THE NERVOUS SYSTEM 449 



which supplies general sensation to this region. The second 

 branch is the buccal (ramus buccalis), accompanied in its turn 

 by the maxillary branch of the Trigeminus. The third is 

 the external mandibular, divided into anterior and posterior 

 branches. The companion branch from the Trigeminus, 

 associated with the anterior of the two subdivisions, is the 

 mandibular of that nerve (ramus mandibularis Quinti). 

 In the Dipnoi there is a communicating branch between this 

 part of the system and that belonging to the Vagus, but this 

 seems to be wanting in other cases. 



The remaining branches of the facial nerve are divisible into 

 two portions, sensory and motor. The sensory portion pos- 

 sesses at its origin the large genicular ganglion, from which 

 proceed (i) a large palatine branch and (2) a small internal 

 mandibular. The motor portion incorporates within itself the 

 external mandibular branch of the lateral line system given 

 above, and this forms the mixed hyo-mandibular branch which 

 supplies the region of the lower jaw and the hyoid arch. 



Much of the Trigeminus has already been described in as- 

 sociation with the Facialis. There remain to be mentioned 

 the large semilunar ganglion (often fused with the sensory 

 ganglia of the lateral line nerves of Facialis) which lies at 

 the base of the three branches already described, and the 

 deep ophthalmic branch (ramus ophthalmicus profundus). 

 This latter possesses a ganglion of its own and issues from the 

 skull by a separate foramen. It is thus semi-distinct from the 

 remainder and may be considered a separate nerve, originally 

 anterior to the Trigeminus, and secondarily associated with 

 it. There are some indications to show that it may have 

 once been associated with the Trochlearis, as sensory and 

 motor roots, respectively, of the same elementary nerve. The 

 mandibular branch of the Trigeminus possesses a few motor 

 elements, which prevent the nerve from being classed as 

 wholly sensory. 



The later history of the parts above considered may be fol- 

 lowed from the second diagram [Plate VII], which represents 

 in a general way the terrestrial type, but which in its propor- 



