56 THE SKELETON OP THE FROG. 



3. The Jaws consist of two cartilaginous arches on each side, 

 maxillary and mandibular, in connection with which 

 cartilage -bones and membrane -bones are developed. 

 Each arch meets its fellow in the middle line in front; 

 and the maxilliary arches, forming the upper jaw, are 

 firmly connected with the cranium by anterior and 

 posterior bony struts. 



a. The Maxillary Arch. All the bones of the upper jaw 

 are membrane-bones except the quadratojugal. In the 

 case of the pterygoid and palatine bones ossification 

 may extend into the underlying cartilage. 



-PIVl 



MM 



Fig. 10. The frog's skull from the right side, 



A, parasphenoid : AS, angulosplenial : B, anterior cornu of hyoid : 

 C, columella : D, dentary : E, exoccipital : F, nostril : FP, frontoparietal : 

 H, body of hyoid : L, aperture for exit of ojDtic nerve : M. maxilla : 

 MMi mentomeckelian : M', aperture for exit of fifth and seventh nerves : 

 N, nasal : O, pro-otic : P, pterygoid : PM, premaxilla : Q, quadratojugal : 

 R, aperture for exit of ninth and tenth nerves : S, squamosal : SE, sphen- 

 ethmoid : T, posterior cornu of hyoid. 



i. The iJterygoid is a large triradiate bone, the inner 

 limb of which is connected with the auditory 

 capsule ; while the posterior limb runs back to 

 the angle of the mouth, and the anterior limb 

 forwards along the upper jaw to the palatine 

 bone. 



ii. The 'palatine is a slender transverse bone, connecting 

 the upper jaw with the anterior end of the 

 splienethmoid. 



