18S0.] 4oJ [Cope. 



Foramina. — The infraorbital is of good size, and issues above the poste- 

 rior part of the fourth premolar. The lachrymal is rather large, and 

 occupies a space but little below the middle of the lachrymal. The pos- 

 terior infraorbital is large. The supraorbital is double and pierces the 

 base of the postfrontal process. There are two postparietals of rather 

 large size, and at least one large postsquamosal. A well-developed though 

 narrow tentorial ridge defines the position of the lateral venous sinus in 

 front. The mastoid foramen is, as in modern horses, not enclosed poste- 

 riorly on its external side, but winds round upwards and forwards, groov- 

 ing the part of the petrous bone which rises within the mastoid. The 

 meatus auditorius is small and the supraglenoid is large, but not so large 

 as the postglenoid. There is but one, a large condylar foramen. The 

 jugular, carotid and oval foramina are not distinguished from \.\\q foramen 

 lacerum. The /. /. opticum and sphenobrhitale are distinct and close to- 

 gether ; the /. rotundum is further back, entering the skull within the 

 alisphenoid canal. The orbitonareal perforation is quite large, and is 

 posterior to the posterior infraorbital canal, not having a common entrance 

 with it as in the species of Equus. There is but one palatine foramen on 

 each side, whose posterior borders are nearly in line with the anterior bor- 

 der of the nareal excavation. The incisive foramina do not extend poste- 

 rior to the position of the nareal excavation. There is a small foramen on 

 the median line just in front of them. 



Dentition. — The condition of the teeth shows that the individual de- 

 scribed had just reached maturity, since the last molar is not worn on the 

 posterior part of its face. The cups of the incisors are fully enclosed, but 

 the posterior part of the border of the third is not produced quite as far 

 as that of the other teeth, and does not display such results of wear. The 

 cup of the first is iilled with cement ; of the second and third not fully, 

 but with a median fissure remaining. The size of the incisors decreases 

 from the first to the third, not increases, as, e. g., in Equus quagga. The 

 canines are small, and have the equine sharp borders bounded by two 

 grooves of the inner side. 



The fourth premolar is two-rooted, but is small and is more than half 

 overlapped by the third. The latter is not remarkably large nor particu- 

 larly elongate. It is, however, relatively longer than in H. calamarium, 

 where it is very wide. The molars diminish posteriorly by very little, the 

 last being distinctly smaller. The internal free column of the molars has a 

 longitudinally oval section, and its middle is a little anterior to the middle 

 of the crown. It has a small apiculate angle directed forwards and out- 

 wards. On the large third premolar it has a round section, and joins 

 the internal anterior crescent by a very narrow isthmus. The posterior 

 column is connected with the posterior inner crescent by a narrow isth- 

 mus in all the molars, and has in all the flattened form of the anterior 

 column. The lakes as usual are enclosed, and the crescents communi- 

 cating; this is true of the third premolar as of the others, except that 

 the anterior lake opens forwards and inwards. The adjacent borders of 



