( 336 ) 



caudalward breadth of a skin-area innervated b) a ganglion of the 

 sympathetic column, having an average length of 20 cm. ma\ be 

 approximated at 7 mm., and that the areas overlap one another 

 somewhat more than half. 



The foregoing' having been duly stated, a comparison between 

 the scheme of the spinal and that of the sympathetic innervation of 

 the skin lay very near indeed. Once the ventral (and dorsal) branches 

 of a couple of spinal nerves having been cut through together with 

 the sympathetic connecting branches, il is easy enough to define the 

 extent and the distribution of the insensible zone of the skin resulting 

 from this operation, and to establish a comparison between these 

 and those of the dark zone. In order to facilitate this definition, I 

 augmented the irritability for reflex actions in the animals by 

 intoxicating them with a small quantity of a solution of the sulphuric 

 salt of strychnia in sea- water (1 : 10.000). After this a slight scratching 

 of the skin by means of a pin's point was sufficient to produce a 

 plainly visible general reaction, making it possible to define the 

 boundaries between the sensible and insensible areas- with great 

 precision. I found the results of a series of experiments to be nearly 

 invariable, so that I may communicate them here with sufficient 

 certainty. 



Generally then the anaesthetic areas and the dark zones, observed 

 after the section of spinal nerves and their corresponding sympathetic 

 connecting branches are found to accord completely as regards their 

 extent, distribution and arrangement. Consequently the pigmento-motor 

 sympathetic tibres, originating in a certain ganglion of the N. sympa- 

 thies and ils connecting branch, are distributed precisely within 

 that area of the skin that is supplied with sensory tibres by the 

 corresponding spinal ganglion. Both schemes therefore cover one 

 another completely, and the above given particulars about the inner- 

 vation of the pigment-cells, holds good likewise for the sensory 

 innervation of the skin. Thus the central innervation of the skin in 

 Pleuronectidae is divided into a series of segmental areas, which 

 considered in their functional significance, may be distinguished in 

 sensory and pigmento-motor skin segments, but according completely 

 as regards their distribution and extent. 



II. The sympathetic innervation of the pilo-motor muscles and 

 llir spinal sensory innervation of the skin in cats. 



The well-known researches of Langley (1893) ') have shown that 



') J. N. Langley. — Preliminary account of the arrangement of the sympathetic 

 nervous system, based chiefly on observations upon pilomotor nerves. Proceedings 





