4(30 REFERENCES TO THE PLATES. 



Figs. 5-7. PcEBROTHERiUM WiLSONi. See page 141. 



Fig. 5. View of the tritunitiug surfaces of the riglit upper molars of the skull represented in Fig. 1, 

 PI. I, of the Ancient Fauna of Nebraska. The first premolar is situated far in advance of the others; 

 the succeeding three teeth belong to the temporary dentition, the three following to the permanent 

 series. 



Fig. 6. View of the triturating surfaces of the right lower molars, from the same specimen as the 

 jjrcccdiug. The anterior three teeth belong to tlie temporary scries ; those behind to the permanent 

 series. 



Fig. 7. The third and fourth right upper premolars of the permanent series, from a small specimen 

 obtained by Dr. Hayden in his trip to the Mauvaises Terres in 1866. 



PLATE XIV. 



All the figures of the natural size, except 5, 6, 7, 8 and 10. 



Figs. 1-8. Leptomeeyx Evansi. See page 165. 



Fig. 1. Left lateral view of a skull ; the ujjper jaw with a complete series of molars ; the lower jaw, 

 with the last premolar and the true molars, from another specimen. 



Fig. 2. Upper view of the left, side of the same skull. 



Fig. 3. Occipital view of the same. 



Fig. 4. Inferior view of the left side of the base of the same skull. 



Fig. 5. Triturating surfaces of a comj^lete series of molar teeth of the left side, from the same skull, 

 magnified two diameters. 



Fig. 6. Triturating surfaces of a last premolar and the succeeding true molars of the right side, con- 

 tained in a fragment of the lower jaw, magnified two diameters. 



Fig. 7. Triturating surface of the lower first and second temporary premolars of the right side, mag- 

 nified two diameters. 



Fig. 8. The same teeth, from another and little worn specimen, also magnified two diameters. 



Figs. 9, 10. Merycodus necatus. See page 162. 



Fig. 9. Portion of the right ramus of a lower jaw, containing a complete series of molars ; the first 

 being restored from another specimen. 



Fig. 10. Triturating surfaces of the same teeth, magnified two diameters. 



Fig. 11. Oeeodon Culbertsoni. 



Upper view of a natural cast of the cranial cavity.'*' 



* The cast would appear to indicate that the brain was as simple in its construction ns in the Coney, [ffyrax,) or as 

 in living rodents. The cerebrum, in comparison with that of ordinary living ruminants and suilline animals, is of 

 greater simplicity, as regards the number and arrangement of its convolutions, and the cerebellum is more symmetrical. 

 It resembles more in character that of the Musics than of other familiar ruminants. The cerebrum is pyriform, com- 

 pressed from above downward. Its fore part is broken off in the specimen. The position of the interhemlspheral or 

 great longitudinal fissure, in the cast, is occupied by a ridge expanding at the extremities. Each cerebral hemisphere, 

 in the cast, exhibits, from the position of the interhemlspheral fissure to that of the sylvian fissure, four distinct ridges 

 corresponding with cerebral convolutions. These, in comparison with Prof. Owen's figures, (Anatomy of Vertebrates, 

 Vol. Ill, London, 1868,) appear to agree in succession with the medial, medilateral, supersylvian and sylvian convolu- 

 tions, of which the former three are visible in the upper view of the cast. The medial convolution, hardly separated 

 from the frontal, together with it, extends the length of the hemisphere. Posteriorly it doubles forward to become 

 continuous with the medilateral convolution, which extends forward about two-thirds the length of the hemisphere ; 

 and in the same manner the frontal bends backward to become continuous with the supersylvian convolution. The 

 supersylvian and medilateral fissures form sigmoid grooves, extending the length of the hemisphere ; and the medi.al 



