in tlie JShills of AnimaU, 321 



pkccs of lead still remained at *the same 

 distance from each other that they were before. 

 From this experiment we learn, that a cylin- 

 xlrical bone is not extended in its middle, but 

 is lengthened by addition to its extremities, 

 where the body of the bone is joined to its 

 epiphysis; the chief intention of the epiphysis 

 being to allow the intervention of a vascular 

 organ, which may conveniently deposit bony 

 materials, without interfering with the joint 

 itself. 



As cylindrical bones are lengthed at their 

 extreme parts, we are led by analogy to con- 

 clude, that the same general plan is pursued 

 in the extension of the flat bones of the body : 

 and although we have no direct experiment by 

 which this has been proved, there are circum- 

 stances which leave little doubt but they are 

 extended by addition to their edges. Thus to 

 take the parietal bone as an example ; as 

 ossification begins in a central point and ex- 

 tends towards the circumference, it is probable 

 that to the completion of the process, it con- 

 tinues to go on in the same direction ; and the 

 same circumstance taking place in every bone 

 of the cranium, it is probable, that even after 

 the whole of the brain is incased in bone, the 

 addition is still made at the edge of each, and 

 that the general enlargement originates where 

 4 



