GENERAL SOMATIC SYSTEMS OF CONDUCTION PATHS 173 



the gray matter of the dorsal column of the same side. After 

 a synapse here the axons of the neurons of the second order cross 

 to the opposite side of the cord and ascend in the spinal lemniscus 

 to the thalamus. For further details of these connections see 

 pages 138-140, 163-169, and Figs. 59, 63, 64, 75, 77, 78, 80, 81; 

 on the pain path, see also p. 251. The pathway for cutaneous 

 sensibility from the head follows the trigeminal lemniscus (pp. 

 157, 180, and Figs. 64, 75, 77, 78, 81). The more important 

 exteroceptive pathways are assembled in Fig. 81. 



It will be recalled that in the spinal lemniscus the pathways for 

 touch and pressure, for pain and for temperature are assembled 

 in three distinct tracts, those for pain and temperature being 

 close together (Fig. 63, p. 139). From this it follows that small 

 circumscribed injuries in the white substance of the spinal cord 

 may destroy all sensibility to pressure in a part of the body with- 

 out any disturbance whatever of pain or temperature sensibility, 

 or conversely, it may destroy pain or temperature sensibility 

 without any involvement of the other qualities of sensation. 

 And, in fact, in numerous clinical cases these conditions are 

 found, as will be clear from the following example.. 



Figure 82 illustrates such a case from Dr. Head's experience. 

 The patient suffered from an injury to the lower part of the 

 spinal cord caused by the overturning of a truck of concrete, 

 and when admitted to the London Hospital was paralyzed from 

 the hips downward. In the course of a year he partly recovered, 

 but showed a permanent loss of some sensation qualities over 

 the shaded area in the figure. The right leg below the knee was 

 insensitive to pain (prick) and to all degrees of temperature. 

 But over the whole of this area he could appreciate all tactile 

 stimuli and could localize accurately the spot touched or pressed 

 upon. Yet it was not possible to produce pain anywhere over 

 the right leg and foot by excessive pressure, although he fully 

 recognized its gradual increase. Referring to Fig. 63 (p. 139), 

 it is evident that to produce these symptoms the lesion must 

 have involved the conduction path for pain and temperature in 

 the lateral funiculus (fiber 8 of the figure) of the left side of the 

 spinal cord, and spared the path for touch and pressure in the 

 ventral funiculus (fiber 9). Both superficial pain (prick) and 

 deep pain caused by excessive pressure were abolished. This 



