'0 



BONES OF THE HEAD. 



to be seen, and the styloid process cartilaginous. After bu-th the external' 

 auditory meatus is gradually foiined, superiorly by the arching outwards of the 

 united squamous and peti'o-mastoid portions, and inferiorly and laterally by the 

 development of the tymjnjnic jtlatc, a lamina developed from the outer surface of 

 the tympanic ring, and which becomes united behind with the petro-mastoid, but 

 is separated in front by the fissui-e of Glaser from the squamosal. The mastoid 

 process is developed about the second year, but au--cells are not formed till near 

 puberty. About puberty also ossification begins in the styloid process, but osseous 

 rmion with the temporal only takes place in adult life. 



The sphenoid bone presents in infancy traces of a natui-al division into a 

 posterior ov j>o.-<t.^jjfunoid part, to which the sella turcica and gi-eat -n-ings belong, 

 and an anterior or 2J''<'''<jf^tctiot(l part, to which belong the body m front of the 

 olivary process and the small wings, — a division which is found in many animals 

 complete and persistent through life. The first osseous nuclei of the postsphe- 

 noid division appear about the eighth week in the great wings, one on each side, 

 between the foramen rotundum and foramen ovale, and spread thence outwards 

 into the wing and do\\Tiwards into the external pterygoid jjrocess. About the 

 same time also two granules appear in the postsphenoid jjart of the body, placed 

 side by side in the sella turcica ; these unite about the fourth month, and after 

 their union two others appear, from which are fonned the lingulaj, inside wliich 

 are placed the carotid grooves. The internal pteiygoid processes, corresponding- 

 to the pterygoid bones of animals, are ossified from distinct nuclei, which appear 

 in the fourth month ; they unite with the external pterygoid processes in the 

 fifth or sixth month. 



Fis. 60. 



^pm^^' 



Fig. 60. — Ossification of the Sphenoid Bone (R. Quain). 



A, sphenoid bone from a foetiis of three months, seen from above ; 1, 1', the greater 

 wings ossified ; 2, 2', the lesser wings, in which the ossification has encircled the optic 

 foramen, and a small suture is distinguishable at its posterior and inner side ; 3, two 

 round gi-anules of bones in the body below the sella turcica, the rest being cai-tilaginous. 



B, copied fi-om llcckel (Archiv, vol. i. tab. vi. fig. 23), and stated to be from a fretus 

 of six months ; 2*, additional nuclei for the lesser Avings ; 5, separate lateral processes 

 of the body : the otlier indications are the same as in A. 



C, sketch of the back part of the bone shoAvn in A ; 4, the internal pterygoid processes 

 still separate. 



D, the sphenoid at the iisual period of birth. The great -wnngs are still separate. The 

 anterior sphenoid is now joined to the body, and the internal pterj'goid jarocesses (not 

 seen in the figure) are united to the external. 



The great wings are united to the lx)dy in the first year. In the presphenold 

 division the first pair of nuclei appear in the eighth or ninth week outside the 

 optic foramina, and extend by their gi-owth into the small -n-ings : another pair 

 of granules appear on the inner sides of the foramina, and the presphenoid por- 



