28 ON THE NERVOUS SYSTEM ly. 



forwards, and joins the principal root of the trigeminus, into the ganglion of which 

 it enters. The third (b) root is equally peculiar, and is longer and far more slender 

 than either of the others ; it is so delicate, that, vinless great caution be used, it 

 will be torn away in the removal of the membranes. The facility with which it 

 is destroyed offers a probable explanation of the fact, that it has so frequently 

 escaped observation. Its origin is about midway of the medulla on its lower 

 face, and quite near to the median line ; this also joins the principal root, and 

 becomes involved in the Gasserian ganglion. The origin of the last-described 

 root corresponds with that of the ahducens, of which there can be no doubt that 

 it is the homologue, as shown by Vogt.* 



We have here, then, one interesting feature of the trigeminus ; namely, that all 

 the roots, whether motor or sensitive, pass through the ganglion, a condition not- 

 usually found in the same nerve in other animals. All the roots thus united and 

 connected with the ganglion escape from the cranial cavity through one and the 

 same foramen in the (wing of the ?) sphenoid. The ganglion is usually quite near 

 to this foramen, may even occu])y it, or be exterior to it. The Gasserian ganglion 

 in its shape somewhat resembles the same part in the human body, but has the 

 characteristic yellow color of that of the vagus and spinal nerves. From its convex 

 surface, three large trunks and one smaller one are given off. 



A. Ophthalmic or Orhitar Branch. (Plate II. Figs. 2, 3, a.) — After leaving the 

 ganglion of Gasser this nerve is directed forwards parallel to the sides of the 

 cranium, till it reaches the co-ossified frontals or the " os en ceinture " ; this it per- 

 forates, gains its cavity, and is again directed forwards, and divides into two 

 branches ; one of these, the superior, crosses the olfactory pouch and branches of 

 the olfactory nerve above, and, inclining towards the median line, is distributed to 

 the skin on the lips over the intermaxillai-y region ; the other, passing externally to 

 the olfactory pouch, is lost in the skin behind the preceding. The upper branch, 

 crossing the olfactory nerve at an acute angle, gives as it passes small branches to 

 the pouch itself (Plate 11. Fig. 11.) 



Of the collateral branches of this nerve, the first is quite small, and may be 

 traced as far as the sclerotic, which it perforates near the optic nerve, while other 

 filaments enter it nearer to the cornea, and these may therefore be regarded as short 

 and lon.ff ciliary nerves. The next, which is the longest of the collateral branches, 

 from its distribution might be denominated palatine (Plate II. Fig. 2, 6), though not 

 the homologue of the same nerve in man, since this last is derived from the spheno- 

 maxillary ganglion, which is a dependence of the maxillary branch of the trigemi- 

 nus. The palatine nerve in Frogs is quite easily detected on raising the mucous 

 membrane of the roof of the mouth, to which it gives numerous filaments, and is di- 

 rected parallel and runs quite near to the median line, lying just beneath the base of 



" The abducens takes its origin from the anterior end of the medulla oblongata near the median line, 

 runs obliquely forwards towards the cavitas occuli under the fifth nerve, passes near the ganglion Gasseri, 

 sendnig a branch to it, while the greater part passes beyond this ganglion and is lost in the muscles." 

 C. Vogt, Beilrage zur Nevrohgie der Reptilien. Neuchatel, 1840. See Fischer, Ampkibiormn Nu- 

 dorum NeurologicB Specimen, p. 5. 



