1910.] AJferents of Third, Fourth, and Sixth Cranial Nerves. 457 



their way into tlie orbital muscles, in luanj^ instances accompany blood- 

 vessels, and in a small number of instances we have been able to trace some 

 of them actually to termination in the walls of arterioles. 



The third, fourth, and sixth cranial nerve pairs are therefore afferent- 

 efferent, their afferents belonging to the receptive (sensorial) endings with 

 which all the extrinsic eye-muscles are richly provided. The afferent 

 divisions of these cranial nerves are by their distribution exclusively 

 proprio-ceptive,* supplying no other organs either extero-ceptive or intero- 

 ceptive. 



As regards the reflexes obtainable from these nerves our experiments 

 have dealt chiefly with tlie brancli from third nerve to inferior oblique. 

 When this muscle after detachment is briskly stretched between ivory- 

 tipped forceps reflex movements (of ear, etc.) are obtainable. 



As regards the normal functions of these afferents of the eye-muscles, it 

 was shown previously]- that after the conjunctiva, both palpebral and ocular, 

 and the cornea of both eyes have been rendered deeply anaesthetic by cocaine, 

 the eyes can still be directed to any given point with considerable accuracy 

 in a completely dark room. One must think that for such performance tlie 

 exercise of some peripheral apparatus of sense is required. Under the above 

 conditions, the superficial fifth and optic nerves having been excluded, the 

 only possible channels seem the proprio-ceptive sense-organs and afferents 

 of the third, fourth, and sixth nerve-pairs themselves. 



The occurrence of degeneration of the third, fourth, and sixtlij cranial 

 nerves in cases of tabes, a disease defined as " primary progressive degenera- 

 tion of the first afferent (sensory) projection system of neurones " (Mott),§ 

 becomes less anomalous in view of these nerves being afferent-efferent, and 

 not purely efferent. The ocular deviations common in tabes may be 

 referable to loss of reflex tonus, owing to degeneration of the proprio- 

 ceptive afferents rather than to actual paralysis from destruction of the 

 motor fibres of these nerves. 



The fuller consideration of these and other points we leave to be dealt 

 with in a more complete account which we hope soon to furnish. 



* Sherrington, * Integrative Action of the Nervous System,' p. 336, 1906. 



t Sherrington, 'Eov. Soc. Proc.,' vol. 64, p. 120, 1898. 



X Oppenheim and Siemerling, ' Archiv f. Psychiatric,' vol. 18, p. 161, 1887. 



J5 ' System of Medicine,' vol. 7, p. 98, 1901 (Allbutt). 



