THE CHONDROCKANIUM IN THE ICHTHYOPSIDA. Ill 



tectum. The parachordals are reduced to a narrow trans- 

 verse band immediately in front of the base of the occip- 

 ital arch, and short lateral bands fused with the floors of 

 the otic capsules. The greater part of the wall of the otic 

 capsule is ossified, but enough of the lateral wall remains 

 to show the most important relationships. In this lateral 

 wall of the capsule, further dorsally than in the Urodele 

 skull described, is the fenestra ovalis and in it a small 

 stapes (Fig. 20, s) which is connected b}' a rod running 

 forward and downward with the lateral border of the 

 tympanic annulus (ta). 



The trabeculoe are small, cylindrical rods extending 

 forward from the ventro-median angles of the anterior 

 ends of the otic capsules and fusing in the broadly ex- 

 panded ethmoid phite. In the median line the ethmoid 

 plate is continued forward into the nasal septum. At 

 the sides of the posterior end of the septum the ethmoid 

 plate is perforated by the olfactory foramina {ol). A 

 triangular lamina cribrosa (I) projects outward, down- 

 ward and forward from each antero-lateral margin of the 

 ethmoid plate. This and the septum with the connecting 

 rods compose the nasal capsules. 



From the ventro-lateral margin of the lamina cribrosa 

 (Fig. 21) a slender cartilage projects horizontally inward 

 to beneath the inner border of the lamina where it splits 

 into two cylindrical rods, a dorsal and a ventral. The 

 dorsal rod {d) extends forward inward and upward to the 

 antero-dorsal point of the septum, while the ventral rod 

 (vjp) curves sharply inward, touches the ventral margin 

 of the septum and then, slightly expanding in width, ter- 

 minates in a process projecting freely forward. A small 

 foramen for the orbito-nasalis, seen only when the skull is 

 viewed from below (oji), passes beneath the posterior end 

 of the lamina-cribrosa just outside the anterior end of the 



