236 THE MERYCOIDODONTID^ 



remarkably robust, while the squamosal part of the zygomatic arch is lightly constructed. The 

 maximum expansion of the zygomata is just back of the postorbital bar, from which point the zygo- 

 mata trend inward very rapidly. The squamosal portion is about half the depth of the malar, slopes 

 gently upward and backward, and is nearly uniform in width anteroposteriorly. The facial vacuities 

 are large, longer than wide, and extend somewhat posterior to the antorbital margin. The nasal 

 bones are wide above the anterior nares, diminishing rapidly aft in width and terminating posteriorly 

 in points. Anteriorly they extend to a point above the incisors. These bones are flat anteroposte- 

 riorly and very slightly convex transversely. The lacrimal bone extends well onto the face and bears 

 a rather small and shallow lacrimal fossa. The frontals are narrow and slightly depressed between 

 the orbits. They do not extend in advance of the anterior orbital margin, except as a short wedge 

 between the nasal bones. The orbits are closed. They are unusually large and are oval in shape, 

 and their superior margins rise above the general level of the frontals. They look decidedly out- 

 ward and upward. The low temporal ridges quickly unite to form a long, narrow sagittal crest. 

 The supraoccipital crest overhangs slightly beyond the posterior of the occipital condyles, and the 

 wings are nearly transverse. 



The brain case is much flattened and laterally expanded. The relatively large external auditory 

 meatus is peculiar in that it is directed straight backward and somewhat upward. Its external orifice 

 is situated almost on a line with, but well above, the posterior of the condyles. The angle of the 

 basicranial axis is shallow. The palate is vaulted, while the palatonarial border is opposite the 

 posterior margin of M 3 . The glenoid surface slopes mainly upward and backward, and the post- 

 glenoid process, as such, has no separate existence but is fused with, and becomes a part of, the 

 mastoid-paroccipital process complex. The whole basicranial region is very much contracted antero- 

 posteriorly, and the bullae are oval in outline and very large, up to 22 mm. anteroposteriorly and 

 about 1 6 mm. transversely by 1 5 mm. deep. The paroccipital processes are plate-like, in contact 

 with the bulbs, and extend downward but slightly below the inferior border of the latter. 

 Index: 0.69a. 



Mandible: The symphysis is straighter than in most of the oreodonts, making an angle that is 

 between 50° and 60° with the tooth row. The horizontal ramus is similar to that of Merycoidodon, 

 with the angle but slightly below the level of the straight inferior border. However, the jaw is 

 proportionally short anteriorly and of much greater depth posteriorly. As Leidy pointed out, the 

 disproportion between the anterior and posterior parts is so great that it is suggestive of the howling 

 monkeys. The coronoid process is thin, slender, and short, with the sigmoid notch open. The 

 condyle lies almost above the angle, that is, forward of the posterior edge of the ascending ramus, and 

 is sharply convex, with the articulating surface sloping downward and forward. The masseteric 

 fossa descends as low as the alveolar parapet and is deep but narrow. 



Foramina: The infraorbitals lie above the middle of P 3 . The supraorbitals are about midway 

 between the median suture and the supraorbital borders. The posterior palatines are opposite the 

 anterior lobe of M 1 . 



Dentition: Superior: The molars are hypsodont, with styles well developed and with fairly 

 regular reduction of anteroposterior diameter from M 3 to M 1 . This form has the full complement 

 of forty-four teeth. The incisors are very small, and the canines are much reduced. The premolars 

 1-3 have a tendency to slope backward. All the teeth are crowded, and the only diastema is between 

 C and P 1 , slightly more than 1 mm. in diameter. P 4 and M 1 are nearly square in outline, while the 

 posterior lobes of M 2 and M 3 are noticeably smaller than the anterior. 



Skeleton: Sinclair's notes (1910, pp. 198-199) on the skeleton follow: 



The dorso-lumbar vertebral formula is twenty, of which fourteen are dorsals. [The normal number of 

 dorsals in the merycoidodonts is 13, and since this specimen of Sinclair's is a composite, the writer believes that the 

 formula should be D 13, L 7. — M.R.T.] Six vertebra; are coossified in the sacrum, three of them being in 

 contact with the ilium. As shown in the restoration, the anterior dorsals have high narrow spines, sloping back- 

 ward. These decrease in elevation posteriorly and probably about the twelfth or thirteenth dorsal begin to 



