22 



BONES OF THE HEAD. 



ment ; about one inch from the head is the tubercle, a prominence 

 with an articular face, for the transverse process of the vertebra ; 

 just beyond this is a smaller tubercle, for the insertion of the external 

 transverse ligament. 



Each rib is twisted and bent ; this bend constitutes the angle of 

 the rib ; upon the external surface is a mark, showing the insertion 

 of the sacro-lumbalis muscle. The lower edge of the rib is thin and 

 cutting, and just within it is a groove,*^ running two-thirds of its 

 length, and containing the intercostal vessels and nerve. The v/pjyer 

 edge is rounded for the insertion of the intercostal muscles. 



The first rib is small and semicircular, its surfaces looking 

 superiorly and inferiorly; the superior surface has upon its middle a 

 slight fossa, for the subclavian artery ; in front of this is a roughness 

 for the insertion of the scalenus anticus muscle, behind it another for 

 the insertion of the scalenus medius ; the head has a single articular 

 surface, its angle is at the tubercle, and it has no intercostal groove. 



The eleventh and tivclfth,'^^ are called floating ribs, because they 

 are not connected with the others ; they have no tubercles, and their 

 heads have but a single articular surface; the twelfth is very short, 

 but slightly curved, and has no intercostal groove. 



BONES OF THE HEAD. 



These are twenty-two in number, and are divided into those of the 

 cranium, which are eight in number; and those of the face, which 

 are fourteen. 



CRANIUM. 



FRONTAL BONE. 



This forms the forehead of common language; it is usually a 



single, symmetrical bone, 



Fig. 



though occasionally divided 

 by a suture into two parts; 

 its shape resembles that of 

 a shell. 



The external surface is 

 convex, and about the middle 

 upon each side there is the 

 frontal protuberance^'^ being 

 the original centre of ossifi- 

 cation; below this and nearer 

 the median line is an oblique 

 ridge, called the vasal or 

 sujierciliarij iirotuherancc? 

 The inferior edge of the 

 bone is formed on either 

 side by the orhitary ridge ^ 

 formint!; the anterior boun- 



