4<^4 



MAMMALS. PHYLUM CHORDATA 



LAGOMORPHA 



This order includes the rabbits and hares, and has been ade- 

 quately illustrated in our study of Oryctolagus cuniculus. The 

 incisors are developed for gnawing, but the large upper pair 

 are backed by a smaller pair, hence the earlier name for the group 

 of Duplicidentata. There is no canine, but a long diastema 

 between incisors and cheek teeth. These last have sharp transverse 

 ridges and are therefore called lophodont. There is much freedom 

 of movement of the lower jaw, the articular surface of the 

 squamosal being broad and flat. The animals are almost entirely 

 herbivorous. The hind legs of rabbits and hares are elongated 

 to give a semi-saltatorial or jumping type of locomotion and the 

 tail is short. The only native British lagomorphs are the brown 

 hare (Lepiis europcBus) of the lowlands and the blue or variable 

 hare [Lepiis timidus) of the Scottish Highlands. They are larger 

 than the rabbit, but closely resemble it in structure. The chief 

 differences are in habits and psychology ; hares do not burrow and 

 are solitary, and the antics of the courting males in spring 

 have led to the saying, ' Mad as a March hare '. The variable 

 hare becomes white in winter. The rabbit was introduced into 

 this country probably in the twelfth century. 



RODENTIA 



These, the Simplicidentata of older classifications, differ 

 obviously from the Lagomorpha in possessing but a single pair 

 of upper incisors. There are in addition so many differences of 

 detail between the jaws of the two groups that the resemblance 

 between them may be due to convergence, that is, the approach 

 to a single result by two different routes. The incisors have enamel 

 on the anterior surface only, and so become chisel-shaped by 

 wear, the lophodont cheek teeth bite with the upper set inside 

 the lower (the reverse of rabbits), and the two dentaries are not 

 sutured. Instead, they can be drawn apart by muscles, and when 

 this happens the lower incisors are pressed together ; when the 

 antagonistic muscle pulls the mandibles together the incisors 

 are separated, and by this alternating scissors action they can 

 be used for holding or for separating small objects. This facility 

 is perhaps connected with the fact that the hand is often prehen- 

 sile, so that food is held to the mouth to be eaten. There is an 



