CHAP. IV.] CARTILAGE. 89 



without the expenditure of any vital force. Thus we find this 

 variety of cartilage in the external ear, in the Eustachian. tube, in 

 the nostrils and eyelids, and in the larynx, trachea, and bronchial 

 ramifications. 



Physical Characters. Cartilage, in colour, varies from an azure, 

 or pearly white, to a whitish yellow. The temporary and articular 

 varieties present the former colour; the membraniform, for the 

 most part, the latter. 



Elasticity, flexibility, and considerable cohesive power, are the 

 chief physical properties of this texture ; and in these qualities, and 

 especially in the first, consists its great value, both in contributing 

 to the perfection of the locomotive apparatus, and in its adaptation 

 to other purposes. Cartilage is not brittle; a thin piece may be 

 broken across by being suddenly bent at a very acute angle ; but, 

 in general, cartilage will bend easily without the occurrence of 

 fracture, and will speedily resume its former direction on the 

 bending force being removed. 



Structure. The simplest kind of cartilage consists merely of 

 nucleated cells, and exceedingly resembles the cellular tissue of 

 plants. The cells are very large, roundish or ovoidal, and more or 

 less flattened by their mutual contact. Each has a diminutive 

 transparent nucleus attached to the inner surface of the cell-mem- 

 brane, and containing within it a minute granule, or nucleolus. 

 We have also met with other transparent globules, of variable size 

 and extreme delicacy, within the cells. Some white fibrous tissue 

 usually encloses the mass of cells, and penetrates to a certain dis- 

 tance among the more superficial of them, which are smaller and 

 more densely packed than the rest. 



This kind of cartilage is found in the Fig. IB. 



chorda dorsalis, or rudimentary spinal column 

 of the early embryo : it also exists in the per- 

 manent chorda dorsalis of the cartilaginous 

 fishes, and may be well seen in a thin piece 

 of that structure from the lamprey (fig. 13). 



But, in other kinds of cartilage, the cells 

 are imbedded in an intercellular substance, 

 or matrix, more or less abundant in the dif- 

 ferent kinds, and presenting certain varieties 

 of appearance. In all, it is possible to see 

 that the cells have a proper membrane of their 

 own, and are not mere excavations in the 

 intercellular substance ; this may often be determined at a broken 



