100 



ELEMENTAR Y 



[LESS. 



Generally, as in man, the two parietals meet, but, as has 

 been said in treating of the occipital, they may be encroached 

 upon, and depressed to the side of the skull (as in the Cetacea), 

 by the union of the last-named bone with the frontal. 



The great size of the parietals of man is very exceptional, 

 and has direct relation to the immense development of his 

 brain. On the other hand, they may be in great part mere 

 bars, as in many Lizards. 



The parietal may give off a lamellar expansion helping to 

 roof over the temporal fossa as in the Turtle and the curious 

 African Rodent Lophiomys. 



The exclusion of the parietal from any junction with the 

 sphenoid by that of the frontal bone with the temporal, which 

 occasionally occurs in man, is very common in Apes. On 

 the contrary, it may extend to join not only the greater but 

 also the less, or orbital, wing of the sphenoid. 



The parietal may be one with the frontal, forming a fronto- 

 parietal bone, as in the Frog and Lepidosiren, 



FIG 97.- UPPER SURFACE OF THE SKULL OF A FROG. {After Parker.} 



c, os en ceinture, or girdle-bone ; eo, exoccipital ; /", frontal part of fronto- 

 parietal bone ; mx, maxillary bone ; n, nasal ; op, opisthotic ; p, parietal 

 part of fronto-parietal bone ; fn, pre-maxilla ; po, pro-otic ; pi, pterygoid ; 

 .7, quadrato-jugal ; ^7, squamosal ; sus, suspensorium of lower jaw. 



From within the parietal an ossified falx may extend into 

 the cranial cavity, as in the Ornithorhynchus, while the junc- 

 tion of the parietals may be extended upwards into a large 

 sagittal crest, as in many Carnivora, and even in the 

 Gorilla. 



