A MONOGRAPH OF THE HATS OF NORTH AMERICA. 15 



External loop and superior loops not (tccupied with bone: 



Xoctilio. 



MacrulK.s (occasioually i-xccptcd). 



Hemiderma. 



Chiluntfvterin. 



The tympanic bono is sometimes incomplete, as in VeHpertUlo^ at its 

 upper arc, where it limits tlie zona tympanica 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 the sterno-mastoid muscle is much greater than in 

 mammalia generally. This interval in Artibeus equals one-seventh of 

 the greatest length of the skull, while in Canis it equals one-nineteenth. 



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

 tends from the region of the proencephalon to the upper border of the 

 anterior nasal aperture. On the side the region of the face is equal 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 defined by the bony limits, as seen in many 

 other mammals. Since custom has sanctioned an acceptance of an or- 

 hital re(7(o» which would be limited posteriorly 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 Emballonuridic, the post-orbital proc- 

 ess is constantly present, and in the Pteropidte varying degrees of 

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

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

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

 upper border of the orbit. The inflation 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 

 inflation is greater. This peculiarity gives the face a broad effect at its 

 junction with the brain-case and modifies the shape of the orbit. The 

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

 rule, the frontal bone here permits the ectoturbinal parts to be in part 

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

 position to inflation; hence the peculiarities of the inflation give char- 

 acter to this portion of the cranium. On the vertex the inflation causes 

 the face to widen from the proencephalon 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 well as of the palatal notch, due to the rudimentary state of 

 the premaxilliB, aft'ord l)ases for some (characters of minor value. The 

 length of the infra-orbital canal and the peculiarities of the outer wall 

 of the canal are of interest. In Artibeus the canal is long and for the 



