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that the difference of extent of their concave and convex surfaces, renders 

 it necessary that the parts of which they are formed, should be shaped 

 obliquely, he explains the advantages of the sqaamous articulation be- 

 tween the temporal and parietal bones. 



When the arch of the cranium is loaded with a very heavy burthen, 

 the temporal bones prevent the parietals on which the effort is immedi- 

 ately applied, from being forced inwardly, or from being separated out- 

 wardly. Hunauld very aptly compares them to buttresses which are to 

 the parietal bones of the same use as walls to the arches which they sup- 

 port. 



Bordeu* endeavoured to apply to the bones of the face, the principles 

 by which Hunauld has been guided in his investigation with regard to 

 those of the skull. According to Bordeu, the greater part of the bones 

 of the upper jaw, but particularly the superior maxillary bones, resist the 

 effort of the lower jaw, which, by acting on the upper dental arch, has a 

 perpetual tendency to force upward, or to separate outwardly, the bones 

 in which the teeth of that ja\v arc inserted. As the greatest stress of the 

 effort determines them upward, it is, likewise, in that direction, that the 

 bones of the upper jaw rest more powerfully on those of the skull. The 

 author concludes this very ingenious memoir, by proposing to physiolo- 

 gists, the solution of the following problem, " When a man supports a 

 great weight on his head, and holds at the same time any thing very 

 firmly between his teeth, which is the bone of the head that is most 

 acted upon ; which supports the weight cf the whole machine ?" 



The body of the sphenoid, and especially the posterior half, appears 

 to me to be the central point on which the united efforts of the bones of 

 the skull and of the face act, in the case supposed by Bordeu. 



The sphenoid is connected with all the other bones of the skull ; it is 

 immediately connected with several of the bones of the face, as with the 

 malar bones, with the palatine bones, with the vomer, and sometimes, 

 with the superior maxillary bones. These bones of the face, in the case 

 in question, alone support the lower jaw against the upper. The ethmoid 

 bone, the ossa unguis, and the inferior turbinated bones, are thin and frail, 

 and serve merely to form the nasal fossae, of which they increase the 

 windings, and do not deserve to be' attendee^* to in this investigation. 

 The vomer may, it is true, communicate to the ethmoid, in an inferior 

 degree, a part of the effort; for, the anterior part of its upper edge is 

 articulated with the perpendicular lanffclla of that bone ; but this quan- 

 tity is very small, as the vomer is thin and transmits it almost wholly, 

 to the body of the sphenoid, with the lower face of which it is articu- 

 lated. 



The effort exerted on the bones of the upper jaw, is transmitted, by 

 means of the nasal processes of the upper maxillary bones, by the orbital*- 

 and zygomatic processes of the malar bones, and by the upper edge of the 

 palate bones and of the vomer, to the frontal, to the temporal, and sphenoi- 

 dal bones. 



If we wish to determine what becomes of the greater part of the effort 

 transmitted to the frontal bones by the maxillary and malar bones, we may 

 observe in the first place, that it is articulated with the sphenoid bone, by 



* Academe des Sciences, Memoircs presentes par les savans strangers. Tome EL 



2M 



