MAMMALIA, 541 



of the fore-limb, Flower and Lyddeker remark : '' The fore- 

 limbs are thus brought opposite the sides of the neck, and 

 from this position a three-fold advantage is derived : in the 

 first place, as this is the narrowest part of the body, they 

 add but little to the general width, which, if increased, would 

 lessen the power of movement in a confined space ; secondly, 

 this position allows of a longer fore-limb than would other- 

 wise be possible and so increases its power; and, thirdly, 

 although the entire limb is relatively very short, its anterior 

 position enables the animal, when burrowing, to thrust the 

 claws so far forward as to be in a line with the end of the 

 muzzle, the importance of which is evident. Posteriorly the 

 hind-limbs are similarly removed out of the way by approxi- 

 mation of the hip-joints to the centre of the body." The 

 pelvis is bent inwards towards the middle line in the 

 acetabular region and there is no pelvic symphysis. 



The hind-limbs are not so abnormal as the fore-limbs, 

 burrowing being effected only by the latter. The lower half 

 of the fibula is fused with the tibia. There are five clawed 

 toes and the animal is plantigrade. 



We may notice that the mole is a type not only extremely 

 specialised for one habitat, but, like the sloth, it has certain 

 primitive characters which have persisted from early times. 

 We already mentioned that the more primitive types have, 

 as a rule, survived in arboreal or fossorial habitats : in the 

 mole we recognise primitive characters in the form and 

 number of the teeth, in the '^ intercentra," the episternum 

 and possibly the prepollex. 



Fossorial Adaptation. 



The fossorial type is to be derived directly from the primitive 

 terrestrial and like the others is found in varying degrees. We may 

 take the following as examples : — Echidna, badger, anteater, armadillo, 

 aard-vark, rabbit, bandicoot, marmot, prairie-dog, mole. 



As in the other types, we may take three groups : — 



I. Incidental group : Echidna, anteater, Proteles, banded ant- 

 eater ( Myrmecobiiis). This consists of animals which prey upon 

 earth-loving insects, such as ants. The limbs show strong claws on each 

 digit, and in most cases the tongue and salivary gland are modified for 

 ingestion of ants, or at least the teeth show an approximation to the 

 insectivorous type or a degeneration from a carnivorous type (Proteles). 

 They are really little modified from the primitive terrestrial group. 



