BONES OP THE HEAD. 



28 



(lary of the orbit of the eye; this ridge is terminated outwardly by the 

 external angular process,"* just within which is a depression for 

 the lachrymal gland, and inwardly by the internal angular® process; 

 between the internal angular processes is a prominence called the 

 nasal spine,^ which serves as an abutment for the nasal bones. 

 Upon this orbitary ridge, half an inch distant from the internal 

 angular process, a small depression exists, upon which plays the 

 tendon of the superior oblique muscle ; to the outside of this depres- 

 sion is a notch or foramen, for the transmission of the supra-orbital 

 artery and nerve. ^ 



The frontal sinus opens near the internal angular process, and is 

 formed by the separation of the tables over the orbitary ridge ; its 

 capacity varies and there are no means of determining it in the living 

 being ; it empties into the infundibulum of the ethmoid. 



The internal surface is concave and has numerous depressions 

 corresponding with the convolutions of the brain; in the middle is a 

 fossa for a superior longitudinal sinus, and a ridge for the attachment 

 of the dura mater ; at the bottom of this ridge is ihe foramen ccecum, 

 transmitting a vein, which forms the commencement of the sinus. 



The orhitar processes are two horizontal plates, forming the roofs 

 of the orbits, separated by a large space, which is occupied by the 

 ethmoid bone. The internal edges of these processes have two 

 grooves, which are converted into foramina, called ethmoidal or orbi- 

 tary, by the articulation of the ethmoid. The anterior transmits the 

 internal nasal nerve. 



Laterally the bone articulates with the parietal and sphenoid, in- 

 feriorly with the bones of the face and the ethmoid. 



PARIETAL BONES. 



These occur in pairs, and form the middle and lateral portions of the 

 cranium ; they are quadran- p- g 



gularand flat, externally con- 

 vex and internally concave. 



The external surface has 

 in its middle the parietal pro- 

 tuberance, the centre of ossi- 

 fication ; below this is the se- ■ 

 micircular ridgejndicating the 

 attachments of the temporal 

 fascia and muscle. 



The internal surface is con- 

 cave, with numerous depres- 

 sions for the convolutions of 

 the brain, and is also tra- 

 versed by furrows showingthe 

 course of the middle artery of 

 the dura mater. The s7^perior edge* is the thickest and much dentated; 



--^SL 



