A TUSK OF A PROBOSCIDIAN MAMMAL. 
77 9 
preserved. At the larger end (ib., fig. 8) the diameters are 1 inch 4 lines and 1 inch 
1 line ; at the smaller end they are 9 lines and 6 lines ; but here a line’s breadth should 
be added to both admeasurements, through lack of the outer layers of ivory with its 
thin coating of smooth cement. 
Besides the three portions of tusk above described many fragments remained after 
the adjustment of the pieces forming the parts of the tusk figured in Plate 51. I 
estimate the length of the part of the tusk collected by Mr. Isaac and transmitted to 
me at 16 inches ; adding the portion wanted to connect the part fig. 5, with the 
part fig. 7, about 2 feet in length of the tusk would be represented. The size of the 
pulp-cavity in figs. 1-3 indicates the portion so figured to have come from near 
the exit of the tusk from its socket. Of some of the detached fragments micro¬ 
scopical sections have been ma.de. 
These sections of dentinal (Plate 51, figs, 9, 10) and cemental (ib., fig. 11) portions 
of the tusk demonstrate the characteristic structures of these tissues, which have 
been described by Retzius* * * § and myself.t 
The dentinal tubes present, at a little distance from the pulp-cavity, the charac¬ 
teristic minute size—y^ooth of an inch in diameter; and soon, as they recede toward 
the cement, show the peculiar, strong undulatory course (fig. 9) answering to the easier 
‘‘secondary curves” of those tubes in the dentine of most other kinds of Mammalian 
teeth. The degree of curvature in the ivory of the present extinct Proboscidian is 
even greater in the section of the fossil ivory here figured (fig. 9) than in the section 
of recent ivory of the Indian Elephant, the subject of plate 149, d, in the ‘ Odonto¬ 
graphy.’J In the section of dentine shown by the higher power (fig. 10), are seen 
the strata of extremely minute opaque cells, unusually numerous in ivory, in the 
interspaces of the tubes. 
The cemental part of the fossil repeats the elephantine characters: the radiated 
cells (fig. 11) are larger, averaging awoth of an inch in diameter, and are more uniform 
in size and shape than in most other Mammalian teeth ; they also show, in transverse 
section, the circular figure characteristic of Proboscidian incisors.§ 
Fractured portions of a single tooth may seem to be a slender basis for predicating 
of a wider geographical distribution of the Proboscidian order than has, hitherto, been 
assigned to it. And, moreover, if the rest of the elephantine structures should be 
conformable, as I presume they would be, we here have, supposing the Dingo to be a 
human introduction into the Australian continent, a gyrencephalous exception to the 
characteristic aboriginal Mammalian organisation of that remote southern continent. I 
am encouraged, however, to submit the present evidence to the Society, by the successive 
* Mikroskopiska Undersokningar ofver Jadernes sardeles Tandbenets st-ruktnr. Stockholm, 1837. 
f ‘ Odontography,’ 4to., 1840-45. 
t Ibid. 
§ Ibid., p. 641. 
