56 THE FROG 



The premaxilla meets its fellow of the opposite side in 

 the middle line anteriorly. Each bears teeth and gives off 

 from its dorsal surface a backwardly directed process which 

 forms part of the boundary of the nasal opening. In life 

 the premaxillae are movable and when pressed against by 

 the tip of the lower jaw they are turned slightly backward, 

 closing the nares. 



o 



The quadrato-jugal is the only cartilage bone of the upper 

 jaw. Its anterior end articulates with the posterior end of 

 the maxilla and its posterior end articulates with the squa- 

 mosal. It does not bear teeth. 



(2) The suspensorium. The jaws are attached to the 

 cranium by means of a suspensory apparatus in which the 

 following bones are to be distinguished on each side : 



The tympanic or squamosal, a T-shaped bone forming 

 the postero-lateral wall of the skull. The stem of the T 

 unites with the quadrato-jugal, and the posterior arm of 

 the cross of the T abuts against the lateral wall of the 

 prootic. 



The pterygoid, a triradiate bone lying beneath the tym- 

 panic. What are its relations to other parts of the skull? 



The palatine, a slender transverse bone lying in the roof 

 of the mouth, and passing between the maxilla and the an- 

 terior end of the sphenethmoid. 



Draw (X2) a dorsal view of the skull; also a ventral 

 view, excluding the lower jaw and the hyoid apparatus. 



(3) The mandibular arch, or lower jaw. Each half 

 consists of a cartilaginous core, Meckel's cartilage (best 

 seen in a wet preparation), on which are deposited the fol- 

 lowing membrane bones : 



The angulo-splenial, a long bone forming the posterior 



