Franklin P. Mall 444 
smaller than before, but after this they grow in size, and on the 105th 
day they are united. The alisphenoid grows rapidly, is 8 mm. long on 
the 73d day, and reaches out towards the frontal and temporal on the 
105th day. By the same time the orbitosphenoid is hook-shaped, encircles 
the optic foramen and measures 5 x 4 millimeters. 
Palate bone.—On the 57th day both horizontal and vertical parts of 
the palate bone may be seen. ‘They are very thin, are united, and each 
part measures a square millimeter in area, Next day the horizontal part is 
larger than the vertical and from now on they grow gradually, the parts 
remaining of equal size. On the 58th day the area of each part is 4 square 
millimeters; on the 90th day 6 square millimeters, and on the 105th day 
9 square millimeters 
Vomer.—The vomer is present in embryo No. 266 as a delicate double 
bone measuring about 2 mm. in length; in 263, b, 1, it is a little shorter. 
On the 58th day the two centers are 3 mm. long, and on the 65th day 
they are no longer, but are united at a single point near their anterior 
end. The union spreads rapidly throughout the length of the bone, and 
on the 73d day it appears as a single groove-like bone 4 mm. long. On 
the 83d day it is 6 mm. long; on the 90th day 2 mm. high and 7 mm. 
long; and on the 105th day it is 10 mm. long. 
Nasal bone-—The nasal bone also begins on the first day of the third 
month, although Toldt states that it ossifies during the 12th week. It 
can barely be seen on the 57th day, and is well marked on the 65th day, 
measuring at this time one square millimeter in area. It grows slowly, 
being but 1.5 mm. square on the 83d day and but 2 mm. on the 105th day. 
Lachrymal bone.—The lachrymal bone is the last of the bones of the 
head to appear during the first 100 days of embryonic life. Gaupp states 
that it appears at the end of the second month and Quain states that it 
appears during the 8th week. Cunningham and Gray make similar state- 
ments. Béclard, who always places the time of ossification too early, 
states that the lachrymal appears on the 55th day, and Meckel, who is a 
much more competent observer, states that it does not ossify until the 
5th or 6th month. I find it present in an embryo of the 83d day, and 
not before, as a narrow and very thin bone nearly 2 mm. long. In all 
the specimens studied the eyes were removed in order to bring the region 
of the lachrymal well into view and these specimens were studied with 
the greatest care under the enlarging glass in direct sunlight. In an em- 
bryo 85 days old the bone is much smaller, and in an embryo of the 90th 
and one of the 105th day, it is again about 2 mm. long and a little more 
opaque than before. In the model from Hertwig’s laboratory, which is 
