434 



BONE, NORMAL ANATOMY. 



which is not perforated with the communi- 

 cating branches. Some lymphatics have been 

 discovered in its tissue, but no nerves ; how- 

 ever, the diseases to which it is subject, 

 the symptoms to which these give rise, 

 and the changes that follow, leave no doubt 

 of the existence of both. That cellular 

 substance enters into its formation is inferred 

 from some of its morbid phenomena, as gra- 

 nulation ; and independently of this argument, 

 on which we do not lay much stress, its exter- 

 nal fibres are evidently of a mixed nature, com- 

 bining common cellular membrane with its 

 own peculiar substance. The proper and 

 essential part is the dense, inelastic, and very 

 resisting fibre, by which it is associated with 

 other fibrous membranes. (See FIBROUS 

 TISSUE.) The older anatomists believed that 

 the periosteum had its origin from the dura 

 matei, and might be traced as one continuous 

 membrane over every bone in the body. Boer- 

 haave asserts (Praelectiones Academicae) that 

 if we could remove it without rupture, we 

 should have an exact mould of the skeleton 

 with all the joints. Its origin from the dura 

 mater was said to take place through the fora- 

 mina which transmitted the nerves ; there the 

 dura mater separated into two layers, one of 

 which enveloped the nerves as neurilema, 

 the other the bones as periosteum. But there 

 does not appear, on close inspection, to be any 

 actual identity between the dura mater and 

 periosteum, although they are most intimately 

 connected ; and there certainly is no continuity 

 of the latter membrane over the joints. It is 

 true that we may, at least in young subjects, 

 after boiling, tear off the articular ligaments 

 with the periosteum, but the tendons come off 

 with it too ; and in both cases the fibres are 

 seen to be interlaced, not continuous. 



Various uses have been assigned to the peri- 

 osteum, such as modelling the bone in its 

 growth and adding new layers to it, for the 

 further consideration of which we refer to the 

 article OSTEOGENY. It is, moreover, also said 

 to be useful for the purpose of protecting the 

 bone from the impression of surrounding 

 muscles, arteries, &c., and vice versa, shield- 

 ing them from the rough and unyielding 

 osseous substance ; permitting the soft parts to 

 move freely without injury ; and serving as a 

 centre for the fibrous system in general. This 

 last is, in Bichat's opinion, a most important 

 use ; he considers its attachment to bone is 

 more for the purpose of affording a point 

 d\ippui to the fibrous system than for any 

 office it can fulfil with regard to the osseous 

 system .* 



B. Medulla or marrow. When a longitu- 

 dinal section of a long bone is made, we ob- 

 serve a large tubular cavity occupying the 

 shaft, becoming smaller as we recede from the 

 centre, and replaced in the extremities by the 

 spongy tissue. This tube is rounded, not 

 having exactly the triangular form so commonly 

 presented by the bone externally. Its surface 

 is rough, especially near the ends, as if it had 



* Anat. Gen. tome iii. Par. 1812. 



originally contained cells which were in some 

 way or other broken up. All this cavity is 

 filled with a peculiar, soft, adipose substance 

 the medulla (quasi in media), contained in a 

 membrane of extreme delicacy. 



The medullary membrane, or internal peri- 

 osteum as it is often called, resembles the 

 pia mater in structure, being composed of 

 vessels ramifying minutely in fine cellular 

 tissue. Its tenuity is such that some anato- 

 mists have doubted its existence, but we have 

 only to look into any well-boiled marrowbone, 

 and we shall no longer doubt. It may be 

 shown too by roasting a bone, or macerating 

 it for some time in a diluted mineral acid. 

 This membrane sends numberless prolonga- 

 tions from its inner surface into the medulla 

 which it contains. It is to these processes 

 that the marrow is indebted for its consistence ; 

 they form cells and areolse whicli support and 

 maintain the vesicles in which the medullary 

 fat is lodged. They are exquisitely fine, and 

 almost invisible; we lacerate them with a 

 touch. The oily substance of the marrow is 

 not in immediate contact with these cells. It 

 is contained in distinct vesicles,which are beau- 

 tifully figured by Havers. The vesicles are 

 little bags which do not communicate with 

 each other, but look like a cluster of pearls, 

 as Monro observes. When bones have been 

 long buried or macerated, the marrow often 

 assumes a granular appearance depending on 

 this vesicular arrangement. A fine artery runs 

 to each, ramifies on it minutely, and is the 

 source of its secretion. This vessel may be 

 demonstrated. Each artery has its accompa- 

 nying vein, and, though we cannot see absor- 

 bents and nerves, their presence is inferred 

 from analogy and various phenomena. Mar- 

 row is merely a variety of adipose substance, 

 and to the article on that subject we refer for 

 the chemical properties and some generalities 

 respecting it. 



Marrow is not confined to the medullary 

 canal. It is to be found in the cells of tlie 

 spongy extremities of the long bones, and in 

 the areolae of the short. It exists in the diploe 

 of the flat bones, and even in the longitudinal 

 canals and pores of the compact tissue every 

 where. In all these situations a membrane 

 lines the osseous cell or_pore, and secretes the 

 contents. The membrane is still finer than 

 that of the medullary canal, and the oil is less 

 consistent. The communication between the 

 membranous lining is kept up by vascular 

 prolongations, not by a continuity of cavity. 

 In the bones of the head we find certain cells, 

 called sinuses, which contain air, not marrow. 

 They are distinct from the cells of the diploe, 

 with which they have no communication. 

 There is a free anastomosis between the vessels 

 of the medullary membrane and those of the 

 bone and periosteum everywhere. 



Near the middle of the long bones a fora- 

 men is observed by which an artery of con- 

 siderable size passes in to the medullary cavity, 

 where it divides into two branches, one for 

 either end. These extend to the extremities 

 of the canal in a beautiful network on its lining 



