MAMMALIA. 475 
This family, as far as our knowledge extends, existed during the tertiary 
epoch, under the same generic form as in our days. Several species of the 
genus Hrinaceus, and one of the genus Centetes, have been found in Kurope; 
none yet in America, where the living types are also absent. 
The genus Hrinaceus (hedgehog) has its body covered with spines instead 
of hairs, showing thus a resemblance to the porcupine. The skin of the 
back is furnished with powerful muscles, by which, when the head and the 
feet are brought towards the abdomen, the animal can shut itself up, pre- 
senting to its enemies spines all around. ‘The tail is very short, and there 
are five toes to each foot; there are six incisors in each jaw, the middle 
ones being the longest; on each side three false molars, three true molars 
bristled with points, and a small one studded with tubercles. 
The common hedgehog, H. europeus (pl. 118, fig. 18), is common in the 
woods and hedges, and also in houses. It passes the winter in its burrow. 
Its skin, it is said, was formerly used to dress hemp. . 
The genus Centetes (tenrecs) is composed of four species, inhabiting 
tropical Africa and the Island of Madagascar. Their body is covered with 
spines, like the hedgehog, but much shorter; and the animals do not 
possess the faculty of rolling themselves so completely into a ball. The tail 
is absent; the snout is sometimes elongated, always much pointed; there 
are four or six incisors, and two great canines in each jaw; there are one or 
two false molars, and four true ones, triangular and bristled; each foot has 
five distinct toes, armed with crooked spines. They are nocturnal animals, 
passing three months in the year in a state of lethargy, although inhabiting 
the torrid zone. We are even told that it is during the greatest heat that 
they grow torpid. 
The Oriental or Asiatic hedgehog constitutes the genus Gymnura. 
ORDER 6. CHEIROPTERA. 
This order is composed of the animals commonly known as bats, and 
easily distinguished from all other mammals by a membranous expansion 
which extends from the sides of the neck between the fore limbs and toes 
down to tke tip of the tail, and which enables them not only to sustain 
themselves in the air, but also to move through it in any direction they 
may desire. They thus possess the power of true flight as in birds, with 
which indeed they are frequently confounded. The bones of which the 
anterior extremities are composed are very much elongated, especially 
those of the fingers, and constitute an umbrella-like framework, over which 
is spread a thin, naked membrane continued from the membranous expan- 
sion of the body. The whole locomotive power of these animals seems 
concentrated upon this organ of flight. It can only move along a solid 
surface by folding its wings and using the hooked thumbs to lay hold of any 
irregularity, and thus draw itself forwards. Hence its motions are awkward 
and shuffling; and on a polished surface, like that of a table, it is greatly 
embarrassed. But in the hollows of trees, the crevices of masonry, and the 
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