ON OSSIFICATION CENTERS IN HUMAN EMBRYOS LESS 
THAN ONE HUNDRED DAYS OLD. 
BY 
FRANKLIN P. MALL. 
(From the Anatomical Laboratory of the Johns Hopkins University.) 
WITH 6 TEXT FIGURES AND 7 TABLES. 
As the study of the bones preceded that of the other structure of the 
human body, so their ossification was the first subject investigated in em- 
bryology. The early anatomists became interested in the development of 
bones on account of the difference between them in adults and children, 
and it was but a step to their study, first in the fcetus and then in the 
embryo. 
More than one hundred years ago the early ossifications were studied 
with vigor and in a short time the subject was closed, and we may say that 
our present knowledge dates mostly from before 1820. With the improve- 
ment in embryological methods so many new fields were opened that it 
did not seem worth while to destroy good specimens nor to make laborious 
reconstructions to study a subject which seemed so unpromising in re- 
sults. However, it is apparent that there is considerable difference of 
opinion regarding the time of ossification as well as the number of centers 
in certain bones, which frequently diminish as they are studied more 
carefully. 
We notice in looking over the older literature that the ossification was 
studied by means of ordinary dissection after which the very small spect- 
mens were dried upon a glass slide. Such specimens show sharply marked 
bone centers, and are very useful, but unfortunately the embryos 
are pretty well destroyed in their preparation. Furthermore, very small 
centers and delicate attachments are difficult to see, and this defect in the 
specimens has led to numerous erroneous conclusions. The time of ossi- 
fication and the order of the appearance of the centers has never been 
definitely settled, mainly because the specimens were not numerous and 
were much injured in their study, and because the various investigators 
did not determine correctly the age of the embryos. Thus, for instance, 
we read in Béclard’s article that the centers for the mandible, maxilla, 
clavicle, humerus, ulna, radius, femur and tibia are present in an embryo 
35 days old (16 lines long) which, according to my table, must be 
54 days old. Numerous other embryos are studied in this article, each 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
