SKULL OF THE FROG. 449 



splenial, outside this a thin dentary, and anteriorly uniting 

 with its fellow a minute mento-meckelian. 



A delicate rod — the columella auris — extends from the 

 tympanum to the fenestra ovalis in the internal capsule of 

 the ear. According to Parker, it represents the upper part 

 of the hyoid arch, the lower portion of which forms a 

 cartilaginous or partially ossified hyoid plate which lies in 

 the floor of the mouth, and is produced into two anterior 

 and two posterior cornua. According to Villy, however, the 

 columella is morphologically connected with the ear-capsule. 



Teeth are borne by the premaxillae, maxillae, and vomers. 



The cartilage which bears the quadrate at its lower end, and runs 

 between pterygoid and squamosal, connecting the articulation of the 

 lower jaw with the side of the skull at the auditory capsule, is called 

 the suspensorium. In Elasmobranchs, the hyomandibular is the 

 suspensorium ; in Teleosteans, the name is applied to the hyomandibular 

 and S3niiplectic ; in Sauropsida, the quadrate occasionally gets the same 

 confusing title. 



When the lower jaw is connected with the skull wholly by elements 

 of the hyoid arch, as in most Elasmobranchs and Ganoids and all 

 Teleosteans, the term hyostylic is used. When the connection is due 

 to a quadrate element only, as in Amphibia and Sauropsida, it is 

 called autostylic. When there is both a hyoid, and a quadrate element, 

 as in Lefidosteus among Ganoids, or a hyoid and a palatoquadrate, as in 

 Cestracion among Elasmobranchs and perhaps also in Holocephali, the 

 term amphistylic is used. Finally, it may be noted here that in 

 Mammals the lower jaw articulates with the squa.mosal. 



Summary in regard to the Skull, 



(3) The chondrocranium, developed from parachordals and trabeculfe 

 at the anterior end of the notochord, and including the auditory 

 and the less important olfactory capsules, persists in great part. 



{V) The exoccipitals, the pro-otics, and the sphenethmoid, are 

 cartilage-bones developed from the ossification of part of the 

 chondrocranium. 



(c) There are more numerous membrane-bones, namely : — 



On the roof of the skull, parieto-frontal and nasals ; 



On the floor of the skull, vomers and parasphenoid ; 



On the sides of the skull, the squamosals ; 



In association with the upper jaw, the premaxillEE, maxillae, 



pterygoids, and palatines. 

 In association with the lower jaw, the dentaries and angulo- 



splenials. (The mento-meckelians seem to arise from 



two lower labial cartilages. ) 

 2 F 



