I860.] Cerebral System of the Class Mammalia, 183 



in detail. The subdivisions of the orders Perissodactyla and Artio' 

 dactyla were next pointed out. 



A well-marked, and at the present day extensive, subordinate 

 group of the Artiodactyles, is called Ruminantia, in reference to the 

 second mastication to which the food is subject after having been 

 swallowed ; the act of rumination requiring a peculiarly complicated 

 form of stomach. The Ruminants have the ' cloven foot,' i.e. two hoofed 

 digits on each foot forming a symmetrical pair, as by the cleavage of a 

 single hoof: in most species there is added a pair of small supple- 

 mentary hoofed toes. The metacarpals of the two functional toes 

 coalesce to form a single ' cannon-bone,' as do the corresponding me- 

 tatarsals. The camel-tribe have the upper incisors reduced to a single 

 pair ; in the rest of the ruminants, the upper incisors are replaced by a 

 callous pad. The lower canines are contiguous to the six lower inci- 

 sors, and, save in the Camel-tribe, are similar to them, forming part of 

 the same terminal series of eight teeth, between which and the molar 

 series there is a wide interval. The true molars have their grinding 

 surface marked by two double crescents, the convexity 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 structures which are 

 transitory and embryonic in most existing Ruminants, as, e.g. upper 

 incisors and canines, first premolars, and separate metacarpal and meta- 

 tarsal bones ; these are among the lost links that once connected more 

 intimately the Ruminants with the Hog and Hippopotamus. The 

 speaker, pursuing the retrospect of the twofold division of Gyrencephala 

 as represented in the tertiary geological series, remarked that it was 

 interesting, in relation to the needs of mankind, to find that, whilst 

 some groups of Ungulata, e.g. the Perissodactyles and omnivorous 

 Artiodactyles had been gradually dying *out, other groups, e.g. the 

 Ruminants, had been augmenting in genera and species. Most inter- 

 esting also was it to observe, that in existing Ungulates there is a more 

 specialized structure, a further departure from the general type, than 

 in their representatives of the miocene and eocene tertiary periods : and 

 that such later and less typical Mammalia did more effective service 

 by virtue of their adaptively modified structures. The Ruminants, c.^., 

 more thoroughly digest and assimilate grass, and form out of it a more 

 nutritive and sapid kind of meat, than did the antecedent more typical 

 and less specialized non -ruminant Herbivora, 



The monodactyle Horse was a better and swifter beast of draught 

 and burthen than its tridactyle predecessor the miocene Hipparion 

 could have been. The nearer to a Tapir or a Rhinoceros in structure, 

 the further would an equine quadruped be left from the goal in con- 

 tending with a modern Racer. 



The geological distribution of the existing hoofed mammalia was 

 next touched upon, and contrasted with that of the extinct forms. 



The Unguiculata, as restricted in the cerebral system of the 

 Mammalia, form the third division of the Gyrencepeala, They enjoy 

 a higher degree of the sense of touch than the Ungulata through tlie 



o2 



