660 PHYLUM CHORDATA : CLASS AMPHIBIA 



Muscular system. — The muscles are enswathed in con- 

 nective tissue. They consist of bundles of striated fibres, 

 and at their ends or at one of them they are usually con- 

 tinued into tendons, which are more or less directly 

 attached to parts of the skeleton. 



For an account of the musculature of Vertebrate types, 

 the student is referred to the guides to practical work 

 cited in the Appendix. 



Nervous system. — The brain, covered with a darkly 

 pigmented pia mater, has the usual five parts. 



The elongated cerebral hemispheres have " olfactory 

 lobes " in front of them, and are connected by an- 

 terior and posterior commissures, and by a hint of a 

 " corpus callosum." 

 The thalamencephalon gives origin dorsally to a pineal 

 outgrowth. The pineal body lies outside the skull in 

 the tadpole, but is partially atrophied in the adult, so 

 that little more than the stalk is left. On the ventral 

 side will be seen the chiasma or interlaced crossing of 

 the optic nerves, and a tongue-shaped mass (the tuber 

 cinereum or infundibulum), to which the pituitary 

 body is attached. 

 The optic lobes, a pair of oval bodies, between and 



below which is the iter. 

 The cerebellum, a very narrow transverse band. 

 The medulla oblongata, on the roof of which the pia 



mater forms a very vascular " choroid plexus." 

 The cavities of the brain and the canal of the spinal cord 



are in the adult lined by ciliated epithelium. 

 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 ; 



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



(4) Pathetic, to the superior oblique eye muscle ; 



(5) Trigeminal, with ophthalmic, maxillary, and mandibular 



branches ; 



(6) Abducens, to the external rectus eye muscle ; 



(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 ; 



