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in tbe middle, to allow of the convenient arrangement of 

 large mufcks round them ; they become expanded at their 

 extremities to afford an extent of furface for the formation 

 of joints, and the fupport of the weight of the body. A 

 cavity is left in the midcle ; for if all the earthy matter had 

 been compafted into the fmalleft poffible fpace, the bones 

 would have been fuch flender ftems, as to be very uufuitable 

 to their offices ; and if they had been of their prefent dimen- 

 fions and folid throughout, they would have been unnecefla- 

 rily (Iron J and weighty. Befides, it can be proved by ma- 

 thematical demonltratlon, that the ftrength of the bone be- 

 comes augmented, in proportion as its fibres are placed at a 

 greater dillance from its centre. 



With regard to the vafcular ftrufture of bones, there can 

 be no doubt but that it exaftly refembles that of the reft of 

 the bo.ly. That bones pofiVTs numeioii^ arteries, is proved 

 by the injeftion of young bones from the general arterious 

 fyftcm of the fubjecl ; for they are made very red br the 

 injedlion conveyed into them by numerous, though minute 

 arteries, which enter them by pores evident on their furface. 

 The effect of feeding animali with madder is an additional 

 and ftriking proof of the fame facl ; for the bone becomes 

 deeply tinged with the red colour of the madder. The 

 caufe of this phenomenon has of late been cxpla:ned by 

 Dr. Rutherford : he has (hewn that itarifes from a chemical 

 attraction that exifts between earths an i certain colouring 

 materials, which caufes them to combine fo intimately as to 

 form pigments which are called lakes by painters. Dr. 

 Rutherford diflblved madder in dillilled water, and added to 

 it muriate of lime, which produced no change of appearance 

 in the folution ; on the further addition of pholphat of 

 foda, a double decompofuion took place ; the muriatic acid 

 combined with the foda, and the phofphoric acid with the 

 lime. The pholphat of lime alfo combined with the mad- 

 der, and they were tos;ethcr precipitated, forming a beautiful 

 red p jwder. If blood be conftantly conveyed into bones by 

 numerous arteries, it mult be returned from them again by 

 veins, or otherwite it mull accumulate in them in confiderable 

 quantities. That bones poffefs abforbents in common with 

 other parts is equally clear, and is proved by their mode of 

 growth, and alfo by their dileafts. The growth of the 

 tube of a bone is a proof of the mutation ol its parts by ab- 

 forption ; for if bones grew merely by new matter depofited 

 on the furface, the tube of the bone fhould be of the fam.e 

 dimenfions in the adult as in the foetus : on the contrary, 

 however, the tube enlarges, and bears the fame proportion 

 to the whole bone in either ftate. If any number of lamins 

 of the iides of a bone, or if a portion of its whole fubltance 

 perifh, the mortified part is detached in the fame manner that 

 it is in foft parts ; and this detachment is manifeftly the 

 effedl, in the firtl inftance, of the agency of the abforbing 

 vclFcls. Though a portion of animal fuljftaiice has perillied, 

 it (till pofieffes the fame po.vcrs of cohelive attraction that 

 It did while living ; it (till tenacioully adheres to the living 

 parts ; but a fpace takes place all round the dead portion, 

 and the produflion of tliat fpace can only rationally be at- 

 tributed to the removal of parts by the abforbents. In 

 diftafes of bones tlicir form becomes entirely altered, if an 

 increafed depoiition of matter takes place in their intennal 

 parts ; and this alteration of form could not happen unlefs 

 the walls were removed by abforption, and depolited anew 

 in conformity to the augmented buik and figure, which the 

 difeafed dcpofition had occalioned. Not to cite lefler in- 

 {lances, one may be mentioned, which Mr. Hunter ufed to 

 (hew in his leftures, of a very large and globular bony 

 tumour, which had formed in the extremity of one of the 

 bones of the leg in an ox. The tumour was fo folid, that 



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the feAion of it admitted of being polilhed, and the walls of 

 the bone had become thin, and of a fpherical form, fo as to 

 make a neat kind of cafe containing this bony tumour. 

