274 



CLASS AMPHIBIA. 



contain lateral ventricles. In the Anura the olfactory lobes are 

 united across the middle line, in the Urodela they are separate. 

 The pineal body is disconnected from its stalk and lies outside 

 the skull in Anura. There does not appear to be any parietal 

 organ or pineal eye. 



There are ten pairs * of cranial nerves arranged very similarly 

 to those of fishes, excepting that in 



lJI II the abranchiate forms the sense-organ 



branches (ophthalmicus superficialis, 

 mandibularis externus, buccalis of the 

 7th, and lateral line branch of the 

 vagus) have disappeared. 



In the frog, as an example of the abraiichi 

 ate forms, the roots of the fifth and seventh 

 are separate though their ganglia are united 

 into a ganglion which may be called the 

 ganglion prooticum (Gasserian and geniculate 

 ganglia fused). The ophthalmic nerve (a 

 purely sensory nerve except for glandular and 

 vascular branches) passes below the rcctus 

 superior muscle. The superior maxillary nerve 

 contains motor fibres and supplies the depres- 

 sor muscle of the lower eyelid and the levator 

 bulbi. The sixth nerve joins the ganglion 

 prooticum and passes out in the ophthalmic 

 nerve ; it supplies the retractor bulbi as well 

 as 'the external rectus. The seventh nerve 

 divides in the ganglion prooticum into its two 

 branches, the palatine and the hyomandibular. 

 The palatine except for vascular and glandular 

 branches is purely sensory; the hyomandi- 

 bular is a mixed nerve, and is connected by 

 an anastomosing branch with the glossopharyn- 

 geal. The vagus group of nerves arises from 

 the medulla by four roots, which contain the 

 elements of the glossopharyngeal and vagus. 

 They pass out of the skull by the foramen jugulare and unite into a single 

 ganglion, the ganglion jugulare, from which pass out the glosso pharyngeal 

 and the vagus. The glossopharyngeal immediately dilates into a ganglion. It 

 is a mixed nerve, supplying the anterior slip of the petrohyoid muscle and 

 the mucous membrane of the pharynx and tongue, and, as stated above, 

 it is connected by an anastomosing branch with the hyomandibular of 

 the seventh. The vagus usually leaves the ganglion jugulare in two 



* von Plessen u. Rabinovicz, Die Kopfnerven v. Salamandra maculata 

 im vorgeruckten Embryonalstadium, Miinchen, 1891. Strong, The cranial 

 nerves of Amphibia, Journal Morphology, 10, 1895, p. 101. 



J. 152. Dorsal view of the 

 brain of Triton cristatus (after 

 Burckhardt). 1, olfactory 

 nerve ; 2, olfactory lobe ; 3, 

 cerebral hemisphere ; 4, me- 

 dulla oblongata ' 5, cerebel- 

 lum; 6, optic lobes]; /"/pineal 

 body ; 8, thalamencephalon ; 

 9, choroid plexus. 



