344 THE INSECTIVORES 



Our notice of the mole family may conclude by a reference to the 

 yellow-tailed mole (Scaptonyx fusticaudatus) of Eastern Tibet. This 

 mole, which has only two pairs of lower incisor teeth, and conse- 

 quently but forty-two teeth altogether, differs from the true moles in the 

 considerably lesser width of the fore-feet, and thus approaches the mole-shrews 

 noticed on p. 338. 



THE TENRECS 

 Family CENTETID^E 



With the curious-looking animal represented in the figure on the next page> 

 we reach the first member of a group of Insectivores, comprising four families, 

 which differ from all those yet noticed in the characteristics of their upper molar 

 teeth. In all the preceding families the upper molar teeth have broad crowns, with 

 their cusps arranged somewhat in the form of the letter W. On the other hand, in 

 all those remaining for consideration, the crowns of these teeth are narrow, and 

 carry on their crowns only three cusps, arranged in the form of 

 the letter V. These cusps, or tubercles, thus form a triangle, with 

 the apex directed inwardly ; and this type of molar tooth, of which 

 an example is represented in the accompanying illustration, is 

 consequently known as the tri tubercular. It may seem that such 

 CROWN SURFACE pojnf- o f distinction is of comparatively slight importance. Such, 



OF AN UPPER 



MOLAR OF THE however, is by no means the case, since the researches of palaeon- 

 TRITUBERCU- tologists have shown that nearly all the earlier Mammals had these 

 tri tubercular molar teeth, from which we infer that Mammals still 

 retaining them in their primitive form belong to an extremely ancient stock. 



From this and other structural peculiarities it may be taken as certain that the 

 Insectivores of the present and three following families belong to a much lower type 

 of organization than those already mentioned. And this is borne out in a remarka- 

 ble manner by their geographical distribution. Africa and more especially Mada- 

 gascar, are characterized by the number of Mammals belonging to ancient and 

 primitive types still living there, as is well exemplified by the host of lemurs found 

 in Madagascar. Now of the Insectivores with tritubercular molar teeth, the present 

 and largest family is restricted to Madagascar and a few of the neighboring islands ; 

 a second is found both in Madagascar and Africa ; the third is solely African ; 

 while the fourth is confined to the West Indies a region also peculiar for the 

 ancient types of its few Mammals. The whole of the tenrecs, which, as already 

 mentioned, are confined to Madagascar and a few small islands in the vicinity, are 

 characterized by their long skulls, which are not constricted between the eyes, and 

 have no zygomatic arch below the socket for the eye to connect the upper jaw 

 with the region of the ear, while the so-called tympanic bulla is in the form of. a 

 simple ring. 



