42 



vexity of which is turned inwards in the upper and outwards 

 in the under jaw. 



Many fossil Artiodactyles, with similar molars, appear to 

 have differed from the Ruminants chiefly by retaining struc- 

 tures which are transitory and embryonic in most existing 

 Ruminants, as, e. g. upper incisors and canines, first pre- 

 molars, and separate metacarpal and metatarsal bones ; these 

 are among the lost links that once connected more intimately 

 the Ruminants with the Hog and Hippopotamus. 



The Pachyderms in the Cuvierian system included all the 

 non-ruminant hoofed beasts ; they were divided by the great 

 French anatomist into the Proboscidia, Solidungula, and Pachy- 

 dermata ordinaria, the latter again being subdivided according 

 to the odd or even number of the hoofs. I have on another 

 occasion 1 adduced evidence to shew that the right progression 

 of the affinities of the UNGVLATA was broken by the interpo- 

 sition of the Horse and other Perissodactyles between the 

 non-ruminant or omnivorous and the ruminant Artiodactyles ; 

 and that too high a value had been assigned to the Rumi- 

 nantia by making them equivalent to all the other Ungulates 

 collectively. 



It is interesting, in relation to the needs of mankind, to find 

 that, whilst some groups of UNGULATA, e. g. the Perissodactyles 

 and omnivorous Artiodactyles, have been gradually dying out, 

 other groups, e. g. the Ruminants, have been augmenting in 

 genera and species. Most interesting also is it to observe, 

 that in existing Ungulates there is a more specialized struc- 

 ture, a further departure from the general type, than in their 

 representatives of the miocene and eocene tertiary periods : 

 such later and less typical Mammalia do more effective work 

 by virtue of their adaptively modified structures. 



The Ruminants, e. g., more effectually digest and assimi- 

 late grass, and form out of it a more nutritive and sapid kind 

 of meat, than did the antecedent more typical and less spe- 

 cialized non-ruminant Herbivora. 



1 Proceedings of the Geological Society, November 3, 1847, P- 



