310 



INTRODUCTION TO NEUROLOGY 



reflex response may in a literal physiological sense act into the cortical stim- 

 ulus complex and become an integral part of it. 



But there is another aspect of the problem which has recently been 

 brought to our notice by Kappers. 1 It is a well-known fact, which is not 

 often taken account of in this connection, that the descending cortical 

 paths (pyramidal tracts) do not typically end directly upon the peripheral 

 motor neurons whose functions they excite, but rather upon intercalary 

 neurons which lie in the reticular formation or even in the adjacent sensory 



muscle 



Fig. 137. Diagram of the relations of the pyramidal tract in a rabbit or 

 similar lower mammalian brain. Sensory stimuli enter the spinal cord from 

 the skin through the peripheral sensory neuron, S, and ascend to the cere- 

 bral cortex through the lemniscus, L. The descending pyramidal tract, 

 P, lies in the dorsal funiculus of the spinal cord. Its intercalary neuron, 7, 

 may be stimulated by both the peripheral neuron, S, and by the pyramidal 

 tract, P. It discharges upon the peripheral motor neuron, M . 



centers. These intercalary neurons, in turn, oxcito the peripheral motor 

 neurons. The same intercalary neuron which receives the terminals of the 



^ * KAPPERS, C. U. ARIENS. Ueber die Bildung von Faserverbindungen auf 

 Grund von simultanen und sukzessiven Reizen. Bericht iiber den III 

 Kongress fur experimentclle Psychologic in Frankfurt a. Main, 1908. Also 

 Weitere Mitteilungen iiber Neurobiotaxis. Folia Neuro-Biologica, Bd. 

 I, No. 4, April, 1908, pp. 507-532. 



See also DEARBORN, G. V. N. Kinesthesia and the Intelligent Will, 

 Amer. Jour, of Psychol., vol. xxiv, 1913, pp. 204-255. 



