472 MAMMALIAN ANATOMY 



anterior or malar part of its outer surface is a curved ridge, to which 

 the masseter muscle is attached. The inner surface is concave, and 

 gives attachment also to the masseter. 



Under the posterior root of the zygoma is the auditory bulla, in 

 the outer wall whereof is seen the large external auditory meatus, 

 across which is stretched the drum of the ear, or tympanic mem- 

 brane. Around the margin of the meatus is attached the cartilagi- 

 nous external ear. Behind the external auditory meatus is the 

 small stylo-mastoid foramen, and behind this, again, the mastoid 

 process, the outer surface of which faces also backward and appears 

 on the posterior aspect of the skull. Concealed by the tip of the 

 mastoid is the hyoid pit for the attachment of the tympano-hyal. 



The strong lambdoidal crest forms the posterior outline of the 

 lateral region, and is continued down the front of the mastoid. It 

 gives attachment to muscles which are directed anteriorly on the skull, 

 namely, the temporal, the occipito-frontal, and some of the small 

 auricular muscles, and to others which are directed backward to the 

 trunk, namely, the cephalo-humeral, the sterno-mastoid, the splenius, 

 and the trachelo-mastoid. 



On the side of the skull above the posterior end of the zygoma 

 is the arched squamous or temporo-parietal suture uniting the 

 squamous of the temporal and the parietal bone. It turns behind 

 upward and backward parallel with the lambdoidal crest as the parieto- 

 mastoid suture, ending at the asterion above. The front part of the 

 squamous suture is joined in the temporal fossa to the coronal suture 

 and the fronto-sphenoidal suture by a short longitudinal suture. As 

 this suture separates the parietal from the sphenoid, it is called the 

 spheno-parietal suture. The region marked by this H-shaped arrange- 

 ment of sutures is known as the pterion. 1 The region of the skull 

 behind the greatest lateral convexity, which is on a vertical line passing- 

 through the auditory meatus, becomes gradually concave from before 

 backward, but still remains slightly convex from above downward. 

 The temporal muscle covers almost the entire lateral wall of the 

 cranium, and is attached principally to the lambdoidal crest, along 

 the temporal ridge, and to a narrow strip of the surface lying above 

 the posterior root of the zygoma and curving upward and forward to 

 reach the frontal postorbital process. 



1 From (Gr.) pteron, a feather, a wing. 



