i6o 



ANIMAL BIOLOGY. 



[Part I. 



the frog or rabbit. These trabeculce (tr.) are united behind, but 

 diverge forwards, and then curve in so as to enclose a pituitary 

 space (pit.). Anteriorly they unite again, and thus are some- 



t.o. 



B. 



FIG. 51. DIAGRAMS OF SKULL DEVELOPMENT. 



A. Plan of cartilaginous embryonic skull. B. Section of a somewhat 

 older skull. 



a. s. Ali-splienoid region, aw. Auditory capsule, "b. o. Basi-occipital region. 

 &. p. Basilar plate. &. s. Basi-sphenoid region, cli. Notocliord. cr. pi. 

 Cribriform plate, e. o. Ex-occipital region, n. s. Nasal septum, ol. Olfactory 

 capsule, op. Optic capsule, o. s. Orbito-splienoid region, p. s. Pre-sphenoid 

 region, pit. Pituitary space, s. o. Supra-occipital region, tr. Trabeculee. 



what lyre-shaped. They lie beneath the fore-brain, the base of 

 which, to begin with, projects downwards into the pituitary 

 space. 



The basilar plate represents the future basi-occipital region of 

 the skull. Its sides grow up fusing with the periotic capsules of 

 the auditory sacs, and eventually meet above. Thus the whole 

 occipital segment is preformed in cartilage, and in this cartilage 

 are subsequently formed ossifications starting from basi-occipital, 

 ex-occipital, and supra-occipital centres (b.o., e.o., s.o.), while in the 

 periotic capsules the otic bones are subsequently formed. 



The trabeculse grow together so as to almost completely 

 close the pituitary space. In the region of the fore-brain they 



