

85 



and the mesoderm enclosing them is soon converted into cartilage, forming the 

 cartilaginous ear-capsules. These cartilaginous ear-capsules, which are of an oval 

 shape, fuse with the sides of the basilar plate, and from them arise the petrous 

 and mastoid portions of the temporal bones. The trabeculae cranii (Fig. 69) are 

 two curved bars of cartilage which embrace the hypophysis cerebri; their posterior 

 ends soon unite with the basilar plate, while their anterior ends join to form the 

 ethmoidal plate, which extends forward between the fore-brain and the olfactory 

 pits. Later the trabeculse meet and fuse below the hypophysis, forming the floor 



Crista galli 



Cribriform plate 



Small wing of sphenoid 

 Optic foramen 



- Great wing of 



sphenoid 



Sella turcica 

 Dorsum seUoe 



Canal for facial 

 nerve 



Ear capsule 

 Ductus endol. 



MeckeVs cartilage 

 Malleus 

 Incus 



^m 



Int. acoustic meat. 



Jugular foramen 

 -Fossa subarcuata 



Canal for hypoglossal nerve 



Foramen magnum 



Fio. 70. Model of the chondrocranium of a human embryo, 8 cm. long. (Hertwig.) The membrane bones are 



not represented. 



of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis 

 from the stomodeum. The median part of the ethmoidal plate forms the bony 

 and cartilaginous parts of the nasal septum. From the lateral margins of the 

 trabeculse cranii three processes grow out on either side. The anterior forms the 

 ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle 

 gives rise to the small wing of the sphenoid, while from the posterior the great 

 wing and lateral pterygoid plate of the sphenoid are developed (Figs. 70, 71). 

 The bones of the vault are of membranous formation, and are termed dermal or 

 covering bones. They are partly developed from the mesoderm of the membranous 



