40 THE FROG CHAP. 



4. The suspensoria (sus), a pair of projections spring- 

 ing from the outer and upper portions of the auditory 

 capsules, and directed downwards, outwards, and backwards. 

 To them the ends of the lower jaw are attached. 



5. The upper jaw ', a half-circle of bone and cartilage, 

 united in front to the olfactory capsules and behind to the 

 auditory capsules and suspensoria. On either side of the 

 skull, between the cranium and upper jaw, is a large space, 

 the orbit, in which the eye is contained, 



6. The lower jaw ', a roughly semicircular bar of bone and 

 cartilage, articulated at each end with the corresponding 

 suspensorium. 



7 . The tongue-cartilage or hyoid (b. hy), a shield-shaped 

 cartilage connected by delicate curved rods (a. c. hy) with 

 the auditory capsules. 



On the posterior surface of the brain-case is a large hole, 

 the foramen magnum (fig. 9, c, for. mag), on either side of 

 the lower edge of which is an oval elevation covered with 

 cartilage, the occipital condyle (oc. en). The foramen magnum 

 leads into the cavity in which the brain is contained. If the 

 first vertebra is placed in its natural position with regard to the 

 skull it will be seen that the foramen magnum corresponds 

 with the neural canal of the vertebra, and that the condyles 

 fit into its articular surfaces. Thus the skull readily moves 

 up and down upon the vertebra, the condyles acting as' 

 rockers ; a space between the neural arch and the dorsal 

 edge of the foramen magnum covered by membrane in 

 the fresh state, allows of the requisite amount of play. 



The discrimination of the separate bones and detailed structure of the 

 skull is rather difficult, and may very well be omitted by the beginner at 

 the present stage. 



The occipital condyles are borne on a pair of irregular bones 

 (EX.OC) which bound the sides of the foramen magnum, nearly uniting 



