IX rOXODON AND NESODON 2 I 5 



the free eud of the nasals, which may he related to the presence 

 of a short proboscis. The zygomatic arch is strong and broad ; 

 the mandibles are provided with a long symphysis. The dental 

 formida is I | C ^^i Pm 3^^ M |. The teeth are prismatic and 

 hvpselodont, growing from persistent pulps. The molar teeth are 

 slightly arched in form, whence the name of Toxodon, " bow teeth." 

 The strong chisel-shaped incisors suggest the Rodents and Hyrax. 

 The cheek teeth, moreover, are by no means unlike those of Eodents 

 in their pattern. They are at any rate not at all like those of ex- 

 isting Ungulates. The small size of the canine and of the first pre- 

 molar produces a diastema in the tooth series. The sacrum consists 

 of five vertebrae, and the ischium does not articulate with it. 



The shoulder blade has a strong spine, but only a rudimentary 

 acromion ; nor is the coracoid well developed. The radius crosses 

 the ulna, as in the Elephant ; the whole fore-limb is shorter than 

 the hind-limb, which must have exaggerated the hang-dog ex- 

 pression of the creature when alive. The elements of the carpus 

 interlock in the modern fashion. Those of the tarsus, however, 

 are primitive in lying below each other without alternation. The 

 carpus has a centrale. The libula articulates with the calcaneum. 

 The femur has no third trochanter. There are three toes to all 

 the limbs. It is clear that this assemblage of characters will not 

 allow the placing of Toxodon in any living Ungulate order. If 

 the middle toes appear by their slight pre-eminence to approach 

 the Perissodactyle form, the peculiar surface contour of the molar 

 teeth, letting alone the absence of a third trochanter on tlie femur, 

 will not permit this classilication. 



Allied to Toxodon is the genus Nesodon. It was so named 

 from an " island lobe " on the inner side of the upper molars. 

 This creature, smaller than Toxodon, also differs from it in the 

 fact that the dentition is complete, and in the pattern of the 

 molars, which is rather more complex. There is still the slight 

 projection upon the premaxillary bones, but the nostril is directed 

 more forwards than in Toxodon. The zygoma, too, is massive. 

 The second pair of incisors in the upper jaw and the outer (third) 

 pair in tlie lower jaw form biggish tusks in the adult. These and 

 the molar teeth are, however, finally rooted, and do not grow, as in 

 Toxodon, from persistent pulps. The genus is from the older 

 Tertiary of Patagonia. Five or six species have been described. 

 Some are as large as a Ehinoceros, others as small as a Sheep. 



