A N D D E A T H. 473 



and dudile ; and, the following year, when the 

 hud at the top of the hranch begins to expand, 

 the fap rifes through the foft fibres of each 

 membrane, and converts them, by its fediments, 

 into other woody plates. The fame procefs 

 goes on annually ; and, in this manner, the tree 

 or branch gradually increafes in thicknefs. The 

 internal cavity likewife augments in proportion 

 to the growth of the branch ; becaufe the inter- 

 nal membrane extends along with the other 

 parts, and the woody plates are only applied 

 fucceffively to the plates already formed. If we 

 examine a branch, or a joint, which has been the 

 produdt of one year, we fhall find, that it uni- 

 formly preferves the fame figure through all the 

 ftages of its growth. The joints or knots which 

 mark the produdlon of each year, become fixed 

 points for the reaction of thofe powers that ex- 

 pand the contiguous parts during the following 

 year. The fuperior buds readl againft thefe 

 points, and, by expanding thcmfelves, form new 

 branches or joints in the fame manner as thefirft 

 were produced. 



The procefs of oflification would be very fi- 

 milar to that we have now defcribed, if the fixed 

 points of the bones began at the extremities, in 

 place of the middle. At firft the bones of the 

 foetus are only fmall threads, or tubes, of a duc- 

 tile matter, which are cafily perceived through 

 the delicate and tranfparent fkln. The thigh- 

 bone, for example, is then a fmall fhort tube, 



like 



