2() Noirni a:mi:ki('an hats — ii. ALLIEN. 



[111. rill' liinl, ill wiiicli llir liiiiacriis is ciirNod, iiim(< or less sliMuler; pfctoral 

 riduc pioiiiiiuMit. not ;iiij;ul;ir ; ulna larue, curvod, not uiiitod with tin- 

 slender and inon- diniinntive radins ; cai]>ns or two bones; nietat'ar|ins of 

 I wo, soniet lines of three bones — ihe lirsl lieiiiL; small and eylindrii al,, the 

 other two of larger dimensions and united so ;is to form a bone resenildiiig 

 those of the forearm ; ulnar jihalanx ol' one joint, united to the radial, 

 whieh is eoiuposed ol'two. 



The power ot'snstam in j; llii;ht not <lei)endent nimn the exjiansion of skin, 

 but npiui the exeessLve tlevelojtment of dermal a]»i)endages (featliers). 

 \y . The Areha'ojttervK agrees with the typieal bird in <ier.t>ral particulars, but 

 dilfers in the nnniber of nu^taearpal bones, whieh are here four iu number : 

 the tirst and seeoud are slender, free and separate from one another; the 

 third and fourth bear ei>nsiderable icsemblanee to those of extant birds, in 

 beinglarge, stout, and closely ap])roxiniated; but are in)t, however, united. 

 Flight is sujuiosed to li.ive been maintained in the same maniu'r as in 

 liviui;' bii-ds. 



Til addition to the instances alri'ady given, ccitain tislics, as tlic 

 Ejcovaius and l><(('ti/l()i>tcnis, ])()ssess tlio power ot snstaini.u' true llijilit. 

 The nieeluiiiisui that lifts the body of the tish from the water, and up- 

 holds it tor a short tinio iu the air. is (»1»tained iu the peetoral tins, 

 whieh, iu these animals, are euormously developed. The structure of 

 these lius is houioloji'ous to that of the anterior extremities of other 

 vertebrates — their form alone bcin,<i- uuxlilied to adapt the animal lo 

 the uu'dium iu which it is ])lacd. Thus we have, iu each iireat subdi- 

 visit)U of vertebrate animals, a representative capable of sustaininu' 

 lliiiht. 



Another sonu'what similar modilication of the animal economy is met 

 with in a few animals of arboreal habits. Here a i)eciiliar arraniic 

 mcut of the skin is observed, which enables the possessor to break the 

 force of downwiird leaps. In the I'lyiuii' Leuuir [(iaJcopitlKcii.s). iu the 

 Myinu- iSquirrel { rtrn>))i if.s), i\\\i\ in the I'lyin^' Opossum {I\t((iirist((), 

 tiu' furred skin extends laterally tVom the sides ol' the body, and is 

 attached to anterior and i)osterior extremities at the metacarpal and 

 metatarsal reii'ions resi)ectivcly. The oidy instance of osteoloi^ical 

 development is obtained in the Draiiou ( /);vfc(> ^o/fo/.v). a snmll lizard 

 frt»in Sumatra, in which lonu, tiausverse processes from either sideof the 

 lumbar vertebra' support a thin utembranous yiowth which is capable 

 of beiujn" opened and sliut by means of nuiscles attached to tlu^ bony 

 frame work. 



TKETH. 



In deseribinii' the teeth \\w uomenchiture of Prof. II. F. Osborn will 

 be followed. The diajiram herewith presented is copied fr(»m this 

 writer's paper in the American Naturalist, December, 1888, p. 1072. 



ri'ri:i; moiaks. 



Antero-internal <'usp Protoeone. ])r. 



roatero-internal cusp or sixth i-usp Hypoeone. liy. 



Aniero-external eusp Paracone. pa. 



rostent-external cusp Metaeoue. me. 



Anterior intermediate eusp I'rotoeonule. pi. 



Posterior iuteruiediate eusp Metacouule. ml. 



