Order 7. Insectivora[137].
This order contains a large number of small generally terrestrial mammals. The limbs are plantigrade or subplantigrade, and are generally pentedactylate. All the digits are armed with claws, and the pollex and hallux are not opposable. The teeth are diphyodont, heterodont, and rooted. The cheek teeth have tuberculated crowns, and there are never less than two pairs of incisors in the mandible; often the incisors, canines, and premolars are not clearly differentiated from one another, and special carnassial teeth are never found. The cranial cavity is small, and the facial part of the skull is generally much developed; often the zygomatic arch is incomplete. Clavicles are well developed (except in Potamogale), and the humerus generally has an ent-epicondylar foramen. The femur frequently has a ridge representing the third trochanter. There are two suborders:
Suborder (1). Dermoptera.
This suborder includes only a very aberrant arboreal genus Galeopithecus, remarkable for its greatly elongated limb bones, and peculiar dentition. The incisors of the lower jaw are deeply pectinated or divided by several vertical fissures, the canines and outer upper incisors have two roots. Ossified inter centra occur in the thoraco-lumbar region of the vertebral column.
Suborder (2). Insectivora vera.
This suborder includes all the ordinary Insectivora, such as moles, shrews and hedgehogs. The upper and lower incisors are conical, not pectinated.
Order 8. Chiroptera[138].
This order is perhaps the best marked and most easily defined of all the orders of mammals. The anterior limbs form true wings and the whole skeleton is modified in relation to flight.
The anterior limbs are vastly larger than the posterior; for all the bones except the carpals are much elongated, and this applies specially to the phalanges of all the digits except the pollex.
The pollex is clawed and so is sometimes the second digit; the other digits of the manus are without nails or claws. The teeth are divisible into the four usual types and the series never exceeds i 2/3 c 1/1 pm 3/3 m 3/3 × 2, total 38. The milk teeth are quite unlike the permanent teeth. The orbit is not divided by bone from the temporal fossa. The vertebral column is short, and in old animals the trunk vertebrae have a tendency to become partially fused together. The cervical vertebrae are remarkably wide, and the development of spinous processes is everywhere slight. The presternum has a prominent keel for the attachment of the pectoral muscles. The clavicles are very long and strong, and the scapula has a long spine and coracoid process. The ulna is vestigial, consisting only of a proximal end ankylosed to the radius. All the carpals of the proximal row—the scaphoid, lunar and cuneiform—are united, forming a single bone. The pelvis is very weak and narrow, and only in the Rhinolophidae do the pubes meet in a symphysis. The anterior caudal vertebrae are frequently united to the ischia. The fibula is generally vestigial, and the knee joint is directed backwards instead of forwards. The pes has five slender clawed digits, and the calcaneum is often drawn out into a spur which helps to support the membrane connecting the hind limbs with the tail.