Skull of Frog. 95 



These cartilage bones are not so numerous as the membrane 

 bones. 



On either side of the foramen magnum, through which the 

 brain becomes continuous with the spinal cord, is a bony mass 

 which also bears the occipital condyles for articulation with the 

 vertebral column. These paired bones are the exoccipitals} 

 Continuous with each of these above, so as to appear to form 

 but one bone, is an ossification in the auditory cartilage, the 

 pro-otic. Beneath the anterior pointed end of the paraphenoid 

 is a complete ring of bone, the ethmoid. On each side is a 



^^ MK 



Fig. 41. -Skull of Frog. Lateral view. (After W. K. Parker.) 

 BH, basihyal ; mk, Mechel's cartilage ; ar, articular ; dent, dentary ; 

 M.MK, mentomechelian ;' PTR, pterygoid. Other letters as in 

 F'g^- 39. 4°- 



Y-shaped bone running forwards, the pterygoid. This is hidden 

 for a short space anteriorly by the tooth-bearing maxilla, 

 which latter abut in front upon the premaxilte. The pterygoids 

 are connected in front with \he palatines, which lie transversely 

 to the longitudinal axis of the skull. Finally, there is some 

 ossification of the quadrate, which articulates with the lower 

 jaw. The bones, cartilage, and membrane, which have just 

 been enumerated, belong to the skull proper and to the sense 

 capsules 'and the upper half of the first visceral arch, the 

 palatopterygoid arcade. There is left a small bone, the 

 columella auris, lying within the ear cavity and representing 

 the top end of the second visceral arch ; the lower jaw, which 



' The existence of only a pair of ossifications in the occipital ring is not 

 a character of frogs in general, but only of certain frogs. In others there 

 are the four ossifications referred to above. 



