Use of the Sutures in the Skulls of Animals. 25? 



they may occasionally check the progress (if I may be 

 allowed the expression) of a fracture nearly spent j — or 

 vibrations, communicated to the bones of the skull, will be 

 propagated with less force to the brain, in consequence of 

 the bones being separated at the sutures. It is, however, 

 abundantly evident, that these are not the main purposes 

 for which the sutures are formed ; otherwise they would 

 not begin to be obliterated at a period of life when they 

 would perform these offices more usefully than ever. 

 Consistent with this remark, we shall find that the true pur- 

 pose for which they are formed, and the particular process 

 with which they are connected, is fully completed before 

 their obliteration takes place. 



When we take a view of the mode of junction between 

 many bones and parts of bones in the human body, which 

 do not admit of motion, we find that with little exception 

 they all agree in this particular ; that sooner or later the car- 

 tilage or periosteum, which once was interposed, ^s obliterat- 

 ed, and these different portions, or entire bones, coalesce. 



The separate portions, which originally compose the ver- 

 tebrae, are early in thus uniting: after these the sides of 

 the lower jaw; at a later period the epiphysis of a cylindrical 

 boneis united to its body : and still later the bones of the skull 

 usually coalesce, and the sutures are obliterated. Other bones, 

 as those of the face, which have no motion and sustain little 

 weight, are irregular in this respect ; sometimes uniting, but 

 generally remaining distinct to the end of a long life. 



The original formation of the osseous system in several 

 distinct pieces, respects principally its speedy ossification at 

 an early period of life, and its future convenient extension, 

 till it has arrived as its full growth ; and we may consider it 

 as a general principle, that where two part* of one bone are 

 separated from each other by an intervening cartilage, or 

 two distinct bonesj merely by periosteum, at that part osse- 

 ous materials arc added to increase their length or extend 

 their superficies. This we shall find takes place, whether 

 the junction be effected by comparatively smooth surfiaces, 

 its between the body of a bone and its epiphysis ; or between 



Vol. 21. No. 95. April 1S06. R the 



