598 



CHEIROPTERA. 



it would reqviire the constant exertion of such 

 a degree of antagonizing muscular force to 

 prevent it, as would be incompatible with the 

 essential structure of these organs of flight. 



The carpus is of a very peculiar structure. 

 The first series of bones consists but of two ; 

 one very large, on which the radius rests, and 

 which is probably formed of the three outer 

 bones, the scaphoid, the semilunar, and the 

 cuneiform bones ; the other extremely small, 

 which is undoubtedly the pisiform, on the ulnar 

 side. 



The second series consists of the four bones 

 of which it is usually constituted. 



The metacarpal bones and phalanges of all 

 the fingers excepting the thumb are extremely 

 elongated. They extend outwards and down- 

 wards in a slightly curved direction to the 

 margin of the flying membrane, the second 

 finger being the shortest and extending to the 

 upper angle of the outer margin, the third, 

 fourth, and fifth to the inferior margin of the 

 membrane. There is a slight enlargement at 

 the articulation of the metacarpal bones with 

 the phalanges ; but otherwise these bones are 

 extremely slender and cylindrical. The thumb 

 is of no extraordinary length, and the ultimate 

 phalanx is hooked and sustains a nail, by 

 which the animal is enabled to climb on any 

 rough perpendicular surface, or to suspend 

 itself from some projecting part. 



The pelvis is remarkably strait, rather elon- 

 gated, somewhat wider inferiorly. The ilia 

 are narrow and elongated ; the ischia in several 

 species, instead of receding from each other, 

 approach so that their tuberosities touch each 

 other, and in some instances come in contact 

 with the coccygeal bones. In some species of 

 Pteropus, the anterior portion of the ossa pubis, 

 instead of meeting at the median line, recede 

 more or less from each other, and the space is 

 filled by ligament. In some species there is a 

 sexual difference in this respect ; the two pubic 

 bones being in contact in the male and sepa- 

 rated in the female. 



The sacrum and the ilia are connected by 

 absolute bony union at an early period. The 

 femur is of moderate length, slender and cy- 

 lindrical. It is turned outwards and upwards, 

 so that the side which is usually anterior is 

 directed nearly backwards. The tibia, offers 

 no peculiarity which requires particular notice. 

 The Jibula is exceedingly small, slender, 

 pointed towards its femoral extremity, and has 

 this singular peculiarity, that it does not rise 

 to the head of the tibia. In other cases where 

 this bone is defective, it is at its inferior ex- 

 tremity, but in the present case it is the supe- 

 rior portion which is wanting. As the femora 

 are directed outwards, the leg-bones are in 

 some measure turned round, so that the Jibula: 

 are at the inner side of the tibia and a little 

 behind them. 



The foot of the Cheiroptera does not ex- 

 hibit the same deviation from the normal 

 structure which we have seenin the hand. On 

 the contrary, it is not extraordinarily developed, 

 and the different parts of which it is composed 

 are in the usual relative proportions. 



The tarsus is composed of the usual bones. 

 There is a peculiarity in the heel, however, 

 which is worthy of notice. There is a long, 

 slender, pointed, bony process from the pos- 

 terior part of the foot which is inclosed within 

 the folds of the margin of the interfemoral 

 membrane, and extends about half-way to the 

 tail. Whether this process is a portion of the 

 os calcis, according to Cuvier, or a distinct 

 bone according to Daubenton, it is perhaps 

 difficult to decide ; but the opinion of Meckel 

 is probably the correct one, that it is nothing 

 more than a development of the tuberosity of 

 that bone, remaining disunited from its body. 



The metatarsul bones are rather short, slender, 

 and of nearly equal length. 



The phalanges of the five toes are nearly 

 equal, the inner toe reaching almost to the 

 same length as the others, in consequence of 

 the greater elongation of its first phalanx. 

 The ultimate phalanges are furnished with 

 hooked nails, by which these animals constantly 

 suspend themselves when at rest with the head 

 downwards. 



The whole of this structure is so perfectly 

 adapted to the peculiar habits of the animals, 

 as to require no comment. The great deve- 

 lopment of the ribs, sternum, and scapula, for 

 the attachment of strong muscles of flight, the 

 length and strength of the clavicle, the exten- 

 sion of all the bones of the anterior extremities, 

 all admirably tend to fulfil their obvious end. 

 The existence of a tail for the support and 

 extension of the interfemoral membrane, which 

 is found in the insectivorous Bats, compared 

 with its absence or comparative inefficiency in 

 many of the frugivorous, also points out an 

 interesting relation to the different habits of the 

 two groups, the former structure being calcu- 

 lated to afford a powerful and effective rudder 

 in guiding their rapid and varying evolutions 

 in the pursuit of their insect food. 



The general nervous system in the Cheiro- 

 ptera does not exhibit any very remarkable 

 peculiarity, but some of the organs of sense 

 require a particular notice. 



Organs of the Senses. The organ of vision 

 is principally remarkable for its diminutive 

 size. The eye in many of the insectivorous 

 group, in which the external ear is very largely 

 developed, is placed within the margin of the 

 auricle and almost concealed by hair. In the 

 frugivorous group, on the other hand, it is 

 of the usual proportional size. The organ 

 of hearing, on the contrary, though in the 

 latter forms not more developed than in most 

 other quadrupeds, in the former seems to take 

 the place of the diminutive organ of vision, 

 being greatly extended both in its external and 

 internal organization. The external ear in 

 Pteropus is of the usual form and dimensions, 

 and the eminences are not in any respect extra- 

 ordinary : but in most of the insectivorous Bats 

 the conch of the ear is enormously large ; in 

 many species being considerably larger and 

 longer than the head, and in the common long- 

 eared Bat of this country, Plecotus auritus, it 

 is nearly as long as the body. The tragus is 

 proportionally larger than in any other animals ; 



