Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/58

 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.

—Side view of the skull. (After Sobotta.)

The petrous portion, which contains the organ of hearing, is between and somewhat behind the other two portions, 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 below projects a long sharp spine called the styloid process, to which several minor muscles are attached. In the same angle between the petrous and squamous portions 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