260 



AN INTRODUCTION TO ZOOLOGY 



system of the lateral line sense organs, and so termed lateralis fibres. 

 Such lateralis nerves are found generally in fishes, and in those 

 members of the class Amphibia that permanently inhabit the water, 

 but are absent from all the air-breathing vertebrates. The anterior 

 or ophthalmic branch of the seventh is a lateralis nerve, and runs into 

 the orbit, where it accompanies the ophthalmic branch of the 

 trigeminus forward to the snout. There it serves the sensory 

 ampullae and canals of the supra-orbital and snout regions It even 

 arises by a separate root from the brain. The second branch of the 

 seventh, the buccal, is also composed of lateralis fibres, and passes 

 in company with the maxillary and mandibular branches of the fifth 



.V * vHt 



vil M 



FIG. 85. Diagram of distribution of cranial nerves in Scy Ilium. The factors 

 of the acustico-lateralis system shown in black. 



Au., auditory capsule ; G.C., gill cleft ; M., mouth ; O., orbit ; O.C., olfactory capsule. 



I.-X., cranial nerves; V.M., maxillary; V.Mn., mandibular; V.O., ophthalmic; VII.B., 

 buccal; VII.H., hyoidean; VII. Hm., hyomandibular; VII.Mn., external mandibular; VII. O., 

 ophthalmic; VII. P., palatine ; VII.Ps., prespiracular ; IX.Po., post-trematic branch ; IX. Pr., pre- 

 trematic branch; X.B., branchial dividing into pre- and post-trematic branches; X.L., nervus 

 lineae lateralis ; X.V., visceral. 



nerve to the sensory canals in the infra-orbital region and on the 

 ventral surface of the snout. Immediately on entering the orbit, 

 the palatine or first branch of the facialis proper passes forwards 

 and outwards, at first behind and then below the maxillo-mandibular 

 of five to the lower jaw. Here it divides into two, one penetrating 

 the jaw and the other passing to the muscles of the roof of the buccal 

 cavity. The fourth and largest trunk of the seventh nerve runs 

 along the hinder wall of the orbit, giving off several pre-spiracular 

 twigs which supply the anterior wall of the spiracle, and then crosses 

 the hyomandibular cartilage, just beneath the skin, to the posterior 

 wall of the spiracle. Itfseparates^into threejnain portions ; two 

 post-spiracular twigs consisting of true facialis fibres, supplying the 



