THE SKELETON. 29 



elements. The temporal, into squamosal, tympanic, mastoid, 

 epiotic, opisthotic, and pro-otic. The superior maxillary, 

 into maxillary proper and intermaxillary. The lower max- 

 illary, into angular, articular, opercular, and dentary bones. 



As a rule, the tendency to union increases as we ascend 

 the vertebrate scale. Exception in Batrachia, where the 

 frontal and parietal bones of either side are united. 



Pisces. Skull articulates with vertebral column through 

 body of occipital bone and first cervical vertebra. Bones of 

 face greatly developed. First and second cervical vertebrae 

 very large. Yomer of great size, often tooth-bearing; supe- 

 rior maxillaries of small size, rarely tooth-bearing; inter- 

 maxillary bones always distinct ; para-sphenoid bone ex- 

 tending antero-posteriorly beneath cranial series. Inferior 

 maxillary bone represented in five centres on either side, 

 recognized as dentary, articular, angular, and opercular 

 bones; the fifth is obscure. JThe articulation between bodies 

 of vertebrae markedly biconcave. Bones generally flat, never 

 hollow; sutures generally squamosal, rarely serrate. 



Batrachia. Skull articulates with vertebral column by 

 two condyles on ex-occipital bones. Basi-occipital cartila- 

 ginous. i Girdle bone,' placed in anterior part of cranial 

 cavity of frog-like Batrachia, represents the ethmoidal and 

 orbito-sphenoidal elements of skulls of higher vertebrates. 

 Para-sphenoid present as in Pisces. Frontal and parietal 

 elements on either side united into a single bone the fronto- 

 parietal. Bodies of vertebrae may articulate by double con- 

 cave surfaces, as in Spelerpes (salamander), by convex surface 

 in front and concave behind, as in Rana (frog). Long bones 

 very generally without epiphyses; exception in femur of 

 Rana; tibia and fibula of same animal united in one shaft. 

 Lower jaw commonly composed of three bones dentary, 

 angular, and articular. 



Reptilia. Skull articulates with vertebral column by a 

 single condyle formed by portions of basi-occipital and 

 ex-occipital bones. Para-sphenoid absent. Basi-sphenoid re- 

 markably compressed antero-posteriorly in Crocodilia. The pe- 

 culiar 'transverse* bone extends from the internal pterygoid 



