XI 



SKULL 



577 



pituitary body (Fig. 152 C). The cranial cartilage does not 

 become segmented, but gives rise to a pair of horizontal 

 hz.x?,,\h& parachordals (PE): these are continued forwards, 

 diverging around the pituitary body, as the trabecules cranii 

 {Tr), and thus a support is formed for the developing 

 brain. The two parachordals and trabecule then unite 



TJ* 



Fig. 152. — A and B, two stages in the development of the chondrocranium, 

 A. eye ; AF. antorbital process ; B. basal plate, formed from the parachordals ; 

 C. notochord ; Ci. anterior process of trabecula ; N, Nk. nose ; O. ear ; 01. 

 position of foramina for olfactory nerves ; PE. parachordal cartilage ; PJ^. post- 

 orbital process ; PR. pituitary space ; S. nasal septum ; Tr. trabecula. (From 

 Wiedersheim's Anatomy.) 



respectively with one another, and so form a firm 

 floor (B) for the future brain-case, which is gradually 

 developed by the floor growing up on either side and 

 eventually meeting to a greater or less extent above the 

 brain : there is never, however, a complete cartilaginous roof 

 to the cranium, parts of which are only membranous and 

 form the fontanelles (pp. 43 and 420). In the meantime 



Peact. Zool. p p 



