On a Case of Abnormality in the Human Foetus. 421 



built of birch twigs, and lined with down, and was appa- 

 rently the work of the bird itself, and not the old one of any 

 other bird. Instances of wild ducks occasionally using the 

 nests of other birds, have been observed, and even at as 

 great a height as thirty feet from the ground. In these in- 

 stances, it is believed, the young birds are brought down to 

 the ground by the bill of the mother. 



II. Note on a case of Abnormality in the Ossification of the Parietal 

 Bones in the Human Foetus. By R. H. Traquair, M.D. 



Some time ago I dissected the head of a human foetus of 

 between the eighth and ninth months, in which the parietal 

 bones presented a condition apparently at variance with the 

 well-known rule, that these bones are two in number, and 

 each developed from a single ossific centre. 



In this cranium the parietal bone of the left side is per- 

 fectly normal, being ossified from one centre, which corres- 

 ponds with the well-marked parietal eminence. 



On the right side, however, the part which represents the 

 parietal bone is divided into two distinct pieces, in a line ex- 

 tending from the middle of its posterior margin obliquely 

 forwards to a little above its anterior inferior angle. Of 

 these two pieces, each of which is of course ossified from its 

 own centre, the lower is accordingly somewhat triangular, 

 and is equal in size to one-half the upper rudely quadran- 

 gular part ; and the two pieces form together a double 

 parietal bone, which is larger by about one-fourth than the 

 single bone of the opposite side. 



This cranium is therefore abnormal— 



1. In possessing three parietal bones instead of two. 



2. In the asymmetrical disposition of these bones, two 

 being on one side, one on the other. 



3. The vault of the cranium is also asymmetrical in this 

 respect, that the double parietal bone of the right side is 

 considerably larger than the single one of the left. 



The only other analogous case of wbich I am at present 

 aware, is one recorded by Yon Sommering.* He has de- 



* Tiedemann ncd Treviranus Zeitschrift fur Physiologie, ii. 1828. 



