On the Cranial Nerves of Elasmobranch Fishes. 529 



mandibular branch. This large nerve first gives off a number of small 

 twigs which pass under the buccal division of the facial to assist in 

 supplying the muscles in front of the spiracle. It then divides into 

 branches which pass forwards and outwards supplying the mandi- 

 bular and other muscles, and finally sends branches to the skin in the 

 vicinity of the mandibular arch and the posterior labial cartilage. 

 Some fibres from both the maxillary and mandibular nerves penetrate 

 between the sensory tubes, and lie in close contact with the mucous 

 canals, but in no case have T found them terminating in the ampul Ise 

 or penetrating the mucous canals to end in the sensory tissue lodged 

 in their cavities. 



The Facial Complex. In describing the cranial nerves of Hexanchus, 

 Gegenbaur considered the trigeminal and facial nerves as forming a 

 single group, and he included amongst the roots of the trigeminal 

 the roots of two nerves (ophthalmicus superficialis and buccal) now 

 all but universally acknowledged as belonging to the facial. 



While in the higher vertebrate the trigeminal nerve is of far more 

 importance than the facial, in the lower fishes it is otherwise ; for 

 while the trigeminal proper consists of but a single root the so-called 

 facial is made up of three large roots, one of which seems to be 

 double. Hence, instead of grouping the trigeminal and facial nerves 

 together, it will be more convenient to consider the facial nerves by 

 themselves and speak of them as the facial complex. This complex 

 includes four separate nerves, viz., (1) the ophthalmicus superficialis, 

 (2) the buccal, (3) the palatine, and (4) the hyomandibular. In the 

 meantime it is only necessary to mention that the enormous develop- 

 ment of the so-called facial is owing to the presence of a complex 

 system of lateral sense organs sensory tubes and mucous canals. 



4. The Ophthalmicus Superficialis. This nerve (4, fig. 1) arises by a 

 large root from the so-called trigeminal nucleus which occupies the 

 most dorsal portion of the medulla. The root, in a large fish, lies on a 

 higher level (by about 4 mm.) than the other roots of the facial 

 complex, and it is also the most posterior root, i.e., the furthest from 

 the snout. Arising far apart from the other divisions of the facial it 

 runs forwards and then bends downwards to reach the buccal nerve, 

 with which it freely communicates as it passes through the cranial 

 walls at a higher level than the trigeminal and ophthalmicus pro- 

 fundus. Immediately beyond the walls of the cranium it presents a 

 ganglionic swelling, which consists of large bipolar cells, similar to 

 those of the Gasserian ganglion. The main trunk of the nerve then 

 arches round the conical orbital process of the palato-pterygoid arch, 

 and extends forwards above the eye muscles to send branches to the 

 sensory tubes and mucous canals of the snout. 



In Lcemargus the ophthalmicus superficialis of the facial supplies 

 (1) the ampullae of the sensory tubes on the dorsal aspect of the snout, 



