. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 930 PISCES. come elongated by the addition of successively calcified portions of their pulp to their basal or posterior extremities; the opposite end exerts a proportional pressure against the circum- ference of the foramen, and causing its ab- sorption begins to protrude. The tuberculate crown of the denticle is exposed about the time when its sides become anchylosed to those of the previously protruded row. Thus, from the close apposition of the protruding den- ticles, the whole of the outer parietes of their common al
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 930 PISCES. come elongated by the addition of successively calcified portions of their pulp to their basal or posterior extremities; the opposite end exerts a proportional pressure against the circum- ference of the foramen, and causing its ab- sorption begins to protrude. The tuberculate crown of the denticle is exposed about the time when its sides become anchylosed to those of the previously protruded row. Thus, from the close apposition of the protruding den- ticles, the whole of the outer parietes of their common alveolar cavity subjected to the sti- mulus of their pressure is finally removed, and is replaced by the pavement of mutually an- chylosed teeth (fig. 515, «). In the Diodom and Tet radons the structure of the teeth is equally peculiar, but of a very different character from what has been described above. In the former genus each jaw is fur- nished with a double compound tooth adapted to crush and bruise the food, the structure of which at once reminds the anatomist of the> molar teeth of the elephant. Each tooth (fig- 517) consists of numerous lamina; super- imposed upon each other, the upper ones being the oldest and most worn, while the lower ones are the largest and most recently formed. In consequence of this arrangement Jig. the Tet radons a somewhat similar structure of the dental organs is met with. The rostral teeth of the Saw-fishes, Pristls, are quite unique among the whole race of Fishes from the singular position which they occupy, as will be perceived by the following account of this strange apparatus extracted from Professor Owen's elaborate treatise. " The maxillary teeth of the Saw-fish, which is an active and predatory Shark, are, notwith- standing its habits, extremely small, simple, obtuse, and wholly inadequate to destroy and secure the prey requisite for its subsistence. But this seemingly imperfect armature of the mouth is compensated for by
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