528 COMPARATIVE ANATOMY 



arising from cells within the brain are unique in amniotes, although such 

 relations are not uncommon in invertebrates and amphioxus. (Fig. 516) 

 In the anamnia the ophthalmic branch of the trigeminus divides into 

 a superficial branch, which innervates the skin of the snout but not the 

 lateral line sense organs of that region, and a deep or profundus branch 



Fig. 438. — The twelve cranial nerves shown as if projected upon a median section 

 of the head. I. Olfactory lobe. II. Optic. III. Oculomotor, IV. Trochlearis. V. 

 Trigeminus. VI. Abducens. VII. Facialis. VIII. Acusticus. IX. Glossopharyngeus. 

 X. Vagus. XI. Accessorius. XII. Hypoglossus. 



which passes through the orbit to the snout. Both contain general 

 somatic sensory fibers. As stated above, in cyclostomes the deep ophthal- 

 mic is an independent nerve with a separate ganglion and root and is 

 therefore regarded by many morphologists as a "segmental" nerve. In 

 most anamnia, however, the root of the profundus nerve joins that of the 

 rest of the trigeminus and persists in amniotes as a branch of that nerve. 



