Kay Lankester, on the Tooth in Ziphius Sower biensis. 59 
limited development, the section in fig. 2 being taken further 
away from the terminal cap of dentine than that in fig. 1 . 
Cement (PI. VI, fig. 3). — The lacunae of the cement are 
disposed in regular concentric series (figs. 1, 2, c ), abound- 
ing more along certain planes than others, thus giving 
the structure a banded character. At various parts of the 
periphery the formation of nodular protuberances gives an 
irregular character to their arrangement. They are rounded 
and very irregular in form, with but small though very 
numerous diverging canaliculi : their size is very great, 
varying from the -5-^-oth to the t A 0 th of an inch and less. 
They are less numerous than in the cachalot or porpoise, 
and of larger size. The ultimate ramuscules of the canaliculi 
could be seen, by some care in the lighting and focussing of 
the object, to enclose square or polygonal spaces of struc- 
tureless material of an average diameter of ■ 5 - fr 1 T5 -th of an 
inch. In some parts the canaliculi united to form small, 
much elongated lacunae (fig. 3, «), this variation in the 
structure having apparently some connection with the pro- 
duction of the cement into a surface-ridge or tuberosity. 
Globular matter and dentine . — The parts of the opaque 
stratum of globular matter nearest the cement presented no 
structure excepting an indistinct botryoidal character, visible 
with a low magnifying power. This was more distinct nearer 
the dentine (fig. 1, 2, g), where variations in the opacity 
of the layer disclosed such a disposition. The amorphous 
matter at length shades off into the dentine, as seen in Plate VI, 
fig. 4, numerous distinct, minute, “ interglobular spaces ” be- 
coming more and more distinct as one recedes from the opaque 
stratum and their number diminishes. The “ interglobular 
spaces,” sometimes known as “ dentinal cells ” (not of Owen), 
have no very definite form, but are simply minute transverse 
lacunse intercepting the light, and by their superabundance 
contributing to the opacity of the amorphous stratum of 
globular matter. They had an average breadth of ToVoth 
of an inch. The dentinal tubes have nothing remarkable in 
their character. They are rather coarse, though finer than 
in many Cetacean teeth, or than those of the walrus tusk, 
and communicate frequently with one another near their 
peripheral origin or rather emersion from the opaque stratum. 
Osteo-dentine and globular matter . — The osteo-dentine 
and the globular matter which in many cases surround the 
periphery of an osteo-dentinal canal or cavity and its tubules, 
in intimate character do not differ materially from the similar 
parts just described. The canals of the osteo-dentine are 
numerous and large, appearing in section as circular, fusi- 
vol. xv. f 
