Skull and Hyoid 



219 



At birth only the central part of the carotid canal is covered in : subsequent 

 growth of the opisthotic and of the tympanic plate completes the process. The growth 

 of the plate outwards is brought about largely by the spread of ossification from two 

 main points of the ring, which by their ultimate fusion form the floor of the external 

 meatus : when they first join a small hiatus may exist between them and is normally 

 present (foramen of Huschke) up to the age of five or six, and may persist beyond this. 

 Other points of interest in the young temporal bone are mentioned in the section 

 on the " Postal Skull." 



SPHENOID. 



A single bone situated in the base of the skull, but reaching the side walls : con- 

 sisting of a centrally placed body from which two wings, great and small, project on each 



r. 



KIG. 179. Sphenoid seen from above and behind. A., marginal articulation with ethmoid; 

 />'., with frontal ; C., with parietal ; D., with squama of temporal, a.. Small wing ; 6., great 

 wing ; c., sphenoidal fissure ; d., jugum sphenoidale ; e., optic groove ; (., olivary eminence ; 

 g., optic foramen ; h., anterior clinoid process ; '., posterior clinoid process ; A., dorsum 

 sellae ; /., foramen rotundum ; m., carotid groove ; n., lingula ; o., foramen ovale ; p., foramen 

 spinosum ; r., vidian foramen. 



side, and two plerygoid plates project downwards on each side, the inner from the body 

 and the outer from the under surface of the great wing. 



The body, on the whole cuboidal, articulates behind with the occipital, with which 

 it is synostosed about twenty-five, and in front carries the ethmoid : it is hollowed out 

 by the sphenoidal air sinuses f * which extend into it from the nasal fossa within a 

 few years after birth, and when fully developed occupy practically the whole of 

 the body and may extend even into the attached parts of the wings and pterygoid 

 processes. The two sinuses are separated by a septum, which may be incomplete 

 and is usually asymmetrical : there are as. a rule two partial septa also present, one in 

 each sinus near its upper and outer part. The sinuses are partly closed by two 

 sphenoidal turbinals,* thin paper-like bones, that have openings above their centres 

 through which the cavities are connected with the ethmo-sphenoidal recesses in the 

 nasal fossae. 



* For further details, see p. 249 (sphenoidal sinus), and p. 227 (sphenoidal turbinals). 



