182 PROCEEDINGS OF THE ACADEMY OP [1894. 



bullte, or other parts of the base of the skull, but by the inflation of 

 the diploic structure of the frontal and parietal bones. 



In Edentata the difference between the long- faced Tattisia, Myr- 

 mecopliaga and the short-faced Megatherium, Bmdypus and Cholopus, 

 is about what has been already noted in the foregoing examples. 

 The zygomatic arch in the group last named, although incomplete, 

 is high. The tympanic bulla, it is true, is inconstantly inflated, but 

 that of the sinus in the frontal bone, compared with what is noted 

 in the long- faced types, is like that which is seen in Elephas as com- 

 pared with Mastodon. 



Similar points can be established in the Quadrumana. Macacxis 

 can be separated from Cynopithecus, not only by the length of the 

 face, but by Macacns having a more inflated tympanic bone. The 

 same remark is true of Propithecus and Nyctlcehus as compared with 

 Lemur. 



The genera of Carnivora, as illustrated in Melursus and Helarc- 

 tos, are in evidence of the same. 



Even in birds, as was suggested by Mr. Fred. Lucas to Dr. Allen, 

 the difference between the owl and the pelican and stork can be de- 

 noted by the amount of diploic structure in the head, as well as by 

 the length of the face. 



In Artiodactyla the evidence is obscure. In the remarkable fossil 

 genus Cyclojyidius, described by Prof. Cope, all the co-ordinates ap- 

 pear to be well established, namely, an extreme short face-axis is 

 accompanied with great increase of width of the zygomatic arches 

 and large tympanic bones. But these bones are generally large in 

 the long-faced artiodactyles. The influence of many factors of neces- 

 sity must be borne in mind before all the terms of the equation can be 

 determined. 



Care must be taken not to confound an isolated inflation of the 

 tympanic bulla with the probable co-ordination above named. In 

 (Jorynorliinus, Euderma and Dipus, as in some species of Vulpes, 

 the inflation is correlative with the size of the auricle, at least is 

 independent of the problem of face-shortening. 



Many suggestive features present themselves in the skull of man. 

 The inflations here, while basic, are not seen in the tympanic bones, 

 but in the tissue at the median aspect of the petrosal bones, and at 

 the sides of the exoccipitals. Prognathic and orthognatic forms can 

 be distinguished, as a rule, readily by these parts of the base of the 

 skull ; but, as in all things pertaining to the study of the human skull 

 co-ordinations are exceptionally difficult to establish. We are here 

 dealing not with characterizations of a generic kind, but with those 

 which are mutatory in tribal or racial groups of sub-species, and it is 

 not reasonable to look for features so sharply defined as are those of 

 genera of quadrupeds. 



Hyperostosis on the Inner Side of the Human Lower Jaw. Dr. 



