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 Constrictor, passing from the internal pterygoid plate towards the pharyngeal tubercle on the basiocciput. As it hes 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.
Front margin of inner plate, vertical plate of palate ; lower front of both plates, tuberosity of palate.
-Front border, frontal.
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 basisphenoid has four centres-on each side one for the floor of the sella turcica (two according 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 intertemporal^), in which case this portion may join the frontal or the temporal instead of the sphenoid, or may remain separate (os epiptericum).
Pterygoid processes: the outer is developed in continuity with the great wing. Each inner plate has a separate centre of ossification and fuses secondarily with the mass of the bone.
The centres for the great wing and internal plates appear towards the end of the second month, those for the presphenoid and small wings early in the third month, while the basisphenoid begins to ossify in the latter part of this month. The centre for each lingula is the last to appear, during the fifth month. The bony parts of the internal pterygoid plates and the two halves of the basisphenoid unite in the fourth month, and are joined some time later by the linguke. The orbito-sphenoids and their corresponding presphenoid centres also unite on each side in the fourth month, but it is not until the eighth month that the two halves of the presphenoid unite with each other and the basisphenoid, and even at birth the fusion is not complete, but is represented in part by a cartilaginous junction. In the dried specimen the situation of this cartilage is shown by one or two centrally or laterally placed fossae or foramina, sometimes termed " cranio-pharyngeal canals," but they should not be confused with the canal properly so called that may result from partial persistence of the track of Rathke's pouch ; the latter is normally hardly distinguishable in the cartilaginous skull before ossification, and should be completely obliterated by extension forward of the basisphenoidal centres.