6 NORTH AISlKKirAN 1?ATS II. ALLEN. 



Tlio wiuo" inoinbranc may 1k' said to W redinulaut wlieii the oxi>anse 

 above the arm and Ibrcaiin extends IVecly to tlte ear|>iis and embraces 

 the small tluiiid) to a point beyond tlie tirst phalanx of the thumb; 

 when it extends down to the foot beyond an oblicpie musole line whieh 

 extends upward and outward IVom the lower part of the le^": when the 

 space between the second and third digits is ample, and that between 

 the thund) and second diiiit is ])rovided Avith a well-defined hem of 

 membrane. 



Skin folds are often disposed along" the lines represented by the 

 palmar fascia, at the proxinml end of the tifth digit.* The tiexor ten- 

 dons at the radio digital angle are often covered with similar disposi- 

 tions of the skin. 



The nu'mbranes are supported not only by the parts of the skelatal 

 frame- work, as these parts are usually defined, but by a number of special 

 adaptations. An accessory cartilage at the somad margin of the ter- 

 nunal tifth digit has been already named (^folossiand \'esi)ertiliouida', 

 except Plecoti). The interfemoral nHMubrane is supported at the free 

 margin by a special cartilage (calcar) fnun the tarsus in all bats except- 

 ing the rteropi, Khinolophida', and the Steuodermida\ The calcar 

 may have a process from its under margin, as in Xoc/j^/ixm noctuln. 

 The terminal Joint of the tail may be spatulate, as in Xi/ctcris. Termi- 

 nal cartilages of the third and fourth digits are present except in Ptero- 

 pida\ Khiuolophida', and End)allounrida\ They are of varying 

 shajjes. the whole arrangement having for its object the sui)port of the 

 free margin of the wing mendtrane. These cartilages, as a rnle, are 

 defiected outward, though they may remain axial, as in Phyllostomida^ 

 and Plecoti. 



All things remaining the sanu\ the degree of strain may be measured 

 by the extent and variety of these special supports, and may be said 

 to be in the line of specialization for aerial nu>vements. Hence, in forms 

 in which they are absent the nunnbranes are broad and may be said to 

 exhibit more of a parachute arrangement than in other types in which 

 thcNiare ])resent, and the uu>tion of the wings to be like that of a slow 

 fanning rather than a rapid, varied tliglit. 



Strain on the membranes is also shown in the angle form between 

 the portions of the wing farthest away from the body, namely, the 

 region of the second and third digits. These- are pulled away from the 

 fourth and tifth digits, which remain nearly passive by the traction of 

 the muscles which extend these bones (extensores carpi radiales longior 

 et brevior), and the whole membrane becouu's tense. The contrast be- 

 tween the shapes of the wing in this regard is considerable when such 

 forms as Artibeiis, Xifctinomu!^', and Atalapha are compared. 



When the wing of a bat is held up between the eye of the observer 

 and a bright light the mend)rane is seen to be translucent. The deli 

 cate connective tissue lines (trabecuhi)) are seen uniting the various 



* Vospcrtilionidu' (exocptiug rieooti") ami Molossi. 



