GENERAL CHARACTERISTICS. 



113 



parts which in most of the other mammals are 

 more or less covered by the hemispheres of 

 the great brain (the cerebrum) — the parts 

 called the olfactory lobes, the corpora quad- 

 rigemina, and the cerebellum — remain among 

 the members of this group, as among the 

 marsupials, uncovered. The mental qualities 

 of these animals, in accordance with this low 

 structure of brain, are little developed. 



This small insignificant brain lies in a 

 small brain -case, which even remains in 

 places membranous at the base, and onlv 

 seldom, as in the hedgehogs, develops crests 

 and ridges for the attachment of the muscles. 

 Usually this brain-case is prolonged without 

 anv constriction into thin, weak, lonq- jaws. 

 In many cases even the jugal arches which 

 support the jaws are wanting, as also bonv 

 orbits, and these even when present are 

 always incomplete. 



These weak jaws, moreover, have a very 

 remarkable dentition, which cannot be ex- 

 pressed by any general formula. There are 

 indeed always incisors, canines, and molars, 

 but their number, position, and lorm vary so 

 Sfreatlv that investigators have not been 

 always able to agree as to the character of 

 certain teeth. 



In many genera all the teeth are separate 

 from one another as in reptiles, and in most 

 only the molars are arranged in close series, 

 the others standing isolated. In many cases 

 the total number of teeth amounts to 44, 

 which appears to have been the normal 

 number of the old mammals. The total 

 number may, howe\'er, fall as low as 30. 

 This variety is likewise exhibited in respect 

 of the form of the teeth. 



Incisors, canines, and premolars often agree 

 with one another in form and size, and 

 present the form of a pointed cone or a 

 slighdy curved fang. In other cases we find 

 a large pyramidal or recurved incisor taking 

 the place of the canine, while in others again 

 the incisors of the upper jaw may even be al- 

 together wanting. The lower jaw frequently 



carries horizontallv placed incisors, and in 

 other cases the incisors in both jaws stand 

 in closely set rows as in the Carni\-ora. A 

 projecting recurved canine is met with only 

 in the tanrecs. In most of the other mem- 

 bers ot the order the canine resembles an 

 incisor in form and size, or ao-rees closelv 

 with the premolars in external form and in 

 the possession ot two roots. The premolars, 

 which are often very numerous, always have 

 a pointed cusp, but by the gradual appear- 

 ance of lateral tubercles and gradual increase 

 in size, pass o\'er into true molars so imper- 

 ceptibly that no hard-and-tast line can be 

 drawn between the two. The remaining 

 molars, finallv, almost always possess three or 

 tour sharp cusps, and in the upper jaw are 

 always broader than in the lower. The 

 grinding surface of these teeth presents the 

 form of a reversed W or V, the points ot 

 which, directed inwards, rest on a sharp and 

 narrow heel. 



This whole dentition accordingly is ad- 

 mirablv adapted for the transfixing and re- 

 taining of the prey, but not for dividing or 

 even for chewing it. It is altogether different 

 from that of the Carnivora, with which the 

 Insectivora were formerly combined. It is 

 distinguished by the absence of constant 

 formulas, bv there being no well-marked car- 

 nassial tooth, and by the poor development 

 of the canines. It can only be compared 

 with the dentition of the bats and some living 

 or fossil marsupials. With respect to the 

 position that must be assigned to the Insec- 

 tivora in a natural classification of mammals, 

 these facts are of great importance. 



The structure of the feet in the Insectivora 

 presents many variations due to the habits of 

 life. The tupaias living on trees have elegant 

 long limbs, the hind ones being, as in all 

 climbing animals, more powerful than those 

 in fVont. This disproportion becomes still 

 greater in the elephant-shrews, in which the 

 ankle is remarkably elongated, the lower part 

 of the leg. on the other hand, correspondingly 



