ELASTIC TISSUE. 225 



in the areolar tissue, they confer a distinctly fibrous aspect to the parts which they 

 compose, accompanied by the acquisition of certain properties, which are mainly due 

 to the parallel disposition of the elements of the tissue, and to the preponderance of 

 the white fibres over the elastic (see below). This fibrous tissue is met with in the form 

 of ligaments, connecting the bones together at the joints ; it also 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 mem- 

 branous form, and constitutes a class of membranes termed " fibrous." Examples of 

 these are seen in the periosteum and perichondrium which cover the bones and carti- 

 lages, in the dura mater which lines the skull and protects 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 enclose the tender internal parts of these organs. 

 Fibrous membranes, named " aponeuroses " or " fascias," are also employed to 

 envelop 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, the fascicular and the membranous. 



The fibrous tissue is white, with a shining, silvery, or pearly 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. Accordingly the ligaments and tendons do not 

 sensibly yield to extension in the strongest muscular efforts ; and though they some- 

 times snap asunder, it is well known that bones will break more readily than tendons 

 of equal thickness, and the fibrous membranes are proportionally strong and alike 

 inextensible. 



Elastic tissue. In other situations in the body a tissue is found which, while 

 allowing a considerable amount of extension, will readily return, to its original con- 

 dition when the extending force is relaxed. This is provided for by the prepon- 

 derance of elastic fibres in the connective tissue, and these in themost typical examples 

 of the tissue, such as the ligamentum nuchse of quadrupeds and the ligamenta sub- 

 flava of the human spine, give it a yellowish colour. The tissue is extensible and 

 elastic in the highest degree, but is not so strong as ordinary fibrous ligament, and it 

 breaks across the direction of its fibres when forcibly stretched. 



Examples of the texture on a large scale are seen in the horse, ox, elephant, and 

 other large quadrupeds, in which it forms the great elastic ligament, called ligamentum 

 nuchce, that extends from the spines of the vertebras to the occiput and aids in sus- 

 taining the head ; in the same animals it also forms an elastic subcutaneous fascia, 

 which is spread over the muscles of the abdomen and assists in supporting the 

 contents of that cavity. In the human body it is met with chiefly in the following 

 situations, viz. : 



1. Forming the ligamenta subflava, which extend between the arches of 

 adjacent vertebras ; these ligaments, while they permit the bones to be drawn apart 

 in flexion of the body, aid in restoring and maintaining their habitual approximation 

 in the erect posture so far, therefore, relieving the constant effort of the erector 

 muscles. There is, moreover, an obvious advantage in having an elastic band in 

 this situation, instead of an ordinary ligament, which would be thrown into folds 

 when the bones are approximated. 2. Constituting the chief part of the stylohyoid, 

 thyrohyoid, and cricothyroid ligaments, and those named the vocal cords. Also 



