The family Galeopithecidae contains but one genus, which has been at times referred to the Lemurs, to the Bats, or has been made the type of a special order of mammals. It is better to regard it as an aberrant Insectivore—so different indeed from other forms that it requires a special sub-order for its reception.
Galeopithecus[[383]] inhabits the Oriental region. It is a larger animal than any other Insectivore, about the size of a Cat, and has a patagium extending between the neck and the fore-limb, between the fore-limb and the hind-limb, and between the hind-limb and the tail. This patagium is abundantly supplied with musculature, but the fingers are not elongated as in the Bats for its support. In the degree of its development, however, the patagium of this creature is midway between that of Sciuropterus on the one hand, and the Bats on the other. It presents many remarkable features in its organisation. The brain is like that of the Insectivora in the exposure of the corpora quadrigemina by the slight extension backward of the cerebral hemispheres; but its upper surface is marked by two longitudinal furrows on each side, a state of affairs (in combination) which is unparalleled among the Mammalia. The teeth are peculiar by reason of the singular "comb-like" structure of the lower incisors. This, however, is an exaggeration of what is to be found in Rhynchocyon and Petrodromus, while the same style of tooth, though not so highly developed, characterises certain Bats. The Tupaiidae and certain Lemurs show what Dr. Leche regards as the beginning of the same thing. As in Tupaia also there is an indication of the characteristically Lemurine sublingua. The stomach is more specialised than in other Insectivores, the pyloric region being extended as a narrowish tube. There is a caecum. A peculiarity of the intestinal tract is that the large intestine is longer than the small.
Order XII. CHIROPTERA.
We may thus define the Bats:—Flying mammals, with the phalanges of the four digits of the hand following the pollex greatly elongated, and supporting between themselves and the hind-limbs and tail a thin integumental membrane, which forms the wing. The radius is long and curved; the ulna rudimentary. The knee is directed backwards, owing to the rotation of the limb outward by the wing membrane. From the inner side of the ankle-joint arises a cartilaginous process, the calcar, which supports the interfemoral part of the wing
membrane. The mammae are thoracic; the placenta discoidal and deciduate. The cerebral hemispheres, which are smooth, do not extend over the cerebellum.
Fig. 254.—Barbastelle. Synotus barbastellus. × ½. (After Vogt and Specht.)
This large order of mammals was once placed with the Primates. There is no doubt, however, that they form a perfectly distinct order; no knowledge of fossil forms in any way bridges over the gap which distinguishes them from the highest mammals. The most salient feature in their organisation is clearly the wings. These consist of membrane, an expansion of the integument, provided with nerves, blood-vessels, etc., which mainly lie stretched between the digits 2 to 5. These digits themselves, which are enormously elongated, act like the ribs of an umbrella, and when the wing is folded they come into contact. Besides this part of the flying apparatus there is a tract of membrane lying in front of the arm, which corresponds to the wing membrane of the bird, but which in the Bats takes quite a subordinate place. In the bird, on the other hand, there is a metapatagium, which is the main part of the wing of the Bat. It seems just possible that in Archaeopteryx the metapatagium was more Bat-like. Furthermore, a steering membrane, like that which fringes the tail in some Pterosaurians, lies interfemorally in Bats, and includes the whole or a part of the tail. The pollex takes no share in the wing, but projects, strongly armed with a claw, from the upper margin.
The bones of this order of mammals are slender and marrowy; they are thus light, and subserve the function of flight. A most remarkable feature among the external characters of the Bat tribe is the extraordinary and often highly complicated membranes which surround the nostrils. These are at least often