154 



ON THE .STRUCTURE OF THE SKULL. 



the tympanic, is Kerckringius' ossicle, " vix aciculee majoris 

 caput adsequans." (Fig. 61, B, Op.O.) 



Fig. 61. 



F.R. 



tfk S f 



s. 



sc 



Ik 



dfi.o. 



Fig. 61. — Development of the temporal bono. 



A, from a foetus b\ inches long, showing the commencing pro-otic and opisthotic ossifica- 



tion. 



B, from a fetus 8| inches long. The ossification in the tegmen tympani is no longer visible 



from without, but its continuation backwards over the superior, and part of the 

 posterior, vertical semicircular canal is visible behind the squamosal. The epiotic ossifi- 

 cation has made its appearance, and the hinder extremity of the opisthotic ossification 

 appears behind the tympanic as the " third ossicle " of Kerckringius. 



C, from a foetus 10£ inches long, the " tria ossicula " beginning to unite into the pars 



mastoidea. 

 1), from a foetus 10^ inches long, the tria ossicula anchylosed. 

 /•'./.'., foramen rotundum. 



■, superior semicircular canal. 



