The sacrum is particularly elongated and narrow, and the spinous processes large. The number of sacral vertebra varies much. In Pteropus (fig. 280) there is but one. In the other genera they are either three or four. In Pceropus the sacrum is united at its extremity to the tuberosities of the ischium.
The coccygeal vertebra are slender, elon gated, and nearly cylindrical ; the tail being always included within the flying membrane, the only use of this part is to assist in sup porting the interfemoral portion of that mem brane. In most the tail reaches to its margin, in some much beyond, in others only half-way, and in Pteropus (fig. 280) there is not the least appearance of a tail, there is not even a rudi ment of a coccygeal bone. The number of these vertebrw is but six in Noctula, twelve in Ves pertilio and some others.
The number of vertebrx in the whole co lumn is said to be less in Pteropus than in any other mammiferous animal, being only twenty four, namely, 7C+12D+4 L+1S=24.
The ribs are the same in number as the dorsal vertebra. The first rib is very short and remarkably broad, and its cartilage; which is ossified, is still more so. The rest of the ribs follow the usual variations of form.
The Bats are remarkable for the extraordinary proportional length of their ribs, in which they probably exceed all other Mammifera.
The sternum is altogether greatly developed in the whole of this order. Its length is con siderable, and this circumstance,with the length of the ribs, tends to afford a great protection to the thorax in the violent movements re quired by the act of flight. But the most re markable peculiarity exhibited in the structure of this part, is the extraordinary lateral deve lopment of the anterior portion of this bone, termed the manubrium. This expansion is conspicuous in all the Bats, and appears to be intended to afford the strongest possible attach ment for the clavicles,which are also very much developed. In the genus Rhinolophus (the Horse-shoe Bat), this expansion seems to have reached its maximum of development. Its breadth is four times as great as its length, and yet it is nearly as long as the whole remaining portion of the sternum. The inferior surface of the manubrium is also furnished with a crest, which is continued, though much smal ler, on the next piece of the sternum ; it varies in size in the different genera. The remaining
bones composing the sternum are of nearly equal size.
The anterior extremity is the part of the skeleton which in the true Cheiroptera offers the most remarkable deviation from the nor mal form, especially in the metacarpal and Oa langeal bones.
The clavicle, from the extensive motion of the anterior extremities, requires to be much elongated in these animals; some of which in fact exhibit proportionally a greater develop ment of this bone than is to be found in any other order. It is always arched above and intimately articulated both to the scapula and to the sternum, and in some species is half as long as the greatly elong,ated humerus. As far as I have had an opportunity of observing, the clavicle, as well as the other portions of this extremity, is more developed in the in sectivorous than in the frugivorous Bats, for the very obvious reason that the former require more extensive powers of flight in the pursuit of their swift and active prey, than the latter in merely flying from place to place, in search of their stationary food.
The scapula is also developed to the greatest extent, and particularly in the insectivorous Bats. It is greatly elongated towards the base and posterior angle, which in some species reaches nearly to the last rib. The inner surface is very concave, and the foss& above and below the spine are deep, for the attach ment of the powerful muscles which are in serted to it.
The humerus is very long, slender, and cy lindrical, as may be observed in the skeleton of Pteropus in fig. 280. The head of the bone is round and large. The whole anterior part of the inferior articulation or elbow-joint cor responds to the head of the radius.
The fore-arm consists, as in the other mam mifera, of the radius and the ulna. The latter bone is, however, in all the Cheiroptera ex ceedingly small, and in some merely rudimen tary. In several species of Vespertilio, for instance, it forms nothing more than a flat process, only partially separated from the radius. In the example shewn at fig. 280 it is more considerable ; but even here it presents nothing more than a small styliform bone, united to the radius at the head, and diminishing to a thin point, towards the carpal extremity ; the olecranon too is wholly wanting.