A MONOGRAPH OF THE BATS OF NORTH AMERICA. 21 



inusclos which carry the sesamoids. At the point at which stretch- 

 ing- would begin the bones lock with the joint surface and takes tlie 

 strain. They are well developed in the tendons of the extensors of the 

 first, second and third metacarpal bones, especially in the phyl- 

 lostomines. 



The tendency above noted for the second and fifth metacarpal bones 

 to incline toward one another on the palmar aspect of the carpus, and 

 as a result for the second bone to lie in front of the third and for the 

 fifth to lie in front of the fourth, is a notable feature in the manus of 

 tlie bat. Minor differences are seen in the relative lengths of the bones. 

 They are shortest in pteropines and rhinolophines. The second meta- 

 carpal is usually slightly shorter than the others, but in Hipposideros 

 it is much shorter. The fifth metacarpal bone is apt to be the largest, 

 as in Pteropus, hnt in Hipposideros and in the molossines it is the short- 

 est. In the group last named and the related genus Atalapha the bones 

 are marked by grooves for the powerful metacarpophalangeal flexors. 

 The third metacarpal bone is commonly the largest, the fifth the shortest, 

 the fourth being intermediate, yet in North American species of Ves- 

 jiertilio the fourth bone, being slightly shorter than the fifth, is some- 

 times an individual variation. Mcgaderma is remarkable for having the 

 above order reversed — the fifth metacarpal is the largest and the third 

 is the shortest. Viewed as a whole the manus, notwithstanding its 

 enormous longitudinal development in the third, fourth, and fifth ele- 

 ments, is singularly unimportant in the first and second. The second, 

 however, while unsupported by elongated phalanges, has strong archi- 

 tectural functions at the line of its union with the carpus. 



The degrees of rigidity of the joints of the manus vary greatl3\ 

 The metacarpophalangeal joints of the RhinolophidiB are quite rigid 

 in all the forms examined. In most forms this joint in the fifth finger 

 is less flexible than that of the other fingers. All things remain- 

 ing the same, the degrees of rigidity are least marked in the third 

 finger and most marked in the fourth and fifth, a i)roposition in har- 

 mony with the manner of dividing the manus, namely, with the serial 

 movement (abduction) of the first, second, and third digits away from 

 the fourth and fifth, which in their turn are more disposed to remain 

 stationary, and thus tend to make rigid the main portion of the wing 

 membrane. 



The forms in which the second and third digits are approximated, and 

 the digit last named is widely separated from the fourth, embrace the 

 Molossi, the Yespertiliouidfe, and the remote Pteropidiie; those in 

 which the converse appears, at least in whicli the second and third 

 digits are relatively wide apart and the third digit not notably removed 

 from the Iburth, include many widely-removed groups, namely, the 

 IMiyllostomidiie, the Ehinolophidie, the Epomorphi, the Plecoti, and 

 Natalidic. It will be seen the arrangement last named prevails in the 

 largest number of forms. 



The phalanges present few points of contrast. They are uniformly 



