout approximately the lower two-thirds of the bulb 

 close to the median line and parallel to it. It contains the motor 

 supply of the intrinsic and extrinsic muscles of the tongue and of the 

 thyro- and genio-hyoid. Paralysis of it causes deficient movement 

 of the corresponding half of the tongue. When the tongue is put 

 out, it deviates towards the paralyzed side, being pushed over by 

 the unparalyzed genio-hyoglossus of the opposite side, which is 

 thrown into action in protruding the tongue. 



The Functions of the Brain. 



The paths by which the various parts of the central nervous 

 system are connected with each other and with the periphery 

 have been already described, and we have completed the ex- 

 amination of the functions of the spinal cord and medulla 

 oblongata. The events that take place in the upper part of 

 the central nervous stem and in the cortex of the cerebellum 

 and cerebrum now claim our attention. 



From very early times the brain has been popularly believed to 

 be the seat of all that we mean by consciousness sensation, ideation, 

 emotion, volition. And he who loves to trace the roots of things 

 back into the past may see, if he choose, running through the whole 

 texture of the older speculations a belief that the brain does not 

 act as a whole, but is divided into mechanisms, each with its special 

 work a foreshadowing, often in grotesque outlines, of the doctrine 

 of localization so widely held to-day. But until comparatively 

 recent times, cerebral physiology remained a kind of scientific 

 terra incognita ; and no notable additions were made for a thousand 

 years to the doctrines of Galen. Even to-day the utmost limit of 

 our knowledge is reached when in certain cases we have connected 

 a particular movement or sensation with a more or less sharply- 

 defined anatomical area. How the cerebral processes that lead to 

 sensations and movements, to emotions and intellectual acts, arise 



