368 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



attribute of the centric nerve cells, it being borne in mind at 

 the same time that it only becomes actual sensation under 

 certain favourable circumstances. 



The results of physiological inquiry do not at present justify us in 

 confining the process of sensation to any one separate and distinct 

 segment of the nervous system, as, for instance, to the lobes of the 

 cerebrum. In regard to this point, the important fact must not be 

 overlooked, that the lowest member of the vertebrate series, the Lancelot 

 (amphioxus), is provided only with the central grey substance of the 

 spinal cord. To this animal we are nevertheless not justified in deny- 

 ing a conscious animal existence. 



On the other hand, we must not attribute the possession of 

 any other fundamental endowment, such as, for instance, motor 

 power, to any centric cell. The muscles alone are motor 

 organs; and if any excitation of the nerve cell perhaps 

 identical with the sensory process be able to find some paths, 

 by traversing which it can liberate muscular energy ; this 

 arrangement will satisfactorily explain the relation of the 

 central organ to the movements, whether such movement be 

 immediately continuous or discontinuous, in point of time, 

 with the excitor of sensation, and whether the conducting path 

 simply traverses the diameter of the spinal cord, or whether 

 it passes with an indefinite number of interruptions along the 

 conductor-like arches of the hemispheres of the cerebrum. 



2. The second postulate is the law of Bell, so far extended as 

 to admit that a continuation, undisturbed by the multiplication 

 and segmentation of the internodes, of centripetal and centri- 

 fugal conductors reaches the uppermost centres of the brain 

 mass, or, otherwise expressed, arises from them. 



3. The third postulate, lastly, is the law of isolated conduc- 

 tion, the morphological expression of which is found in the 

 fibrillation of the white substance. And even in the grey 

 masses, which doubtless constitute paths for transverse con- 

 duction by means of anastomoses, the law of isolated conduction 

 holds good, though only conditionally. Here, too, it finds its 

 morphological expression in the fact that the axes of the nerve 

 cells appear to be elongated in the direction of the nerve fibre 

 with which they are continuous. This fact strongly suggests 



