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 foss@ (sf). 
On each side of the parietal and forming the 
posterior corners of the rectangular postero-dorsal 
region of the skull are the sguamosals (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- 
