SKULL — ^OSSIFICATION 



75 



mentioned of the cranial membrane bones are a pair of septomaxil- 

 laries (fig. 77) which he in the floor of the nasal cavities. Their 

 relations are very uncertain. They occur in all living groups of 

 Amphibia, in Sphenodon and many Theromorphs and lizards, and have 

 been found in at least one genus {Tatusia) of mammals. 



Fig. 77. — Nasal region of {A) 47 mm. Lacerta agilis (Gaupp, '10) and {B) Ranodon 

 olytnpicus (Noble, '21). Cartilage stippled. /, frontal; I, lacrimal; Id, groove for lacri- 

 mal duct; m, maxilla; p, pnt, prema.xilla; pf, prefrontal; sm, septomaxillary ; v, vomer. 

 (Gaupp's interpretations modified.) 



The whole dorsal side of the primitive cranium, as shown by many 

 fishes, Stegocephals (fig. 76) and many Theromorphs (Cotylosaurs, 

 fig. 78) is covered by bone, the only gaps, aside from the parietal 



Fig. 78. — Cranium of Prucolophon (Seeley,''88) ;/, frontal; /, lacrimal; m*, ma.xilla; 

 n, nasal; p, parietal; pf, prefrontal; po, postorbital; pof, postfrontal; qj, quadratojugal; 

 sq, squamosal; st, supratemporal; z, zygomatic. 



foramen, being the nares and orbits (stegocrotaphic skull). In 

 other groups there are usually gaps (fossae) between certain of the 

 bones. Occasionally some of these lie in front of the orbits (antorbital 

 vacuities) and are of little morphological importance. Those behind 

 the orbits are separated from each other and from the margin of the 

 cranium by bars (arcades) of bone. At most there are three of these 



