A MONOGRAPH OF THE BxVTS OF NORTH AMERICA. 23 



ill TJiyropfera (an aimectaiit <ieiius between the Anieiicaii naked-nosed 

 and leaf-nosed forms), where the leugtli of the second and third pha- 

 langes about equals that of the second phalanx of the same digit in 

 the allied genera Furia and Xatalns. 



The much greater length of the third digit, as comijared with that 

 of other digits, is a noteworthy feature of the bat wing. Its relativ^e 

 length in different forms serves as a guide to generic and sometimes 

 to specilic distinctions. 



The peculiarities of the thumb are so marked that they can be best 

 considered apart from the other manal parts. The thumb, as a rule, is 

 free from membrane beyond t\ie basal third of the first phalanx, but 

 may be almost entirely inclosed, as in Thyroptern. The extent of the 

 enwrapping membrane determines the size of the little fold of skin 

 which lies between the thumb and the second metacarpal bone. The 

 thumb is relativelj' large in pendent forms, since it is here of value in 

 prehension ; per contra, in Thyroptera, in which genus a suctorial disk 

 takes the place of a prehensile thumb, this digit is also small, though 

 the animal is unadapted to activity in the prone attitude. It has been 

 already noted (p. 5) that the thumb is bent downward and the under 

 surface of the first metacarpal bone fairly well outlined in the pendent 

 forms. It is not known how DesmoduH and Diphylla^ which process 

 with large in^ojecting thumbs, support the body when at rest. The 

 claws on the feet are weak, and the animals are probably not pendent 

 at rest. With these exceptions, the phyllostommes possess the serai- 

 flexed thumb, as do all the other families excepting the molossines and 

 vespertiliones. 



Fosfcrlor limb. — The innominate bone always exhibits a narrow rod- 

 like ilium which occasionally projects slightly above tlie line of the ilio- 

 sacral articulation, but as a rule is level therewith. The dorsum of the 

 ilium is flat, in most forms, but it may be concave and broad, as in 

 molossines, Afulaphu and (lulonycteru. The pubis is, as a rule, defined 

 in the males, but is absent and has a wide interval defined between the 

 innominate bones anteriorly in the females. Tlie sliape of the ischium 

 and of the thyroid ftn-amen is subject to slight variation in genera and 

 even in species. The innominate bone is in most forms distinct from 

 the vertebral column. In molossines, Chilonycteris, and in rhinolo- 

 phines, it is anchylosed, both at the sacroiliac junction and the ischio- 

 sacral or ischio-coccygeal junctions. ChUonyctcrh is an instance of the 

 union last named. In all l)ats a disposition exists for the tuberosity of 

 the ischium to approach the vertebral cohimn, t luis [(resenting a marked 

 contrast to tliat seen in terrestrial (piadrupeds. Aiifrozous exhibits a 

 facet between the tuberosity and the first joint of the coccyx. Tlie shitli 

 is the only animal I can recall which exhibits a fixation of the ischium 

 similar to that found in tlie bats. The ilio-iu'ctineal spine is marked; 

 often a large tubercle, it may be a needle like spine. In Hippoi^idcrox 

 it is of enormous length and is ancliylosed to tlie ilium near its ui)i)er 

 border. 



