TEE CRANIAL OR ENCEPnALIC XI.RVES. ^27 



r. To this collection of collateral ramuscules are added the terminal branches, 

 formed by their anastomoses with the superficial temporal nerve — 



14. The subzijgomaHf plexus. 



A. Collateral Branches.— 1. Great Superficial Petrosal Nerve.— 

 This is a very remarkable ramusculc, which is deLachcd from the bend of tlie 

 facial nerve to proceed to Meckel's <ranglion. llie importance of the peculiarities 

 attaching to the study of this nerve requires us to call special attention to its 

 origin, course, and termination ; though the details into which we are about to 

 enter may be omitted by the student. 



Origin. — Ganglion geniculare. — The manner in which the great superficial 

 petrosal nerve comports itself at its origin is yet an obscure and disputed subject, 

 on which, however, light is beginning to be thrown. The following is the most 

 general opinion : This nerve arises from a small grey enlargement, the geniculate 

 ganglion (or intiimescmtia gangliformis), placed on the course of the facial nerve, 

 at the summit of the angle which that trunk describes after its entrance into the 

 aqueduct of Fallopius. The presence of this small ganglion on the seventh 

 pair should assimilate the facial to a mixed nerve, the sensitive root of which 

 would be represented by the portio intermedia of Wrisberg — a thin filament com- 

 prised between the seventh and eighth paii-s, and which emanates directly from 

 the medulla oblongata to pass into the posterior part of the ganglion geniculare. 



We have constantly found this ganglion in the domesticated animals. There 

 exists, in fact, on this angle or elbow of the facial nerve, a very slight, grey, 

 conical prominence, composed of ganglionic cells wliich a microscopical examina- 

 tion readily reveals, and giving origin on its apex to the great superficial petrous 

 nerve. This prominence, which, we repeat, is very small, forms part of the facial 

 nerve, on which it only presents a kind of swelling. We have never seen the 

 sharp and precise limitation of its base that is figured in the majority of icono- 

 graphies of human anatomy. 



On the other hand, when, on portions steeped for several weeks in water 

 acidulated by nitric acid, we have studied the constitution of the great petrosal 

 nerve, even at its origin, we have found it formed of two fasciculi very easily 

 separated^one internal, the other external. The latter alone is continuous with 

 the geniculated ganglion ; the other traverses the facial nerve from before to 

 behind, then it is suddenly inflected inwards to ascend to the origin of the nerve, 

 and mix with its fibres. But this fasciculus very often maintains its independence 

 as far as the medulla oblongata, into which its fibres penetrate separately ; they 

 then appear as a small particular trunk beside that of the principal nerve, and 

 comprised between it and the auditory nerve. The great petrosal nerve does not, 

 therefore, proceed exclusively from the ganglion geniculare, as considerable por- 

 tions of its fibres— entirely destitute of ganglionic cells — ^emerge directly from the 

 facial nerve. With regard to the external fasciculus, the separation of its fibres by 

 the action of the acid shows very plainly that the grey substance of the ganglion 

 is found almost exclusively on their track ; and if we trace these fibres — like 

 those of the preceding fasciculus — into the substance of the facial nerve, we shall 

 find that, instead of proceeding towards its origin, they appear to be directed to 

 its termination — a remarkable circumstance, which we believe may be explained 

 by admitting that they come from the anastomosing branch of the pneumogastric 

 nerve, of which we will speak hereafter. 



From this arrangement, it results that the great petrosal nerve arises from 

 the facial by two real, though intimately connected, roots : the internal is 



