448 Ossification Centers in Human Embryos 
from an embryo 90 days old, the lachrymal is not over half as large as 
the nasal, and Schultze’s picture of an embryo of the 3d month does not 
show it at all. 
It appears then that the blunder of Béclard regarding the time the 
lachrymal begins to ossify, made nearly a century ago, has crept into the 
anatomies and has remained there unchallenged. 
OSSIFICATION OF THE RIBS AND VERTEBRZE. 
The ribs-—The ribs appear on the 55th day (202), no ossification 
centers being present in an embryo of 54 days. In the embryo in which 
they first appear they are not quite symmetrical on the two sides, the left 
side having two centers more than the right. On the right side the 6th 
rib is the largest, while on the left side it is the 7th, these two probably 
being the first to ossify in this embryo. They evidently make rapid prog- 
ress in their growth, for on the 56th day 10 ribs are present, giving a well 
proportioned thorax. On the 57th day the first rib makes its appearance, 
and it is not missing in any of the succeeding embryos. The first rib is 
then the 11th to appear and the 12th rib the last. Table III shows at a 
glance that the 12th rib is variable, not being present in all cases. Ac- 
cording to Bardeen,” this variation is very rare, being present but once 
in 46 embryos studied by Paterson, Rosenberg and himself. The 13th 
rib, which is not present in the specimens I have studied, seems to be 
quite common in those reported by Bardeen. In adult skele- 
tons, according to Bardeen, the absence of the 12th rib is about as com- 
mon as the presence of a 13th rib, being nearly 1% for each variation in 
908 skeletons studied. 
A cervical rib is present in two of my specimens, and were it not for a 
very accurate count, it would be easy to call the number of ribs in one 
of them (288, b) normal, and those in the other (300) as an embryo with 
ai13thrib. Of the 908 skeletons referred to above a cervical rib was found 
but twice (having been found by Topinard in 350 skeletons) being, there- 
fore, much rarer in the adult than in the embryos I have studied. How- 
ever, we have found it three times in about 250 subjects “ dissected in our 
dissecting room, without looking for it especially, and for this reason we 
do not know with certainty whether we found every cervical rib. The 
nucleus representing a cervical rib was noticed by Albinus nearly two cen- 
turies ago, and is spoken of by Meckel, Oken and Béclard as a rudiment 
of a cervical rib” I think it probable, therefore, that careful search will 
18 Bardeen, Anat. Anz., 25, 1904. 
“Brush, Johns Hopkins Hospital Bulletin, 1901. 
% Hildebrandt, Anatomie, II, 1830, p. 164. 
