THE FRONTAL BONE. 115 



With this object in view, the writer of this article has given more space to the description of 

 the skull as a whole and in section than is usually the case. Such a plan has doubtless given 

 rise to some repetition ; at the' same time it renders more complete, and, it is hoped, also more 

 useful from a practical standpoint, the account supplied. 



It must, however, be borne in mind that a text-book of Anatomy serves the double purpose 

 of a " Manual " of instruction and a work of reference. In view of this, the author has furnished 

 a detailed account of the disarticulated cranial bones, such as has been hitherto supplied in works 

 of a like kind. 



The student, however, must not assume on this account that this section of the article should 

 be neglected. He will find most of the more important details described in the article on the 

 skull as a whole ; but he would do well to supplement his knowledge by a reference to the more 

 detailed account for information regarding the development, ossification, and variations of the 

 individual bones. 



OSSA CRANII. 

 (The Bones of the Skull.), 1 



The term skull (cranium) is commonly employed to signify the entire 

 skeleton of the head. This comprises the bony envelope which surrounds 

 the brain (cranium cerebrale), and the osseous structures which support the face 

 (ossa faciei). 



The cranium cerebrale is composed of the occipital, the sphenoid, the ethmoid, 

 the frontal, the two parietals, and the two temporals, the inferior nasal conchse 

 (O.T. inferior turbinated bones), the lacrimals, the nasal, and the vomer fifteen 

 bones in all. 



The bones of the face (cranium viscerale, ossa faciei) include the following : 

 One single, viz., the mandible, and six bones, arranged in pairs, viz., the 

 maxillae, zygomatic (O.T. malar), palate seven bones in all. 



The hyoid bone is usually described along with the skull. If, in addition, the 

 bones of the middle ear, three on each side (malleus, incus, and stapes), are in- 

 cluded, the skeleton of the head consists of twenty-nine bones. 



THE SEPARATE BONES OF THE SKULL. 

 Os Frontale. 



The frontal bone, situated in the anterior part of the cranium, is a single 

 bone formed by the fusion in early life of two symmetrical halves. It consists 

 of a frontal part, which corresponds to the region of the forehead ; an orbital part, 

 which enters into the structure of the roof of the orbits ; and a nasal part, which 

 assists in forming the roof of the nasal cavities. 



Pars Frontalis. The frontal part is the shell-like portion of the bone which 

 rises upwards above the orbital arches. Its external surface is rounded from side 

 to side and from above downwards. This convexity is most pronounced about 

 1J inches above the orbital arches on either side of the median plane, constituting 

 what ^are known as the frontal tuberosities. These mark the original sites of 

 the centres from which the bone ossifies. The inferior margin oi' this part is 

 formed on either side of the median plane by the curved supraorbital margin, 

 the lateral and medial extremities of which constitute the zygomatic process 

 (O.T. external angular) and the medial angular process, respectively. The 

 latter, which descends to a lower level than the former, articulates with the 

 lacrimal bone, and is separated from its fellow by a rough articular surface 

 the nasal notch for the nasal and maxillary bones. The curve of the supra- 

 orbital margin varies in different individuals and races ; towards its medial third 



1 In catalogues of craniological collections the terms used are as follows : 

 Skull = entire skeleton of head, including the mandible. 

 Cranium = the skull, minus the mandible. 



Calvaria = that part of the skull which remains after the bones of the face have been removed 

 or destroyed. 



