452 AMPHIBIA. 



The cranial nerves are, as usual, on each side the follow- 

 ing :— 



(i) Olfactory, from the olfactory lobe to the nose ; 



(2) Optic, crossing and interlacing with its fellow 



in the optic chiasma beneath the thalamen- 

 cephalon ; 



(3) Oculomotor, to four muscles of the eye ; 



(4) Pathetic, to the superior oblique muscle of the 



eye; 



(5) Trigeminal, with orbito-nasal, maxillaiy, and man- 



dibular divisions ; 



(6) Abducens, to the external rectus muscle of the 



eye J . . , 



(7) Facial, arising along with the auditory, with a 



ganglion uniting with the Gasserian ganglion of 

 the trigeminal, with a palatine branch to the 



roof of the mouth, and a hyoid branch to the 



lower jaw ; 



(8) Auditory, to the ear ; 



(9) Glossopharyngeal, to the tongue and some of 



its muscles ; with a ganglion which unites with 

 that of the tenth ; 



(10) Vagus, with branches to stomach, lung, heart, 



etc. 



The student should refer back to the description of the 

 skate, and to the chapter on the structure of Vertebrates. 



The spinal cord gives origin to ten pairs of spinal nerves, 

 and is swollen at the origin of those which supply the limbs. 

 Around the union of the anterior and posterior roots lie sacs 

 with crystals of carbonate of lime. 



The " sympathetic system " consists of about ten pairs of 

 ganglia — (a) united by branches to the spinal nerves, (^) 

 united to one another by longitudinal trunks which accom- 

 pany the dorsal aorta and the aortic arches, and end an- 

 teriorly in the Gasserian ganglion, (c) giving off branches to 

 the heart, the aorta, and the viscera in the pelvic region. 



Sense-Organs. — The eyes project on the top of the head 

 and on the roof of the mouth. There are two lids, the 

 upper thick and very slightly movable, the lower trans- 

 parent and movable. The transparent cornea in front, the 



