FIBHOUS TISSUE. 63 



riBROUS TISSUE. 



Bistribution. — This s-vibstance is one of those which are serviceable 

 in the body chiefl}' on account of their mechanical properties, being em- 

 I^loyed to connect together or to support and protect other parts. It is 

 met with in the form of ligaments, connecting the bones together at the 

 joints ; it forms the tendons of muscles, into which their fleshy fibres 

 are inserted, and which serve to attach these fibres to the bones. In its 

 investing and protecting character it assumes the membranous form, 

 and constitutes a class of membranes termed "■ fibrous." Examples of 

 these are seen in the periosteum and perichondrium which cover the 

 bones and cartilages, in the dura mater which lines the skull and pro- 

 tects the brain, and the fibrous layer which strengthens the pericardium, 

 also in the albugineous coat of the testicle, and the sclerotic coat of the 

 eye, which inclose the tender internal parts of these organs. Fibrous 

 membranes, named " aponeuroses " or " fascia," are also employed to 

 envelope and bind down the muscles of different regions, of which the 

 great fascia inclosing the muscles of the thigh and leg is a well-known 

 example. The tendons of muscles, too, may assume the expanded form 

 of aponeuroses, as those of the broad muscles of the abdomen, which 

 form strong fibrous layers in the walls of that cavity and add to their 

 strength. It thus appears that the fibrous tissue presents itself under 

 two principal forms, t\\Q fascicular and the membranous. 



Physical Properties. — The fibrous tissue is white or yellowish white, 

 with a shining, silvery, or nacreous aspect. It is exceedingly strong 

 and tough, yet perfectly pliant ; but it is almost devoid of extensibility. 

 By these qualities it is admirably suited to the purposes to which it is 

 applied in the animal frame. By its inextensible character it maintains 

 in apposition the parts which it connects against any severing force short 

 of that sufficient to cause actual rupture, and this is resisted by its 

 great strength, whilst its flexibility permits of easy motion. Accord- 

 ingly the ligaments and tendons do not sensibly yield to extension in 

 the strongest muscular efforts ; and though they sometimes snap 

 asunder, it is well known that bones will break more readily than ten- 

 dons of equal thickness. The fibrous membranes are proportionafly 

 strong and alike inextensible ; they will gradually yield, it is true, 

 when the extending force acts slowly and for a long time, as when 

 tumours or fluids slowly gather beneath them ; but perhaps this gradual 

 extension is accompanied with some nutritive change affecting the pro- 

 perties of the tissue. 



Structure. — The fibrous tissue is made up of fine filaments, agree- 

 ing in all respects with the white filaments of the areolar tissue already 

 described. Like these they are collected into bundles, in which they 

 run parallel and exhibit the same wavy character, cohering very 

 intimately. The bundles appear to the naked eye as fine shining threads 

 or narrow flattened bands, for they vary greatly in thickness. They 

 either run all in one direction as in long tendons, or intersect each 

 other in different planes as in some aponeuroses, or they take various 

 directions and decussate irregularly with each other as in the dura 

 mater. And when they run parallel to each other, as in tendon, they 

 do not keep separate throughout their length, but send off" slips to join 

 neighbouring bundles and receive the hke in turn ; so that successive 



