220 



THE GROWTH OF THE BRAIN. 



diameter from the distal portions of the peripheral nerve 

 it has been suggested that the neuron undergoes a 

 conical diminution, so that its cross-section becomes 

 gradually smaller as it passes away from the central 

 .a w - system (Schwalbe). 1 Since 

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largest neurons can be 

 followed into the branches 

 which are given off to the 

 different muscles of the 

 thigh, a further explanation 

 of their absence from the 

 main trunks at the periphery 

 appears unnecessary. 



These observations on the 

 innervation of the frog's leg 

 harmonise with the obser- 

 vations of Ross 2 and of 

 Kaiser to the effect that it 

 is the smaller cells, and 



those lying at the periphery 

 of the various cell groups 

 in the spinal cord, which 

 send their neurons to the 

 more distal segments of the 

 limb. These cells, develop- 

 ing late, are known to have 

 bodies of small size, and 

 since it is found that the 

 neurons passing to the more distal segments of the 

 limb are small in diameter, there is nothing incon- 

 gruous in connecting such neurons with such cell-bodies. 



1 Schwalbe, Ueber die Kaliberverhaltnisse der Nervenfasern, 

 Leipzig, 1882. 



2 Ross, The Diseases of the Nervous Svstcin, New York, 1883. 



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