THE INTERNAL EAR IN VERTEBRATES 591 



SP-6ACC 



AMPH I BlAN 



c ov 



SC ■ VEST 



LIZA R D 



Bird 



SC VST 



hlctr 



P. OV. 



MONOTREME 



SC VSTi 



A9 P 



SC TY. 



SO v&T 



CARN I VORE" 



MAN 



Fig. 3. — Four diagrams, based mainly on Mr. Harrison's and Dr. Gray's papers, illus- 

 trating the transformation of the perilymph spaces in Amphibia, Reptiles, Birds, and 

 Mammals. 



The perilymph spaces are dotted, the endolymph labyrinth white. In each case the ear is the left in section, 

 seen from behind. The scala media of the cochlea is marked P. bas (in amphibian), Cock. can. in the 

 rest ; the saccular chamber, SP. SACC. ; the connexion with the brain cavity, AQ. PLPH, or AQ. PL. 

 The open connexion between the two perilymph scate in Monotreme is marked HLCTR. 



this sac are present in adult monotremes and it may still be 

 recognised in many of the lower mammals, sinking gradually 

 33 



