. On the anatomy of vertebrates [electronic resource] . reptiles, hatched by external heat, indepen-dently of incubation, the course of developemeDt may be inter-rupted for longer periods, without hurt to the embryo, than in thewarm-blooded Ovipara. Agassiz states that in Testudinata thecommon period of hatching may be e postponed for months. In Snakes and Lizards a sharp tooth is developed in tbe pre-maxillary of the embryo, towards the close of incubation, where-with they cut through the tough The operation of thistransitory and purposive weapon has been observed by Weinland :2it
. On the anatomy of vertebrates [electronic resource] . reptiles, hatched by external heat, indepen-dently of incubation, the course of developemeDt may be inter-rupted for longer periods, without hurt to the embryo, than in thewarm-blooded Ovipara. Agassiz states that in Testudinata thecommon period of hatching may be e postponed for months. In Snakes and Lizards a sharp tooth is developed in tbe pre-maxillary of the embryo, towards the close of incubation, where-with they cut through the tough The operation of thistransitory and purposive weapon has been observed by Weinland :2it totally disappears in the adult of most Ophidia. For breakingthrough the more brittle shell in Chelonia the embryo is providedwith a sort of horn or hard excrescence above the end of the upperjaw: this afterwards disappears. In the Crocodilia the snout ofthe nearly hatched young is sufficiently hard to break the egg-shell ; but there is no distinct tubercle, nor any precociouslydeveloped premaxillary 1 cccxxxvi. 2 cccxxxvr. 3 ccc. p. 288. 452. Initial steps of Vertebrate Developement. Germ-yolk ofRana temporaria. cccxxxn. WORKS REFERRED TO BY ROMAN NUMERALS IN THE FIRST VOLUME. I. Carus. Urtheilen des Knoehen- und Schalengeriistes. Fol. Geoffroy St. Hilaire. Memoires du Museum. 4to. t. ix. 1822, p. 119. III. Von Baer. Meckels Archiv fiir Physiologie. 1826. Heft iii. IV. Bibra. Chemische Untersuchungen iiber die Knoehen und Ziiline. 8vo. 1844 V. Owen, B. Odontography. 4to. Owen, B. Bossil Mammalia, Zoology of the Vogage of the Beagle. 1838. VII. Hunter. Manuscripts printed in the Catalogue of the Physiological Seriesin the Museum of the Boyal College of Surgeons. 4to. 5 vols. 1832-1840 VIII. Purkinje and Deutcsh. De Penitiori Structura Observationes. 4to. Treviranus. Beytrage des Organischen Lebens. Bremen, 1835. X. Muller, Ino. Ueber die Structur, &c, der Knorpel und Knoehen, Poggen- dorfs Annalender Physik, 1836, vol. viii. p
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