ENDOSKELETON AND VOLUNTARY MUSCLE 



57 



beneath and between the prootic bones, from the center of which 

 a narrow longitudinal tongue extends forward (Fig. 32). 



The anterior end of the cranial cavity is closed by the cylin- 

 drical sphenethmoid bone which is overlapped above by the 

 frontoparietals and below by the anterior end of the parasphenoid. 

 In front of the sphenethmoid is the nasal cavity, which is divided 

 by a median partition. The side walls of the cranium between 

 the sphenethmoid in front and the prootic bones behind, and the 

 frontoparietals above and the parasphenoid below, are formed of 

 cartilage. The large spaces on either side of the frontoparietal 

 bones are the orbits of the eyes. 



pre maxillary 

 men to- Meckel ictn 



vomer 

 palatine 



dentate 



sphen - ethmoid 

 paras ph e no/ d 



squamosa/ 



angulare 



pterygoid 



exoccipi+al 



columella 



Fig. 32. — Ventral view of skull of Rana catesbeiana. 



The paired nasal bones, lying just in front of the frontoparietals, 

 meet in the mid-line, overlying the cartilaginous nasal capsules. 

 From each nasal bone a narrow process extends laterally to the 

 upper jaw. Below the nasal capsules and forming the floor 

 of the cranium in front of the sphenethmoid bone are the paired 

 vomer bones. Each vomer bone bears a tooth on its ventral face. 



Suspensorium of the Frog's Skull. — Three pairs of bones, the 

 squamosals, pterygoids, and palatines, attach the jaws to the 

 cranium and constitute the suspensory apparatus of the skull. 

 The squamosal bone can be seen best in a side view of the skull 

 (Fig. 33). It consists of a narrow stem extending from the 

 angle of the jaw diagonally upward to a shorter cross piece, which 

 is articulated at its upper end to the prootic bone and whose 

 lower end curves downward toward the upper jaw. The ptery- 



