124 



THE ANATOMY OF VERTEBRATED ANIMALS. 



In the Sturgeon (Fig. 40), the membrane bones of the roof 

 of the skull are more numerous and distinct than in SjMtularia, 

 and large dermal bones (Z A'j JO) are united with them, to 



Fig. 40. — The cartilai^inous skull of a Sturgeon, with the cranial bones. The former is 

 shaded, and supposed to be seen through the latter, which are left unshaded : a, ridge 

 formed by the spinous processes of the anterior vertebrae ; &, b, lateral winglike pro- 

 cesses; c, rostrum; Au, position of the auditory organ; A^a, position of the nasal sacs; 

 Or, that of orbit. The membrane bones of the upper surface are : A, the analogue of 

 the supra-occipital ; £, B, of the epiotics ; E, of the ethmoid ; 6r, G, of the postfrontals ; 

 U, H, of the prefrontals ; (7, C, the parietals ; Z>, i>, are the frontals, and F, F, the squa- 

 mosals ; JT, the anterior dermal scute ; /, /, and Z, Z, dermal ossilications connecting tba 

 j^^'ctoral arch with the skull. 



form the great cephalic shield. The suspensorium (y, g^ A, 

 Fig. 41) is divided into two portions, to the lower of which 

 (at h) the proper hyoid is attached ; and the palato-quadrate 



Fig. 41. — Side-view of the cartilaginous cranium of Accipenser: a, rostrum; 6, nasal 

 chamber ; Or, orbit ; c, auditory region ; d, coalesced anterior vertebrae ; e, ribs \f,g,\ 

 BUfipensorium ; k, palato-maxillary apparatus ; Mn^ mandible. 



cartilages, with their subsidiary ossifications, are so loosely 

 connected with the floor of the skull, that the jaws can be 

 protruded and retracted to a considerable extent. 



In Lepidosteus^ Polypterus^ and A)nia, the skull presents 

 not only membrane bones, but, in addition, basi-occipital, ex- 

 occipital, and prootic ossifications of the primordial cartilage, 

 to which others may be added. The vomers are double, as in 

 the Amphibia (? JPolypterus). The apparatus of the jaws has 

 become modified in accordance with the Teleostean type of 



