230 



ELASTIC TISSUE. 



the operation of that agent, is rent into shreds or segments, mostly annular or spiral, 

 which cause the constrictions. In other cases the union of branches of the cells 

 around a bundle may be the cause of the appearance. 



The areolae, or interstices of the areolar tissue, are intercommunicating cleft-like 

 spaces between the bundles and laminae. They are not present in the immature 

 tissue, in which the ground-substance is continuous through- 

 out, but as the matrix becomes fibrillar the areolae are formed, 

 probably by the liquefaction of ground-substance. 



In fibrous tissue the bundles of white filaments run 

 parallel, cohering very intimately. 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 like in turn ; so that successive cross-sections of a tendon 

 or ligament present different figures of the sectional areas of 

 the bundles. A sheath of dense areolar tissue covers the 

 tendons and ligaments on the outside (fig; 264, a), and a 

 variable amount of the same tissue (d, e) "lies between the 

 fasciculi into which the smaller bundles are grouped, sepa- 

 rating them from one another, and also occurring, in greater 

 amount, between the largest fasciculi (c). It is in these 

 areolar tissue septa that the blood-vessels and lymphatics of 

 a tendon or ligament run. 



The surface of a tendon or of any other part consisting 

 of this texture, appears marked across the direction of the 

 fasciculi with alternate light and dark streaks which give it 

 a peculiar aspect, not unlike that of a watered ribbon. This 

 appearance is owing to the wavy course of the filaments, for 

 when the light falls on them their bendings naturally give 

 rise to alternate lights and shadows. 



The fibrous and areolar tissues thus agreeing in their 



ultimate structure, it is not to be wondered at that sometimes the limits between the 

 two should be ill-defined, and that the one should pass by inconspicuous gradations 



into the other. Instances of such a transition 

 may be seen in many of the fascise : these 

 at certain parts consist of dense areolar tissue, 

 but on being traced farther are seen gradually 

 to become fibrous ; and fascise, which in one 

 body are areolar in character, may be decidedly 

 fibrous in another. 



In the elastic tissue, there is a great 

 proportionate development of the elastic fibres, 

 the white bundles being relatively few and 

 indistinct, but considerable variation is met 

 with in the proportion of the two kinds of 

 elements. The white bundles are, for the 

 most part, disposed irregularly and course in 



different directions, as in areolar tissue ; but, in some elastic ligaments, there are 

 bundles of white fibres, which run as in an ordinary ligament parallel with one 

 another, and from end to end of the structure. The elastic fibres in an elastic licra- 



Fig. 265. ELASTIC FIBRES 



FROM THE LIGAMENTUM 



NUCH.S OF THE ox, 



SHOWING TRANSVERSE 

 MARKINGS 0~N THE FI- 

 BRES ; HIGHLY MAGNI- 

 . FIED. (E. A. S.) 



Fig. 266. CROSS- SECTION OF ELASTIC FIBRES 



FROM THE LIGAMENTUM NUCH.E OF THE 



ox (drawn by T. P. (Jostling. ) 



