1884.] 



MR. J. B. SUTTON ON THE CRANIAL ARCADE. 



569 



examined some cases of cleft-palate and can support Albrecht's 

 statements, but in the normal condition there is only one centre for 

 each premasillary bone. The discrepancy may be thus explained : — 

 the premaxilla is originally developed in membrane, and at some 

 little distance from the median line, which, in the foetus, is occupied 

 by the thick cartilage known as the ethmo-vomerine plate. After a 

 time the premaxillary ossifications involve the anterior extremity of 

 this cartilage, so that the inner portions of these bones are really of 

 cartilage origin. If anything interfere to prevent the premaxillary 

 bone or bones meeting the etlimo-vomerine plate, the tip of this 

 cartilage ossifies on its own account, and gives rise to the false notion 

 of two independent centres occurring normally. This fact may be 

 verified easily in the majority of mammals. In other parts of the 



Fig. 1. 



Pre.M 



Three views of the human superior maxilla, to visually express the disposition 



of its four ossiQc centres. 



M. Malar centre, Max. Maxillary centre, Pre-M. Pre-maxillary, and 



Pre.P. Pre-palatiue centres. 



skull instances of a bone arising in membrane and invading cartilage 

 might be quoted in support of my opinion. 



The next centre to be considered forms the palate process of the 

 maxilla and a considerable portion of the inner wall. Fig. I represents 

 it as an L-shaped piece of bone, forming by means of its horizontal 

 plate the roof of the mouth, whilst its vertical plate extends upwards 

 as far as the orbital surface of the bone. 



This centre will be referred to throughout this paper as the " pre- 

 palatiue " centre. 



