NERVOUS SYSTEM OF THE FROG. 451 



The skeleton of the hind-limb consists of a thigh bone or 

 femur; a lower leg formed from the united tibia and fibula; 

 an ankle region or tarsus including two long proximal 

 elements — the astragalus or tibiale and the calcaneum or 

 fibulare — and two imperfectly ossified distal elements ; five 

 metatarsal bones; five toes, the first or hallux with two 

 phalanges, the second also with two, the third with three, 

 the fourth with four, the fifth with three ; and, finally, 

 outside the hallux a " calcar " which looks like an extra toe 

 and consists of three pieces. 



Muscular System. — I shall not describe the myology of 

 any of the Vertebrate types. By help of the guides to 

 practical work which I have cited, the student will readily 

 find out what he wishes to know. 



The muscles are enswathed in connective-tissue. They 

 consist of bundles of muscle fibres, while at their ends or at 

 one of them they are usually continued into strong tendons, 

 which are more or less directly attached to parts of the 

 skeleton. 



Nervous System. — The brain, covered with a darkly 

 pigmented pia mater, has, as usual, the following parts : — 



The elongated cerebral hemispheres, with " olfactory 

 lobes " in front of them, with anterior and posterior 

 commissures and a slight corpus callosum connecting 

 them ; 



The thalamencephalon gives origin dorsally to a pineal 

 outgrowth, which, passing through the skull, ends 

 beneath the skin and between the eyes in a pineal 

 body, while on the ventral side there will be seen the 

 chiasma or interlaced crossing of the optic nerves, a 

 tongue-shaped mass called the tuber cinereum, and 

 the 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." 



