INSECTITOBA. 49 



Ord. INSECTIVOEA. 



Incisor teeth various in number and almost always different in the 

 two jaws ; no distinct canines in most ; molars with acuminated tuber- 

 cles. Feet usually pentadactylous, plantigrade. 



The insectivorous mammals are mostly of small size, with short limbs, 

 and some of them superficially much resemble the Rodents. Many live 

 under ground, and most are nocturnal. They feed chiefly on insects. 

 Some are torpid in winter in cold countries. They are timid and un- 

 obtrusive in their habits, and rather slow in their motions. The tail 

 is variously developed. In running they place the entire sole of the 

 foot upon the ground. 



The skull is of sUght make and elongated form, the bones of the 

 face and jaws being much produced, and the latter are weak. The 

 distinct division of the teeth into sets is not apparent here, and it is 

 sometimes difficult to say to which set particular teeth belong. There 

 are usually eight teeth in front of each jaw, of which the outermost 

 are regarded by some as the canines, though often smaller than the 

 others, no placental mammal having more than six incisors in each jaw. 

 The orbit and temporal fossa are confounded in one cavity, except in 

 Tupaia. The molar teeth are studded with sharp cusps or tubercles, for 

 the purpose of breaking down the hard elytra of beetles, on which they 

 chiefly subsist. All have clavicles, and the number of ribs is large. The 

 deciduous teeth of the moles and shrews are developed and disappear 

 before birth. The stomach is perfectly simple ; and, except Tupaia, they 

 have no ccecum. The brain and organs of sense closely resemble those 

 of the Eodents. The mammae are ventral and generally numerous. 

 The testes pass periodically from the abdomen into a temporary scro- 

 tum. 



Insectivorous mammals are nearly confined to the old continent, none 

 being found in South America, if we except the curious Solenoden para- 

 doxus of St. Domingo ; and only a few moles in North America. They 

 are represented on that continent chiefly by small species of Didelphys or 

 Opossum, a marsupial animal. There are likewise none in Australia, but 

 several marsupials resemble them so closely that, were it not for their 

 special anatomical structure, they would undoubtedly be classed with them. 

 BlainvOle looks on the Insectivora as being intermediate between Bats 

 and the Edentata. Cuvier places them next the Bats, as do most sys- 



H 



