PASSIVE ORGANS OF LOCOMOTION. 547 



They are insoluble in acetic acid. The cells are less numerous than the free nuclei. They 

 are spherical or slightly polyhedric, contain a few pale granulations, are rendered pale 

 but are not dissolved by acetic acid, and they measure about yyV^ of an inch in diameter. 



Myeloplaxes. These are irregular, nucleated patches, also described by Robin, more 

 abundant in the spongy portions of the bones than in the medullary canals, and are 

 applied to the internal surfaces of the bones. They are exceedingly irregular in size and 

 form (measuring from y^^ to ?%-$ of an inch in diameter), are finely granular, and present 

 from two to twenty or thirty nuclei. The nuclei are clear, ovoid, generally with a nucle- 

 olus, and are from ^-^ to ^Vo * an mc ^ l n g> by -j-oVcr or ^^ of an inch broad. The 

 myeloplaxes are rendered pale by acetic acid, and the nuclei are then brought out more 

 distinctly. 



In addition to the anatomical elements just described, the marrow contains a few very 

 delicate bundles of connective tissue, most of which accompany the blood-vessels. In 

 the foetus, the adipose vesicles are few or may be absent ; but in the adult they are quite 

 numerous, and in some bones they aeern to constitute the whole mass of the marrow. 

 They do not differ materially from the fat-cells in other situations. Holding these different 

 structures together, is a variable quantity of semitransparent, amorphous, or slightly 

 granular matter. 



The nutrient artery of the bones sends branches to the marrow, generally two in 

 number for the long bones, which are distributed between the various anatomical elements 

 and finally surround the fatty lobules and the fat-vesicles with a delicate capillary plexus. 

 The veins correspond to the arteries in their distribution. The nerves follow the arteries 

 and are lost when these vessels no longer present a muscular coat. Nothing is known 

 of the presence of lymphatics in any part of the bones or in the periosteum. 



The only point of physiological interest connected with the marrow is, that it has 

 been found to possess, in common with the periosteum but in a less degree, the property 

 of generating true bony substances. We shall see farther on, that the periosteum is not 

 only very important to the nutrition of the bones, but that it will generate bone when 

 transplanted into vascular parts. M. Oilier, who has made a very extended series of 

 experiments upon the physiological properties of the periosteum, endeavored to produce 

 bone by transplanting portions of marrow, but was unsuccessful. M. Goujon, however, 

 has lately been more fortunate. He has found that frequently, but not always, marrow 

 transplanted into the muscular tissue will generate bone, particularly the marrow taken 

 from young bones, but the bony tissue thus formed is soon absorbed. 



Periosteum. In most of the bones the periosteum presents a single layer of fibrous 

 tissue, but in some of the long bones two or three layers may be demonstrated. This 

 membrane adheres to the bone but can generally be separated without much difficulty. 

 It covers the bones completely, except at the articular surfaces, where its place is supplied 

 by cartilaginous incrustation. It is composed mainly of fibres of the white inelastic variety, 

 with numerous small elastic fibres, blood-vessels, nerves, and a few adipose vesicles. 



The arterial branches ramifying in the periosteum are quite numerous, forming a close, 

 anastomosing plexus, which sends numerous small branches into the bony substance. 

 There is nothing peculiar in the arrangement of the veins. The distribution of the veins 

 in the bony substance has been very little studied. 



The nerves of the periosteum are very abundant and form in its substance quite a 

 close plexus. 



The adipose tissue is very variable in quantity. In some parts it forms a continuous 

 sheet, and in others the vesicles are scattered here and there in the substance of the 

 membrane. 



The importance of the periosteum to the nutrition of the bones is very great. Instances 

 are on record where bones have been removed, leaving the periosteum, and in which the 

 entire bone has been regenerated. The importance of the periosteum has been still 



