18&5.] 



OF THE HUMAN SPHENOID BONE. 



581 



The details of the ossification of the presphenoid, or that portion 

 in relation with the optic nerves, may be summarized as follows : — 



Fig. 



P.S, 



L.S 



O.F. 



F. F. 



A series of figures to show the disposition of the various nuclei of the human 



sphenoid bone. 



The upper figure shows the relation of the centres to the cartilage ; the 



latter in all cases is represented by dots. 

 In the middle figure the basisphenoidal nuclei haye coalesced, the orbito- 



sphenoids have joined the presphenoids, and the internal pterygoids 



have joined the alisphenoids. 

 In the lowest figure the sphenoid bone is represented as at the eighth 



month of foetal life. 



^..S, Alisphenoid ; 2?.S, basisphenoid; i, lingulse; J?', pterygoids ; 0.5, orbito- 

 sphenoids ; P.S, presphenoid ; O.F, optic foramen ; F.li, foramen rotun- 

 duui ; F. 0, ibramen ovale ; C, cranio-pharyngeal canal. 

 The dorsum sellaj at this date is cartilaginous, and therefore it is not repre- 

 sented in the f gurcs. The foramen ovale, until souje time after birth, is ouly 

 a notch in the alisphenoid, 



Ossific matter is deposited immediately external to the optic foramen, 

 and extends rapidly outwards to form the orbitosphenoid. This 

 occurs about the commencement of the third month. 

 Proc. Zool. Soc— 1885, No. XXXVIII. 38 



