5. The vestigial form of M3 is frequent in the upper and rare in the lower. The lower M3 disappears suddenly without intermediate steps.

6. There are no clear differences in the reduction phenomena, as shown bt the diminution of cusp number in the tooth crown and fusion of the tooth root between the upper and lower M3s.

7. The atavistic increase in tooth roots appears considerably more in iht: triple division of the upper premolars than in the double division of the lower.

8. A fourth molar and supernumerary incisors are more frequent, in thtb upper jaw.

9. Irregularities of the teeth are more frequent in the lower than in the upper.

The author holds t,hat, due to the increased degree in reductions of the lowet teeth, the lower dental arch is shortened and shifted posteriorly, bringing about the overbite (Scherenbiss) from the form of edge-to-edge bite (Zangenbiw). (The question is whether this is true. The primitive bite relation in t,he early forms, as pointed out by Gregory, is one in which the upper teeth overhang the lower. Moreover, in the course of individual development in man the edge-to- edge relation develops with age. Although both forms are to be found in all races and at all ages, the overbite is more frequent in early stages of develop- ment than later in life. This is repeated twice in life, in the deciduous and in the permanent dentitions. As each reaches maturity, the frequency of edge-to- edge becomes predominant over the overbite.)

The conclusion drawn by the author is that “The reduction of the dentition has gone a step forward in the civilized races, introducing a difference between the upper and lower jaws, wherein the lower has shortened more than the upper. ” If measured by the forms of occlusion of the entire dentition and not by the bite relationship of the incisors alone, it is very questionable whether a sweeping con- clusion of this sort will find much support.

Hi10 We7lnurn.

Anat- for Dental Studeats. By Six Teachers (W. Wright, T. Yeates, ,J. M. B. Stopford, S. E. Whitnall, Mary F. Lucas Keenc), edited by E. P. St&be, Baltimore, 1934, William Wood & Co.

This book is intended to give the dental student, a thorough knowledge of general anatomy, and it is also intended to serve as a reference book for the dentist.

The first part, the systematic anatomy, covers practically all the topics of a medical anatomy book but places special emphasis on those regions. which are of .immediat,e concern to the dentist. The bones of the skull, for instance, are de- scribed in 31 pages, while only one page is devoted to the bones of the limbs.

Besides the chapter on bones, the systematic part covers the joints (with special emphasis on the temporomandibular articulation) ; the muscles (mastiea- tion, deglutition, respiration) ; the circulatory system (arteries of head and neck, lymphatic system of head and neck) ; the ccnt,ral nervous system; and the ab- dominal viscera.

Two general chapters, one dealing with histology and the other wit.11 em- bryology, close the first part of: the volume. Like the preceding ~haptcrs, t IICJ discuss only medical topics and not the specific dental structures.

The second part of the book gives, with the aid OC numerous illustrations. detailed instructions for the dissection of the various rrgions.

E. N.