THE CENTRAL NERVOUS SYSTEM 815 



by a single puncture what can be also performed by section of all 

 the respiratory nerves at a distance from the medulla oblongata. 

 But while nobody speaks of the destruction of a ' centre ' when a 

 reflex action is abolished by division of the peripheral nerves con- 

 cerned in it, there is a tendency, when the same effect is brought 

 about by a lesion in the brain or cord, to invoke that mysterious 

 name, and to forget that the cerebro-spinal axis is at least as much 

 a stretch of conducting paths as a collection of discharging nervous 

 mechanisms. 



It is, perhaps, a profitless task to enumerate all the so-called 

 centres in the bulb and cord with which the perverse ingenuity of 

 investigators and systematic writers has encumbered the archives 

 and text-books of physiology. In addition to the great vaso-motor, 

 respiratory, cardio-inhibitory and cardio-augmentor centres in the 

 bulb, which, perhaps, have more right than the rest to be regarded 

 as distinct physiological mechanisms, if not as definitely bounded 

 anatomical areas, there had been distinguished ano-spinal, vesico- 

 spinal, and genito-spinal centres in the lumbar cord, a cilio-spinal 

 centre for dilatation of the pupil in the cervical cord, and in the 

 medulla centres for sneezing, for coughing, for sweating, for sucking, 

 for masticating, for swallowing, for salivating, for vomiting, for the 

 production of general convulsions, for closure of the eyes, for the 

 secretion of tears, and even a ' diabetes ' or ' sugar ' centre (p. 518). 

 It would be just as correct, and more practically useful (for it would 

 perhaps encourage the student who has lost his way amidst these 

 interminable distinctions), to say that the cerebral cortex contains 

 a centre for learning sense, and another for forgetting nonsense, 

 and that in a healthy brain it is the latter which is generally thrown 

 into activity in the study of a list like this. 



The Cranial Nerves. 



Unlike the spinal nerves, which arise at not very unequal 

 intervals from the cord, the nuclei of the cranial nerves, with 

 the exception of the olfactory and optic, are crowded together 

 in the inch or two of grey matter of the primitive neural axis 

 in the immediate neighbourhood of the fourth ventricle and 

 the Sylvian aqueduct. Of these nuclei some are the end nuclei 

 or ' nuclei of reception ' of sensory fibres that is to say, collec- 

 tions of nerve-cells around which the sensory fibres break up 

 into terminal arborizations. Such are the sensory nuclei of the 

 fifth, the nuclei of the eighth, and the sensory nuclei of the 

 glossopharyngeal and vagus nerves (Figs. 339, 340). The nuclei 

 of origin of the motor fibres lie, upon the whole, in two longi- 

 tudinal rows a median row, which consists of the nuclei of 

 the third and fourth nerves in the floor of the aqueduct, and 

 those of the sixth and twelfth nerves in the floor of the fourth 

 ventricle ; and a lateral row comprising the motor nuclei of 

 the fifth, seventh, tenth, and eleventh nerves. The clumps of 

 grey matter which make up these nuclei may be considered as 

 homologous with the grey matter of the ventral or anterior 



