94 Vhe Marrcw. [Book fX; 



which is in general towards the ends of the long bones,- 

 their ftrufture is very cavernous throughout. The 

 marrow pervades the whole fubfbnee of the bones, but 

 is moft remarkable in the middle part of the cavities 

 of the long bones. Its appearance and nature alfo 

 differ in different bones, or in the ^ame bone in the 

 progrefs of life. Thus the marrow is bloody in chij- 

 dren, oily in adults, and thinner and more watery in 

 aged people. 



At the time of birth, the bones are very imperfect, 

 particularly thofe of the head 5 fo that by being move- 

 able in this part, and folding over each other during 

 the time of delivery, an eafier pafiage is procured for 

 the infant. There are many, projections from the 

 bones, which in infancy are foft, but which in the 

 adult ftate are bony j and the fame tendency to the for- 

 mation of bone increafing with our years, bones which 

 were feparate in the prime of life concrete in old age. 

 In the decay of the body, however, the bones are di- 

 minimed with the other parts, fo as in extreme old age 

 to weigh a third lefs than in the middle periods of 

 life. 



To far the greater number of bones whofe ends are 

 not joined to other bones by immoveable articulation, 

 are annexed, by the intervention of cartilage, fmaller 

 bones, called epiphyfes or appendages. Iii young fub- 

 jects thefe are eafily feparable, but in adults the point 

 of conjunction is not very perceptible. 



The bones are furnifhed with a tough membrane, 

 called the periofteum, which is fpread on their furface, 

 and the principal ufe of which fcems to be to convey 

 blood-refiels for their nourifhment ; thefe blood-vefiels 

 are very numerous and remarkable in the bones in the 

 infant liate, but become gradually lefs fo in the progrefs 

 of life. 



It 



