78 



THE NERVOUS SYSTEM OF THE FROG 



To dissect the cranial nerves expose the brain by removing the 

 roof of the skull as already described, and then follow the special 

 instructions given in the case of the moi'e important nerves. 



1. The olfactory nerve, the special nerve of smell, arises 



from the anterior end and outer side of the olfactory 

 lobe, and is distributed to the membrane lining the 

 nasal cavity. 



To see the course and distribution of the olfactory nerve, dissect 

 from the dorsal surface, removing the roof of the anterior part of 

 the skull, including t/ie nasal bone. 



2. The optic nerve, the nerve of sight, arises from the side 



FIG. 16. The trigeminal, facial, glossopharyngeal, and pneumc- 

 gastric nerves of the frog, dissected from the right side. 



a, stomach ; e, Eustachian tube; h, h>poglossal nerve; i, lung ; 

 m, second spinal nerve ; s, sinus venosus ; /, squamosal ; t.a, truncus 

 arteriosus ; w, right auricle ; v, ventricle ; v.c, right anterior vena 

 cava ; Va, ophthalmic bianch of trigeminal ; Vb, maxillary branch of 

 trigeminal ; Vc, mandibular branch of the trigeminal; Vila, palatine 

 branch of facial ; VI Ib, hyoidean branch .of f cial ; IX, glosso- 

 pharyngeal ; Xa, laryngeal branch of pneumogastric ; Xb, pulmonary 

 branch of pneumogastric ; Xc, cardiac branch of pneumogastric ; 

 Xd, gastric branch of pneumogastric ; 2, transverse process of secocd 

 vertebra ; 3, transverse process of third vertebra. 



