i8o 



HUMAN ANATOMY. 



millimetres thick in early childhood, and from the antrum or upper mastoid cells by 

 a very thin one in adult life.^ Behind the groove a small, smooth surface forms a 

 part of the cerebellar fossa. 



Fig. 199. 

 A B 



Carotid canal 



Tympanic cavity 

 Jugular fossa 



Facial canal 



External auditory 

 meatus 



Groove for lateral sinus 



Tympanic cavity 



Facial canal 



External auditory 

 meatus 



Groove for lateral 



sinus 



Mastoid canal 



Horizontal sections through a right temporal bone with slight development of the mastoid cells. A, just above the 

 floor' of the external auditory meatus ; S, near the roof of the same canal. ^ 



Fig. 200. 

 A 



Tympanic 

 cavity 



External 

 auditory 

 meatus 



Facial 

 canal 



Groove for 

 lateral 

 sinus 



Facial canal 



External 

 auditory 

 meatus 



■Groove for 

 lateral 

 sinus 



Similar sections of a right temporal bone with considerable development of the mastoid cells and consequent 



removal of the lateral sinus from the surface. 



A small canal, the mastoid foramen,^ transmitting a vein, runs from the sinus to 

 the outside of the bone, which it sometimes reaches as far back as the suture between 

 * Clarke : Journal of Anatomy and Physiology, vol. xxvii, 1893. 



-Foramen mastoideum. 



