THE BONES OF THE HEAD 



91 



petrosal process for the attachment of the petro-sphenoidal ligament, which 

 connects it with a projection sometimes present on the inner part of the superior 

 border of the petrous portion of the temporal. This Ugament, which is some- 

 times ossified, bridges over a foramen through which the inferior petrosal 

 venous sinus and sixth cranial nerve pass. (5) Pterygo-spinous foramen. 



(6) Foramen ovale and foramen spinosum are sometimes incomplete. 



(7) Foramen Vesalii. (8) Canahculus innominatus. (9) The cranio-pharyn- 

 geal canal may remain persistent, opening into the pituitary fossa. 



Ossification. — The sphenoid is developed in cartilage, with the exception 

 of the internal pterygoid plates, which are developed in fibrous tissue.* The 

 bone is originaUy di\'ided into two parts — presphenoid, representing the part 

 of the body in front of the ohvary eminence, and the small wings ; and post- 

 sphenoid, including the part of the body behind the oUvar^- eminence, the 

 great wings, and the pter^^goid processes. The postsphenoid division is 

 developed from four pairs of centres. One pair appear in the eighth week 

 of intra-uterine life, one at either side in the great wing between the foramen 



SmaU Wing 



Presphenrnd Portion of Body 

 I 



Great Wing 



Dorsum Sellz 

 TL Internal Pterygoid Plate 



Fig. 56. — The Sphenoid Bone in Early Life. 



I, Presphenoid Division ; II, Postsphenoid Portion of Body ; III, Great 

 Wing and Pterygoid Process; IV, Elements of Pter^'goid Process. 



rotundum and foramen ovale, and from this ossification extends outwards 

 into the great wing and dovs-nwards into the external pter^'goid plate. Another 

 pair appear about the same time in the sella turcica on either side of the 

 cranio-pharj-ngeal canal, from which ossification extends around the canal. 

 graduaUy constricting it, and finally leading to its closure. At this time another 

 pair (sphenotics of Bland-Sutton) appear, one at either side, for the Ungula. 

 In the fourth month (ninth or tenth week, Fawcett) another pair of centres 

 appear in fibrous tissue, one at either side, for the internal pterygoid plate, 

 which unites ^^-ith the external pterygoid plate before the sixth month. 

 The presphenoid division is developed from two pairs of centres. Two 

 appear in the ninth week, one at either side, external to the optic 

 foramen, for the smaU wing. Another pair appear in the eleventh week 

 internal to the optic foramina for the presphenoid portion of the body. 

 The latter pair soon unite with each other, and also with those for the small 

 \vings. The presphenoid division, bearing the small wings, joins the post- 

 sphenoid dix-ision shortly before birth in the region of the oUvary eminence. 

 At birth the place of junction is indicated by a wide depression on the under 



* According to recent observations made by Fawcett the external pterygoid 

 plates are also developed in fibrous tissue. 



