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 placetl between the occipital 



Fig. 38. — Right Squamous Temporal Bone op New-bohn Foal; Lateral 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; Injunction 

 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. 



Fig. 39. — Right Squamous Temporal Bone of New-born Foal; Medial 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 

 ventrally in the interval between the posterior process of the squamous temporal 



