THE TEMPORAL BONES 61 
forming the squamous suture. The ventral border joins the temporal wing of the 
sphenoid at the spheno-squamous suture. The anterior border unites with the 
frontal bone at the squamo-frontal suture, and the posterior with the occipital 
and petrous temporal bones. 
2. The petrous temporal bone (Os petrosum) is placed between the occipital 
Fic. 38.—Ricut Squamous TremporaL Bone oF NeEw-BoRN Foat; Laterat View. 
1, Zygomatic process; 2, glenoid cavity; 3, condyle; 4, postglenoid process; 5, notch; 6, posterior process; 7, 
temporal crest; 8, junction with parietal; 9, junction with frontal; 10, junction with supraorbital process; 11, junction 
with zygomatic process of malar; 12, junction with sphenoid; 13, junction with petro-mastoid: 14, junction with oc- 
cipital. 
behind and the parietal in front, and is largely overlapped by the squamous tem- 
poral. It has the form of a four-sided pyramid, the base of which is ventral. 
The lateral surface is mainly concealed by the squamous temporal, but two 
features are visible. A short tube of bone, the external acoustic process (Processus 
acusticus externus), protrudes from the lowest part through the notch of the squa- 
mous temporal. The process is directed outward, upward, and a little forward, 
Fic. 39.—Ricut Squamous TEMPORAL BoNE OF NEw-BORN Foat; Meprat View. 
F.c., Cerebral surface; 1, zygomatic process; 2, junction with parietal; 3, junction with temporal wing of sphenoid; 
4, posterior process (overlaps petro-mastoid). 
It gives attachment to the annular cartilage of the ear. Its lumen, the external 
acoustic meatus (Meatus acusticus externus), conducts to the cavity of the middle 
ear (tympanum) in the dry skull, but is separated from it by the tympanic mem- 
brane in the natural state. The mastoid process (Processus mastoideus) projects 
