SKULL 



595 



surrounding which cartilages appear and give rise to the 

 vertebrae, the notochord becoming constricted by the in- 

 growing cartilage, and eventually disappearing more or less 

 completely (compare pp. 441 and 584) : it at first extends 

 into the head as far as the pituitary body (Fig. 163, C). The 

 cranial cartilage does not become segmented, but gives rise 



. sora proces . 



Tr. trabecula. (From Wiedersheim's Comp. Anatomy.) 



to a pair of horizontal bars, the parachordals (PE] : these are 

 continued forwards, diverging around the pituitary body, as 

 the trabecula cranii (Tr\ and thus a support is formed for 

 the developing brain. The two parachordals and trabeculse 

 then unite respectively with one another, and so form a firm 

 floor (B) for the future brain-case ; this is gradually 

 developed by the floor growing up on either side and 



Q Q 2 



