^'7s9^i^''] PROC'KEJ)IN(JS OF THK NATIONAL MUSEUM. 25 



directed proxiuially. In Iihi)tolophu,s the ealciineuni enters into the 

 tinkle joint. In other tonus the Cidciinenm is independent of the. joint. 

 In Phi/Jlosfomidd', inclndinji' Xdtalus, as Avell as in the genus Rhycho- 

 nycteris, the calcar* is phxced in axial line with the calcaneum. In 

 other families it joius the calcaueum to its outer side at a well-defined 

 angle. As a rule the astragalus and ealcaneum are nearly of one size, 

 but in the genus last named the calcaneum is notably the smaller (Am. 

 Naturalist, Feb., 1886, 170). 



GENERAL PLAN OF ANTERIOR EXTREMITIES IN FLYING VERTE- 



BRATED ANIMALS. 



From tiie above consideration it will be seen that the wing mem- 

 branes possess various features which can be used in distinguishing 

 the members of the order. But after what manner are the tlyiiig mam- 

 mals distinguished from other flying vertebrates? 



There are two distinct types of moditication which the vertebrate 

 skeleton has undergone in adapting the animal for flight, both of wliich 

 depend upon some peculiarity in the structure of the anterior extremi- 

 ties; and in order to obtain a correct opinion of them we proi)ose to 

 cast a glance at each in turn. 



/'/(/*( o/hoiui nfntctnre of the wings of flijing veriehrate animals. 



a. Bones of carpus uimuited 

 distinct; flight main- 

 tained l>y dermal ex- 

 panse. 



I. Wing membrane supported l)y all fingers. 



Bats (Vespertilio), order of Mammalia. 

 II. Wing membrane supported by the fourth finger 

 only (which is innnensely developed), the 

 others remaining free. 



rterodactyh's, order of Reptilia. 

 III. Bones of metacarpus, two to three in number; 

 Bones of carpus united; feathers not radiating. 



flight maintained by J ^'"'"f ^"'^^^ (AvEs)-clas8. 



dermal appendages. I ^"^- ^^^nes of metacarpus, tour in number ; feathers 



I radiating. 



I Arclueoptenjx (AvES) — subclass, 



f I. Tlie Bat, in which the humerus is long and slender, with a small pectoral 

 ridge. Ulnarudimeutai'y. The radius constitutes the bulk of the forearm; 

 carpus composed of six bones ; the metacarpal bones, five in nunil»er, sepa- 

 rate and distinct; the phalanges generally, two in number; thumb, and in 

 some genera the index finger, surmounted by a claw. 

 II. The Pterodactyle, in which the humerus is short and straight, very broad 

 at head, with angular and prominent pectoral ridge ; ulna and raclius dis- 

 tinct, of nearly equal si/e; carpus comjjosed of five bones; metacarpus of 

 four bones, se})arate and distinct; first finger with three joints, second 

 with four, third with five, fourth with four joints, all provided with claws, 

 with the exception of the fourth, Avhich is remarkable for tlie extraordinary 

 development of its several joints. It is from this last-mentioned finger to 

 the base of the foot that the skin was stretched by which the animal was 

 enabled to fly. 



*The calcar is an element of doubtful homology. It supports the free border of 

 the interfemoral membrane, and is of the same significance as the atu-i^ssory carti- 

 lage of the fifth manal digit. 



