1910.] Elements of the Mammalian Skull. 423 



telic" or so called "morphological" characters in order to strengthen the 

 theory (c/. pp. 111-112) that such characters preserve evidences of interordi- 

 nal kinship and separation better than "adaptive" or ca'notelic characters. 

 The auditory ossicles for example, as figured l)y Doran (1S79), show that 

 animals having approximately the same life-habits and which are outwardly 

 similar, such as the Wolf and the Thylacine, may yet possess very different 

 ossicles, which conform in each case to a recognizable ordinal type. In cer- 

 tain cases, however, the differences in the auditory ossicles between forms 

 that are nearly related and of similar habits are so pronounced that the 

 question is raised whether an abnormal range of variation may not some- 

 times occur in these paheotelic characters (p. 423). Many characters of this 

 class require reexamination. What for exam[)le is the phylogenetic or the 

 adaptive meaning of the fact recorded below that Insectivores contrast both 

 with the Marsupials and with many Placental orders in the slight extent of 

 the vertical plate of the palatine ? 



Such in brief appears to be some of the problems and recjuirements of the 

 study of osteology, if that study be approached not as a descriptive cata- 

 logue of unmeaning facts but as a vital element of the science of mammalian 

 evolution. 



Notes on the mammalian skull. 



The general characteristics of the skull in INIonotremes and Marsupials 

 has been described above (pp. 155, 217-225). The skull of the ancestral 

 Placentals doubtless resembled that of the Marsupial Marmosa in all those 

 characters relating directly to minute size and insectivorous habits, such 

 as the relatively large brain case, triangular, rather brachycephalic skull, 

 pointed muzzle, elongate row of incisors, small canines, pointed premolars, 

 sharp-cusped triangular upper molars, etc. But the ancestral Placental skull 

 at a very early date became different from the ancestral Marsupial skull in 

 many characters which have been listed above (pp. 253, 279) as "primitive 

 Placental characters." From such a minute insectivorous type of skull, 

 with a diphyodont dentition and a dental formula of Ixjil:) ^^^^ various types 

 that are characteristic of the most primitive representatives of all the Pla- 

 cental orders may have been derived, in the manner outlined in preceding 

 chapters. 



A few notes upon some of the principal elements of the skull in the more 

 primitive mammals may now be given. 



Prema.rillce. Derived from the pointed type seen in Galesaurus. Sur- 

 rounding the anterior palatine foramina, which appear to be continuous 

 with the primitive reptilian choante. Ascending process originally far 

 removed from frontals. In Rodents secondarily extending backward and 



