208 OSSEOUS SYSTEM. fsECT. 107. 



regulate the conditions of the vascular system. This end they 

 may fulfil by conveying to the spinal cord or central organ, through 

 means of their afferent fibres, impressions depending on the con- 

 dition of the vessels, the quantity of nutrient fluid and the change 

 of material in the bones, and conducting, by their efferent fibres, 

 the reactive influence of the cord to the blood-vessels, which are 

 evidently furnished with contractile coats. These nerves do not 

 habitually give us distinct conscious sensations, but, in pathological 

 conditions, they are capable of causing pain. 



Pathological Conditions of the Bones. — Fractures, even in circumstances 

 not the most favourable, readily heal by the formation of true osseous sub- 

 stance, which, in the cylindrical bones of animals, is preceded by the forma- 

 tion of true cartilage, but not invariably so in man. In spongy bones, in frac- 

 tures within an articular capsule, and in otherwise unfavourable circumstances, 

 the breach often heals by means of a fibrous callus only, and a kind of joint 

 may be formed between the broken surfaces. After losses of substance, the 

 osseous tissue is readily regenerated, and it is especially the periosteum 

 which here plays a great part, as in the growth of the bones in thickness ; 

 this it effects, of course, by means of the exudation furnished by its vessels. 

 In animals, entire bones of the extremities, as well as the ribs, may be 

 regenerated when the periosteum is spared, as shown by many preparations 

 in Heine's collection in the Wiirzburg Museum ; but even after complete 

 excision of the periosteum, a rudiment of bone is reproduced {Heine). In 

 man, there are a good many examples known of the reproduction of entire 

 bones, as of the lower jaw, ribs, and scapula (Chopart) ; and cases of partial 

 reproduction, comprehending large portions of bone, are very numerous. It 

 is more especially the diaphyses which are thus readily restored, no matter 

 in what way they have been destroyed ; more rarely, the spongy bones or 

 spongy parts of bones, and the cranial bones ; still, in the latter, the defi- 

 ciencies after the operation of trepanning become, in many cases, occupied by 

 separate osseous pieces, instead of a mere fibrous membrane, or are even 

 completely filled up with bone ; nay, pieces cut out with the trephine may 

 be reunited, and the same has been observed to happen with pieces which 

 have been partly hacked off (Pauli). Hypertrophy oj 1 the bones occurs in 

 the most various forms, all of which may be reduced to two principal, viz., 

 1, deposition upon the exterior, or external hyperostosis, which is chiefly 

 formed from the periosteum ; 2, dejjosition in the interior, sclerosis, or filling 

 up of the medullary spaces, or Haversian canals, with new bone. These two 

 forms occur either isolated or combined : the former occurs in inflammation 

 of the periosteum alone, and in company with cancer, arthritis, syphilis, etc. ; 

 the latter, consecutively in rachitis, osteomalacia, and syphilis, also in old 

 age. With reference to the microscopical conditions, Yirchow has the merit 

 of having first demonstrated with distinctness, that in many cases of patho- 

 logical formation of bone, this is effected by the ossification of connective 

 tissue without the previous formation of cartilage. The new-formed osseous 

 tissue is sometimes like the normal, sometimes firmer, with small vascular 

 spaces and large irregular lacunae. Atrophy of the bones shows itself in 



