52 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 55. — The right temporal bone seen from the outer (lateral) surface (\). 

 Fig. 56. — The right temporal bone seen from the cerebral surface (|). 



Each temporal bone consists of four portions: (1) A squamous portion; (2) a petrous por- 

 tion; (3) a mastoid portion; (4) a tympanic portion. The petrous portion is also termed the 

 pyramid. 



The squamous and mastoid portions are placed almost vertically, while the pyramid is 

 practically horizontal. At the external auditory meatus, the individual portions of the temporal 

 bone are grouped in such a manner that the smallest portion, the tympanic portion, is situated 

 in front of and below the auditory canal, the mastoid portion is behind, the squamous portion 

 above, and the petrous portion internally and anteriorly. 



THE SQUAMOUS PORTION. 



The squamous portion of the temporal bone (Figs. 55, 56, and 57) consists of an approxi- 

 mately semicircular vertical bony plate which is concave internally and convex externally. An- 

 teriorly it articulates (Figs. 39 and 40) with the temporal surface of the greater wing of the sphenoid 

 by the sphenosquamosal suture (sphenoidal border), and superiorly with the parietal bone by 

 means of the squamosal suture (parietal border, see page 38). A deep notch, the parietal notch, 

 accommodates the sphenoidal angle of the parietal bone and separates the squamous portion 

 from the mastoid portion, which is situated inferiorly and posteriorly. 



The zygomatic process (Fig. '55) springs from the external surface of the squamous portion 

 of the temporal bone and aids in the formation of the zygomatic arch, by articulating with the 

 temporal process of the zygomatic bone by means of the zygomaticotemporal suture. It is almost 

 horizontal at its origin, but later it rotates through about 90 degrees, so that it assumes a vertical 

 position and forms a bony process flattened from side to side. Its posterior prolongation above 

 the external auditory meatus forms a supramastoid ridge, which posteriorly becomes continuous 

 with the terminal portion of the inferior temporal line (see Fig. 39). 



The part of the squamous portion which lies below the zygoma forms part of the external 

 surface of the base of the skull and is consequently almost horizontally placed (Fig. 58), and 

 borders upon the infratemporal surface of the greater wing of the sphenoid bone. It is there- 

 fore advantageous to subdivide the squamous portion of the temporal bone into a larger vertical 

 portion and a smaller horizontal portion. 



In the vertical portion there may be recognized an external temporal surface and an internal 

 cerebral surface (the latter is absent in the horizontal portion). The temporal surface forms 

 a part of the planum temporale and of the jossa temporalis (see Fig. 39), and is usually smooth, 

 though its lower portion may sometimes be roughened by the origin of the temporal muscle. 

 It presents a shallow groove for the middle temporal artery, beginning above the external audi- 

 tory meatus and running upward. 



At the junction of the horizontal and vertical parts is situated the roof of the external auditory 

 meatus, the remaining walls of the auditory canal being formed by the tympanic portion, and 

 just above the external auditory meatus, at the transition into the mastoid portion, there is 

 frequently found a small bony spine, the suprameatal spine (Fig. 55). 



