181] OSTEOLOGY OF LORICATI — GUTBERLET 11 



the lateral edge of the skull. A foramen for a lateral line canal occurs 

 at the posterior end; the whole surface being more or less perforated. 

 The lateral surface of the pterotic is bounded cephalad by the sphenotic 

 and the prootic and ventrally by the prootic, exoccipital, and opisthotic. 

 At the anterior end of the bone there is a depression which forms 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 shallow 

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

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

 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 opisthotic. 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 depression forming, 

 together with a flange-like expansion of the prootic, a broad groove 

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

 surface of the pterotic forms the dorso-posterior part of the lateral wall 

 of the brain case, there being a large cavity passing latero-caudad from 

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

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

 circular canal. 



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

 surface of the cranium. The lateral surface of each forms the mesial 

 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; ventrally and postero- 

 ventrally by the exoccipital and mesially by the supra-occipital. It 

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

 and the opisthotic above the exoccipital, and nearly parallel to the 

 pterotic. The supra-scapular lies on the dorsal surfaces at the caudal 

 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 overlapped 

 by the supra-occipital and the parietals. The internal surface forms 

 the dorso-caudal wall of the brain case. These parts form posteriorly 

 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 process, extending 



