466 SYDNEY E. JOHNSON 



parasphenoid. The anterior end of the bone enters into the 

 composition of the orbital rini (fig. 5). 



The sphenodc (spo.) is of irregular shape and its exact bound- 

 aries could not be determined. Inunediately posterior to the 

 orbit it bears a prominent process which extends downward 

 and unites with the anterior tuberosity of the prootic. The 

 anterior ball on the head of the hyomandibular articulates in a 

 socket formed by the posterior angle of the sphenotic. The bone 

 is pierced by a relatively large sensory canal (figs. 5 and 7). 



The alisphenoid (als.) is a small rectangular lamina of bone 

 located in the posterior wall of the orbit. It articulates above 

 with the frontal; posteriorly, with the sphenotic and the prootic, 

 and below with the middle of the parasphenoid (figs. 5 and 7). 



The parasphenoid (pas.) bone consists of an expanded body 

 which articulates superiorly with the alisphenoid, the sphenotic, 

 and the prootic, and an anterior rod-like process which passes 

 forward under the orbit to articulate with the vomer and the 

 prefrontals. Rib-like processes extend upward from the body 

 of the bone on each side and articulate with the prootics. Pos- 

 terior to these processes the central part of the bone is compressed 

 to form a deep median keel which unites posteriorly with a similar 

 median lamina of the basioccipital. On either side of this proc- 

 ess are the openings of the canals which lead forward to the 

 myodome (figs. 5 and 7). 



The frontals {Jr.) are wide, arched bones forming the greater 

 part of the superior wall of the orbit. They meet in the median 

 line where the interorbital space is strongly concave. The supra- 

 orbital ridges are prominent and each bears a small sharp spine 

 posteriorly above the orbit (fig. 5). 



Lateral to the anterior end of each frontal is the corresponding 

 prefrontal (pf.). The distal end of each is expanded to articulate 

 with the palatine bone. The posterior end tapers to a slender 

 process which unites with the anterolateral margin of the frontal. 

 Anteriorly each bone takes part in the formation of the nasal 

 canal (figs. 5 and 6). 



The ethmoid (e.) is elongated and slightly convex superiorly. 

 From its central part a prominent process extends upward to 



