^°\x''] PROCEEDING.S OF THE NATIONAL MUSEUM. 13 



1893. 



in the same mediiitn the com|uu'isoiis are sufficiently exact for purposes 

 of identiiication of museum alcoholics. It is barely possible that the 

 color description may require some modification as contrasted with 

 these drawn up from living specimens. 



SKELETON. 



Simll. — In describing the skull in bats, 1 have borne in mind that the 

 form of the brain gives expression to the shape of the brain-case to a 

 far greater degree than is the case in other mammals. The divisions 

 of the brain are readily outlined externally, and yield convenient bound- 

 aries, since the shapes of associated parts harmonize in some degree to 

 them. Thus the region of the proencephalon, of the mesencei)halon, 

 and of the metencephalon are defined. In like manner the impressions 

 made by the lines of attachment of the temporal and masseter muscles, 

 the former on the cranium, the latter on the lower jaw, are valuable. 

 For the temporal muscles I have named the median line between the 

 two the sagittal crest or line, and the anterior and posterior temporal 

 impressions the anterior and i)osterior temporal ridges or lines. 



On the under surface of the skull the size and direction of the proc- 

 ess (sphenoidal tongue) which extends backward and outward from 

 the basisphenoid is worthy of notice. As compared to other mammals, 

 the cochlea is nniisually large at the base of the skull, and is, as a rule, 

 but partially concealed by the tympanic bone. 



The otic capsule varies in the degree in which bony lamiuie occupy 

 the spaces created by the semicircular canals. On the side of the skull 

 the surface (opisthotic) which adjoins the squama in mammals gener- 

 ally is in bats crossed by a ]>rocess of the squama uniting with one from 

 the exoccipital, as in Atalapka, or the surface is free as in N'yctinomits. 

 The old-world genus Hipposideros resembles Xyctinomus in this par- 

 ticular. When the otic capsule falls out, as it is apt to do in the over- 

 macerated skull, a foramen or a notch is always defined between the 

 squama and the occipital bone. Sometimes a foramen of the same sig- 

 nificance, viz, one occupied by the opisthotic during life, is seen on 

 the occiput. 



The otic capsule in Pteropidfe alone is inclosed in bone, to form a 

 triangular wedge comparable to the os petrosa of other mammals. As 

 a rule, the form of the cochlea and semicircular canals are outlined as 

 though in the human skull the encapsuling petrosal bone had been 

 chiseled away, the degrees in which thin i)lates of bone fill in the 

 semicircular canals being alone subject to change. The horizontal loop 

 in all forms examined is filled with bone. 



The following scheme of the otic element will be found useful: 

 External loop entirely occupied with bone : 



Superior loop anguLitecl, open Artibeus. 



Superior loop nearly filled Niivtinomns {N. braailiensis). 



Superior loop about half filled AUdapha. 



