THE FROG 55 



median suture and forming the roof of the cranium. With 

 what bones do they come in contact ? 



The parasphenoid or parabasal is shaped like a dagger 

 lacking the handle; it lies on the ventral side of the cranium. 



The nasals are two triangular bones on the dorsal surface 

 in front of the sphenethmoid ; they are set transversely and 

 a little obliquely, and form the roof of the nasal capsules. 



The vomers are two bones on the ventral surface of the 

 cranium in front of the sphenethmoid. Each bears a group 

 of teeth, the vomerine teeth. 



(3) The cartilaginous cranium. In a wet preparation 

 from which the membrane bones have been stripped off, the 

 unsegmented cartilaginous cranium is exposed to view. On 

 its dorsal surface observe the large anterior and two small 

 posterior fontanelles window-like openings in the car- 

 tilage closed by membrane only. Observe that the exoccip- 

 itals, prootics and sphenethmoid are ossifications in this 

 cartilage. Observe that cartilage also forms the basis of 

 both the olfactory and auditory capsules. Compare the car- 

 tilaginous cranium of the frog with the entire cranium of 

 an elasmobranch (e. g., a dog-fish or a skate). 



(&) Jaws and suspensorium. The jaws consist of two 

 cartilaginous and bony arches, maxillary and mandibular. 

 A cartilaginous and bony framework, the suspensorium, 

 serves to attach the jaws to the cranium. 



( i ) The maxillary arch, or upper jaw, contains the fol- 

 lowing bones in each lateral half : 



The maxilla, a long thin bone forming the greater part of 

 the upper jaw. It bears teeth along its entire length. An- 

 teriorly it meets the premaxilla, and posteriorly the quad- 

 rato-jugal. 



