40 THE FROG CHAP. 



united with one another in the middle line. They lodge 

 the organs of smell. 



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

 ing from the outer and upper portions of "the auditory 

 capsules, and directed downwards, outwards and back- 

 wards. 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 its ends with the sus- 

 pensoria. 



7. The 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 a large 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 



