32 NORMAL HISTOLOGY. 



merit, the group being the descendants of the original occupant of the space. 

 The matrix immediately surrounding the lacunae is specialized as a layer of 

 different density, which is described as a capsule ; a further differentiation of 

 the intercellular substance is often exhibited by the more recently formed 

 matrix, which often stains with intensity and thereby produces the local ter- 

 ritories known as the cell-areas. The lacunae of hyaline cartilage are homol- 

 ogous with the lymph-spaces of other dense connective tissues, although 

 channels establishing communication between the adjacent lacunae are not 

 demonstrable in the higher vertebrates. 



The free surface of cartilage is covered by an envelope of de"nse connec- 

 * tive tissue, the perichondrium. The latter consists of a compact external 

 fibrous layer and a looser inner or chondrogenetic layer, containing many 

 connective tissue cells. These elements are disposed in rows parallel to the 

 surface of the cartilage, and during the peripheral growth of the tissue, 

 gradually assume the characteristics of cartilage cells, being at first spindle- 

 shaped and later ovoid and spherical. N The young cartilage cells thus 

 formed become gradually separated by increasing tracts of the newly depos- 

 ited intercellular matrix. As the groups of cells arising from the division of 

 the transformed elements recede from the perichondrial surface, they lose 

 their parallel disposition and become irregularly arranged and further sep- 

 arated. In addition to the perichondrial growth at the surface, cartilage 

 also increases by interstitial growth effected by the formation of new cells 

 and the associated matrix in the interior of the cartilage. The interstitial 

 method is identified with the expansion of the primary cartilages, while the 

 perichondrial one is conspicuous in bringing about the additions of new 

 cartilage during the development and growth of the long bones. 



In articular cartilage the superficial zone contains sparsely distributed 

 groups of small cells arranged parallel to the free surface. Within the deeper 

 strata, these groups are replaced by elongated rows of larger elements lying 

 perpendicular to the articular surface. This columnar disposition of the carti- 

 lage-cells is particularly evident towards the underlying epiphyseal bone. 



In parts of the cartilage remote from the perichondrium, the matrix 

 sometimes exhibits a glistening fibrous structure; more often patches of 

 opacity and granularity, due to deposits of lime-salts, affect the hyaline 

 matrix. Such areas of calcification are common in the tissues, as the costal 

 cartilages, of aged subjects, although similar changes are almost always pres- 

 ent in the laryngeal cartilages, particularly the thyroid and the cricoid, as 

 early as the twentieth year. They may progress until complete calcification 

 of the cartilage occurs. ' Histologically this alteration consists of a deposit 

 of the inorganic material within the matrix and is not true osseous tissue, 

 as implied by the frequently misapplied term "ossification." 



The blood-vessels of cartilage are usually limited to the periphery, 

 within the perichondrium or the associated synovial membranes. Nutrition 

 of the cartilage is maintained by imbibition of the tissue-juices through the 

 matrix into the lacunae. In the thicker masses, as in the cartilages of the 

 ribs, nutrient canals exist in those portions most remote from the perichon- 

 drium. Such spaces contain a small amount of areolar tissue supporting the 

 blood-vessels ; the latter, however, are limited to the canals and the nutri- 

 tion of the cartilage-tissue is effected here, as elsewhere, by absorption 

 ^ through the matrix. The lymphatics are sparingly present in the perichon- 



i' drium. ' Nerves never have been demonstrated within the cartilages, which 



fact is in accord with the insensibility of these tissues and their adaptation to 

 the friction, concussion and compressions incident to their functions. 



