1892.] On the Posterior Roots of some Spinal Nerves. 333 



III. " Experiments in Examination of the Peripheral Distribu- 

 tion of the Fibres of the Posterior Roots of some Spinal 

 Nerves." By C. S. SHERRINGTON, M.A., M.D., Lecturer on 

 Physiology at St. Thomas's Hospital, London. Commu- 

 nicated by Professor M. FOSTER, Sec. R.S. Received 

 December 2, 1892. 



(From the Physiological Laboratory, of St. Thomas's Hospital, London.) 

 (Abstract.) 



After reference to the experimental researches of Eckhard, Peyer, 

 Krause, Koschewnikoff, Meyer, and Tiirck, and to the anatomical of 

 Herringham and Paterson, mention is made of clinical observations 

 by Thorburn, Starr, Mackenzie, Head, and others. The methods 

 employed by the author in experiments on the Frog, Cat, and Monkey 

 are then detailed. In the two latter animals the effect of consecutive 

 sections in ascending or descending series upon the reflex movement 

 elicitable by electrical excitation of the central end of a peripheral 

 nerve was observed, and followed as a guide to the central connexions 

 of the nerve. In the first- and last-mentioned animals mechanical 

 excitation of the cutaneous surface, after previous section of a number 

 of posterior roots above and below the root to be examined, was em- 

 ployed to detect the peripheral distribution of the nerve-root in 

 the skin. The various experiments performed are individually 

 described, and the results of each series are collated. The cutaneous 

 fields of the thoracic and post-thoracic afferent spinal roots are shown 

 in photographs, and in sketches made at the time in the laboratory. 

 The photographs illustrate also the chief outlines of the segmental 

 skin-fields of the cervical sensory roots ; but description and discus- 

 sion of the roots, above the 1st thoracic, are reserved for a future 

 communication. 



The author finally proceeds to draw conclusions of the following 

 nature : 



The field of skin belonging to each sensory spinal root may be 

 called the segmental skin-field, in each segmental field reflex reaction 

 is less easily elicitable near the edge of the field than from the field 

 elsewhere. The segmental fields do not present the same configura- 

 tion as do the fields of the peripheral nerves. 



Although in a plexus each posterior spinal root gives separate con- 

 tributions to many several nerve-trunks, the cutaneous distribution of 

 the root is composed not of patches which are disjoined, but of patches 

 which are so joined that the distribution of the entire root forms 

 one continuous field. Similarity of the root composition of neigh- 



