181] OSTEOLOGY OF LORICATI—GUTBERLET 11 



the lateral edge of the sknll. A foramen for a lateral line canal oceors 

 at the posterior end ; the whole surface being nune or lew performted. 

 The lateral surface of the pterotic is bounded eephalad by tiie spl^notie 

 and the prootic and ventrallj bv the prootie, exocdpital, and opisthotie. 

 At the anterior end of the bone there is a depression wfaidi fmns the 

 posterior edge of the dilatator fossa and immediately posterior and 

 slightly dorsal to the fossa is a facet for the articulation of the posterior 

 head of the hyomandibular. Posterior to the facet is a broad AaXUxm 

 groove, the dorsal edge forming the edge of the groove, extending to tlie 

 posterior end of the bone, where it narrows as does the bone itadf. 

 Ventro-caudad to the facet are two or three, more or less developed 

 ridges, extending from the lower edge of the facet to the ventro-poste- 

 rior edge of the bone where it unites by suture with the opisthotie. The 

 ventral edge of the bone curves sharply inward, thus forming a broad 

 rounded ridge between the facet and the point where it unites with the 

 prootic and the exoccipitaL The antero-ventral edge of the facet forms 

 a flange-like shelf beneath which there is a slight depiesBion forming, 

 together with a flange-like expansion of the prootie, a tooad gtoofve 

 extending from that point antero-ventrad on to the piootie. The inner 

 surface of the pterotic forms Hie dorso-posterior part of the lakenl wall 

 of the brain case, there being a large cavity passing latero-eaudad fron. 

 the main portion of the brain case, and lying ventro-mesad to the faeet 

 of the hyomandibular. This cavity harbors a part of the external soni- 

 circular canal. 



Epiotic. — The epiotics (Fig. 1, epo) form a part of the dorsal 

 surface of the cranium. The lateral snrfaee of each forms the mnrial 

 boundary of the temporal fossa ; its mesial edge forms the lateral border 

 of the supra-temporal pocket. The bone is bounded laterally by the 

 posterior process of the parietal and pterotic; ventraUy and postero- 

 ventrally by the exoccipital and mesiaUy by the supra-oeeipitaL It 

 forms a tall ridge extending postero-laterad as far caudad as the pterotie 

 and the opisthotie above the exoccipital, and neariy parallel to the 

 pterotic. The supra-scapular lies coi the dorsal surfaces at tiie eandal 

 ends of the epiotic and pterotic, thus forming a roof at the posterior 

 end of the temporal fossa. At the anterior end the bones are oveilai^ied 

 by the supra-occipital and the parietals. The internal sur&ee fomH 

 the dorso-caudal w^ of the brain case. These parts form postmociy 

 pockets for the posterior semicircular canals, directly above and in 

 connection with the exoccipitaL 



Parietal. — The parietals (Fig. 1, p) form a part of the 

 dorsal surface of the cranium, their lateral edges forming the mesial 

 borders of the temporal fossa. Each is somewhat irregular in shape 

 with its broadened end cephalad and a long slender proeess, extending 



