xin PHYLUM CHORDATA 457 



all elongated, chisel-like, and growing from persistent pulps ; the 

 pre-molars and molars are usually few, and often also grow from 

 persistent pulps. There is a large ccecum. The cerebral hemi- 

 spheres have smooth surfaces, and do not much overlap the other 

 parts of the brain. The testes are retained in the abdomen or 

 descend to the groin. The uterus is two-horned or double. The 

 placenta is deciduate and disc-shaped (discoidal). 



This extensive order includes the Rats and Mice (Muridce), 

 Hares and Rabbits (Leporidce), Squirrels (Sciuriclce), Jerboas 

 (Dipodidce), Beavers (Castoridce) and Porcupines (Hystricidcc.} 



ORDER 7. IXSECTIVOKA. 



Small insectivorous Eutheria with the nose usually produced 

 into a short soft muzzle, with furry (sometimes spiny) integument,- 

 clawed digits, and usually pentadactyle plantigrade limbs. The 

 dentition is diphyodont and complete, and all the teeth are rooted ; 

 the incisors are small ; there are never fewer than two incisors on 

 each side of the lower jaw ; the molars are small and provided 

 with pointed cusps. A clavicle is present. The brain is simple 

 and devoid of convolutions. The testes are situated in the groin, 

 and are not enclosed in a scrotum. The uterus is two-horned or 

 double. The placenta is deciduate and discoidal. 



Included in this order are the Moles (Talpidce), Shrews 



rwidce), and Hedgehogs (E-rinaceidce). 



ORDER 8. CHIROPTERA. 



Eutheria in which the pectoral limbs are modified to form 

 wings, the bones, more especially those of the second to the fifth 

 digits, being greatly elongated so as to support a broad web of 

 skin extending back to the hind-limbs. The sternum has a keel 

 for the attachment of the pectoral muscles, which play an im- 

 portant part in bringing about the movements of flight. The 

 ulna is vestigial ; the pollex is small, the remaining digits greatly 

 elongated. The hind-limb is rotated outwards so that the knee 

 is directed backwards. There is a cartilaginous rod (calcar) 

 attached to the inner side of the ankle-joint and helping to 

 support a fold of skin (interfemoral membrane) which extends 

 from the hind-limbs to the tail or caudal region of the body. The 

 cerebral hemispheres are smooth and do not overlap the cerebellum. 

 The dentition is complete, heterodont and diphyodont. The penis 

 is pendent ; the testes abdominal or situated in the groin. The 

 uterus is simple or bicornuate ; the placenta deciduous and 

 discoidal. 



Sub-order a. Megachiroptera. 



Large frugivorous Chiroptera with elongated snout, without 

 foliaceous appendages to the nose and ears, the second digit of the 



