138 OSTEOLOGY. 



below in the bamulus pterygoideus (pterygoid booklet), which, reaching a lower level 

 than the lateral plate, curves backwards and laterally, furnishing a groove on 

 its lower surface in which the tendon of the tensor veli palatini muscle glides ; 

 superiorly, the sharp posterior margin of the medial plate bifurcates, so as to 

 enclose the shallow scaphoid fossa from which the tensor veli palatini muscle 

 arises, and wherein may occasionally be seen the inferior aperture of the foramen 

 Vesalii. To the medial edge of this fossa, as well as to the posterior border of 

 the medial pterygoid plate, the pharyngo-basilar fascia is attached. Here, too, 

 the cartilage of the auditory tube is supported on a slight projection, and the 

 pharyngo-palatinus muscle receives an origin, whilst the superior constrictor of 

 the pharynx arises from the inferior third of the same border and from the 

 pterygoid hamulus. Superiorly and medially the medial plate forms an incurved 

 lamina of bone, the processus vaginalis (vaginal process), which is applied to the 

 inferior surface of the lateral aspect of the body, reaching medially towards the 

 root of the rostrum, from which, however, it is separated by a groove, in which, in 

 the articulated skull, the ala of the vomer is lodged. The angle formed by the 

 vaginal process and the medial edge of the scaphoid fossa forms a projection called 

 the pterygoid tubercle, immediately above which is the posterior aperture of the 

 pterygoid canal, through which the nerve and artery of the canal (O.T. Yidian) are 

 transmitted. On its inferior surface the vaginal process displays a groove (sulcus 

 pterygopalatinus), which in the articulated skull is converted into the pbaryngeal 

 canal by its union with the palate bone. In front, at its root, the pterygoid 

 process displays a broad smooth surface (facies spbenomaxillaris), which is confluent 

 above with the root of the great wing around the foramen rotundum, and forms 

 the posterior wall of the pterygo-palatine fossa. Here, to the medial side of the 

 foramen rotundum, is seen the anterior opening of the pterygoid canal. Below, 

 the pterygoid laminae are , separated by an angular cleft, the pterygoid fissure ; 

 in this is lodged the pyramidal process of the palate bone, the margins of which 

 articulate with the serrated edges of the fissure. 



Connexions. The sphenoid articulates with the occipital, temporal, parietal, frontal, 

 ethmoid, sphenoidal conchae, vomer, palate and zygomatic bones, and occasionally with the 

 maxillae. 



Ossification. The sphenoid of man is formed by the fusion of two parts, the pre- 

 sphenoid and the post-sphenoid, each associated with certain processes. In most mammals 

 the orbito-spbenoids or small wings fuse with the pre-sphenoid, whilst the alisphenoids or 

 great wings, together with the medial pterygoid lamina, ankylose with the post-sphenoid. 

 The ossification of these several parts takes place in cartilage, with the exception of the 

 medial pterygoid lamina, which is developed from an independent centre in the connective 

 tissue of the side wall of the oral cavity (Hertwig). 



At the end of the second month a centre appears in the root of the great wing between 



the foramen ovale and foramen rotundum; from this the ossification spreads laterally and 



c b a b c backwards and also downwards into the lateral 



^^^^^i rf^) pterygoid lamina. According to Fawcett the 



^H 5>^tr3/ks^i=v^^^[ pterygoid laminae or the common root of the 



N>x. ^i IT -'-li j ' 



X ^vS3r^9E3^8H two I amm8e m the adult is practically the 



^\^^^^St^JSm. -/ on ly P ar t f the ala temporalis preformed in 



^*~/& cart ^ a e > t ^ ie wno ^ e f the lateral pterygoid 



NI ^ I ^^^|^^^>' lamina and that part of the alisphenoid pro- 



Jlrm iT^ jected into the orbital and temporal fossae are 



ossified in membrane ; so too are the foramen 



PIG. HG.-OSSIFICATION OF THE SPHENOID. ovale *^ foramen spinosum. Meanwhile two 

 i. -j * ^ ^-^ centres appear about the same time in the 



a, Pre-spnenoid ; o, Orbito-spheuoids ; c, Ahsphenoids ; i r -j - -\ ' c j.-u 



d, Medial pterygoid lamina; e, Basi-sphenoid. basi-sphenoid in relation to the floor of the 



fossa hypophyseos and on either side of the 



cranio-pharyngeal canal, around which they ossify, ultimately leading to the obliteration 

 of that channel. Somewhat later a spbenotic centre appears on each side, from which 

 the lateral aspect of the body and the lingula are developed. Fusion between these 

 four centres is usually complete by the sixth month. 



In the pre-sphenoid a pair of lateral nuclei make their appearance about the middle of 

 the third month, just lateral to the optic foramina; from each of these the orbito- 



