124 



THE ANATOMY OF VERTEBRATED ANIMALS. 



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

 ol the skull are more numerous and distinct than in Spatularia, 

 and large dermal bones (I K, JL) are united with them, to 



Fig. 40. — The cartilaginous skull of a Sturgeon, with the cranial bones. The foiiner is 

 shadud, and supiiosed to be seen through the latter, which are left unshade.l : a. ridge 

 formed by the spinous processes of the anterior vertebrse ; 6, ^, lateral wingliitt: pro- 

 cesses; e, rostrum; Au^ position of the auditory organ; iVtz, position of the nasal sacs; 

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

 the suiira-occipital; B, £, of the eiiiotics; E, of the ethmoid; O, G, of the postfrontals ; 

 //, //, of the prefrontals ; C, C, the parietals ; D, If, are the frontals, and E, J''', the squa. 

 mosals ; A', the anterior dermal scute ; /, /, and X, Z, dermal ossifications connecting th« 

 p'^ctoral arch with the skull. 



form the great cephalic shield. The suspensorium (/, ^, h, 

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

 (at A) the proper hj'oid is attached ; and the palato-quadrate 



g^<3. 41, — Side-view of the cartilaginous cranium of Accipenser : a, rostrum; b, nasal 

 chamber ; Or, orbit ; c, auditory region ; d, coalesced anterior vertebrae ; e, ribs ; /, g, A, 

 Buspeusorium ; k, palato-majtillary apparatus ; Ifn, 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 Amia, 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 (? Polypterus). The apparatus of the jaws lias 

 become modified in accordance with the Teleostean type of 



