170 



THE SKELETON. 



coronal suture. The posterior border, deeply denticulated, articulates with the 

 occipital, forming the lambdoid suture. 



Angles. The anterior superior angle, thin and pointed, corresponds with that 

 portion of the skull which in the foetus is membranous and is called the anterior 

 fontanelle. The anterior inferior angle is thin and lengthened, being received in 

 the interval between the great wing of the sphenoid and the frontal. Its inner 

 surface is marked by a deep groove, sometimes a canal, for the anterior branch of 

 the middle meningeal artery. The posterior superior angle corresponds with the 

 junction of the sagittal and lambdoid sutures. In the foetus this part of the skull 

 is membranous, and is called the posterior fontanelle. The posterior inferior angle 

 articulates with the mastoid portion of the temporal bone, and generally presents 

 on its inner surface a broad, shallow groove for lodging part of the lateral sinus. 



Development. The parietal bone is formed in membrane, being developed by 

 one centre, which corresponds with the parietal eminence, and makes its first 

 appearance about the seventh or eighth week of foetal life. Ossification gradually 

 extends from the centre to the circumference of the bone : the angles are conse- 

 quently the parts last formed, and it is in their situation that the fontanelles exist 

 previous to the completion of the growth of the bone. 



Articulations. With five bones : the opposite parietal, the occipital, frontal, 

 temporal, and sphenoid. 



Attachment of Muscles. One only, the Temporal. 



The Frontal Bone. 



The Frontal Bone (from, the forehead) resembles a cockle-shell in form, and 

 consists of two portions a vertical or frontal portion situated at the anterior part 



Nasal 

 FIG. 135. Frontal bone. Outer surface. 



of the cranium, forming the forehead ; and a horizontal or orbito-nasal portion 

 which enters into the formation of the roof of the orbits and nasal fossae. 



