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Show 5'.] ON THE DEVELOPMENT OF THE SPHENOID BONE. 577 3. On the Development and Morphology of the Human Sphenoid Bone. By J. BLAND SUTTON, F.R.C.S., Lecturer on Comparative Anatomy at the Middlesex Hospital Medical School. [Received May 25, 1885.] (Plate XXXV.) It has been truly remarked that the mode of ossification of the sphenoid bone is one of the most difficult questions in osteogenesis. W e may go further and say that the morphological relations of the precursors of the sphenoid bone, the trabeculae cranii, present even greater difficulties. For some years past I have been, with the kind assistance of my pupils, gradually accumulating material for a thorough investigation of this interesting and important region of the skull. The result of the inquiry I propose to embody in this paper. In order that the various constituent nuclei of the complex human sphenoid bone may be correctly comprehended, it is essential that the early stages of the human chondro-cranium be briefly sketched. The embryological history of the cranial skeleton clearly shows that a uniform plan of construction underlies the skull in all Craniata ; and that it may be divided into a basi-cranial region, formed by two cartilaginous plates enclosing the notochord, known as the parachordals, which later on fuse and form a continuous platform known as the basilar plate. The anterior limit is marked off by the pituitary body. This basilar plate or notochordal region of the skull-base forms a floor for the hind and mid brain. The second portion is composed of a pair of bars, the trabeculae, embracing posteriorly the termination of the notochord, then separating to enclose a space, which is afterwards occupied by the pituitary body, they again come into contact, in most cases coalesce, and extend forward into the nasal region. This section of the primordial skull may be conveniently termed the basi-facial region, the trabeculae forming a support for the fore brain (see fig. 1, p. 578). The third element in the skull consists of the sense-capsules, auditory and olfactory; the optic capsules as a rule remain distinct. Lastly, the appendicular elements claim consideration ; they comprise the palato-pterygoid, meckelian, and hyoid cartilages, and the remaining branchial bars. The portion which more immediately concerns us in this paper is the trabecular region. It is now admitted unreservedly by those anatomists who have dealt with the morphology of the skull from the vantage point afforded by embryology, that the basi-cranial region-the portion |