igo 



HUMAN ANATOMY. 



Great wing 

 (alisphenoid I 



Small wing 

 (orbito-sphenoid ) 



Optic 

 foramen 



Sphenoidal 



fissure 



Foramen Vidian Presphenoid | Ext. pterygoid plate 

 rotundum canal Int. pterygoid plate 



Sphenoid bone at about birth, seen from before. 



nence bounding a groove below, which supports the Eustachian tube. The posterior 

 border of the outer plate is irregularly scalloped. Near the top a transverse ridge 

 crosses its inner surface ; if well marked, this forms the top of the pterygoid fossa. 

 It may be barely discernible (Waldeyer ^j. Just above the scaphoid fossa is the 

 hind end of the Vidian canal opening into the middle lacerated foramen opposite the 

 apex of the petrous. The development of the pterygoid plates varies greatly. The 

 upper part of the outer may be prolonged to the spine of the sphenoid, just outside 

 of the foramen ovale, with a perforation at this point, so that some of the branches 

 of the third division of the fifth cranial nerve may pass on either side of it. This 

 occurs by the ossification of a band of fibrous tissue, connecting the back of the 



plate with the spine, and thus 

 Fig. 213. forming the foramen pterygo- 



spinostan o{ Civinini (Fig. 212). 

 This is always behind the fora- 

 men ovale, or internal to it. 

 Just outside of the foramen is 

 found, very rarely, a little canal 

 on the under side of the great 

 wing, transmitting a branch of 

 the mandibular division of the 

 fifth nerve, the porus crotaphit- 

 ico-buccinatorius of Hyrtl. 



Articulations. — Much 

 has been already said incident- 

 ally on this point in the fore- 

 going description. The sphenoid bone joins the occipital behind. The great wjngs 

 send the spine into the entering angle between the squamous and petrous portions 

 of the temporal. These two bones — the sphenoid and the temporal — form the 

 entire middle fossa of the skull. The middle lacerated foramen is just behind the 

 carotid groove at the side of the body and in front of the end of the petrous. At 

 the side of the skull the great wings join the squamous behind, the parietal and the 

 frontal above, and the malar in front. The ethmoid covers the front of the body of 

 the sphenoid, its vertical plate joining the crest. The vomer covers the rostrum 

 below. The palate bone fills 



up the pterygoid notch, com- Fig. 214. 



pleting the fossa, and by its 

 sphenoidal process touches 

 the edge of the body. The 

 frontal bone joins the lesser 

 wings. 



Development. — The 

 presphenoid and basisphcnoid 

 each ossify from a pair of 

 nuclei, those of the former 

 appearing at the end of the 

 second month of foetal life and 

 the latter a litde later. At 

 about the eighth week a nu- 

 cleus is to be seen in each of 



the greater wings near the body and extends outward, involving also the external 

 pterygoid plate. The internal pterygoid plate has a nucleus of its own, which 

 is present in the fourth month and joins the outer a month later. Two little gran- 

 ules appear in the fourth month for the lingula and a neighboring piece of the 

 bone. The orbito-sphenoids have each two centres, — one on either side of the optic 

 foramen. It would seem that the inner may in some cases take the place of those for 

 the presphenoid. In any case the presphenoid and the lesser wings unite before birth. 

 In the seventh or eighth month the presphenoid and basisphenoid unite, but at birth 

 they are still separated by cartilage on their lower surface. At birth the bone con- 



' Sitzungsber. Acad. Wissen., Berlin, 1893. 



Presphenoid 



Jugum sphenoidale 



Small wing (orbito-sphenoid) 

 Foramen rotundum 

 Great wing 

 falisphenoid) 



Basisphenoid Lingula Foramen ovale 

 Sphenoid bone at about birth, seen from behind. 



