268 
JOUKNAL OF MAMMAiOGY 
Gregory, William K. The Origin and Evolution of the Human Dentition. 
Baltimore: Williams & Wilkins Co., pp. i-xviii, 1-548, including plates. 1922. 
The Origin and Evolution of the Human Dentition is primarily a review covering 
a wide field of research, carried over a number of years, both by the author and 
other authorities. It therefore constitutes an authoritative and comprehensive 
treatise in which the author has brought together and presented in a masterful 
way a vast fund of highly important and valuable information. Incidentally, 
many important controversial questions have been discussed. The author 
doubtless will not be followed by some in all his deductions and conclusions re- 
garding these questions, yet it cannot be denied that they have been frankly and 
fairly argued . Doctor Gregory has presented both sides of all controversial points 
in his usual fair-minded manner, and has handled the facts in a way to inspire the 
confidence of the reader in his ability to observe clearly and to interpret intelli- 
gently. Regardless, therefore, of what may be the verdict of other authorities 
in accepting or rejecting some of the theories defended by its author, this book 
must stand as a most valuable and convenient reference work on the subjects 
treated therein. 
The book is splendidly illustrated with 353, for the most part, accurately exe- 
cuted line drawings and half-tone figures. Although most of these have appeared 
in various earlier publications, either of the same author or those of others, their 
reproduction here adds immeasurably to the value of the work. 
Lack of space does not admit a complete or even adequate partial review of 
this important work, hence little more is attempted here than to give a very 
general outline of the subject matter contained in it. 
The book, which contains more than 500 pages, consists of five major parts 
which were first published in five successive numbers of the Journal of Dental 
Research, to which have been added an important preface and several corrections 
of errors which crept into the original publications. 
Part I deals principally with the earliest stages in the development of teeth in 
the vertebrates and with the principal steps in evolution leading up to the early 
mammalian types of dentition. It includes an exhaustive review of the general 
theory of tooth-cusp development in the mammals, in which the author upholds 
in part the Cope-Osborn trituberculy theory, and accepts in general but not in its 
entirety the “premolar-analogy” theory as defended by Wortman and Gidley. 
In this connection he has introduced a hypothesis of his own, which is mentioned 
here only because of the very vital bearing it has on a very fundamentally impor- 
tant deduction postulated by the author in its assumption, namely, that the type 
of upper molar in which the paracone and metacone are fused, or but slightly 
separated, and set well inward from the buccal side of the tooth crown (such as 
Centetes, Potamogale, Solenodon, etc.) is nearest to the basic type of dentition 
from which have been derived all the more modern forms of tooth structure of the 
placentals and marsupials. This is based on an assumption denied by Gidley 
(1906) that the main internal cusp in the upper molars of such forms as Dryolestes 
of the Upper Jurassic is not homologous with the corresponding cusp in modern 
mammals, but that it represents the primitive reptilian cone, which, through 
the inward building of a cingulum cusp (the “protocone”) finally became the 
paracone-metacone of modern mammals. There is not space to discuss this im- 
portant question here, but it may be stated on the authority of the present re- 
