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 twoexternal thefirst 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 V or Y-shaped lobe. When the lobe is crescentic, the convexity is external, 

 the posterior outer triangle being borne 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. 



