380 MUSCULAR MOTION. 



The following are the average proportions, according to Lehmann, 1 

 from his own analyses, and those of two other observers. 



Sebastian. Lehmann. Frerichs. 



Compact Bone. Spongy Bone. 



Organic . . 63'66 32-28 31'2 37-82 



Earthy . . 63-34 67-72 68'8 62-18 



Dr. Stark 2 affirms, from the results of his experiments, that the 

 mean proportion of animal matter in the bones of all vertebrate animals 

 is 33*91; of earthy 66*09; the mean proportion in the bones of man 

 33*39 of animal matter; 66*61 of earthy. 



The bones are enveloped by a dense fibrous membrane, termed, in 

 the abstract, periosteum ; but assuming different names according to 

 the part it covers. On the skull, it is called pericranium: and its 

 extensions over the cartilages of prolongation are called perichondrium. 

 The chief uses of this expansion are, to support the vessels in their 

 passage to and from the bone, and to assist in its formation ; for we 

 find, that if the periosteum be removed from a bone, it becomes dead 

 at the surface previously covered by the membrane, and exfoliates. In 

 the foetus, it adds materially to the strength of bone, prior to the 

 completion of ossification. In the long bones, ossification commences 

 at particular points ; one generally in the shaft, and others at the 

 different articular and other processes. These ossified portions are, 

 for some time, separated from each other by the animal matter, which 

 alone composes the intermediate portions of the bone ; and, without 

 this fibrous envelope, they would be too feeble, perhaps, to resist the 

 strains to which they are exposed. The periosteum, moreover, affords 

 a convenient insertion for muscles destined to act upon bones ; and 

 enables them to slide more readily when contracting : hence friction is 

 avoided. 



The cavity of lon^ bones is lined by a membrane called medullary 

 membrane or internal periosteum which is supplied with numerous 

 vessels ; adheres to the internal surface of bone, and is not only con- 

 cerned in its nutrition, but in the secretion of the marrow, and likewise 

 of a kind of oily matter, which differs from marrow in being more 

 fluid, and is contained in cells formed by the spongy substance, and in 

 areolae of the compact substance. This is called oil of bones. 



Marrow is considered to be lodged in membranous cells, formed by an 

 extension of the internal periosteum ; whilst, according to Mr. Howship, 3 

 oil of bones is probably deposited in longitudinal canals Haversian 

 canals which traverse the solid substance of the bone, and through 

 which its vessels are transmitted. If a thin transverse section of long 

 bone be examined under a high magnifying power, the bony matter is 

 observed to be arranged in concentric circles around the orifices of the 

 canals as in Fig. 164. These circles are marked by a number of stel- 

 lated dark spots formerly termed osseous corpuscles; but as they are 

 minute cavities in the bony substance, now more appropriately called 

 lacunse. From these, fine pores or tubes, termed canaliculi, proceed, 



1 Schmidt's Jahrbncher, No. vi., 1843. 



2 Edinburgh Medical and Surgical Journal, April, 1845, p. 313. 

 MedicoChirurg. Transact., vii. 393. 



