538 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 48. 



with the premolar on the left side is such as to show very accurately 

 the relation of the parts. 



If now we multiply the width of the skull at the rear of the orbits, 

 175, by 100 and divide the result by the basilar length, 414, we ob- 

 tain the cephalic index, 42.3. That of Equus hemionus, is 44.4, which 

 is somewhat less than that of a specimen measured by Tscherski. 

 On referring to the tables on pages 559 and 560, the reader will find 

 that the Texan skull is intermediate in width between the narrow- 

 faced horses and the broad-faced ponies. 



The facial index (facial length X 100 -f- basilar length) of the 

 Texas specimen is 76.1, that of E. hemionus 76.4. The face of both 

 these animals is, as shown by the tables referred to, rather long. 

 The length of the nose of the Texas specimen makes 27.3 per cent 

 of the basilar length; in E. hemionus the corresponding index is 

 24.2. In the Arabian horse (No. 172454 Nat. Mus.) this index 

 is 26.4. Hence the Texas horse had a relatively long nose. The tooth 

 row is relatively very short, forming only 30.4 per cent of the basilar 

 length ; while in the specimen of E. hemionus it forms 34.1 per cent, 

 and in the Arabian horse 34.5 per cent. In a very large horse skull 

 in the National Museum (No. 174960), with a basilar length of 610 

 mm., the index of the tooth line is 30.6. The basioccipital bone of 

 E. francisci is different from that of any of the other horses at hand. 

 In all of them and in E. hemionus this bone, immediately in front 

 of the articular surfaces of the condyles, slopes away gradually on 

 each side. In the Texas horse the sides are nearly perpendicular. 

 The thickness of the bone from side to side is 20 mm. The distance 

 from the lower border of the foramen magnum to the notch on the 

 hinder end of the vomer is 111 mm.; from the notch to the hinder 

 border of the hard palate 100 mm. In this respect the skull of E. 

 francisci agrees with the true horses and differs from the domestic 

 ass and from E. occidentalis of California. 1 The hard palate ends 

 in the midline opposite the middle of the length of m 2 . The pos- 

 terior palatine foramina are situated on the line joining the hinder 

 ends of the second molars. There is no indication of any pit on the 

 side of the face in front of the orbit. 



The teeth (pi. 35; figs. 1, 2; text-figs. 4, 5) have furnished the 

 following measurements. In the second column are expressed the 

 measurements obtained from Owen's figure of Equus tau; in the third 

 column the measurements of the teeth of E. hemionus. 



1 See page 530. 



