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Show 1885.] OF THE HUMAN SPHENOID BONE. 583 fuses with the corresponding lingula, with which element the internal pterygoid also has after birth an osseous union; the space left between this triple union of ala, lingula, and pterygoid being occupied by the vidian or great superficial petrosal nerve, a nervous cord of no small morphological significance, as I have previously shown. The external pterygoid plate is simply an apophysis from the under surface of the alisphenoid, becoming conspicuous about the third month of intra-uterine life. As a matter of convenience and ready reference, the dates of appearance of the individual centres and their fusion with one another are here given in a collected form. At the eighth week the following centres appear quickly one after the other, in the following order :- I. Alisphenoids. 2. Basisphenoids. 3. Lingulae sphenoidales. 4. Internal pterygoids. During the third month the ossific points fuse in the following order :- 1. Basisphenoidal nuclei coalesce, and the 2. Lingulae join the basisphenoid. At the third month the following centres appear :- 1. Orbito-sphenoid. 2. Presphenoids. At the fourth month the orbito-sphenoids fuse with the presphenoids and the internal pterygoids join the alisphenoids. At the seventh month the presphenoid and postsphenoid coalesce. At the eighth month the presphenoids fuse together. During the first year after birth the alisphenoids bearing the internal pterygoids coalesce with the lingulae, and the so-called sphenoidal tubinals develop. The strip of cartilage which is prolonged from orbito-sphenoid to the anterior lateral fontanelle (the pterion) now disappears. W e must now deal with the morphology of the various centres of the sphenoid. In the determination of the regions of the skulls in different types we are greatly assisted by the disposition of the cranial nerves, which in the majority of cases serve as fairly reliable guides. The optic nerves always embrace the presphenoid, whilst the third division of the fifth cranial nerve usually quits the skull between the most anterior part of the periotic capsule and the alisphenoid, whilst the auditory nerve stands in very definite relationship with the various constituent nuclei of the periotic capsule, in those forms ia which this cartilage undergoes ossification, so that as a rule we have no difficulty in distinguishing between the regions. W h e n dealing with the individual ossific nuclei the case is very different, it being absolutely necessary to watch every stage of the development to avoid falling into the numerous pitfalls which abound on every side. The presphenoid uuclei do not offer very much that is important, |