512 
U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
abruptly indented by an elongated fossa situated against the root of the posterior molar ; the 
two leave between them a short azygos process. Between these fossae is a fissure which reaches 
to a point opposite the middle of the molar. There is thus a step from the plane of the bony 
palate to the bottom of the fossa, and another thence to the base of the skull or body of the 
sphenoid. The palatine lateral outline is considerably excavated anterior to the molars, rising 
rapidly to the incisors. The incisive foramina communicate with each other, and extend from 
the anterior molar over two-thirds the distance to the incisors. 
The lower jaw is short and massive ; the distance from the molars to the tips of the incisors 
about one-third the whole length. The condyloid process is long, its sides sub-linear and 
narrow, the coronoid process curved, and rising as high or higher than the level of the condyle. 
The descending ramus is long, narrow, and bent upwards, with, at .the same time, an outward 
twist. 
The incisors are stout, the upper ones rather short, rounded off anteriorly a little on the 
internal edges, more extensively externally, so as to cut down to the middle line of the lateral 
outline. Sometimes the anterior surface is more plane, and only one-third of the anterior surface 
visible from the side. 
The molars are all prismatic, with acute salient and re-entrant angles on each side, and 
without roots, even in the adult, the teeth appearing to grow for a considerable time from a 
persistent pulp. Each tooth is composed of an aggregation of triangular prisms, more or less 
alternating with each other, or, more strictly, of a prism of dentine with a continuous enveloping 
wall of enamel, which is indented in subacute re-entrant angles which either alternate or are 
opposite. When the enamel of opposite sides meets, the apex of an angle against a side or 
another apex, the two lines generally fuse into one no wider than either separately; this is 
especially the case in the upper jaw. Sometimes, however, both are distinguishable. 
The anterior outline of each upper molar is a transverse, slightly curved line, which is itself 
the longest side of a spherical closed triangle. The anterior molar, in all species, exhibits four 
succeeding triangles—two internal and two external—the first being internal, the second external. 
In the second molar, the anterior triangle is succeeded by either three or four lateral triangles, 
and is very similar to the first molar, except that here the first one is external, not internal. 
Where there are but three lateral angles, there is one internal and two external. The posterior 
molar has one internal and one or two external angles, with either a crescentic loop ending the 
tooth, or else a Y or Y-shaped lobe. When the lobe is crescentic, the convexity is external, 
the posterior outer triangle being home on its back, or just at the stem of the crescent; the 
anterior loop of the crescent forms one of the internal salient angles; the posterior is the last 
internal or terminal salient angle ; between the two there is sometimes a third salient angle. 
The lower molars are somewhat similar to the upper, but the transverse triangles’are posterior, 
not anterior. In the anterior molar there are two or more lateral triangles on either side 
anterior to the transverse one, and an anterior trefoil loop with one or more lateral indentations. 
The tooth varies in exact pattern with the group. The middle molar has one posterior trans¬ 
verse triangle, and generally two lateral alternating ones on either side anterior to this. 
Sometimes one or both lateral triangles are opposite to and confluent with each other, giving 
rise to one or two additional transverse triangles ; if to two, then the whole tooth is composed 
of three transverse triangles. The posterior molar is narrower than the rest, and always 
composed of three transverse spherical triangles or ellipses. This last lower molar and first 
upper one are very unchangeable ; all the rest vary more or less. 
