PHYSICAL PROPERTIES OF THE MUSCLES. 419 



Cartilage -cells are, however, to be found in the textures entering 

 into the synovial capsules of the muscles ; though genuine carti- 

 lage has not yet been found on the opposed and gliding surfaces of 

 muscles and bone, except in case of the cuboid bone. 



4. Fibro- Cartilages and Sesamoid Bones. 



A layer of fibro-cartilage is found covering the grooves on bones, 

 in which tendons glide (tibialis posticus, peroneus brevis, &c.) ; and 

 frequently the tendon also is thickened by a layer of the same 

 tissue on the surface which glides on the bone. But on the cuboid 

 bone, under the tendon of the peroneus longus, is a layer of true 

 cartilage, 3^ to 2 J ? of an inch thick. 



Fibro-cartilages also exist normally in the flexor tendons of the 

 fingers and toes ; their free surface presenting towards the articu- 

 lations. If they become ossified, they are called sesamoid bones (e. g. 

 in flexor tendon of thumb, great toe, in ligamentum patellae, &c.). 

 These are covered by a thin layer of cartilage next the joint, and 



blend with the tendinous structure on the other side. 



i 



Physical Properties of the Muscles. 



In the muscular tissue of man (i.e. including the perimysia, &c.), 

 there are usually .72.56 to 74.45 per cent, of water, and 25.55 to 

 27.44 per cent, of solid residue. The analysis of the latter has been 

 given on page 396, where the highest extreme of the water is put 

 at 80 per cent. 



The bright red color of the muscles has already been accounted 

 for (p. 397). 



' The muscles are capable of being stretched even the tendons 

 are not totally inextensible in their natural condition (p. 409) and 

 also manifest a certain degree of the physical property of elasticity. 

 This is exemplified by the return to their former condition of the 

 muscles of the abdomen, after being stretched during pregnancy 

 and by dropsical accumulations. The muscles even of a dead 

 animal still return thus after being stretched, though they do not 

 altogether resume their original form, and therefore are more rea- 

 dily torn. Still, such a slender muscle as the gracilis may support 

 a weight of eighty pounds after death, without breaking. Kolliker 

 thinks the rigor mortis is produced by an increase of elasticity, and 

 is not a vital phenomenon, as the author of the present work has 



