Distribution of Fibres of Posterior Roots of Spinal Nerves. 409 



roots, and to the skin distribution of the cranial nerves. The com- 

 munication is divided into four sections. In Section I the field of 

 peripheral distribution of each root is described from the Yth cervical 

 to the lower end of the brachial region. The description given is 

 taken in each case from one particular experiment, which has proved 

 a typical one for the root in question, and then deviations from this 

 type are appended to it in the form of annotations. Particular 

 attention was paid to the question of the skin-fields of the several 

 divisions, ophthalmic, maxillary, and inandibular of the cranial Vth, 

 in order to see if the fields possessed the characters of segmental 

 skin-fields, or those of peripheral nerve-trunk skin-fields. They 

 were found to conform with the latter, not with the former. A 

 curious relation of the posterior edge of the field of the Vth to the 

 external ear is found to exist, indicating that the position of the 

 visceral cleft is still adhered to as a boundary line for the field of the 

 trigeminus. The sense of taste as well as of touch is foand to be 

 destroyed in the anterior two-thirds of the tongue after intracranial 

 section of the Vth ; this makes it extremely doubtful whether the corda 

 tympani can have gustatory functions in the monkey, as has been 

 believed in some cases in man. No loss of eye-movements, or inter- 

 ference with them, has been found to result from intracranial section 

 of the Vth. 



The results obtained on the various successive nerve-roots cannot 

 well be abstracted. The glossopharyngeal field on the tongue has 

 been successfully delimited. 



After cranial Vth and all the upper cervical posterior roots have 

 been severed, there still persists a small field of sentient skin, which 

 includes the external auditory meatus and a part of the pinna. This 

 field, although not corresponding to the situation given by anthro- 

 potomists to the distribution of the auricular branch of the vagus*, comes 

 either from it or the glossopharyngeal. It presents interest as being 

 the only field representing the whole cutaneous distribution of an entire 

 nerve, which does not conform with the rules of zonal distribution 

 holding good in the case of each of the other nerve-roots examined, 

 and these now include the whole series. The posterior root of the 

 1st cervical nerve has a skin-field in the cat which includes the 

 pinna. The posterior root of the same nerve in Macacus has no 

 skin-field at all, its skin-field having apparently been included in the 

 Ilnd cervical of Macacus, not in the cranial Vth. The root fields con- 

 tributing to the surface of the brachial limb are Illrd, IVth, Vth, 

 Vlth, Vllth, and VHIth cervical, and 1st, Ilnd, and Illrd thoracic. 

 Of these, the VIII th cervical is the only one which includes the 

 whole of the surface of the free apex of the limb ; its distribution in 

 this respecb closely resembles that of the Vlth lumbar sensory root 

 in the pelvic limb. 



VOL. LX. 2 I 



