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I.P.M. passing downwards to insertion into the lower jaw L.J,, above 

 and to the outer side of this muscle, can be seen a wedge-shaped 

 cellular mass E.P.P., the external pterygoid plate; this is unossified 

 and: from its outer side springs the external pterygoid muscle EP.M. 

 Above the hamular process can be seen the palate bone P. surrounded 

 by its periosteum. 



P.S. and O.S. represent the back part of the ethmoid and the 



Fig. 1. Coronal section of liead of an 11 weeks embryo. E.P.3I. extei-nal pterj^- 

 goid muscle. E.P.P. external pterygoid plate (membranous). 1.P.3I. internal pterygoid 

 muscle. I.P.P. internal pterygoid plate (membranous). H.P. hamular process (mem- 

 branous). M.G. Meckel's ganglion. P. palate bone. L.J. lower jaw. T.P. tensor 

 palati muscle. T. tonsil. P.S. presplienoid or ethmoid (cartilaginous). O.S. orbito- 

 sphenoid (cartilaginous). IX. glossopharyngeal nerve. 



orbito - sphenoid respectively, they are cartilaginous and unossified. 

 It will be noticed that the two halves of the palate are still unfused. 

 Figure 2 is from a section taken somewhat behind that which 

 Fig. 1 represents. It is from the same embryo. Where the hamular 

 process joins the internal pterygoid plate a centre of ossification is 

 seen. This is membranous (ectochondral) ossification O.C. In the 

 external pterygoid plate E.P.P. at the outer basal angle can be seen 

 cartilage. This is the cartilage of the great wing in the neighbourhood 



