24 PARIETAL BONE. 



interval formed by the articulation of the posterior and inferior angle 

 of the parietal with the mastoid portion of the temporal bone. 



Development. By seven centres ; four for the four parts of the ex- 

 panded portion divided by the crucial ridge, one for each condyle, and 

 one for the basilar process. Ossification commences in the expanded 

 portion of the bone at a period anterior to the vertebrae ; at birth the 

 four pieces are distinct ; they are united at about the fifth or sixth 

 year. After twenty the basilar process unites with the body of the 

 sphenoid. 



Articulations. With six bones; two parietal, two temporal, sphe- 

 noid, and atlas. 



Attachment of Muscles. To thirteen pairs ; to the rough surface 

 above the superior curved line, the occipito-frontalis ; to the superior 

 curved line, the trapezius and sterno-mastoid ; to the rough space 

 between the curved lines, complexus, and splenius capitis ; to the space 

 between the inferior curved line and the foramen magnum, the rectus 

 posticus major and minor, and obliquus superior ; to the transverse pro- 

 cess, the rectus lateralis ; and to the basilar process, the rectus anticus 

 major and minor, and superior and middle constrictor muscles. 



Fig. 13.* 



PARIETAL BONE. The parietal bone is situated at the side and 

 vertex of the skull ; it is quadrilateral in form, and divisible into an 

 external and internal surface, four borders and four angles. The 



* The external surface of the left parietal bone. 1. The superior or sagittal 

 border. 2. The inferior or squamous border. 3. The anterior or coronal bor- 

 der. 4. The posterior or lambdoidal border. 5. The temporal ridge ; the 

 figure is situated immediately in front of the parietal eminence. 6. The parietal 

 foramen, unusually large in the bone from which this figure was drawn. /. 

 The anterior inferior angle. 8. The posterior inferior angle. 



