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120. The premaxillary and prnmmdibular bones of a species of Scant* \ the denticles 

 composing the apparently continuous enamel-casing of the beak-shaped jaws 

 are unusually large and well defined. lluttrria*. 



121 . The premandibular and preinaxillary bones and teeth of a species of Scartu. 



\-2~2 Tin- premaxillary luid premandibular lx>ne of a large Parrot-fish (Scant* 

 mitricatiu). 



The maxillary bone it teen from iu outer side where the beak-fthapcd portion presents 

 Mirfarr checkered by small loscitge-shaped plates of an enamel-like substance, arranged in 

 a quincunrial order. The premandibular bone is teen from iu inner side which exposes thr 

 marginal raw of procumbent denticle*, the crowns of which form the lozenge-shaped plate* 

 above mentioned. A longitudinal section ha* been removed from this bone to show the 

 vertical series of twelve successive denticle* anchyloted to each other and to the dense texture 

 of the jaw, of which series the apparently enameled tessellated covering of the jaws consists : 

 below this series one of the alveoli of a denticle not yet anchylosed is exposed ; and beneath 

 this the cavity or closed alveolus common to the germs of several succeni-m- il< ntirles. It 

 will be seen by the relative position of the teeth to the jaw, that the marginal scries 

 in use in the upper and lower mandibles oppose each other by their sides instead of their 

 clonus. 



Hunlerian. 



\-l'-\. The section removed from the preceding prcmandibular bone, showing some 

 of the separate denticles in the dentiparous cavity. 



These denticles present the form of short, thick and conical, four-sided columns, the base 

 forming the crown : the opposite contracted end is excavated, and contained the remains of 

 the formative pulp. The ossification of the capsule of each matrix, by which the general 

 confluence of the teeth with the jaw is effected, has already commenced in the cavity, and 

 has produced a honeycomb character of the posterior surface of the outer alveolar wall : this 

 wall is absorbed as the jaw rises in the progress) of its growth, and the crowns of the denticles 

 are thus exposed. The symphysial surface of the premandibular bone is remarkable for the 

 regularity of the vertical series of rugged, chevron-shaped ridges by which the firm inter- 

 locking of the two pretnandibulara is effected. The complexity of the dental apparatus and 

 the concomitant strength of the jaws of the Parrot-fishes (Scartu) relate to the peculiar 

 nature of their food. These, for the most part tropical, fishes frequent the vast coral reefs 

 which are in course of formation in those Latitude*, and they browse upon the polypes of the 

 lithophytes and their new-formed cells, as the ruminant quadrupeds crop the herbage of the 

 dry land. The irritable bodies of the gelatinous polypes when touched retract into their 

 cells, and the Seari consequently require a dental apparatus strong enough to detach and 



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