122 SKELETON, 



have a powerful influence in producing these diversities. The 

 head is divided into cranium and face. 



SECT. I. OF THE CRANIUM. 



The Cranium is composed of eight bones. The Os Frontis, 

 the Os Occipitis, two Ossa Parietalia, two Ossa Temporum, the 

 Os S.phenoides, and the Os Ethmoides, The Os Frontis is at 

 the front of the cranium; the Os Occipitis is at its hind part; the 

 Ossa Parietalia, one on each side, form its superior lateral parts; 

 the Ossa Temporum, also one on each side, form its inferior la- 

 teral parietes; the Os Sphenoides is in the middle of its bottom 

 part; and the Os Ethmoides is at the fore part of the centre or 

 body of the last bone. 



The cavity thus formed for the brain, has three diameters, 

 which may be learned by sawing vertically through the middle 

 line of one skull, and horizontally through the cavity of another. 

 The first diameter is the longest, and extends from the lower 

 part of the frontal bone to the protuberance on the middle of the 

 Interior surface of the os occipitis; it is commonly about six 

 inches and a half long. The second diameter includes the space 

 between the superior margins of the temporal bones, where they 

 are most distant from each other, and passing over the middle of 

 the great occipital foramen, is about five inches. The third di- 

 ameter is taken from the centre of the large hole in the occipital 

 bone, to the centre of the suture between the parietal bones; it is 

 about five inches, also. Rather more than one-third of the ca- 

 vity of the cranium is placed behind the second diameter, and it 

 diminishes somewhat abruptly; but in front of this diameter the 

 cavity is finished more gradually. 



When the face is separated from the cranium, the exterior 

 surface of the latter, excepting its base, represents tolerably ac- 

 curately the form and proportions of its cavity: allowance being 

 made for the large sinuses in the lower part of the frontal bone, 

 and for the thinness of the upper parts of the temporal bones. 

 The diameters mentioned, can only represent what most fre- 

 quently happens, for daily observation proves remarkable de- 

 partures from them. Sometimes the transverse diameter is in- 

 creased at the expense of the longest, which gives to the head a 

 flatness before and behind. On other occasions, the vertical di- 



