THE TEMPORAL BONE. 



183 



the occipital bone, and is separated posteriorly from the occipital by the jugular 

 forajneyi. A little spine on the edge of the thimble-shaped fossa, or on the plane 

 surface that may take its place, the intrajiigular process, joins the corresponding 

 process of the occipital either directly or by. ligament, so as to divide the foramen 

 into two parts, the posterior for the vein, the anterior for nerves. In front of the 

 foramen a small groove on the cerebral edge of this border marks the position of the 

 inferior petrosal sinus. 



The superior and the inferior external borders are concealed by the other 

 elements of the temporal, except near the front, where they bound the surface which 

 touches the sphenoid. 



The apex of the petrous is mostly occupied by the opening of the carotid canal. 



The styloid process is a part of the hyoid bar (from the second branchial 

 arch), which joins the temporal under cover of the vaginal process. It is thick at its 

 origin, but presently becomes thinner and ends in a sharp point. It is usually about 

 an inch long, but varies greatly. It runs downward, forward, and inward, and is con- 

 tinued as the stylo-hyoid ligament to the lesser horn of the hyoid. Three muscles, 

 the stylo-glossus, stylo-hyoid, and stylo-pharyngeus, diverge from it to the tongue, 

 the hyoid bone, and the pharynx. An ill-defined process of the cervical fascia, the 

 stylo-maxillary ligament, passes from it to the back of the ramus of the lower jaw. 



Canal for tensor tympani 



Carotid canal 

 (anterior end) 



CAVITIES AND PASSAGES WITHIN THE TEMPORAL BONE. 



The Cavity of the Tympanum.^ — The tympanic cavity is a narrow cleft 

 about five millimetres broad at the top, narrowing to a mere line below. It measures 

 about fifteen millimetres 



vertically and from be- Fig. 204. 



fore backward. It is 

 bounded internally by 

 the petrous ; above by 

 a projection from it, the 

 tegmen tympani ; below 

 by the jugular fossa, or, 

 if this be very small, by 

 the bone external to it ; 

 externally by the tym- 

 panic portion of the 

 bone and the membrane, 

 except at the top, where 

 the squamosal is ex- 

 ternal to it. The part 

 above the level of the 

 membrane is the stipra- 

 tyfupanic space ^ th^ attic, 

 or the epitympaman. 

 This is separated from 

 the cranial cavity by a 

 very thin plate, which 



is sometimes imperfect. In front, the cavity of the tympanum narrows to the Eusta- 

 chian tube. It opens behind through the antrum, which serves as a vestibule, into 

 the mastoid cells. The antrum is a cavity of irregular size and shape, compressed 

 somewhat from side to side, with an antero-posterior diameter of from ten to fifteen 

 millimetres, situated behind the epitympanum in the backward projection of the 

 squamosal, which forms the superficial part of what appears to be the mastoid, and 

 contains some of the so-called m.astoid cells. The communication with the tympanum 

 is a narrow one, and a certain number of cells open into the latter independently. 



The antrum and the cells nearest it are lined with mucous membrane continued 

 from the middle ear. The inside of the mastoid varies greatly. Sometimes it con- 



^ The detailed description of this space is given in connection with the ear. 



Mastoid 

 cells 



Carotid canal (inferior end) 



Sagittal section through right temporal bone, seen from outer side. 



