334 



THE BIOLOGY OF THE FROG 



which rotates the eye around its optic axis so that its upper 

 margin turns forward, and an inferior oblique, which pro- 

 duces the reverse movement. The eye is pulled into the 

 orbit by means of the strong retractor bulbi muscle, which 

 arises from the angle between the lateral and median por- 

 tions of the parasphenoid bone and is broadly inserted upon 

 the posterior and median sides of the eyeball. The eyes 



Fig. 93. — Rigbt membranous labyrinth of the frog from the inner side. 

 aa, ae, np, anterior, external, and posterior ampulla; au, aperture of 

 utriculus ; ca, ce, cp, anterior, external, and posterior semicircular canals ; 

 cus, ulriculo-saccular canal ; de, ductus endolymphaticus ; /, lagena ; mu, 

 ms, mn, macula acustica of the recessus utriculi, sacculus, and pars 

 neglecta respectively; pb, pars basilaris ; pl,ppb, papilla acustica lagenas 

 and basilaris; raa, rap, rs, rn, rl, rb, branches of auditory nerve to 

 anterior ampulla, posterior ampulla, sacculus, macula neglecta, lagena, 

 and pars basilaris respectively; s, sacculus; jj.jt/, sinus utriculi superior 

 and posterior; u, utriculus. (After G. Retzius.) 



are pushed outward by the contraction of the levator bulbi, 

 a broad sheet of muscle running obhquely across the ventral 

 side of the orbit. 



The Ear. — In the ear of the frog there are two sets of 

 organs which are fundamentally different in origin and in 

 function. The one constitutes the inner ear which forms 



