1 8 BRITISH MAMMALS 



absent. As regards fore limbs, the hand is usually five- fingered in 

 one great group of the whales (those which retain teeth), and four- 

 fingered in those which have replaced teeth by plates of baleen. 

 The central fingers of some whales develop an extraordinary 

 number of phalanges, or jointed bones. These in the normal 

 mammalian hand are three in number ; in some of the whales 

 there are twelve in the central finger. Another peculiarity of 

 whales (shared, however, by some of the aquatic carnivora, and by 

 certain low types of mammals) is the absence of any external ear, 

 though rudiments of the conch are found in the porpoise. Then, 

 again, the teeth of whales differ from most of those of other 

 existing mammals by their complete uniformity, that is to say, 

 they are not divided up into incisors, canines, premolars, and 

 molars. In one or more forms of river dolphin in the Amazon 

 River (South America) there are said to be traces of additional 

 cusps on those teeth which have replaced the molars. This 

 point, however, is not such an important distinction, because we 

 jiow know through the discovery of fossil forms that ancestral 

 whales (Arch#QCtti) possessed normal mammalian teeth, at any 

 rate so far as the upper jaw is concerned. On each side there 

 were three incisors, one canine, and five molars. Remains of 

 these creatures, which are grouped under a single genus 

 (Zeuglodori), have been found in North America, and more 

 doubtfully in England and other parts of Europe, in Egypt, and 

 even in New Zealand. 



The next marked stage in the development of the whales 

 is represented by the Squalodonts, in which the teeth are 

 very numerous, and are rapidly approximating to a simple, 

 pointed type ; but the molars are still doubly rooted, and their 

 upper surface is notched. The incisors are three on each side, 

 the canines are just distinguishable in form, but the premolars 

 have become simple, single-rooted teeth, and they, together with 

 the molars, have increased in numbers beyond the normal 

 mammalian formula so that in the upper jaw there are as many 

 as twelve of these molar and premolar teeth. Then perhaps 

 next in order of development come the numerous existing 



