177] OSTEOLOGY OF LORICATI—GUTBERLET 7 



tend out from the median line. On each side of the lateral concave sur- 

 faces there is a deep pit produced by several pores. 



Prefrontal. — The paired prefrontals or ectethmoids Fig. 1, 

 6, pfr) are lateral to the ethmoid and anterior to the frontals. Each 

 is a lateral expansion from the ethmoid and the frontals, having a broad 

 base-like portion and a wing-like process extending from it which forms 

 the anterior boundary of the orbit. The anterior portion is somewhat 

 lower than the rest and appears as a shelf at the side of the ethmoid 

 because of a depression on its anterior dorsal surface. This depression, 

 together with a similar depression on the latero-ventral surface of the 

 ethmoid forms a part of the bony wall of the nasal pit. The wing-like 

 process is narrow antero-posteriorly but broad and flattened dorso- 

 ventrally. The end is rounded and forms a facet for articulation with 

 the palatal and the first exorbital bone. A small ventral process on the 

 wing meets a process from the palatine. From the base of the wing- 

 like portion the bone flattens out antero-posteriorly as it extends ventro- 

 mesad to its articulation with the parasphenoid. There is a foramen 

 through the wing near its suture with the ethmoid through which the 

 olfactory nerve and the orbito-nasal vein and artery to the nasal pit 

 pass. Above the point where the prefrontal unites with the parasphe- 

 noid they come in contact with each other in the median line holding 

 between them the ventral edge of the cartilaginous orbito-sphenoid 

 which extends dorsad and caudad forming a partial partition between 

 the orbits. 



Frontal. — The paired frontals (Figs. 1, 6, fr) form the greater 

 part of the dorsal surface of the cranium. At the anterior end of each 

 there is a small groove produced by pores in the bone. The lateral 

 edges of the posterior portion form the mesial boundaries of the orbits. 

 The posterior portion broadens and forms the posterior and dorsal 

 boundaries of the orbits. At this point the frontals are slightly rounded 

 dorsad and the bone is somewhat porous, possessing several striations 

 which start at the posterior boundary of the orbit and radiate caudad 

 and mesad toward the median line to the parietal bones. The lateral 

 edges of the posterior portion form the mesial border of the anterior 

 part of the temporal fossa. At the lateral edge on the posterior border 

 of the orbit the frontal unites with the sphenotic. Its lateral edge rests 

 on the prefrontal and the mesial edge rests on the ethmoid. In the 

 median line on the ventral surface there is a cartilaginous orbito- 

 sphenoid bone, extending to the parasphenoid and forming a partial 

 partition between the orbits. The ventral surface of the roof of the 

 orbit is filled with large pores and two deep grooves which become 

 deeper as they pass caudad into the deeper part of the frontal. The 

 mesial edge of the inner groove forms a large flange which projects 



