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of the foramen rotundum. It is not yet ossified, nor is the 'mem- 

 branous' external pterygoid plate ossified. It has been noticed that 

 ossification has already commenced in the internal pterygoid plate and 

 at the root of the hamular process. 



Figure 3 is taken from a section behind that shewn in Fig, 2. 

 Here the upper part of the internal pterygoid plate is shewn with an 

 ossific centre in it O.C. but this centre is of the 'membranous' type. 



Fig. 2. Coronal sections of 11 weeks embryo, behind Fig. 1. C. cartilage of 

 great wing at outer basal angle of ext. pteiygoid plate. I.N. infraorbital nerve. 

 M.G. Meckel's ganglion. B.N^. buccal nerve. E.P.P. external pterygoid plate. O.C. 

 ossific centre in internal pterygoid plate. P Periosteum at back of palate bone. 



E.T. represents the Eustachian tube: more of the cartilaginous great 

 wing is seen, but it is un ossified. 



Figure 4 is from a section of an early three months embryo. 

 The hamular process H.F. is now seen to have become in great 

 part cartilaginous and this cartilage very rapidly undergoes ossi- 

 fication, so soon in fact that, very little matrix is formed around 

 the cells — at the root of the hamular process 'membranous' ossi- 

 fication can be seen. P. is the palate bone. To the outer side of 



