146 ON THE STRUCTURE OF THE SKULL. 



sphenoids arise each by one centre in the corresponding cartilages. 

 The frontals, on the other hand, are developed, like the parietals, 

 each from one centre in the membranous roof of the skull. 



Thus we arrive at the singular result that, while all the bones 

 of the basi-cranial axis, and all the lateral bones of the three 



of ossification which belong to the apices of the lingulse, and are separated by dis- 

 tinct layers of cartilage from the others. The ossification of the lingida is almost 

 complete in the fourth month, and its size is out of all relation to the dimensions 

 of the other parts. It is a thick, obtusely-cylindrical process, which coalesces 

 primarily with the body, and has nothing to do with the alas. The lingula is there- 

 fore similar to an anterior or inferior transverse process (Parapophysis, Owen) ; and 

 the sulcus caroticus, notwithstanding its position in the inner side of the lingida, 

 resembles an open foramen vertebrcde. However, Arnold's opinion that the Vidian 

 canal answers to the canal for the vertebral artery, notwithstanding it is placed on 

 the inner side of the lingula, deserves the careful attention of comparative anato- 

 mists. The ossification of the body begins in the third month, exactly under the 

 pituitary fossa, which is already preformed in cartilage. Kerckring was the first to 

 point out that here the adjacent osseous centres at first arise, and that they unite 

 and form a biscuit-shaped mass in the fifth month. Once he saw this ' semilunula ' 

 even in the middle of the third month. Kolliker and I myself have met with it in 

 foetuses of three months. Other observers, as Nesbitt and Mayer, speak of a single 

 centre in the third month, and in the fourth of two centres, which must be re- 

 garded as the result of the erroneous combination of different individual cases. I 

 find constantly, in the beginning of the third month, two nuclei, which arise near 

 the upper surface in the anterior wall of the pituitary fossa, and are separated by a 

 broad layer of cartilage. Very soon, however, only a single osseous mass is present 

 in the interior of the body, which extends through the whole thickness of the 

 cartilage, while anteriorly and posteriorly it is still enveloped in cartilage. In a 

 foetus 19 centimetres [7J inches] long, I saw the simple osseous nucleus in the 

 bottom of the sella, as a transverse plate which had not yet united with the lingula." 

 " The anterior sphenoid is developed by the gradual coalescence of four osseous 

 centres, of which again two belong to the body and one to each of the lesser wings. 

 The latter are developed earlier than the former. They commence early in the 

 third month, in the anterior clinoid processes, which are quite thick and osseous 

 at a time when everything else in the anterior sphenoid is hyaline cartilage, and 

 therefore are quite similar to the lingutes. From this point ossification proirn sss - 

 rapidly, at last ere. pint;- round the circumference of the optic foramen to the body of 

 the ala and to its anterior root. About the fifth month the lesser wing is completely 

 solid in all parts. On the other hand, the nuclei in the body mostly appear some- 

 what later, usually in the fourth month, and at the inner edge of the optic foramen, 

 so that they are at first separated by a tolerably broad median lamella of cartilage, 

 which is continued into the ethmoid cartilage and septum narium. A union now' 

 very si ion takes place between the centres of the body and those in the lesser wings, 



so that the optic foramen is surrounded by bone Later, at times, as il 



app< ars, as early as the fifth month, the two lateral masses unite into a larger central 

 piece, which is free superiorly, while below and anteriorly, in the middle line, it is 

 surrounded by broad masses of cartilage." — Virchow, he. r-it., pp. 15-18. 



