CH. XLVII.] FUNCTIONS OF THE SPINAL CORD. 657 



cuneate lobule ; the square piece above it is called the precwneits 

 or quadrilateral lobule. 



The only convolutions now left are those which are placed on 

 the surface of the frontal lobe that rests on the orbital plate of 

 the frontal bone; they are shown in fig. 458, 2 2' 2" (p. 618), 

 and may be seen diagrammatically in fig. 489, the end of the 

 temporal lobe being cut off to expose the convolutions of the 

 central lobe or Island of Reil. 



Along the edge is the continuation of the marginal convolution 

 (M) ; next comes the olfactory sulcus (o) in which the olfactory 

 tract and bulb lie ; then the triradiate orbital sulcus (o.s.) which 

 divides the rest of this surface into three convolutions. 



CHAPTER XLVII. 



FUNCTIONS OF THE SPINAL CORD. 



THE functions of the spinal cord fall into two categories : 

 functions of the grey matter, which consist in the reflection of 

 afferent impulses, and their conversion into efferent impulses 

 (reflex action) ; and functions of the white matter, which are 

 those of conduction. 



The Cord as an Organ of Conduction. 



We have studied at some length the various paths in the white 

 matter, and so we have the materials at hand for recapitulating 

 the main facts in connection with the physiological aspect of the 

 problem. 



Complete section of the spinal cord in animals, and diseases or 

 injuries of the cord or spinal canal in man, which practically cut 

 the cord in two, lead to certain histological changes of a degene- 

 rative nature, which we have already studied, and to physiological 

 results, which are briefly (i) paralysis, both motor and 

 sensory, of the parts of the body supplied by spinal nerves 

 which originate below the point of injury; and (2) increased 

 reflex irritability of the same parts, the reason for which we shall 

 study immediately. 



Hemisection of the cord leads to degenerative changes on the 



