48 A MANUAL OF Z£)OLOGY 



observe tjie optic an^ the auditory nerves. Can you dis- 

 tinguish an epiphysis and a hypophysis? Slcetch the 

 brain from the top, also from the bottom. Open tjie optic 

 globes and the cerebrum. Are there cavities in them? 

 Where do they lead- to? Back of the eye and lateral to 

 the optic lobes find the cavity, of the ear and the ear 

 stones. Open the eye and fina the aqueous humor, lens, 

 vitreous humor, retina, choroid coat, sqlerotic coat, and the 

 cornea. How does the lens compare with 'that In the 

 dog-fish?- Dissect out the eye, commencing first in the 

 roof of the mouth. Between the mem^brane of the roof 

 of the mouth and the ropf find the levator muscle. From 

 the internal posterior part- of tlje optic cavity, as an origin, 

 to the sides of the eyeball, find fgur recti muscles. The 

 two oblique muscles of the eye have their origin at the 

 internal anterior part of the .orbit and extend to the upper 

 and to the lower par^s of the,^yeball. Note the way in 

 which the optiq nerves cross, that .from the left eye going 

 to the .right side of the brain, etc. 



AMPHIBIA 



FROG (Ranai 



Material is best foun^. during the early spf.ing months. 

 Search the shallow p^nds and the grass adjoining thenj for 

 good sized frogs. .Rana c£itesbina. (bull frog) may be ob- 

 tained, at small cost, from the..,dealerg.|n. zoological ma- 

 terial. Frogs can be, kept .alive for long, periods with very 

 little care. It is necessary to have a wire cage, with or 

 without running water, J,t running.water is n;0,t to be liad put 

 some sods with "growing grass in. the cage and keep them 

 moist. Place :a vessel of water In the cage. This water 

 must be changed freauently. The frogs will, need no care 

 as to food, ,asAhej will jiot eat .anything except the frogs 

 of smaller size that may bejn the. cage .witfi them. On 

 this account it is well, to sort them as ,to size and to keep 

 them separate* ,If tjiey shonW freeze no injury is dpne 

 for if left to them^elyea they, ,wiJl gradually thav? put and 

 be as .active as ever. , . . , 



In studying the frog .both, living and preBeryed speci- 

 mens should be at iand. ForniaUn.^fpur per cent, ma ire« 



