14 ' BULLETIN 43, UNITED STATES NATIONAL MUSEUM. 



THE SKELETON. 



The skull. — In describing the skull in bats, I have borne in mind that 

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

 afar 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 proencephalou, of the mesencephalon, 

 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 inedian line bet wee i the 

 two the scKjittal crest, or line, and the anterior and posterior temi^oral 

 impressions the anterior and posterior 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 unusually 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 laminre 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 process of the squama uniting with one from 

 the exoccipital, as in Atalapha, or the surface is free as in Xijcti)io))}U8. 

 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 Pteropidt^ 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 semi(;ircular canals are outlined as 

 though in the human skull the encapsuling petrosal bone had been 

 chiseled away; the degrees in which thin plates 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 elements will be found useful: 

 External loop entirely occupied with bone : 



Superior loop augulated, open Ariiheus. 



Superior loop nearly tilled Xycthiomus (N. brasiliensis). 



Superior loop about half filled Atalapha. 



External loop almost entirely occupied mth bone : 



A7itrozous. 

 Vespertilio. 

 Adelonycterii (A.fuscus). 



