62 OSSEOUS TISSUE. [SECT. 27. 



ossification of a new-formed soft substance, the matrix of car- 

 tilage being dissolved; in the other, by the deposition of calca- 

 reous salts in the fibrous substance of connective tissue, but 

 presents in both cases, as far as is known, essentially the same 

 chemical and histological characters. The nutritive changes of 

 the bones are very energetic, and are accomplished through the 

 agency of the vessels of the periosteum, and by those of the 

 marrow and Haversian canals, when they exist. The bones 

 possess a great capability of regeneration, so that they readily 

 re-unite when broken; and extensive losses of substance may 

 be repaired, or even entire bones restored, when the periosteum 

 has been spared. Accidental formations of bone are also very 

 common. 



Osseous tissue occurs, first, in the bones of the skeleton, to 

 which belong, also, the auditory ossicles and the hyoid bone ; 

 secondly, in the bones of the muscular system, as the sesamoid 

 bones and the ossifications in tendons ; thirdly, in the crusta 

 petrosa or cement of the teeth. Many cartilages ossify pretty 

 regularly in old age, as the costal and laryngeal cartilages. 



Dentine, or ivory, may be regarded as a modification of 

 osseous tissue, in which, instead of isolated lacunas, long canals, 

 the dentinal tubes, occur, and which, also, presents some differences 

 in chemical composition. The mode of its development leads us 

 to regard it as an osseous substance, whose cells have grown out 

 into long tubules which anastomose with each other by fine pro- 

 cesses; a view which also explains the numerous formations ob- 

 servable in animals between the typical dentine and osseous tissue 

 (see below, the section on the Teeth). 



It has been supposed till now, that the stellated bone-cells in part arise 

 from cartilage-cells, in part from cells of connective tissue ; but H. Muller 

 has shown, in a very remarkable paper, that true cartilage-cells never are 

 transformed into real stellated lacunse, and that these arise only from the 

 cells of connective tissue, and from a young growth of cells, formed by a 

 multiplication of the cartilage cells. The only exception of this rule seems 

 to occur in rachitic bones, in which, as I have shown, cartilage-cells are 

 metamorphosed into peculiar stellated lacunae. 



Literature. — Deutsch, Be penitiori Ossii/m Structurd Observationes Diss. 

 Vrat. 1834. Miescher, De Injtammatione Ossium eorumque Anatome generali. 

 Berol. 1836. Schwann, Art. Knochengewebe, in Berl. Encyclop. Worterb. der 

 med. Wiss., vol. xx. p. 102. Tomes, Art. Osseous Tissue, in Cyclop, of Anat., iii. 

 H. Muller, in Zeitsch.j. Wiss. Zool, Bd. ix. 



