656 



THE NERVOUS SYSTEM 



has recently been traced back to the pars intermedia and chorda tympani 

 of the seventh, figures 412 and 413. It forms also one chief sensory link 

 in the nervous circle for reflex action in the secretion of saliva. But, de- 

 ferring this question until the glosso-pharyngeal nerve is to be considered, 

 it may be observed that in some brief time after complete paralysis or division 

 of the fifth nerve, the power of all the organs of the special senses may be im- 

 paired. They may lose not merely their sensibility to common impressions, 



M.G 



I.C. 



OG. 



Sty. hy 



FIG. 412. The Seventh Nerve and Its Branches. VII, Facial nerve; P.I, pars 

 intermedia; VIII, auditory nerve; Ag.Fal, aqueduct of Fallopius; G.G, geniculate ganglion; 

 E.S.P, external superficial petrosal nerve; M.M, middle meningeal artery; G.S.P, great 

 superficial petrosal nerve; G.P.D, great deep petrosal nerve; I.C, internal carotid artery; 

 Vid, Vidian nerve; M.G., Meckel's ganglion; Ty.Pl, tympanic plexus; S.D.P, small deep 

 petrosal nerve; G.Ph, Glosso-pharyngeal nerve; Ty, tympanic branch; S.S.P., small super- 

 ficial petrosal nerve; O.G., optic ganglion; Stap, nerve to stapedius; C.T, chorda tympani 

 nerve; Z,, lingual nerve; A. Va, communication with auricular branch of vagus; P. A, 

 posterior auricular nerve. Sty.hy, nerve to stylo-hyoid; Di, nerve to digastric (posterior 

 belly); T.F, temporal -facial division; C.F, cervico-facial division; T, temporal; M, malar; 

 I.O, infra-orbital; B, buccal, S.M, supra-mandibular; I.M, infra-mandibular branches. 

 (Cunningham.) 



for which they all depend directly on the fifth nerve, but also their sensibility 

 to the special stimuli to which they are adapted. 



The Sixth Nerve, the Abducens. Origin. The sixth nerve arises 

 from a compact oval nucleus, situated somewhat deeply at the back part of 

 the pons near the middle of the floor of the fourth ventricle. The eminentia 

 teres marks its position. It contains moderately large cells with large nerve 

 axis-cylinder processes. It is connected, figure 375, with the nuclei of the 

 third, fourth, and seventh nerves, and with reflex centers of the optic tracts, 

 as previously mentioned. The root is thin, and passes ventrally and laterally 



