14 NOK'Tir AMHRICAN 15ATS II. ALLEN. 



Ijxtcnial loop aliiiost oiitiicly occupied with bono: 



Aiilrozoiix. 

 f'rspcrtUio. 

 Addonyvteris (A. fit sens). 



ExteiiKiI loop and sui)crior looi)S not occupied Avitli bone: 



Xoctilio. 



Mavrotiis (occasioiiiiUy I'xccpteil). 

 Ilrinidcnnd. 

 Chiloiiyvtcns. 



The tympanic boue is sometimes incomplete, as in Vcsjicrtilitt, at its 

 upper arc, where it limits the zona tyjnpauica superiorly. The bone 

 constitutes the bulla, which presents various degrees of extension over 

 the cochlea or forward along the side of the glenoid fossa. The width 

 of the origin of tho sterno-niastoid muscle is much greater than in 

 manunalia generally. This interval in Artibciis equals one-seventh of 

 the greatest length of the skull, which in Can is it ecpials one-nineteenth. 



Seen from above, the face is described as forming a vertex. This ex- 

 tends from the region of the proenccphalon to the npper bm-der of the 

 anterior nasal aperture. On tho side the region of the face is eipial to 

 the length of the dental series. The orbit is, strictly speaking, t-iat 

 portion of the skull which accommodates the eyeball; but this is much 

 smaller than the space as detiued by the bony limits, as seen in many 

 othermammals. Since custom has sanctioned an acceptance of an or- 

 bital region which would be limited j^osteriorly if a process were present 

 extending from the anterior temporal ridge toward the zygoma, a simi- 

 lar region so restricted is held to be a valid one in all bats. In some 

 genera, indeed, as those of the I'^mballonuridu', the post-orbital proc- 

 ess is constantly i^resent, and m the Pteropida^ varying degrees of 

 posterior limitations of the orbital legion are seen. The face, including 

 a part of the frontal bone, is intlated at the side in bats. I have called 

 this the fronto-maxillary inflation. It forms a ridge or swelling at the 

 npper border of the orbit. The intlatiou of the skull at the anterior 

 part of the frontal bone to form the frontal sinus is much less conspic- 

 uous in the Cheiroptera than in some other orders, but the maxillary 

 intlatiou is greater. This peculiarity gives the face a l)rt)ad etVect at its 

 Junction with the brain-case and modilies the shape of the orbit. The 

 ethmoidal plates variously change the shape of the inner wall. As a 

 rule, the frontal bone here i)ermits the ectoturbinal i)arts to be in part 

 delined. The region of the lachrymal bone appears to resist the dis- 

 position to intlation: hence the pt'culiarities of tlie inflation give char, 

 acter to this ])()rtion of the cranium. On the vertex t\w iuHation causes 

 the face to widen from the procncephalon to near the anterior nasal 

 aperture, where it is abruptly narrowed, and to create depressions of in- 

 constant kinds in the line of the conjoined nasal bones. The extent to 

 which the recession of the nasal bone from the anterior nasal aperture 

 occurs, as Avell as (»f the palatal notch, due to the rudimentary state of 



