THE FAMILIES AND GENERA OP BATS. 19 



muscles and strengthening the arch by which the body is suspended 

 to the wings during flight. Somewhat remarkably, however, the 

 largest species, the great Pteropines, 01 in which the mechanical diffi- 

 culties would be expected to be greatest, show little specialization 

 except for the rather unusual development of the keel, particularly 

 on mesosternum, a peculiarity which is most pronounced in the larger 

 members of the group. The elements of the first rib and its attach- 

 ments remain distinct, and except for the usual Chiropterine pecu- 

 liarities show no characters worthy of note. Essentially the same 

 conditions, though with much less development of the keel, are 

 found in most of the Microchiroptera. So far as my observations 

 go it is constant in the Bhinopomidse, Emballonuridse, Noctilionidae, 

 Phyllostomidse, Desmodontidse, Myzopodidae, and in most of the 

 Vespertilionidse. The first stage in the strengthening process is 

 found in the Molossidae, the Mystacopidae and in one subfamily of 

 Vesper tilionidse, the Tomopeatinse. It consists in the slightly greater 

 thickening of the first rib, and the fusing of the last cervical and 

 first dorsal vertebrae into a solid ring. There is no appreciable 

 change in the form of any of the bones, and the keel of the mesoster- 

 num remains very slightly indicated. A peculiar modification of this 

 process occurs in the Thyropteridae where the fusion takes place 

 between the first and second dorsals, the last cervical remaining free. 

 In the Natalidse it is again the last cervical and first dorsal that fuse ; 

 but in this family the supporting arch is further strengthened by a 

 noticeable widening of the horizontal lobes of the presternum, so 

 that the greatest anterior width exceeds the length of presternum and 

 mesosternum together. The first rib is also thickened and its sternal 

 segment is greatly reduced in length. Keel of mesosternum relatively 

 as high as in the Pteropodidae, and a slight keel on xiphisternum. 



The most remarkable series of changes occurs in the four related 

 families Nycteridae, Megadermidae, Rhinolophidae, and Hipposide- 

 ridae. In the Nycteridse the conditions are not very different from 

 those in the Natalidae. The keel is equally high and it extends simi- 

 larly- on the short, wide xiphisternum. The presternum is, however, 

 less broadened and strengthened, and the last cervical vertebra is not 

 fused with the first dorsal. In the Megadermidae the mesosternum 

 and xiphisternum are of the ordinary type, but the presternum is 

 greatly widened, so that it is essentially a heavy transverse bar with 

 a slight median backward projection. Laterally it is fused with the 

 first rib, so that the only break in the continuity of the ring is at the 

 point of articulation of the ribs with the vertebras. As in the Nycte- 



t»The weight of an alcoholic specimen of Pteropus from Tenasserim (Cat. No. 

 104451, U. S. N. M.) is 739.5 grams, while that of a Rhinolophus ferrumequmum 

 from Genoa, Italy (Cat. No. 18472, U. S. N. M.), is only 16.8 grams. Yet in the 

 smaller animal the strengthening process is carried to the extreme. 



