THE CHONDROCKANIUM IN THE ICHTHY0P8IDA. 119 



lamina cribrosa is brought into its usual position. Its 

 distal end is fused with that of the antorbital process thus 

 enclosing the orbito-nasal foramen (Figs. 24 and 26, ofi). 



The ethmoid plate is larger in both directions than in 

 the first stage, and in the median line upon its anterior 

 half arises the nasal septum (ns) . In front, upon the sides 

 of the base of the septum, the ethmoid plate terminates in 

 short free processes. The nasal septum is divided anteriorly 

 into three parts, a short median process which projects 

 freely forward, and two lateral bands which curve forward 

 and outward. At its most anterior point each of these 

 bands divides into a dorsal and a ventral process. These 

 extend backvvard along the lateral surface of the olfactory 

 organ and fuse with the outer end of the cartilage men- 

 tioned in the first stage as arising from near the anterior 

 end of the ventral trabecular rod. Where these three 

 processes meet a plate of cartilage is formed which lies 

 below the lamina cribrosa and is connected with it l)y a 

 short narrow band. No tectal cartilage is formed in the 

 chondrocranium of Ichthyophis. 



As a result of ossification the ascending process of the 

 quadrate has lost its cartilaginous connection with the dor- 

 sal trabecular rod (Fig. 24), and the parts of the ptery- 

 goid process are now united into one continuous rod. 

 The body of the quadrate remains essentially unchanged, 

 it having neither otic nor palato-basal process. The two 

 cartilages of Meckel are now confluent in front, and the 

 palatine cartilage still remains isolated from the rest of 

 the chondrocranium. It appears that the ancestors of the 

 Batrachia had a palato-pterygo-quadrate cartilage similar 

 to that found in sharks. Of these cartilages the Urodeles 

 as a rule retain only the pterygoid and quadrate portions. 

 The Cfecilians have these two parts and an isolated pala- 

 tine portion, while in the Anura all three parts are united 



