Some Considerations respecting the Parietal Bone. 337 



The Oynomolgiis mentioned above and some other monkeys 

 had wormian bones. In one human skull which had a temporo-frontal 

 suture 20 mm long and a sphenoidal alar-frontal suture 11 mm long 

 Wormian bones were found in the lambdoidal suture. 



It is probable that the forward and downward extension of the 

 parietal is due to greater formative activity in that bone developing 

 tissue and that this is brought about by internal conditions or by 

 the condition of the skin tissues without. This would in itself tend 

 to produce an articulation further forward in case the formative activity 

 of the anterior bones were diminished. On the other hand the development 

 of the alisphenoid may be arrested by the pressure of other bones or 

 teeth not to speak of the actual absorption of the bone. Thus two 

 bones may be separated so far as to give place for the advance of 

 other bones into the interval. 



It would seem, therefore, that the size and shape of the parietals 

 depends on: 



a) The nature and vascularity of the nervous parts beneath. 



b) The vascularity and structure of the superficial tissues. 



c) The relative activity of the formative tissue along the 

 margins of adjacent bones. 



d) This includes the greater or less tendency in adjacent bones 

 to advance. 



e) The impulses that are conveyed to the bones from without. 



f) The extension of certain muscular attachments. 



g) The effect of artificial feeding which may alter the formative 

 processes in each case. 



h) Actual disease. 



The writer has to acknowledge his indebtedness to the works 

 of Zittel, Woodward, Huxley, Owen, Parker, and the ever fresh Meckel, 

 Forbes, records have been consulted. 



The Museums of Dublin, Glasgow, Liverpool, Manchester and 

 Galway have furnished specimens from which most of the outline 

 drawings have been made. These sketches explain themselves. 



Internationale Monatsschrift für Anat. n. Phys. XXI. 



22 



