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After the premaxillary bone joins the maxilla it is in general cubical 
in shape, measuring on a side 3 mm. on the 65th day; 44 mm. on the 75th 
day (288, b) ; and 6 mm. on the 85th day (300). 
It is said by Rambaud & Renault that the primary ossification centers 
unite during the third month. 'Toldt states that they appear at the end 
of the second month and unite at the end of the fourth month. If Toldt’s 
statement is correct the primary centers should be present in practically 
all of the embryos given in Table II. 'Toldt is a very reliable observer, 
and in order to verify his statement I tested the maxille in all of my 
embryos by squeezing them between two needles, but at no time could I 
demonstrate, more than one center, exclusive of the premaxillary. The 
75 75 
Op 56 A*) 
Fic. 3. Diagram of the ossification of the occipital bone. The figures upon 
or between the centers indicate the time in days in which they appear or 
unite. 
bone was dissected out in embryo 288, b, and was found to be a single 
bone, and was broken with difficulty when handled with two needles in 
glycerine. The opinion | have reached regarding the ossification of the 
maxilla is fully confirmed by Ziegler’s copy of Hertwig’s model of the 
skull of an embryo 8 em. long, and by Schultze’s illustration of the bones 
of the skull of an embryo of the third month. 
Occipital bone.—According to the embryos I have studied, the occipital 
bone arises from nine primary centers, two less than described by Meckel. 
On the 55th day (202) two cartilages which are thin and transparent, 
and may be ossified, are seen just above the foramen magnum. A little 
later these cartilages are fully ossified, are beginning to unite across the 
