THE PARIETAL BONES. 13 



Between the two tables of the vertical portion in the adult are the 

 Frontal Sinuses, two spaces at the anterior inferior part of the bone, which 

 are lined with mucous membrane, and open into the middle meatus of the 

 nose by means of an Infundibulum for each. 



Describe its horizontal portion, or orbital plates. They each present the 

 following points, viz. 



Fossa, for the lachrymal gland, near the external angular process. 

 Depression, at the nasal margin for the pulley of the superior oblique muscle. 

 Ethmoidal Notch, having the following foramina on its margin. 

 Anterior Ethmoidal Foramen, for anterior ethmoidal vessels and the nasal 



branch of the ophthalmic nerve. 



Posterior Ethmoidal Foramen, for posterior ethmoidal vessels. 

 Grooves, on the cranial surface, for branches of the anterior and middle 



meningeal arteries. 



Describe its articulations, development, and muscles. The frontal 

 articulates with 12 bones, the sphenoid, ethmoid, 2 parietal, 2 nasal, 2 supe- 

 rior maxillary, 2 lachrymal, and 2 malar. It is developed by 2 centres in mem- 

 brane, I for each lateral half. The muscles attached to it are 3 pairs, the 

 temporal, corrugator supercilii, and orbicularis palpebrarum. 



THE PARIETAL BONES. 



Describe their general characteristics. They are 2 quadrilaterally-shaped 1 

 bones situated at the superior and lateral regions of the cranium. The supe- 

 rior border of each joins the other by the Sagittal Suture ; the anterior border 

 joins the frontal bone by part of the Coronal Suture ; the posterior border 

 articulates with the occipital, forming the Lambdoidal Suture ; the inferior 

 border with the sphenoid and temporal bones. Forming the lateral walls of 

 the skull they are named parietal, from Cartes, a wall. 



Describe the points on each Parietal bone. Externally the bone is con- 

 rex and presents for examination, 



Temporal Ridge, continuous with the same on the frontal bone. 



Parietal Eminence, the point where ossification commenced. 



Parietal Foramen, close to the upper border, transmits a vein to the superior 



longitudinal sinus. Is not constant. 

 Internally, the bone is concave, and marked by 



Depressions for the Pacchionian bodies, and for the cerebral convolutions. 



Furrows, for branches of the middle meningeal artery. 



Groove, for the lateral sinus, at the posterior inferior angle. 



Half-groove, along the upper border, for the superior longitudinal sinus of 

 the dura mater. 



