NATURAL SCIENCES OK PHILADELPHIA. H7 



specimen. The jaws contain the third and fourth molars in functional posi- 

 tion. The fifth molar had not protruded and is visible within the jaws. The 

 alveoli of the second molars are partially obliterated, and this is the case 

 also with the inferior incisive alveoli. (Represented in pis. iii, iv, xvii, of 

 Warren's book.) 



4. A lower jaw of a quite young animal. It contains the first, second, and 

 third molars in functional position and but little worn. The crown of the 

 first molar has two transverse divisions ; that of the second, two principal 

 transverse divisions and a less well developed or rudimental third division ; 

 that of the third molar has three divisions. Large sockets for incisive tusks 

 occupy the sides of the symphysis. (The specimen is represented in plate ii 

 of Dr. Warren's work.) 



An examination of many specimens of jaws and teeth of the American 

 Mastodon leads to a confirmation of the view that the dental series consists of 

 an incisive tusk and six molars on each side of both jaws. Whether the 

 usual upper tusks are preceded by a temporary pair has not been determined. 

 Small lower tusks appear to belong to the young of both sexes, but are lost 

 and their alveoli obliterated in the female, while one or both are frequently if 

 not usually retained permanently by the male. 



The molar teeth in the order of protrusion successively follow one another 

 from behind, but none of the series of six appear to have vertical successors. 



The young animal exhibits the anterior two and then three molars together 

 with tusks in both jaws, in functional position. As the third and fourth mo- 

 lars assume a functional position the first and second are shed, and as the fifth 

 molar protrudes the third is shed. With the functional existence of the fifth 

 and sixth molars the fourth is shed. Finally, in the old animal the sixth or 

 last molar may alone remain, though usually the fifth and sixth appear to 

 have been retained to the last. 



In the Museum of Comparative Zoology of Harvard College, Prof. Shaler 

 exhibited some Mastodon and other vertebrate remains, the results of his ex- 

 plorations at Big-bone-lick, Ky. Prof. Shaler incidentally informed me that 

 he had detected no evidences of glacial action in the latter region. He sup- 

 poses that the specimens of teeth and tusks, the wearing off at the sides of 

 which I formerly attributed to. glacial action, probably had been imbedded in 

 stiff clay in the pathway of Mastodons, to whose tread the wearing was due. 



The collection contained a multitude of remains of the Bison, but these 

 Prof. Shaler found more superficially than those of the Mastodon and Ele- 

 phant, and not associated with them. With the remains of the latter two 

 genera were also found those of Bootherium cavifrons, of which the collection 

 contains a skull without the face. There were also found with these some 

 remains of the Horse, and also the fragment of a lower jaw, which appeared 

 to me to belong to the existing Domestic Hog. 



In referring to Bootherium I may add that I had the opportunity of examin- 

 ing a skull of the recent Musk Ox, preserved in the Museum of the Natural 

 History Society of Boston, the first complete skull of the animal 1 have ever 

 seen, 'in this skull I observed that the lachrymal fossa in advance of the or- 

 bit is a shallow depression even less distinct than in the Sheep. In Boothe- 

 rium it is a deep, well defined hemispherical depression, being as different 

 from that of the recent Musk Ox as is that of the Deer. 



In the same museum, besides a few Mastodon remains, I remarked several 

 molars of the American Elephant, interesting from their size. One of them, 

 apparently a last upper molar, is from Brazos R., Texas, and is of the coarse 

 plated variety, corresponding with the Elephas columbi of Falconer. The 

 triturating surface is flat, not terraced, ten inches by four and three quarter 

 inches in extent, including the enveloping cementum, and also fourteen and a 

 half worn lobes or double plates. Behind, are four additional unworn and 

 less well developed lobes. The breadth of the tooth obliquely is thirteen 

 inches ; the depth posteriorly to the broken root, eight inches. 



1870.] 



