124 SKELETON. 



SECT. II. OP THE INDIVIDUAL BONES OP THE CRANIUM. 



1. Frontal Bone, (Os Frontis, Frontal) 



The frontal bone forms the whole anterior, and a portion of 

 the superior, lateral and inferior parietes of the cranium. It is 

 symmetrical, and, occasionally, is completely divided into two 

 bones by the continuation of the suture between the parietal 

 bones. 



Its external face is convex, and the internal concave. On the 

 former may be observed a line, or slightly raised ridge, running, 

 on the middle of the bone from above downwards, which is ex- 

 pressive of the original separation between its two halves. The 

 front surface of the bone is terminated on either side, below, by 

 the orbitary or superciliary ridge, a sharp and arched elevation, 

 forming the upper anterior boundary to the orbit of the eye. 

 This ridge terminates outwardly by the external angular pro- 

 cess, and inwardly, by the internal angular process. Just above 

 the internal half of the orbitary ridge the bone is raised, by the 

 separation of its tables, into the superciliary or nasal protube- 

 rance or boss. Between the internal angular processes a broad 

 serrated surface exists, by which the frontal bone is united to the 

 nasal bones, and to the nasal processes of the superior maxil- 

 lary bones. The centre of this surface is elevated into the 

 nasal spine, which serves as an abutment to the nasal bones, 

 and resists any force which might tend to drive {hem inwards. 

 On its exterior lateral surface, behind the external angular 

 process, the frontal bone presents a concavity, bounded above 

 by a well marked semi-circular ridge, and intended for the 

 lodgement of a part of the temporal muscle. 



On each side of the front of the bone near its middle a promi- 

 nence exists, most frequently better marked in infancy than in 

 advanced life, and called by the French the frontal protube- 

 rance. 



Proceeding backwards from the inferior part of the bone are 

 the two orbitar processes, concave below and convex above. 

 They are much thinner than other parts of the bone, and are 

 separated by an oblong opening which receives the ethmoidal 

 bone. A depression, large enough to receive the end of a fin- 

 ger, is at the exterior anterior part of the orbitar process, be- 



