FUNCTIONAL ANALYSIS, CENTRAL AND PERIPHERAL 61 



plate, which is the primordial motor zone, extends forward of this to 

 include the whole of the peduncle and probably more or less of the 

 hypothalamus and ventral thalamus. This primordial zone contains 

 not only nervous elements with peripheral connections, like the 

 sensory zone, but also an elaborate apparatus of central co-ordination 

 of the neuromotor systems. 



Anteriorly of the peduncle the motor zone has no peripheral con- 

 nections, but the apparatus of motor co-ordination extends forward 

 through the thalamus into the lateral wall of the hemisphere. Since 

 the present analysis is based primarily on physiological criteria, this 

 anterior extension of the motor field is included in the motor zone. 

 The anterior boundaries of this zone are, of course, arbitrarily drawn ; 

 that they are artificial is emphasized by the fact that the large basal 

 optic root terminates in the peduncle, which is in the motor zone as 

 here defined. Efferent fibers have been described as leaving the brain 

 in many places outside the motor zone, even as here broadly defined. 

 Vasomotor and other visceral efferent fibers have been reported in 

 various animals associated with the nervus terminalis and the olfac- 

 tory and optic nerves and in other places for distribution to meninges 

 and chorioid plexuses. We have nothing new to report about Amblys- 

 toma in this connection. 



In the spinal cord and medulla oblongata the peripheral motor 

 neurons are so mingled with the co-ordinating neurons of the tegmen- 

 tum and reticular formation and they are so similar in form that it is 

 often impossible to distinguish the peripheral neurons except in cases 

 where their axons are seen to enter the nerve roots. The cells of the 

 nuclei of the eye-muscle nerves are fairly clearly segregated, and in 

 some reduced silver preparations they react specifically to the chemi- 

 cal treatment (fig, 104); but even here their dendrites are widely 

 spread and intertwined with those of tegmental cells, so that both 

 kinds of neurons would appear to be similarly activated by the 

 neuropil within which they are imbedded. The cell bodies are locally 

 segregated; but their dendrites, where most of the synaptic contacts 

 are made, are not segregated. 



In the medulla oblongata the motor tegmentum contains small and 

 large cells in an endless variety of forms, but these elements are not 

 segregated in accordance with either size or morphological type. It 

 is true that the arrangement of their cell bodies may show some 

 rather ill-defined local segregation, but their dendrites and axons are 

 so intimately intertwined in the neuropil that nothing comparable 



