Editorial. 667 



brain. The acuity of every sense in the action systems of differ- 

 ent animals can be measured by the comparative anatomist in 

 terms of the size and structural complexity of the corresponding 

 primary cerebral sensory centers. The habitual type of motor 

 response is no less accurately registered in the permanent organ- 

 ization of the motor cerebral centers. Furthermore, an action 

 system of the rigidly stereotyped sort will be served by a nervous 

 system with the primary reflex centers highly elaborated per- 

 haps, but with the association centers small, while the more 

 plastic types of action system as found in the more intelligent 

 animals are characterized by highly complex association centers 

 and tracts. 



Studies in cerebral architecture carried on from the point of 

 view of the analysis of functional systems of neurones, each of 

 which is both a physiological and an anatomical unit, are as far 

 removed as possible from the older descriptive neurology which 

 seemed to aim at mere enumerations of tracts and cell masses 

 with little effective correlation. The best recent work on cere- 

 bral architecture aims more or less directly at the analysis of con- 

 duction paths and their correlation into definite functional sys- 

 tems. 



A great impetus was given to such studies in the comparative 

 field by the analysis of the peripheral nerves into their components 

 and the rearrangement of these components into functional sys- 

 tems, thus facilitating the integration of the more diffuse sensory 

 systems, like the tactile and gustatory, and permitting the study 

 of their central reflex pathways with almost as great precision as 

 the concentrated systems, Hke the optic. The analysis of the 

 cutaneous nerves of man into their components by the researches of 

 Henry Head and others by a combination of physiological, path- 

 ological and anatomical methods promises still more important 

 advances in this direction. 



The four-root theory of Gaskell and His has been the point 

 of departure, not only for the study of the components of the periph- 

 eral nerves, but also for the study of the functional zones of the 

 central nervous system. The progress which has been made in 

 the functional analysis of the brain and the illuminating value of 

 a knowledge of peripheral nerve components in this study (par- 

 ticularly in the medulla oblongata) are illustrated in a striking 

 way by a comparison of the second volume of the sixth edition of 



