THE NERVOUS SYSTEM 143 



petrosum laterale by a different opening from the ophthalmicus 

 profundus, and is separated from it by the processus ascendens of 

 the quadrate. 



The homologous comparison of the ophthalmicus profundus and 

 maxillaris nerves of Urodeles with those of Selachians and Anura 

 is not very easy. On the whole it seems most likely that Coghill's 

 explanation is correct, and that the Urodele ophthalmicus profundus 

 contains at least a considerable proportion of the fibres forming the 

 Anuran maxillaris, thus accounting for the apparent difference in 

 the trigemino-palatine anastomosis in these two groups. The Uro- 

 dele maxillaris would then be the equivalent of Strong's 'accessory 

 ramus' of the Anuran tadpole. This hypothesis also explains the size 

 and complexity of the Urodelan profundus nerve, and the smallness 

 of the maxillaris. 



V3. R. mandibularis (n.5c.) (mixed, general cutaneous, and visceral 

 motor). 



R. mandibularis (partim) . . . von Plessen and Rabinowicz. 



R. maxillaris inferior ....... Hoffmann. 



The remaining trigeminal branch leaves the antrum petrosum 

 laterale by the same opening as the R. maxillaris — i.e. between the 

 ascending and otic processes of the quadrate, and immediately 

 turns ventrally towards the lower jaw. It is flat and ribbon-like in 

 shape as it passes through the levator mandibulae muscle. 



(i) Its first branch is a fine twig which turns mesially and dorsally, 

 and innervates the M. levator mandibulae anterior — both superficial 

 and deep portions. This branch leaves the nerve either just before 

 or just after it emerges from the antrum petrosum laterale. The MM. 

 levator mandibulae posterior and externus receive several very fine 

 twigs from the main nerve as it passes ventralwards through them 

 on its way to the lower jaw. 



On reaching the mandible, just anterior to its articulation with the 

 suspensorium, the nerve divides into two branches: — 



(ii) A cutaneous branch (cut.) which turns posteriorly and supplies 

 the skin overlying the angle of the jaw. From this branch is given off 

 an external mandibular nerve — a very fine twig running parallel 

 with the lower jaw and supplying the skin overlying the posterior 

 two-thirds of the mandible. 



(iii) The other main branch is a mixed nerve, and turns antero- 

 ventrally, passing right through the mandible between the dentary 

 and Meckel's cartilage. Within the jaw it gives off: 



{a) An internal mandibular^ or inferior dental nerve (n.m.i.) which 



