INTRODUCTION. 



31 



of which is in the form of a tough round disk, 

 and in all cases, except the peccaries, having the 

 canines of the upper jaw directed upwards. 

 The Ruminants {Didactyla or Ruminantia). With only 

 two digits, and with a complex stomach adapted 

 to the process of chewing the cud. 

 The Chevrotain Family (Tragtilida). With meta- 

 carpal and metatarsal bones not completely fused 

 into a cannon bone, with a low structure of 

 brain, and without a psalterium in the complex 

 stomach. 

 The Deer Family (Cervidd). The males (and in 

 the reindeer the females also) with horns in 

 the form of antlers. 

 The Hollow -horned Ruminants {Cavkoniia). 

 Horns composed of horny matter with a hollow 

 core in which rise bony processes from the skull. 



The Antelopes. 



The Goats. 



The Ibex. 



The Sheep. 



The Ox Family. 

 '1'he Buffalo. 

 The Bison. 

 The True Oxen. 

 The Giraffe Family {Devexa). Composed of a 

 single species, with very long neck, high shoulders, 

 long flexible tongue, and hair-clad horns in the 

 form of bony out-growths from the front margin 

 of the occipital bone. 

 The Camel Family {Camelida). With feet resting 

 on callous pads, and, unhke other ruminants, 

 with incisors in the upper jaw, besides other 

 peculiarities in the dentition. 



The Camels. 



The Llamas. 



THE GNAWERS OR RODENTS {Rodentid). 



Claw-bearing mammals with incomplete dentition, having 

 only two large rootless function.al incisors in the 

 upper and lower jaw, no canines, and cheek-teeth 

 almost uniform, arranged in a continuous series 

 and separated from the incisors by a wide dia- 

 stema. Placenta discoidal. 



The Squirrel Family {Scittrida). With a strong 

 clavicle, four free digits on the fore-feet and 

 three on the hind-feet, all armed with strong 

 claws, and with a peculiar dentition (usually five 

 molars in the upper jaw, and all the molars with 

 triangular crowns). 

 The Squirrels. 

 The Marmots. 



The Dormouse Family (Myoxida). Distinguished 

 from the previous family chiefly by the dentition 



(only four molars in the upper as well as in the 

 under jaw, and all the molars with transverse 

 plates of enamel). 



The Beaver Family. A family consisting only of a 

 single sjiecies {Castor fiber), of considerable size, 

 with five toes both on the fore and hind feet, 

 those on the hind feet united by a web. 



The Mouse Family {Murida). A family composed 

 of a great variety of forms, presenting numerous 

 transition links, with clavicles, usually four digits 

 and the rudiment of a pollex on the fore-feet and 

 five digits on the hind-feet, and usually only three 

 molars. 

 Mole-rats. 

 Hamsters. 

 Rats and Mice. 

 Field Mice. 



The Jerboa Family {Dipodidd). Distinguished by 

 their very long hind-legs adapted for jumping, 

 the excessive length being due to the great 

 elongation both of the tibia and the metatarsus. 



The Porcupine Family {Hystricida). Distinguished 

 by their covering of spines on the back, serving 

 as a defensive armour. 



The Spiny Rat Family {Echimyidd). With four 

 molars with enamel folds, sometimes simple, some- 

 times complex, the fur generally coarse and some- 

 times interspersed with spines. 



The Degu Family {Ociodontidd). With the enamel 

 folds on the grinding surface of the molars arranged 

 in the form of the figure 8. 



The Chinchilla Family {Chmchillida). Distin- 

 guished by the possession of four rootless molars 

 divided into two, or at most three, separate trans- 

 verse ridges by continuous folds of enamel. 



The Agouti Family {Subungulatd). Distinguished 

 by the peculiar structure of the digits, which 

 carry a kind of hoof in place of claws or nails. 



The Rabbit Family {Leporidd). Distinguished by 

 the possession of two small incisors in the upper 

 jaw, placed behind the two functional incisors. 



THE EDENTATES {Edentata). 



Placental mammals with incomplete dentition and root- 

 less teeth without enamel. The free digits carry 

 hoofs transformed into sickle-shaped claws. 



The Sloths {Bradypoda). With very long fore-limbs, 

 incomplete zygomatic arch, and descending process 

 from the cheek-bone. 



The Armadillos {Dasypodd). With a very strong 

 bony fi-amework, part of which is adapted to 

 support an outer skeleton or armour, composed 

 of small plates, usually hexagonal in form, placed 

 side by side. 



