168 THE NERVOUS SYSTEM. 



the second g-roup forms a very slight prominence^ and is covered by 

 a very fine layer of nerve fibres, it also g-ives off some extremely fine 

 nerves to the eyeball; this is perhaps a ciliary gang-lion {^Ganglion 

 ri/iare, Scliwalbe), Beard, however, names it ' mesocephalic gan- 

 g-lion/ The other three groups are simply clusters of cells between 

 the fibres of the nerve.] 



4. The pathetic or trochlear nerve {N. trochlearu^ pathetlcus), 

 (Figs. 102, 103, and T12 IV). From its orig-in it courses forwards 

 with and then crosses the motor-oculi ; it perforates very obliquely 

 the cartilaginous lateral wall of the cranium, in front of the 

 motor oculi but above and very slightly behind the optic foramen 

 (Fig*. 116); it runs parallel to and in company with the Ramns 

 opthalmicus tngemini, and appears to exchange a few fibres with it, 

 which, however, according to de Watteville, Stannius, Cuvier, and 

 Wyman, is not really the case. In this course it lies first to the inner, 

 then to the outer side of the ophthalmic, over which it passes to 

 supply the Rectus nHjjerlor. [The pathetic and ophthalmic nerves 

 are sometimes enclosed in a common sheath (de Watteville).] 



5. The trigeminal nerve {N. trujemhins), (Fig-s. 97, 102, 103, 

 III, 112, 113, and 114 F) is the largest of the cranial nerves in 

 the frog" ; from its origin it runs outwards and forwards to the skull 

 wall, and just before reaching this enters the large Gasserimi 

 (jangllon. It then passes through the cranial wall immediately in 

 front of the au^ditory capsule, and divides at once into two main 

 branches (Fig. m Vg, etc.), the Ramus ojMhalmicus iXi\à\X\e, Ramus 

 wax'dlo-matidibularis. 



The Gasserian ganglion is a large, yellow, oval ganglion placed 

 in a depression in the outer wall of the craniiim ; it is covered by a 

 ' perig-anglionie g-land,"" which is similar in structure to that of 

 a spinal ^ periganglionic ^ gland (see p. 180), the fibrous capsule 

 being stronger. This ganglion receives three other nerves besides 

 the trig-eminal, viz. the sixth and seventh nerves, and branches of 

 the sympathetic. 



According to de Watteville, these nerves are arranged on the 

 lower surface of the ganglion, so that the sympathetic is below, 

 the sixth above it, then the seventh, while the fifth is iippermost ; 

 the sympathetic splits into several bundles which join the various 

 branches of the ganglion ; the sixth divides into two bundles, one of 

 which usually joins the ophthalmic, while the other makes its exit 

 independently; the seventh splits into two bundles, one of which 



