174 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



the lateralis nerves being lost, while, as stated above, the motor por- 

 tions are increased in the mammals, in correlation with the greater 

 development of the facial muscles. 



FIG. 172. Ventral view of brain and cranial nerves of Iguana, after Fischer. I-XII, 

 cranial nerves; 1-3, first three cervical nerves; gp, petrosal ganglion; i, Jacobson's commis- 

 sure; h, hypoglossal; n, nasalis ramus of V; rf, ramus frontalis of V; sy, sympathetic. 



VIII. The Acustic (Auditory) Nerve is closely associated with the 

 seventh, but microscopic analysis shows that it has its own roots and 

 ganglion. It is purely sensory, its branches going to the sensory areas 

 of the inner ear. Its connections inside the brain and the development 

 of the ear itself (see sense organs) show that the nerve belongs to the 

 lateralis system, the ear being a group of modified lateral line organs. 

 Beyond the ganglion the nerve divides into a vestibular branch, 

 supplying the utriculus and semicircular canals, and a cochlear branch, 

 going to the lagena and to its homologue in the mammals, the cochlea. 



