1885.] ON THE DEVELOPMENT OF THE SPHENOID BONE. Oll 



3. On tlie Development and Morpliology of the Human 

 Sphenoid Bone. By J. Bland Sutton, F.R.C.S., 

 Lecturer on Comparative Anatomy at the Middlesex 

 Hospital Medical School. 



[Eeceived 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. 

 We may go further and sa_v that the morphological relations of 

 the precursors of the sphenoid bone, the trabecnlse 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-crauium 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 uotochord, known 

 as the parachordals, which later on fuse and form a continuous plat- 

 form 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 trabeculse, embracing 

 posteriorly the termination of the uotochord, 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 trabeculse 

 forming a support for the fore brain (see fig. 1, p. 5/8). 



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, meckeliau, 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 vvith the morphology of the skull from the vantage point 

 aflorded by embryology, that the basi-cranial region — the portion 



