226 Anatomy of Skeleton 



From the account just given it can be seen that the foramen lacerum is filled in 

 large part by the carotid artery and plexus and petrosal nerves, but these do not pass 

 altogether through it ; in fact, there is only one structure, a meningeal branch of the 

 ascending pharyngeal, that passes quite through it, from below upwards. The 

 remaining parts of the foramen are filled by fibro-cartilaginous tissue, and its outer 

 and posterior part, that receives the great superficial petrosal nerve, is under cover of 

 the Gasserian ganglion. 



Looking at the foramen from below (Fig. 182) we can see that the Eustachian tube 

 lies under it. The cartilaginous portion of the tube is attached to the petrous bone 

 internal to the spine of the sphenoid and passes downwards, inwards and forwards 

 from this to the upper part of the posterior margin of the internal pterygoid plate. 

 Lying in such a situation, it must pass under the foramen lacerum, and its relations are 

 in fact apparent on the skull : above it is the petro-sphenoidal articulation and the 

 foramen and basisphenoid, behind and internal the origin of Levator palati and lateral 

 recess of the pharynx, which reaches the lower aspect of the petrous : outside and in 

 front the Tensor palati and internal pterygoid plate ; below it the fibres of the Con- 

 strictor, passing from the internal pterygoid plate towards the pharyngeal tubercle 

 on the basiocciput. As it lies below the foramen it necessarily has the carotid artery 

 and Vidian nerve above it, and thus the backward-running branches of the nerve, 

 from the spheno-maxillary ganglion, can reach the tube and adjoining pharynx which 

 they supply. 



A small triangular surface of bone outside the posterior Vidian opening forms 

 par of the wall of the foramen and is grooved by the nerve entering the foramen : its 

 lower border gives attachment to the fibrous tissue of the tube. 



Articulations. Great Wing. Front margin, malar ; upper and front margin 

 frontal ; upper margin, parietal ; postero-external, squamous temporal ; postero- 

 internal, petrous temporal. 



Pterygoid Processes. Front margin of inner plate, vertical plate of palate ; lower 

 front of both plates, tuberosity of palate. 



Small Wing.- Front border, frontal. 



Body. Front surface, ethmoid ; back surface, occipital ; lower surface, vomer 

 and palate (vertical plate). 



Development. 



The sphenoid is partly preformed in cartilage : the cartilaginous portion includes 

 the body, the small wings, and the inner parts of the great wings. The rest of the 

 alisphenoids and the pterygoid processes, with the exception of the hamular processes, 

 are ossified in membrane. 



The bone is formed by the coalescence of fourteen centres or more. The basi- 

 sphenoid has four centres on each side one for the floor of the sella turcica (two accord- 

 ing to some authors) and another lateral one, which is really an extension inwards 

 from the centre for the lingula. The presphenoid has two centres, one on each side. 

 The small wings one centre each, which meet above the presphenoid at a later stage 

 to form the jugum. 



Great wings : one centre for each cartilaginous part, which also forms the external 

 pterygoid plate The outer membranous part may be ossified by extension from this, 

 or may have a separate centre for its margin (os intertemporale), in which case this 

 portion may join the frontal or the temporal instead of the sphenoid, or may remain 

 separate (os epiptericum). 



