The Skeleton 59 



bones will be described as seen from the different 

 aspects dorsal, ventral, lateral, posterior, and in 

 sagittal section without particular regard to their 

 grouping into segments or regions. 



The Dorsal Aspect (Fig. 19). At the extreme 

 posterior end of the median line lies the parietal 

 (23), double in the embryo but a single bone in 

 the adult. It forms a part of the roof of the cra- 

 nial cavity and articulates anteriorly with the 

 frontal, laterally with the postfrontals, squamosals, 

 and, according to Reynolds, with alisphenoids, 

 pro-otics and epiotics, and ventrally with the 

 supraoccipital. It forms the median boundary 

 of each of the two supratemporal fossce (sf). 



On each side of the parietal and forming the 

 posterior corners of the rectangular postero-dorsal 

 region of the skull are the squamosals (7). Each 

 squamosal articulates medially with the parietal, 

 anteriorly with the postfrontal, and ventrally with 

 the quadrate and exoccipital. It forms part of the 

 posterior and lateral boundaries of the supratem- 

 poral fossa and a part of the roof of the external 

 auditory meatus. 



Articulating with the anterior border of the 

 squamosals and forming the anterior corners of 

 the rectangular region mentioned above are the 

 postfrontals (6). The postfrontal articulates medi- 

 ally with the parietal and frontal, and ven- 

 trally with the alisphenoid and a small part of 

 the quadrate. It sends, in a ventro-lateral direc- 



