112 THE SKULL [chai-. 



cavity, the former to pass through the bone, escaping by tlie 

 stylomastoid foramen on the outer and under surface, the 

 latter to be distributed on the sensitive portions of the 

 organ of hearing ; and that it has on its outer side two 

 holes, one placed above the other, the fenestra ovalis and 

 the fenestra rotunda, through which the internal ear com- 

 municates with the cavity of the tympanum, or middle-ear, 

 which is situated on the outer side of the petrous part of 

 the periotic bone. 



Externally to the periotic bone are placed two bones 

 separately developed in fibrous tissue, which often acquire a 

 very close connection with the periotic, occasionally, as in 

 Man, becoming firmly ankylosed with it. 



The upper one of these is the squamosal (Fig. 47, Sq), 

 which has a broad, scale like, vertical portion spreading out 

 over the side of the cranial wall, uniting with the supra- 

 occipital behind, overlapping the lower edge of the parietal 

 and the hinder part of the alisphenoid, and also appearing 

 for a very small space in the inner side of the cranial wall. 

 From near its lower border it sends a strong process out- 

 wards, which soon curves forwards, called the zygomatic 

 process. This articulates with another bone {Ma), the malar 

 or jugal, which connects it with the maxilla, and so forms 

 the strong, lateral, nearly horizontal, or slightly arched 

 osseous bridge, which passes from the face to the hinder 

 part of the cranium, called the zygomatic arch. On the 

 under surface of the base of the zygomatic process of the 

 squamosal is a laterally extended, oblong surface, concave 

 from before backwards, for the articulation of the condyle 

 o^ the lower jaw, called the glenoid fossa (gf), the hinder 

 edge of which is projected into the postglenoid process (gp). 



The lower bone, on the outer side of the periotic, is 

 the tympanic {Ty). At birth this is a mere osseous ring, 



