394 THE VERTEBRATE SKELETON. 



The squamosal (fig. 73, 7) is a large bone occupying much 

 of the side wall of the cranial cavity, and articulating above 

 with the parietal, and behind with the supra-occipital, while 

 in front it overlaps the frontal and alisphenoid. But though it 

 occupies so large a space on the outer wall, it forms very 

 little of the internal wall of the skull, but is really like a bony 

 plate attached to the outer surface of the cranial wall. The 

 squamosal is drawn out into a strong forward ly-directed zygo- 

 matic process which meets the jugal or malar. The ventral 

 side of the zygomatic process is hollowed out, forming the 

 glenoid fossa (fig. 75, 8), a smooth laterally elongated surface 

 with which the lower jaw articulates, while the hinder edge of 

 the glenoid fossa is drawn out into a rounded postglenoid 

 process (fig. 75, 23). The articulation is such as to allow 

 but little lateral play of the lower jaw. 



(2) Bones in relation to the Optic capsules. 



The only bone developed in relation to the optic capsule 

 on each side is the lachrymal. This is a small membrane 

 bone lying between the frontal and palatine behind, and the 

 maxilla and jugal in front. It is perforated by a prominent 

 lachrymal foramen (fig. 73, 13) which opens within the 

 orbit. 



(3) Bones in relation to the Olfactory capsules. 



In connection with the olfactory capsules, five pairs of 

 bones are developed, two pairs being membrane bones, and 

 three pairs cartilage bones. 



Of membrane bones, the nasals (fig. 73, 4) are a pair of 

 long narrow bones, lying closely side by side, and forming 

 the main part of the roof of the olfactory chamber. Their 

 posterior ends overlap the froritals, and the outer margin of 

 each is in contact with the nasal process of the frontal, and 

 with the maxilla and premaxilla. 



Lying immediately ventral to the nasals, and on each 

 side of the perpendicular mesethmoid, are the ethmoid or 



