NYCTINOMUS TENUIS. 
femoral membrane. The body is deep brown, inclining to sooty black; intense 
above, and grayish underneath. The fur is extremely soft and delicate, closely 
arranged, and of uniform length throughout. 
DIMENSIONS. 
Inches. Lines. 
Length of the body and head, from the nose to the root of the tail.... 2 5 
the tail 1 # 
Expansion of the wings 12 6 
Length of the arm and fore-aim 2 6 
the phalanges of the middle finger 3 S 
the bones supporting the thumb 0 3^ 
the posterior extremities 1 1 
Breadth of the membrane of the wings at the narrowest part, oppo- 
site to the junction of the arm and fore-arm 1 0 
Greatest expansion of the cars on the summit of the head 0 9 
The general form and the organization of the Nyctinomi are in perfect corre- 
spondence with their habits and mode of life. Of all the various Vespertilionidee 
which I have examined, these have the greatest expansion of wing ; a property 
which, united to a tapering body, terminated by a long and gradually attenuated 
tail, enables them, perhaps with more facility than other animals of this order, 
to dart through the air in rapid flights, and abruptly to change their direction, 
in the pursuit of minute objects. The Nyctinomi have also a system of denti- 
tion, which among all the Vespertilionida? deviates farthest from that of the 
Pteropi. In the latter, which feed on fruits and vegetables, the grinders have an 
almost even and regular crown, divided by one simple longitudinal furrow ; in the 
former, it is complicated to such a degree, that it is difficult, by words, to describe 
it distinctly. Great care has therefore been taken, in the Plate wliich illustrates the 
generic character of Nyctinomus, to exhibit an accurate view of the various points, 
grooves, and processes of the grinders. To this I therefore refer in illustration of 
their description. The canine teeth are remarkable in both jaws : in the upper, they 
present interiorly a very sharp cutting edge ; in the lower jaw, they are of uncommon 
size, greatly distended at the base, and provided with a strong, obliquely diverging 
process, resembling a thorn, which forces the front teeth in an oblique direction 
forward. This peculiar structure serves to prevent the escape, and to secure in the 
interior part of the mouth, the minute insects which are seized in the rapid move- 
ments of the Nyctinomi, until they can be conveyed to the back part of the mouth, 
where the grinders furnish a most effectual apparatus for their immediate destruction. 
