IN PALEONTOLOGY. 165 



Having briefly sketched the use of the microscope in Palae- 

 ontology generally, a few instances of its innumerable uses may be 

 noticed more in detail. Commencing with Bones. These, if any 

 articular surface is preserved, can generally be determined with a 

 moderate amount of ease and accuracy; but if occurring water- 

 worn and rolled, gnawed at the articular ends, or in small fragments, 

 microscopic sections may be of value, as by means of a careful 

 examination and measurement of the average size of the long and 

 short diameters of the lacunae, and consideration of the arrange- 

 ment of the Haversian canals, and of the canaliculi of the lacunae, 

 combined with other details less microscopic, a bone may be 

 classed. And as instances. It is well known how Dr. Falconer 

 was thus aided in determining one of the toe-bones of his 

 gigantic Indian tortoise. Again, the first large Pterodactyle bone 

 found in the chalk was the subject of much discussion on account 

 of its size, until a comparison of microscopic sections settled 

 the question, and future discoveries not only confirmed this, but 

 removed all doubts that its size had raised. 



Taking as our next example. Teeth. These being always most 

 intimately related to the food and habits of the animal, become of 

 the utmost importance to the palaeontologist in the determination 

 of the nature and affinities of extinct species, of whose organisa- 

 tion, from the durability of their tissues, they are often the sole 

 remains discoverable in the deposits of former times. From the 

 external examination of worn fragments of teeth, little indeed 

 could be said about their former owners ; but a magnified section 

 may reveal the most characteristic structure, such as the compli- 

 cated infoldings of cement through the waving lobes of dentine in 

 the teeth of the Labyrinthodonts, a group in which size is no 

 guide, as they vary from a few inches in some species, even when 

 adult and perfect, to others which attain the huge bulk of the 

 Mastodonsaurus. 



Amongst the teeth of extinct mammals, birds, reptiles, and 

 fishes, the microscope demonstrates innumerable variations and 

 modifications in the substance and use of dentine, enamel, and 

 cement, the three components of a typical tooth, and the polari- 

 scope at times aids in showing the structure. Moreover, the teeth 

 of many extinct genera display a structure, mode of growth, and 



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