52 THE CRANIUM AND FACE. 



diseases and the mastoid bone has to be cut to let out pus 

 that has collected. As the lateral sinus is directly behind 

 the mastoid bone, there is very great danger of going 

 through into the sinus and causing a fatal hemorrhage. 



The petrous portion, which contains the organ of hear- 

 ing, is between and somewhat behind the other two por- 

 tions, at the lower edge of the temporal bone, wedged 

 between the sphenoid and the occipital bones. On its 

 outer surface is the external auditory meatus, and from 



Vlrtlf 



FIG. 17. Side view of the skull. (After Sobotta.) 



below projects a long sharp spine called the styloid pro- 

 cess, to which several minor muscles are attached. In 

 the same angle between the petrous and squamous por- 

 tions lies the bony Eustachian tube. 



The sphenoid or wedge bone, so called because in the 

 process of development it serves as a wedge, lies at the 

 base of the cranium, forming as it were the anterior part 

 of the floor of the cavity containing the brain. It is a 



