170 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



of the sphenoidal air sinuses, are then nodules of bone, surrounded 

 by cartilage. They also are separate and form part of the lateral 

 ethmoidal cartilaginous plates. The internal pterygoid plates, 

 formed from the pterygo-palatine bar, become adherent to the 

 external pterygoid plates, which are developed as outgrowths from 

 the ali-sphenoids or great wings. The pre-sphenoid unites with the 

 basi-sphenoid in the 7th month ; the great wings unite with the 

 basi-sphenoid soon after birth. The lingula which bounds the 

 outer side of the carotid groove (Fig. 137) is ossified from a 

 centre which appears during the 4th month of foetal life. The 

 orbito-sphenoids unite over the pre-sphenoid and cover its cranial 

 aspect. 



The Pituitary Body is developed between the trabeculae cranii ; 

 the pre-sphenoid is formed in front of it and the basi-sphenoid 

 behind it (p. 19). A canal may remain in the foetal or even 

 adult bone to mark the point of ingress of the buccal part of the 

 Pituitary, Fig. 167, p. 203. The wings of the vomer cover the 

 opening of the pituitary canal on the pharyngeal aspect of the 

 skull, if it be present. On the cerebral aspect it opens at the 

 olivary eminence which also marks the union of the pre- and the 

 basi-sphenoids. The pre-sphenoid and afterwards the basi-sphenoid 

 are much altered by the growth of the sphenoidal sinuses which 

 commence about the 7th year. The great wings support the 

 temporal poles of the brain, their size depending on the develop- 

 ment of that part of the brain. They are much larger in man 

 than in any other mammal. The small wings project within the 

 vallecula Sylvii. In the early foetus the dorsum sellae is 

 enormously developed, and fills the deep and sharp angle 

 between the mid-brain and fore-brain (Fig. 167). 



Formation of Foramina in Bone. — The foramina of the skull 

 are formed in one of three ways (Sutton) : 



(1) By the union of two bones; examples of this form are 

 the jugular foramen, sphenoidal fissure, Glaserian fissure, etc. 



(2) By the union of two elements of one bone ; the anterior 

 condyloid foramina, optic foramina, the foramen magnum, aque- 

 ductus Fallopii, etc. 



(3) By the enclosure of a notch on the edge of a bone of 

 which the foramen ovale is the best example. This foramen 

 is at first a notch in the posterior border of the great wing of 



