152 Prof. Macalister, Variations in the ossification, etc. 



but may be reduced to three groups, lambdoidal, intermediate and 

 asterial. 



The angle of the lambda may be formed by a single bone 

 or of a pair of lambdoid bones which differ from the preinter- 

 parietal in the depth to which they penetrate into the squama. 

 By overgrowth they sometimes seem to push the preinterparietal 

 element very hardly, but there is generally little difficulty in 

 the way of distinguishing them. Outside these there are often 

 paralambdoid bones, single, paired or multiple; occasionally a pair 

 of paralambdoids may exist while the angle is preinterparietal. 



About the middle of the lambdoidal suture on each side there 

 is a more or less conspicuous reentrant angle on the hinder edge 

 of the parietal into which a projecting angle of the occipital 

 projects. This is the angulus intermedius. On the whole skull 

 this lies along the line of that indefinite rounded ridge that forms 

 the boundary between the medial strip of skull-roof and the 

 lateral skull-wall, which continues from the frontal tuber through 

 the parietal tuber, and here crosses the lambdoid suture to end in 

 the linea nuchge suprema. The parietal notch probably owes its 

 existence to the unequal growth of the twin centres of that bone 

 the limits of whose posterior territories it marks. On the occipital 

 it corresponds nearly to the limit between the preinterparietal and 

 the interparietal. At this spot an angular bone is very commonly 

 developed, often flanked medially by one or more metangular and 

 distally by one or more parangular. 



The third region at which wormian bones may be found is the 

 asterion or point of confluence of the parietal, mastoid, inter- 

 parietal and supraoccipital bones. Here there is often a galaxy 

 of ossicles, sometimes only an asterial or a metasterial bone, 

 flanked perhaps by others not belonging primarily to the lambdoid 

 suture, but to the occipitomastoid or parietomastoid. 



To one or other of these types the larger sutural bones may 

 be referred. There are also minuter ossicles of another category 

 representing detached portions of sutural teeth separately ossifying 

 and often embedded, not penetrating the whole thickness of the 

 bone. 



