138 



THE SKELETON. 



then ossify, and lastly the basilar portion. At birth, the bone consists of four parts, 

 separate from one another, the occipital portion being fissured in the direction 

 indicated in the plate above. At about the fourth year, the occipital and the 

 two condyloid pieces join; and about the sixth year the bone consists of a 

 single piece. At a later period, between the eighteenth and twenty-fifth years, 

 the occipital and sphenoid become united, forming a single bone. 



Articulations. With six bones; two parietal, two temporal, sphenoid, and 

 atlas. 



Attachment of Muscles. To the superior curved line are attached the Occipito- 

 frontalis, Trapezius, and Sterno-cleido-mastoid. To the space between the 

 curved lines, the Complexus, Splenius Capitis, and Obliquus Superior; to the 

 inferior curved line, and the space between it and the foramen magnum, the 

 Rectus Capitis Posticus (Major and Minor); to the transverse process, the Rectus 

 Lateralis; and to the basilar process, the Rectus Capitis Anticus Major, Rectus 

 Auticus Minor, and Superior Constrictor of the pharynx. 



THE PARIETAL BONES. 



The Parietal Bones (paries, a wall) form by their union the sides and roof of 

 the skull. Each bone is of an irregular quadrilateral form, and presents for 

 examination two surfaces, four borders and four angles. 



Surfaces. The external surface (Fig. 92) is convex, smooth, and marked about 

 its centre by an eminence, called the parietal eminence, which indicates the 



Fi. 92. Left Parietal Bone. External Surface. 



point where ossification commenced. Crossing the middle of the bone in as 

 arched direction is a curved ridge, the temporal ridge, for the attachment of the 

 temporal fascia. Above this ridge, the surface of the bone is rough and porous, 



