FAT. CARTILAGE. 59 



pass that keep it in play. It also affords, by its power of re- 

 sisting the passage of neat, a warm covering to animals that 

 are destined to live in cold climates ; and it is in these that 

 we find it accumulated to the largest amount. Further, 

 being deposited when nourishment is abundant, it serves as a 

 store of combustive material, which may be taken back into 

 the system, and made use of in time of need. The causes 

 which peculiarly contribute to the production of fat, will be 

 considered hereafter ( 162). 



47. Another tissue of which cells form the principal part, 

 is that termed Cartilage or gristle. Its simplest state is that 

 of a mass of firm substance, composed of 

 chondrin (20), through which are scat- 

 tered a number of cells, at a greater or less 

 distance from one another. In the simple 

 cellular cartilages, such as those which 

 cover the ends of the bones where they 

 glide over one another so as to form 

 moveable joints, no trace of structure can 

 be seen in the intervening substance. Fig. is. SECTIOK OF 

 But in cartilages which have to resist not CARTILAGE, 



, . . Showing its cells imbed- 



only pressure but also extension or strain, ded in intercellular sub- 

 we find the space between the cells partly stance - 

 occupied by fibres, which resemble those of ligaments ; and 

 such are termed fibro-cartilages. They are found in Man be- 

 tween the vertebrae of which the spinal column is made up 

 ( 71); and also uniting the bones of the pelvis ( 645). 

 Sometimes, where elasticity is required, the fibres are those 

 of the yellow fibrous tissue ( 23) ; this is the case with the 

 cartilage which forms the external ear. Cartilage is not 

 penetrated by blood-vessels, at least in its natural state. The 

 blood is brought to its surface by a set of vessels which bulge 

 out into dilatations or swellings upon it, so that a large quan- 

 tity of fluid comes into the immediate neighbourhood of the 

 cartilage, being only separated from it by the thin walls of 

 the vessels ; and it appears that this fluid, or so much of 

 it as is required, is absorbed by the nearest cells, and trans- 

 mitted by them to the cells in the interior, so that the whole 

 substance is nourished. This is precisely the mode in which 

 the interior of the large sea-weeds (whose tissue consists of 

 cells imbedded in a gelatinous substance, and therefore bears 