 That bones polTefs nerves as well as arteries, veins, and ab- 

 forbents, cannot be doubted ; for though they have naturally 

 but httle fenfibihty, they become extremely painful when 

 difeafed; and again a fungus fometimes grows out of a bone, 

 which is fenlible, though it may have no connection whatever 

 with the furrounding foft parts ; of courfe it muft have de- 

 rived its nerves, by means of which it polfefles its fenfation, 

 from the bone out of which it arofe. That the veflVls and 

 nerves of a bone are connefted together by common cellular 

 fubftances, as in other parts of the body, is demonllrated by 

 feaking a bone in dilute muriatic acid, which diiTolves all the 

 lime, and leaves the vafcular matter a lictle thickened, but 

 perfeftly flexil>le. We then fee that this vafcular and eel- 

 lular matter lias a laminated arrangement coiTefponding to 

 that of the earthy, which has been defcribed, fo that between 

 each layer of earthy matter, ti\cre is a layer of fuit fubllance, 

 and of courfe the different layers of foft fubilance are con- 

 nected by vcffeis and cellular membrane, winch incervene 

 between the bony fibres, and conneft the different flrata to- 

 gether. Bones are covered by a fltong, tinn, fibrous fub- 

 ftance, ter.mtd periofleum, on which the veifels are firft 

 dillributed ; from this they defceud, conncc"ted by cellular 

 fubftance, between the fibres of the bone. The vedels and 

 nerves of the bone enter it through holes which are evident 

 on the furface, and which are larger and more numerous in 

 the extremities of the lo';g bones than in the middle. The 

 vefTcls do not penetrate the bone in a tranfverfe direction, but 

 obliquely, running tranfverfely through a certain number of 

 lamelis,' and then taking a perpendicular courfe between 

 others, which prevents the bone from being weakened, par- 

 ticularly at any onepart, by that want of earthy m.atter which 

 is necefTary to leave room for the admiffijn and dilliibution 

 of veffcls. 



The marrow that is contained in bones is of an unftuous 

 nature, and in herbaceous animals, hardens when it becomes 

 cold ; but it remains fluid in thofe which are carnivorous. 

 Some of the red parts of the blood are depofited with it in 

 young animals, but in thofe that are adult it is no longer 

 tinged with blood. The marrow is contained in fine cells, 

 which do not communicate with one another, like thofe of 

 the common cellular fubllance. This is proved by fawing 

 a bone through, and keeping it in a temperature which will 

 preferve the marrow fluid, with the part which is fawn down- 

 wards. Under thefe circumllaiices, if the cells communi. 

 cated, the gravitatian of the liquid marrow would caule it 

 quickly to drop out, and leave the cells empty ; but this does 

 not happen. The cells which contain the marrow are lodged 

 in the cancelli of the bone, at the extremities of the long 

 bones ; but in the middle they are uni'upportcd by tins kind 

 of olfeous ilructure. The cellular fubllance which contains 

 the marrow, being condenfed upon the infide of the walls of 

 the bone, and adhering to them, has been termed the peri- 

 ofleum interiuim. In the principal bones we perceive arte- 

 ries, m.uch larger than thofe for the nutrition of the bone, 

 which penetrate the wails obliquely, and fpread their 

 branches upon the medullary cells, for the nourllbment of 

 thefe parts. That thefe are the chief nutrient arteries of the 

 m.arrow cannot be doubted ; and it has been contended, that 

 thev have e::cluCvely this power, and that they do not anallo- 

 mofe with the nutrient arteries of the bone. This opinion 

 has been formed, becaufe in fome cafes of accidental injury', 

 in which the medullary artery has been deiiroyed, the mar- 

 row has, as it were, perifhed. This opinion, however, ilands 

 in direft oppofition to all analogy; audit mijfl indeed be con- 

 i; C i fidered 



