34 PARIETAL BONE. 



over every part of its surface by numerous furrows, \vhich cor- 

 respond with the ramifications of the arteria meriingea magna. 

 Along the upper border is part of a shallow groove, completed by 

 the opposite parietal bone, which serves to contain the superior 

 longitudinal sinus. Some slight pits are also observable, near to this 

 groove, which lodge the glandules Pacchioni. 



The anterior inferior angle is thin and lengthened, and articu- 

 lates with the greater wing of the sphenoid bone. Upon its 

 inner surface it is deeply channelled by a groove for the trunk of 

 the arteria meningea magna. This groove is frequently converted 

 into a canal. The posterior inferior angle is thick, and presents a 

 broad and shallow groove for the lateral sinus. 



Developement. By a single centre. 



Articulations. With five bones ; with the opposite parietal bone, 

 the occipital, frontal, temporal, and sphenoid. 



Attachment of Muscles. To one only, the temporal. The occi- 

 pito-frontalis glides over its upper surface. 



FRONTAL BONE. The frontal bone bears some resemblance in 

 form to the under valve of a scallop shell. It is situated at the 

 anterior part of the cranium, forming the forehead, and assists in 

 the construction of the roof of the orbits and nose. Hence it is 

 divisible into a superior or frontal portion, and an inferior or orbito- 

 nasal portion. Each of these portions presents for examination an 

 external and internal surface, borders and processes. 



External Surface. At about the middle of each lateral half of the 

 frontal portion is a projection, the frontal boss or eminence, which 

 denotes the situation of the centre of ossification. Below these 

 points are the superciliary ridges, large towards their inner termina- 

 tion, and becoming gradually smaller as they arch outwards ; they 

 support the ' eyebrows. Beneath the superciliary ridges are the 

 sharp and prominent arches which form the upper margin of the 

 orbits, the supra-orbital ridges. Externally the supra-orbital ridge 

 terminates in the external angular process, and internally in the 

 internal angular process ; at the inner third of this ridge is a notch, 

 sometimes converted into a foramen, the supra-orbital notch, which 

 gives passage to the supra-orbital or frontal artery, veins, and 

 nerve. Between the two superciliary ridges is a rough projection, 

 the nasal tuberosity : the whole of this portion of the bone is some- 

 what prominent, and denotes the situation of the frontal sinuses. 

 Extending upwards and backwards from the external angular pro- 

 cess is a sharp ridge, the commencement of the temporal ridge, and 

 beneath this a depressed surface that forms part of the temporal 

 fossa. 



2. The inferior, or squamous border. 3. The anterior, or coronal border. 4. The 

 posterior, or lambdoidal border. 5. Part of the groove for the superior longitudinal 

 sinus. 6. The internal termination of the parietal foramen. 7. The anterior inferior 

 angle of the bone, on which is seen the groove for the trunk of the arteria meningea 

 magna. 8. The posterior inferior angle, upon which is seen a portion of the groove 

 for the lateral sinus. 



