Vertebroid Homologies of the Cranium in Vertebralia. 55 



which is subsequently so incorporated with both the basi- 

 occipital and sphenoid, that Soemmering described them as 

 a single bone sphenooccipital or basilar in the adult con- 

 dition of the cranium. The petrous is early developed, 

 and besides forming the hyp-otic 6 and 9 the pro-otic, 

 contains the otic capsule. The ossification begins in these 

 in a chondrous state, about the same time as the ossi- 

 fication of the kaulon. The parietals are ossified in mem- 

 brane. 



(iii.) The Axo-prespheno Bivertebra, or the Anterior Spheno- 

 orbital (Beclard) ossifies very early in foetal life, at the margin 

 of the foramen opticum, and extends along the ingrasial 

 wings IS. These are afterwards united in the centre. 

 Towards the close of foetal life this vertebra is closely united 

 with the sphenoid, and is usually in Anthropotomy described 

 as part of that bone. 



The Atlo-sp)henoid centrum 12 with the rostrum 12', and 

 the pedicles of the wings, are ossified in cartilage, but the 

 ala major results from membrane. The ossification begins in 

 the sphenoid soon after the occipital, and is developed from 

 many centres. Beclard divided these into two classes : — 

 1. The posterior or spheno-temporal includes the ala major 

 16, where the first nuclei are seen anterior to the foramen 

 rotundum, from whence the ossification extends outwards 

 and upwards into the ake majores, and downwards into the 

 pterygoids 36, 37. About the same time there are two 

 ossific points for the centrum 12, and the lateral projection, 

 as described by Meckel, anol copied in " Quain's Anatomy" 

 (fig. 26, b. 5). 



(iv.) The Ethmo-f routed Bivertebra. — The perpendicular 

 plate of the ethmoid extends through the atlo-frontal, arising 

 from the frontal protuberance, and forming the axoid portion. 

 The ossification of the front als or the atloid portion com- 

 mences early in membrane, by a central point in each half. 

 They are separate till birth, and in females often remain so 

 during life. 



(v.) The Apo-cranial Bivertebra is formed by the nasal pro- 

 montory 22, with the nasal spine continued into the septum 

 nasi 24 axoid. 



