Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/518

 terior of the jaw-bone, owing to the increasing dimensions of the tooth-roots towards the bottom of the alveoli.

Dimensions of Lower Jaw.

Right ramus. inches.

Length from posterior extremity to the hindermost visible tooth 30

Length of articular surface measured from its ant. int. angle to the postarticular ridge 2.7

Length of postarticular surface 2.7

Distance of coronoid process from the postarticular ridge 7.5

Horizontal distance between coronoid process and angle 4

Distance of angle from posterior extremity of jaw 5

Depth of jaw at angle 4.5

" at coronoid eminence 6

" at articular surface 3.5

Teeth. — Of these several are in situ, some have fallen out of their sockets and lie scattered in the matrix, and others are loose. They vary much in size and in length, but they may very properly be called slender and tapering. They are slightly incurved, and curved slightly backwards. In the fully grown teeth, a long root or fang buried in the alveolus, a long, tapering, enamelled crown, and a relatively long intermediate neck without enamel are distinguishable.

The fang is subcylindrical. Some have a slight lateral compression, giving to their cross section an egg-shape — the smaller end turned backwards. They have a remarkably large, conical pulp- cavity, open below, and ascending through the neck a long distance into the crown. Their outer surface is finely striated longitudinally, and it is distinguished by its light brown colour and by its want of polish from the highly polished deep madder-brown crown. This latter is laterally compressed, unequally convex, the outer surface being less swollen than the inner ; it is also two-edged, and the edges, which are back and front, are finely notched. In a strong light, the serrature is recognizable by the unaided eye, and it is always distinctly perceptible to the touch.

The posterior edge begins rather earlier than the anterior on the neck of the tooth ; and the first two or three lines are unbroken. A shallow marginal depression of the outer surface runs parallel to the notched edges. The highly polished crown is overlaid with very fine, closely-set, longitudinal striae just visible to the unaided eye in a good light, the striae scarcely rising above the surface. On the more convex inner surface a few broader, widely set, parallel striae are prolonged from the lower limit of the enamel for some distance upon the crown, but they do not reach its top. Some of the crowns are marked with faint annular indentations.

Succession of the Teeth. — The presence of the germ of an immature crown in the pulp-cavity of a fully-grown tooth, the occurrence