ANATOMY. 



times grows out of a bone, though it may 

 have no connexion whatever with the sur- 

 rounding 1 soft parts ; of course it must 

 have derived its nerves, by means of 

 which it possesses sensation, from the 

 bone out of which it arose. 



Bones are covered by a strong" and firm 

 membrane, termed periosteum, on which 

 the vessels are first distributed ; from this 

 they descend into the substance of the 

 bone. The vessels enter through holes 

 which are evident on the surface, and 

 which are larger and more numerous in 

 the extremities of the long bones than in 

 the middle. 



OF THE MARROW. 



This is of an oily nature. It hardens, 

 when cold, in herbaceous animals; but 

 it remains fluid in those which are carni- 

 vorous. It has a reddish and bloody ap- 

 pearance in young animals ; but this soon 

 goes off. It is contained in fine membra- 

 nous cells, which do not communicate 

 with each other. The marrow occupies 

 the tube left in the middle of the long 

 bones, and also fills the cancelli of their 

 extremities. 



The cellular substance, which contains 

 the marrow, being condensed upon the 

 inside of the walls of the bone, and adhe- 

 ring to them, has been termed the perios- 

 teum internum. 



We observe in the principal bones arte- 

 ries, much larger than those which nou- 

 rish the bone, penetrating these bodies 

 obliquely, and spreading their branches 

 upon the medullary cells. 



Various unsatisfactory opinions have 

 been proposed concerning the use of the 

 marrow. The utility of the bones be- 

 ing- formed as they are, small and tubular 

 in the middle, expanded and spongy at 

 their extremities, has been already ex- 

 plained. If then spaces are necessarily 

 left in their interior parts, those spaces 

 must be filled with something; for they 

 cannot be left void, or the immense pres- 

 sure of the atmosphere would crush their 

 sides, and destroy the vacuum. There is 

 no matter in the animal body more suit- 

 at^e to fill their spaces than the marrow ; 

 and it is to be regarded as a part of the 

 adipous system of the animal. 



From the circumstances which have 

 been detailed in the foregoing account, 

 viz. the great and general vascularity of 

 bones; the quantity of soft substance ex- 

 isting in every part of them ; their growth 

 and mutation of form in disease, &c. it is 

 natural to conclude, that there exist in 



the composition of every bony fibre, arte- 

 ries for its formation, absorbents for its 

 removal, cellular substance for the con- 

 nexion of its parts, and nerves to give ani- 

 mation to the whole. In this view of the 

 subject, we see no essential difference of 

 structure between bones and other parts 

 of the body ; nor do we expect any essen- 

 nal difference in the functions of their 

 nutrient and other vessels. We naturally 

 conclude that bony fibres are formed and 

 repaired, and that they undergo mutuation 

 and removal, in the same manner, and 

 from the same causes, that soft parts do. 



CARTILAGE 



Is a semi pellucid substance, of a milk- 

 Wiiite or pearly colour, entering into the 

 composition of several parts of the body. 

 It holds a middle rank, in point of firm- 

 ness, between bones, or hard parts, and 

 the softer constituents of the human 

 frame. It appears, on a superficial ex- 

 amination, to be homogeneous in its tex- 

 ture ; for, when cut, the surface is uni- 

 form, and contains no visible cells, cavi- 

 ties, nor pores ; but resembles the section 

 of a piece of glue. It possesses a very 

 high degree of elasticity ; which property 

 distinguishes it from all other parts of the 

 body. Hence it enters into the compo- 

 sition of parts, whose functions require 

 the combination of firmness with pliancy 

 and flexibility : the preservation of a cer- 

 tain external form, with the power of 

 yielding to external force or pressure. 



Cartilages are covered by a membrane, 

 resembling, in texture and appearance, 

 as well as in its office, the periosteum of 

 bones; this is termed the perichondrium. 

 They receive arteries and veins from this 

 membrane : these vessels, however, have 

 never been demonstrated in the cartila- 

 ginous crusts of articular surfaces. Ab- 

 sorbent vessels cannot be actually shewn, 

 but their existence is abundantly proved 

 by many phenomena. The conversion of 

 cartilage into bone is alone sufficient for 

 this purpose. The cartilaginous sub- 

 stance is gradually removed, as the for- 

 mation of the bone advances. In affec- 

 tions of the joints, their cartilaginous co- 

 verings are often both entirely destroyed, 

 or partially removed : which appearances 

 can only be ascribed to the action of ab- 

 sorbent vessels. 



It does not seem to possess nerves, as 

 it is entirely destitute of sensibility. 



The thinner cartilages of the body are 

 resolved by maceration into a kind of 

 fibrous substance : e, ^. those of the or- 



