672 MAMMALIA [CH 



on to the neck, where there is room for them. The clavicles are short, 

 almost square bones, and the humerus of the arm is short and stout. 

 The zygomatic arch is present and the tympanic is a bulla. The 

 TALPIDAE are represented in Great Britain by Talpa europaea, the 

 Common Mole, which feeds on earthworms, constructing a complicated 

 system of underground passages through which it hunts its prey. 

 In North America the commonest is perhaps Condylura cristata, the 

 Star-nosed Mole, the snout of which is encircled by a ring of fleshy 

 outgrowths. 



The Russian Desman, Myogale moschata, belongs to the Mole 

 family once extended as far west as Britain. It lives in burrows by 

 the water-side and feeds chiefly on fresh-water insects and their 

 larvae. In correspondence with its mode of life the hind-feet are 

 webbed and the tail large and compressed, forming an efficient 

 swimming organ. It is hunted for its fur (Fig. 337). 



There still remain four families to be mentioned, each of which 

 however is represented by a few species. These are interesting 

 because, (1) they have a more primitive type of molar tooth than 

 any other living Mammals ; (2) in their distribution, like the ancient 

 genus Peripatus, they belong to the Southern Hemisphere, only over- 

 stepping it when they go into the West Indies. The type of tooth 

 is the tri-tubercular, which is found in the oldest remains of Mammals 

 known : it is distinguished by the reduction of the characteristic 

 cusps of the insectivoran tooth to three which form the points of a 

 triangle. Of these primitive families the (1) CHRYSOCHLORIDAE are 

 the Golden Moles of the Cape, so-called from the iridescent sheen of 

 the fur. They have the reduced eye and enlarged hands and arms 

 of the ordinary Mole, but these hands and arms are placed not at 

 the sides of the neck but at the sides of the thorax, the ribs of 

 which are bent inwards to create hollows for their reception. The 

 zygomatic arch is present and the tympanic is a bulla. The remain- 

 ing families have lost the zygomatic arch and the tympanic is a mere 

 ring. These are (2) POTAMOGALIDAE, represented by a single species, 

 Water-shrews from Central Africa, with a flattened tail, short limbs 

 and no clavicles, (3) SOLENODONTIDAE, and (4) CENTETIDAE, two 

 externally similar but not closely allied families of small hog-like 

 animals with stout limbs, the first from Cuba and Hayti and the 

 second from Madagascar. 



The most interesting circumstance about the Insectivora is the 

 fact that when by means of fossils we trace back the higher groups 

 of Mammals they seem all to merge imperceptibly into forms which 

 from their teeth and general organisation we should class as 



