400 Mi'sceUaneous. 



in succeeding genera. The number of the teeth remained the 

 same untU the Pliocene, when the front lower premolar was 

 lost : and subsequently the corresponding upper tooth ceased to 

 be functionally developed. The next upper premolar, which in 

 Orohippus was the smallest of the six posterior teeth, rapidly 

 increased in size, and soon became, as in the horse, the largest of 

 the series. The grinding-teeth at first had very short crowns, 

 without cement, and were inserted by distinct roots. In Pliocene 

 species the molars became longer, and were more or less coated 

 with cement. The modern horse has extremely long grinders, 

 without true roots, and covered with a thick external layer of 

 cement. The caniue teeth were very large in Orohippiis, and in 

 this genus, as well as those from the Middle Tertiary, appear to 

 have been well developed in both sexes. In later forms these 

 teeth declined in size, especially as the changes in the limbs 

 aiForded other facilities for defence or escape from danger. The 

 incisors in the early forms were small, and without the character- 

 istic pit of the modern horse. In the genera from the American 

 Eocene and Miocene the orbit was not enclosed behind by an 

 entire bridge of bone ; and this first makes its appearance in this 

 country in Pliocene forms. The depression in front of the orbit 

 so characteristic of Anchitherium and some of the Pliocene genera 

 is, strange to say, not seen in Oroliippus or the later MioMppus, 

 and is wanting, likewise, in existing horses. It is an interesting 

 fact that the peculiarly equine features acquired by Orohippus are 

 retained persistently throughout the entire series of succeeding 

 forms. Such, e. g., is the form of the symphysial part of the lower 

 jaw, and also the characteristic astragalus, with its narrow, oblique, 

 superior ridges, and its small articular facet for the cuboid. 



Such is, in brief, a general outline of the more marked changes 

 that seem to have produced in America the highly specialized 

 modern Epius from his diminutive, four-toed predecessor, the 

 Eocene Orohippus. The line of descent appears to have been 

 direct ; and the remains now known supply every important inter- 

 mediate form. It is, of course, impossible to say with certainty 

 through which of the three-toed genera of the Pliocene that lived 

 together the succession came. It is not impossible that the later 

 species, which appear generically identical, are the descendants 

 of more distinct Pliocene types, as the persistent tendency in all 

 the earlier forms was in the same direction. Considering the 

 remarkable development of the group throughout the entire Tertiary 

 period, and its existence even later, it seems very strange that none 

 of the species should have survived, and that we are indebted for 

 our present horse to the Old World. 



Yale College, New Haven, Feb. 20th, 1874, 



The youyig Asiatic Tapir (Rhinochoerus sumatranus). 

 By Dr. J. E. Gray, F.R.S. &c. 



The British Museum has had for many years a specimen of a young 



