THE CRANIUM. 127 



small irregular pits through the internal table, and looking 

 somewhat ulcerated : these are formed by the glands of Pac- 

 chioni, in the dura mater. At the inferior posterior corner of 

 the bone, there is also a fossa, which is made by the lateral 

 sinus of the dura mater. 



The superior, posterior, and anterior margins of the parietal 

 bone are regularly serrated, and nearly straight. The inferior 

 margin is concave, presenting a thin, bevelled, radiated surface 

 before, for articulating with the squamous portion of the tem- 

 poral bone: behind this concavity, the angle of the bone is 

 truncated and serrated, for articulating with the angular por- 

 tion of the os temporis. The anterior inferior angle is the 

 most remarkable, from its being elongated so as to join the 

 sphenoid bone in the temporal fossa. 



A foramen, called parietal, is found at the superior margin 

 of this bone, nearer to its posterior than to the anterior edge; 

 it transmits an artery between the integuments and dura mater, 

 and also a vein from the integuments to the longitudinal sinus. 

 M. Portal says, that in some protracted headaches this vein 

 swells considerably; and that he has seen much good in such 

 cases, arise from the application of leeches to the part : he has 

 also seen, in a child, its tumefaction the precursor of the pa- 

 roxysms of epilepsy. 



The parietal bone articulates with its fellow, with the fron- 

 tal, the sphenoid, the temporal, and the occipital bones. 



3. Occipital Bone, (Os Occipitis, Occipital) 



This bone is quadrilateral, resembling a trapezium. It is 

 convex externally, and concave internally; but both of these 

 surfaces are much modified by ridges and processes. Its 

 thickness is also very unequal; though, Hke the other bones, it 

 has two tables, with an intermediate diploe. It is so placed as 

 to form a considerable share of the posterior and inferior pa- 

 rietes of the cranium. 



The foramen magnum is found in the lower section of this 

 bone, and constitutes a very conspicuous feature in it. This 



