HAPLODONTID^— SKULL OP HAPLODOK RUFDS. 



569 



The lower jaw, as Richardsoa originally observed, is altogether heavier 

 Uian usual among Roden s ; and it is peculiar in the condition of the descend- 

 ing process, which in this case is a b'oad, flat plate, so far twisted around that 

 it is horizontal, and its back edge is a straight transverse line. When the 

 two halves of the jaw are separated, each will stand alone upright ujXin the 

 table, supported by this broad plate, which has twice the width of any other 

 part of the jaw. When the two halves of the jaw are in situ, the distance 

 across from tip to tip of these plates equals the distance from each of them 

 to the ends of the incisors; so that the three extreme points of the whole 

 jaw represent the angles of an equilateral triangle ; while the imier corners 

 of these plates arc only separated by a distance equal to the molar interspace. 

 From the back outer corner of this plate, which is knobbed, and represents 

 the angle of the jaw proper, there sweeps up to the condyle with gentle 

 concavity the edge of a thin plate, which trends strongly obliquely inward 

 and forward as well as upward, so far is the angle of the jaw carried out from 

 the general axis of the bone. The inner end of this plate rounds off to the 

 body of the bone ; it projects so far inward that it is separated from its fellow 

 by a distance only equal to the intermolar space. The condylar process is 

 rather low, rising upward vertically in one plane, but with strong backward 

 ol)liquity (about 45° from the plane of the molar crowns). The articular 

 head is nodular, with some posterior prolongation, excepting which latter it 

 is rather broader across than in the longitudinal direction. The coronoid 

 process is very conspicuous, reaching far abore the condyle ; it is a thin 

 vertical lamina, broadly falciform, with the ape:(, which is not as high as the 

 convex edge anterior to it, twisted somewhat outward. The anterior border 

 of this plate forms a letter S, very convex above where it curves almost semi- 

 circularly over to the apex, less strongly concave below where it sinks into 

 the body of the bone. Similarly, the emargination between the condyle and 

 apex of the coronoid is nearly semicircular. The body of the jaw, on the 

 outer side, opposite the middleof the molar series, shows a strong oblique ridge, 

 indicating the limit of the muscular impression. There is a large foramen 

 at the base of the condylar process on the inner sidei the mental foramen 

 is situated on the outer side, midway betweeti the molars and the incisors. 



It is to be regretted that the maturity of all the specimens (5 in number) 

 examined prevents recognition of most of the individual bones of the skull, 

 most of the sutures being already obliterated. The part taken by the malar 



