DEVELOPMENT OP THE SKULL IN THE MAMMALIA. 
117 
Summary, and we shall then be better able to appreciate the fragmentary nature of 
the existing groups of Mammalia, and to imagine, in some degree, with the help of 
Paleontology, what the lost kinds were like. 
In working out this Order I have had constantly to refer to the structure and 
development of the skull in the Sauropsida, and at the same time to be careful not to 
call any modification of a low Mammalian type of skull Reptilian or even Sauropsidan. 
I want a term of wider import than even Professor Huxley’s title for the Mammalian 
root-stock, namely, “ Hypotheria,” as that would only lie under the Prototheria, and 
not under the Reptiles and Birds too. Proto-Amniota occurs to me, but unfortunately 
the second existing group of Mammalia, the Marsupials or Metatheria, are themselves 
'proto-Amniota, having both that important foetal membrane and its correlated sac, the 
allantois, in a primary, or at least an arrested, condition. 
At present, therefore, I use a term which, I think, cannot be misunderstood, 
namely, quasi-Reptilian, as its use does not suggest the idea of the possessor of such 
a character being derived from a Reptilian stock. 
Using this precaution, I freely, from time to time, refer the reader to my published 
figures of the parts of the growing skull in Serpents, Lizards, Crocodiles, and Birds, 
because that, in some things, these highly specialized modern oviparous Amniota retain 
certain structural characters that are manifestly archaic, and that can be easily 
compared with their counterparts in the skull of the gill-bearing tribes. 
Out of the great number of parts that are in conformity with what is seen in 
the other Classes, especially in the Sauropsida, I have been anxious to eliminate 
and put into prominence, characters that are peculiar to, and diagnostic, of the 
Mammal. Some of these are as much so as the hair, and mammary glands, and are 
therefore of great interest to the Morpho|ogist. Yet the most striking and important 
of these have to be plucked out of the very fire of controversy, so that the survey of a 
wider and still wider field is urgently necessary ; that survey, fully made, will be the 
work of years. 
When speaking of these low forms—the Edentata—and asserting that they are 
archaic, or arrested, or abnormal, I am, of course, thinking of such normal forms as 
the Insectivora, and of the higher types that ascend above them—Lemurs, Carnivora, 
Ungulata, &c. Happily, everyone is familiar with the structure of the skull, in the 
adult, in these groups; and although these high forms have their own highest or 
culminating type—yet that which is highest in a Mammalian skull, as such, can be 
approximatively ascertained. 
Suppression, or even abortive and abnormal development of, the teeth is always 
attended with abnormal development of the extensive facial structures; these, it is 
evident, modify the outward form of the head much more than any difference that can 
arise in the form, or proportional size of the skull proper, so far as it is a mere box to 
contain the central nervous system. 
These remarks, it will be seen, have their bearing on the modifications to be seen in 
