285 



gold plate I. P.P. can be seen to become continuous with the cartilage 



bone in the hamular process E.C. T.P. represents the tensor palati 



muscle, LP. represents the internal pterygoid and outside it, is the 



'membranous' external 



pterygoid plate which / 



is undergoing direct os- /^ 



sification E.P.P. The 



great wing G. W. is shewn 



dorsal to this and on its V, ,, EP. ERP 



outer side can be seen 



Fig. 5. Oblique section 

 of head of a 3 months fetus 

 a little older than that re- 

 presented in Fig. 4. E.P. ex- 

 ternal pterygoid muscle. E.P.P. 

 external pterygoid plate with 

 'membrane' bone in it. I. P.P. 

 internal pterygoid plate with 

 'membrane' bone 31. C. in plate 

 itself, and cartilage bone E.C. 

 in hamular process. I. P. in- 

 ternal pterygoid muscle. T.P. 

 tensor palati muscle. 



membranous ossification which forms at least, the pterygoid crest and 

 possibly, the inferior border of the orbital surface of the great wing. 

 E.P. is the external pterygoid muscle. 



General Conclusions. 



From what has been seen in the various illustrations it is evident 

 that the internal pterygoid plate is the first part of the sphenoid to 

 become ossified. That being so it behaves as it ought to do if con- 

 forming with Hertwig's statement as to its being a "covering" bone. 

 This centre appears probably somewhere about the 9th or 10th week 

 — at about the time the endochondral centre appears in Meckel's 

 cartilage. There is no evidence to shew that this plate appears in 

 cartilage as stated by Sutton and it is certainly ossified before the 

 Eustachian tube has become cartilaginous. 



The hamular process undergoes chondrification before ossification, 

 the cartilage appearing during the 3rd month and almost at once 

 undergoing ossification. This cartilage resembles that, which at the 

 same time appears in the condyle, neck and base, of the coronoid 

 process of the lower jaw. 



The external pterygoid plate is ossified in membrane, as can be seen 

 during the early part of the 3rd month. 



It is ossified at the same time, as the cartilage of the great wing, 



