DIGESTIVE SYSTEM. 231 



character to hold good in a pre-eminent degree. For not only do the 

 dental organs vary in their more minute structure, but in number, 

 form, situation, mode of attachment, and development, so that it is by 

 no means easy to give a general survey of these peculiarities without 

 describing them in the several families and genera. 



All Fishes, with but few exceptions, are provided with teeth. In 

 some, however, they are completely* wanting, as in the Sturgeon, 

 the genera Aodon, Syngnathus, Amphioxus, while others, as the 

 Salmons, exhibit them upon all, or nearly all, the bones that gen- 

 erally support teeth. These bones are chiefly the intermaxillary 

 and inferior maxillary, the palatal bones, the vomer, lingual bone, 

 and branchial arches ; also, though rarely, the superior maxilla, 

 instances of this bone supporting teeth occurring, at least in the 

 Osseous Fishes, only in Salmo, Clupea, and Muraenophis ; it is rare 

 too for the pterygoid bones or the sphenoid to be, as in Sudis, armed 

 with teeth. It is very uncommon for a broad dental plate to be 

 present upon the occipital bone, the base of which in the Carp ex- 

 hibits for this purpose a broad process with a concave surface. 

 Teeth are in some instances met with only upon the pharyngeal 

 bones, which are peculiar bones situated behind the branchial arches, 

 and found both above and ^pelow the entrance to the pharynx, their 

 number varying from one to six. The jaws in the Cyprini are 

 edentulous, but there are teeth upon the pharyngeal maxillae, which 

 in the Carp exhibit broad molar-like crowns ; other forms occur in 

 other Cyprini, so that the several species may be partly distinguished 

 by the varieties of the pharyngeal teeth. In other genera, such as 

 Labrus and Scarus, the true as well as the pharyngeal jaws are 

 furnished with teeth. Occasionally, as in the Lampreys, and in the 

 genus Helostomus among the Osseous Fishes, the teeth are chiefly 

 fastened to the lips. As regards, however, the situation of the teeth, 

 the Rays and Sharks, and then the Chimaera, agree most with Man 

 and Mammalia, for in all three the teeth are limited to the two arch- 

 shaped maxillae. A singular position for the teeth occurs in the 

 Saw-fish (Pristis), where, besides the jaws, the bill-shaped process 

 prolonged from the cranium is armed upon either edge with a row of 

 pointed teeth, giving it the appearance of a double saw. 



Diversities occur, moreover, in reference to the mode of attach- 

 ment of the teeth in Fishes, such as are met with in no other class 

 of Vertebrata. In some instances the teeth are inserted in cavities 

 or distinct sockets, as in the weapon of the Saw-fish. Some teeth 

 have their basis hollow, and implanted like the claws of a cat upon 



