602 UNGULATES. 



jaw (fig. 6, p 1) is the smallest and has a more simple crown than that 

 above ; the crowns of the succeeding teeth to the sixth inclusive are 

 formed externally by two upright half cylinders (m 1, o o), and differ 

 from the same teeth in the Rhinoceros chiefly by the equal height of the 

 demi-cylinders. The seventh tooth, or third true molar (m 3), has a 

 third similar but smaller lobe. On the inner side of the crown a 

 longitudinal impression sinks, as it were, into each of the external 

 convexities, and a corresponding internal convexity receives the 

 enteriflg angle between the two half-cylinders : the anterior of the 

 inner depressions is the shallowest, especially in the second premolar, 

 and both internal depressions contract as they descend. The base of 

 the crown is usually surrounded by a ridge, which is continued at 

 each end obliquely upwards to the angle formed by the backward 

 folding of the half-cylinders. When the summits of those teeth 

 begin to be abraded, two, and in the last molar, three, crescentic 

 tracts of dentine, bordered by enamel, are exposed. 



All the species of Palseotherium became extinct before the close 

 of the middle (miocene) tertiary period. The largest surpassed the 

 Tapir in size, and must have resembled it in external appearance. 



219. Macrauchenia. — An extinct Pachyderm equalling the largest 

 Camel in size, with very long and slender cervical vertebrae, as in the 

 Auchenia, and having imperforate transverse processes, as in all the 

 Camel-tribe, but with three toes on each foot, and an astragalus 

 closely resembling that of the Palseothere, has been in great part 

 restored (I) from fossil remains discovered in the tertiary deposits of 

 South America, of much more recent date than any of those which 

 in Europe have furnished evidences of tridactyle Ungulates. The 

 parts most required to establish the affinity of the Macrauchenia to 

 Palcsotherium were undiscovered when the first account of it was 

 published. A single tooth obtained by Mr. Darwin from a locality 

 near Patagonia (Bahia Blanca) remote from that, (Port St. Julien') 

 where the bones were discovered, bore sufficiently close resemblance 

 to the inferior molars of the Palseothere to lead me to suspect that it 

 might belong to the three-toed Pachyderm of Patagonia. (2) Subse- 



(1) Fossil Mammalia of the Voyage of the Beagle, 4to. 1S39, p. 35. 



(2) See the * Catalogue of Fossil Mammalia in the Royal College of Surgeons,' 4to. p. 229, 

 No. 952. 



