60 THE SUTURES. 



generally said to be made by the radii of ossification, from the 

 opposite bones meeting and passing each other, so as to form 

 a serrated edge. This explanation is however insufficient, for 

 the following reasons : we always find the sutures in the same 

 relative situation, and observing the same course in the cranium ; 

 if they, then, depended exclusively on so mechanical a process, 

 as the shooting ol" the rays of bone across each other when they 

 met, in ossification on one side of the head occurring sooner or 

 faster than on the other, we ought to find the sagittal suture to 

 one side of the middle line ; it should also, in many instances, 

 be found crooked. Moreover, in all cases where bones arise 

 from different points of ossification and meet, particularly in 

 the flat bones, the serrated edges ought to be formed ; this, 

 however, is not the case. The os occipitis, which is formed 

 originally from four points of ossification, and has therefore as 

 many bones composing it in early life, never joins these bones 

 together by the serrated edge ; the acromion process of the 

 scapula is never united to its spine by sutures; the three bones 

 of the sternum never unite by suture, and the same observa- 

 tion holds good in many other instances. Bichat, who rejects 

 this mechanical doctrine, advances an opinion much better 

 founded. The dura mater and the pericranium, before ossifi- 

 cation commences, form one membrane, consisting of two 

 lamina ; it is generally known that the flat bones of the 

 cranium are secreted between these two lamina ; now the out- 

 line of each bone, long before it has reached its utmost limits, 

 is marked off* by partitions passing between these two mem- 

 branes. The peculiar shape of the bony junction, or the suture 

 in adult life, will, therefore, depend upon the original shape 

 of the partitions: when the latter are serrated, the points of 

 ossification will fill up these serrae ; but when they are simply 

 oblique, the squamous suture will be formed. This also 

 accounts for cases where the mode of junction is intermediate 

 to the squamous and serrated suture ; for the formation of the 

 ossa triquetra, and why in some skulls they do not exist, 

 whereas in others their extent and number are very considera- 

 ble. The inference will also be drawn from this, that in all ossi- 



