PRIMORDIAL CRANIUM OF THE CAT 371 



cranium. Parker (75) observed ''a secondary growth of carti- 

 lage beneath the pituitary body" in Sus. A sphenoidal cartilage, 

 independent of the occipital skeleton of the ox, is described by 

 Froriep ('86) as lying beneath the hypophysis. This observation 

 is confirmed by Noordenbos ('05) who found, moreover, that the 

 cartilage was paired. Noordenbos has discovered, by van 

 Wijhe's method, the origin of the middle piece of the cranial 

 base by the fusion of several small islands of cartilage in the cra- 

 nia of mole, rabbit and pig. For these pieces, which surround the 

 stalk of the hypophysis, Noordenbos has proposed the name 

 'insulae polares.' Wincza ('96) noted the independence of the 

 cartilaginous basi-sphenoid and alisphenoid (ala temporalis) in 

 cat. As we have seen, the cranial floor, beneath the hypophysis, 

 is first represented by a crescentic cartilage, which soon grows 

 around the stalk of the hypophysis, probably completely sur- 

 rounding it, although this was not actually observed. The for- 

 mation of the sella turcica is brought about by the union of the 

 hypophyseal cartilage anteriorly with the trabecular plate and 

 posteriorly with the basal plate, the former contributing the 

 tuberculum sellae, the latter the crista transversa which is the 

 beginning of the dorsum sellae. 



Fenestra hasi-cranialis posterior. The existence of an opening 

 in the basis cranii between the anterior end of the basal plate 

 and the hypophyseal cartilage is merely temporary in the cat. 

 In embryos of 12 mm. the fenestra basi-cranialis posterior has 

 no lateral limits, since the cochlear capsule is not yet joined with 

 the basal plate. The anterior boundary is made by the hypo- 

 physeal cartilage, so that the fenestra lies, not within the basal 

 (parachordal) plate, but anterior to it, as Noordenbos insists. 



- Crista transversa and dorsum sellae. The crista transversa rep- 

 resents the anterior, dorsally turned, free edge of the basal plate. 

 The upward bend of this margin just prior to the fusion of the 

 basal plate and hypophyseal cartilage, can be seen in sagittal 

 sections of embryos of 12 nm:i. and its identity with the crista 

 transversa proved by sections of 15 mm. specimens in which the 

 line of fusion of the two plates is still distinct. Noordenbos found 

 that the dorsum sellae of Talpa is formed from the anterior mar- 



