222 LECTURE IX. 



{Lahrus), and the Parrot-fishes (Scarus), have teeth on the pre- 

 maxillary and pre-mandibular, as well as on the upper and lower 

 pharyngeals ; both the anterior and posterior apertures of the mouth 

 being thus provided with instruments for seizing, dividing, or com- 

 minuting the food, the grinders being situated at the pharynx. 

 In most fishes teeth ai"e developed also in the intermediate parts of 

 the oral cavity, as on the palatines, the vomer, the hyoid bones, the 

 bx'anchial arches ; and, though less commonly, on the pterygoids, the 

 entopterygoids, the basi-pre-sphenoid, and even on the nasal bone. 

 It is very rare to find teeth developed on the true superior maxillary 

 bones ; but the Herring and Salmon tribes, some of the Ganoid Fishes 

 and the great Sicdis {fig. 36.), are examples of this approach to the 

 higher Vertebrata. Among the anomalous positions of teeth may be 

 cited, besides the occipital alveolus of the Carp (V. pi. 51. fig. 6.), the 

 marginal alveoli of the prolonged, depressed, well ossified rostrum of 

 the Saw -fish {Pristis, V. pi. 8.) In the Lampreys and in Helostomus 

 (an osseous fish), most of the teeth are attached to the lips. Lastly, 

 it is peculiar to the class Pisces, amongst Vertebrata, to offer ex- 

 amples of teeth developed in the median line of the mouth, as in the 

 palate of the Myxines ; or crossing the symphysis of the jaw, as in 

 Notldanus, Scymnus and Myliohates, 



Nor is the mode less varied than the place of attachment : some 

 teeth, as those of Lophius, Pcecilia, Anableps, are always moveable : 

 in most fishes they are anchylosed to the jaws by continuous ossi- 

 fication from the base of the dental pulp ; the histological transition 

 being more or less gradual from the structure of the tooth to that of 

 the bone. Sometimes we find, not the base, but one side of the tooth 

 anchylosed to the alveolar border of the jaw : and the teeth oppose 

 each other by their sides instead of their summits ( Scarus, V, pi. 49.) : 

 in Pimelodus, however, where the teeth are thus attached, the crown 

 is bent down in the upper teeth, and bent up in the lower ones, at 

 right angles to the fang, so that they oppose each other in the normal 

 Avay. The base of anchylosed teeth is, at first, attached to the 

 jaw-bone by ligament ; and in the Cod-fish, Wolf-fish, and some 

 other species, as calcification of the tooth progresses towards its base, 

 the subjacent portion of the jaw-bone receives a stimulus, and 

 developes a process corresponding in size and form with the base of 

 the tooth : for some time a thin layer of ligamentous substance inter- 

 venes, but anchylosis usually takes place to a greater or less extent 

 before the tooth is shed. Most of the teeth of the Lophius retain 

 the primitive ligamentous connection: the ligaments of the large 

 internal or posterior teeth of the upper and lower jaws, radiate on 

 the corresponding sides of the bone, the base of the tooth resting on 

 a conformable alveolar process. The ligaments do not permit the 



