No. 448.] 



PARIETAL DIVISION. 



ondary ossicles. The occipital bone shows the ordinary at this 

 age separation of the squama, exoccipital and basal portions. 

 The development of the temporal bones, particularly the squa- 

 mae, is much retarded. 



This case is of interest in several ways. It is another instance 

 where the anomaly of parietal division is associated with a pro- 

 nounced pathological condition of the skull. Such association, 

 particularly with hydrocephalus (some degree of which may have 

 existed even in the skull under consideration), is so common m 

 the children and foetal series of the cases reported that the 

 causal relation of these pathological conditions with the divisions 

 becomes more and more firmly established. They, of course, 

 play the role of the exciting cause only, the fundamental condi- 

 tion which makes a parietal division possible being the presence 

 of two starting foci or centers of ossification of the bone. In 

 this connection one is forcibly reminded of the apparent rarity 

 of pathological conditions in the adult human and also in the ape 

 and monkey skulls with parietal divisions. Even if it be granted 

 that much may right itself during the growth of the skull; it 

 would seem that at least some of the parietal divisions m man 

 and most of those in lower primates must be due to other e.\c it- 

 ing causes than rickets or hydrocephalus. 



The second point of interest in the present case i^ the 

 presence of two large and plainly accessory bones ( ante 10- 

 superiorly and postero-inferiorly on the right) which m an at u t 

 skull could easily be taken for primary portions <jf the parietal. 

 As can be seen in the illustration the small true parietal on the 

 right side shows a marked cleft near the middle of the anterior 

 border. This cleft, it has been amply demonstrated before, is a 

 remnant of the original membranous space between the upper 

 and lower parietal centres. We had here, then, the two normal 

 elementary foci of the bone and in the usual position. But the 

 growth of the already fused primary parietal, due to rachitis, 

 was retarded. Such a retardation in any of the bones of the 

 cranial vault and from any reason leads invariably, undoubtedly 

 through some trophic impulse which regulates the cranial 

 growth, to the appearance of more or less numerous secondary 

 foci of ossification, from which result various sized supple- 



