A MONOGRAPH OF THE BATS OF NORTH AMERICA. 7 



and a biiglit light the meuibiaue is seen to be translucent. The deli- 

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

 parts of the bony framework, and the positions of the nerves, blood 

 vessels, and nniscle-fascicles are displayed. The paths of the nerves and 

 blood vessels constitute one system and may be spoken of together, but 

 the trabecuhe and muscles are distinct from these and in some degree 

 from each other. As in the case of the relation which exists between 

 the skin and the bones, so in the arrangement of the parts just named 

 the degrees of strain to which the wing is subjected account in the main 

 for the difference in the various genera. The muscle-fascicles are most 

 numerous in the membrane near the body, and are better developed in 

 the narrow-pointed winged forms, such as Molossi and Aialaplia, than 

 in the broad, parachute-like forms.* The muscle element in the wing 

 is especially weak in the Pteropidae, Rhiuolophidie and Yespertilionidiie. 



The fibrous lines which extend across the membranes are not without 

 system. Many of them are excessively attenuated tendons; such, for 

 example, are the fibers of the palmar fascia, already mentioned. Others - 

 are the fibers whicli connect the joints of digits; more of them yet aj)- 

 pear to be parts of a true derm. The nerves and blood vessels pursue 

 the same courses. Since the directions of nerves are of more impor- 

 tance in morphological study than the vessels, the former will be alone 

 named. In each interdigital sj^ace a nerve tends to enter at its proximal 

 end and, dividing into two branches, incline along the sides of the op- 

 posed metacarpal bones. The departures from this j)lan are numerous, 

 and are so constant in groups of generic and even specific limitation 

 that they constitute valuable additions to diagnoses. 



An oblique raised line passing down on the wing membrane from the 

 upper part of the arm, in most bats, corresponds to the coracohrachi- 

 alia fascicle. It is least marked in highly aberrant forms, and may be 

 of nerve origin, instead of muscular, in Noctilio, Corynorhiniis, and 

 Plecotns. A second, lying near the elbow, in like manner, is caused by 

 a muscular slip from the triceps extensor and therefore becomes the 

 triceps fascicle. In Cori/norhinns and Pfcc/o/^/s this line is represented 

 by one corresponding to a nerve, apparently ulnar, or the internal cuta- 

 neous. Both these lines are offshoots from the muscles named. The 

 intercostal lines are those which pass directly from the sides of the 

 trunk. 



The wing membrane, when expanded, exhibits differences in the width 

 of the iuterdigital spaces. These differences relate in an intimate man- 

 ner with the behavior of the parts in fiight, and consequently with 

 habit. The subjoined table indicates some of these distinctions: 



* Perhaps the highest degree of development of the muscle system is attained in 

 Rhinopoma. 



