892 



THE PONS. 



of either eye (conjunctival reflex). Various stimuli, especially to the 

 region of the first and second divisions of the fifth nerve, provoke this. 

 Its period has been found to be particularly short, even as low as - 035 sec. 

 (Mayhew), 1 more frequently, '04 sec. A flash of light produces the same 

 movement less quickly -08 sec. (Garten).' 2 Excitation of the pinna or 

 dura mater also elicits the closure. Excitation of the buccal mucous 

 membrane near the canine tooth has been noted to very constantly evoke 

 retraction of the lip (reflexus ultimus, Dastre). Twitching of the pinna 

 on stimulating its skin is also obtained in part from this region, and is a 

 very constant reflex in the cat. 3 All these are reflex actions not early 



Fig. 362. — Transverse section of pons Varolii through the origin of the auditory 

 nerve, v. IV, fourth ventricle ; c, white matter of cerebellar hemisphere ; 

 c.d, corpus dentatuni cerebelli ; fl, flocculus ; c.r, corpus restiforme ; B, 

 Roller's ascending auditory bundle ; D, Deiter's nucleus ; VIII, issuing root 

 of auditory nerve; Vlll.d, dorsal nucleus; VIII. v, ventral (accessory) 

 nucleus of auditory ; n.tr, small-celled nucleus traversed by fibres of the 

 trapezium; tr, trapezium; /, fillet; p-l-b, posterior (mesial) longitudinal 

 bundle ; f.r, formatio reticularis ; n.n'.n", nuclei in formatio reticularis ; 

 V.a, ascending root of fifth ; s.g, substantia gelatinosa ; s.o, upper olive ; 

 VII, issuing root of facial ; n. VII, nucleus of facial ; VI, root bundles 

 of abducens ; py, pyramid bundles ; n.p, nuclei pontis. — Schafer (from a 

 photograph). Magnified about 4 diameters. 



annulled by narcotics. The conjunctival seems to involve the myel- 

 encephalon as well as the metencephalon. 4 In the rabbit the tonus of 

 the muscles of the pinna falls after severance of the sensory root of 

 the trigeminus. 5 Binswanger 6 has called attention to the existence of 



1 Journ. exper. Med., N. Y., 1897, vol. ii. 



2 Arch.f. d. gcs. Physiol., Bonn, 1898, Bd. lxxi. S. 488. 



3 Sherrington, Proc. Boy. Soc. London, March 1893. 



4 Exner, Arch.f. d. gcs. Physiol., Bonn, 1874, Bd. viii. S. 520. 

 3 Filehne, Arch.f. Physiol., Leipzig, 1886, S. 432. 



6 Arch. f. Psychiat., Berlin, 1888, Bd. xix. 



