The cranium is generally rounded, and rather broad. 'The posterior aspect more or less con vex in different groups ; in some overhanging requires to be extensive in those animals which prey by night, and especially in such as feed upon insects and pursue them on the wing.
The occipital bone is remarkable from the narrowness of its body, the transverse direction of the condyles, the short, thin, and convex form of its squamous portion, and particularly from the unparalleled proportionate size of the occipital foramen, which is nearly vertical and rounded.
the occipital foramen, in others not so. 'The occipital crest is triangular, stronger in the insectivorous than in the frugivorous form. In many there is also a longitudinal crest. The face is broad. The orbits are not com plete in either group, and the temporal fossa is large, but the zygoma in many very slender ; in some it is horizontal, in others slightly convex above. The nasal opening is very considerable; and in many whole genera, as in Rhinolophus, in Plecotus, and several others, in consequence of the intermaxillary bones not meeting each other, it is not closed at the lower part. In the genus Pteropus, and some others, as is seen in fig. 282, 283, though the intermaxillary bones meet in front, yet, as the arch is very small and narrow from before backwards, the palatine foramina unite and form a single large opening.
From the extreme thinness of the cranial bones, the internal surface corresponds exactly with the external, and there is no vestige of a bony tentorium, which is so strong in many of the Carnivora.
The frontal bone in tbe genus Pteropus presents a prominent orbitar process ; it re sembles that of Man, and of the Quadrumana, in the circumstance of the tvvo portions be coming early united. The parietals, also, unlike those of the examples just named, form but a single bone.
The temporal bone has a very extensive development of its acoustic portion ; a cha racter which is of the utmost importance to their peculiar habits, as the organ of hearing The jugal bone is small in most of the bats and very strait.
The superior maxillary bone is considerably elongated in this order, particularly in the frugivorous genera. The difference in this respect which exists between the frugivorous and insectivorous forms is shewn in the cranium. of a Pteropus belonging to the former (fig.
281, 282, 283), and a Phyllostoma to the latter group (fig. 284, 285, 286). In the former case, the portion occupied by the teeth fully equals in length the portion of the cranium posterior to it ; in the latter it is little more than as two to three. The number of teeth con tained in this bone varies considerably. There is, however, always a single canine tooth on each side, which is tolerably robust and sharp. The molares of the insectivorous Bats are always shorter than those of the frugivorous, and are furnished with sharp points, the latter being truncated and longitudinally grooved. 'They vary in number from g to a, or 2.
The intermax diary bones are always very small and short; they contain small incisores, varying in number according to the genera, from two to four in the upper, and in the lower jaw from two to six, there being always either the same numberin the two jaws, or two more in the lower than in the upper ; thus there is always one of the following formulm—.3 I. The articu lation of the lower jaw is transverse. The ascending ramus, with its coronoid process, is large and strong, rising very high above the level of the condyle.
The vertebral column.—The cervical verte brce are in general very little raised, but they are developed laterally, so as to present the broadest portion of the whole vertebral column, and the spinous processes are wanting from the second to the sixth vertebra. The Atlas is large, the dentata small, and its spinous process inconsiderable. The dorsal vertebra are of a very simple construction ; they are almost without spinous processes, which are replaced by a small tubercle : the bodies are, however, much compressed at the sides, so as to form a sort of crest. The vertebral canal is very large in this region. These vertebree are twelve in number in both forms, excepting in some species of the single genus Vespertilio, in which they are only eleven. The lumbar vertebra retain the peculiar characters which have been mentioned as belonging to the dorsal. They are elongated, and still almost devoid of spinous processes ; they are also compressed into a sort of continuous crest. The number of these vertebrx is four in Pteropus, five in Phyllostoma and Vespertilio, six in Rhinolophus, seven in Noctula.