64 COMPARATIVE ANATOMY 



embryo, but, as growth proceeds, the anterior and inner part 



Fig. ii. 



The Brain, Cranial Nerves, and anterior part of the Spinal Cord 

 of the Frog dissected from the dorsal surface. Cb, cerebral 

 hemispheres ; Thai, Thalamencephalon ; in the middle of 

 it is seen the hole by which the stalk of the pineal body 

 communicated with the cavity of the third ventricle ; O L, 

 corpora bigemina (mid-brain) ; Cer, cerebellum ; B, the 

 bulb or medulla oblongata ; 4V, the fourth ventricle ; /, 

 The olfactory or first pair of cranial nerves ; //, the optic, 

 second pair of cranial nerves ; l-'a, the ophthalmic branch of 

 the trigeminal or fifth pair of cranial nerves ; Vi>, the 

 maxillary branch, and Vc, the mandibular branch of the 

 trigeminal. The two last branches spring from a large 

 swelling on the main stem of the nerve ; this is the 

 Gasserian ganglion ; VII, the main branch of the facial 

 or seventh pair of cranial nerves crossing over Col, the 

 columella auris, and just beyond this sending back a branch 

 to connect with the ninth nerve ; rp, the ramus palatinus 

 of the seventh nerve, passing below the eyeball and 

 distributed to the skin on the snout and anterior part 

 of the palate ; VIII, the auditory or eighth pair of cranial 

 nerves ; IX, the glossopharyngeal or ninth pair of cranial 

 nerves ; X, the pneumogastric, vagus, or tenth pair of 

 cranial nerves. The vagus has a large ganglion on its 

 root which is joined by the anterior extension of the 

 sympathetic system coming from the first sympathetic 

 ganglion lying under Hy, the hypoglossal or first pair of 

 spinal nerves : Br, the brachial second pair of spinal 

 nerves. The third, fourth, and sixth pair of cranial nerves 

 passing to the muscles of the eyeball are not shown in the 

 figure. 



of the wall of each becomes much thickened, and bulges into 



