THE CONNECTIVE TISSUES. 



77 



Fig. 58. 



and appear, even under high powers of the microscope, as fine, trans 

 parent, homogeneous lines. They are usu- 

 ally aggregated into bundles of greater or less 

 thickness, being held together by a small 

 amount of the cement-substance already re- 

 ferred to. In these bundles the fibres run a 

 somewhat wavy course from one end of the 

 bundle to the other, but lie parallel to each 

 other and never branch. When treated with 

 dilute acetic acid, without previous hardening, 

 they swell and become almost invisible. They 

 are converted into gelatin when boiled in water. 

 The yellow, or elastic, fibres (Figs. 59-61) are 

 coarser than the white and more highly refracting, 

 appearing more conspicuous when viewed under 

 the microscope. They may be nearly straight, but 

 more usually run a sinuous course. At intervals they divide, and the 

 branches anastomose with each other to form a fibrous network, the 



Fibres of white fibrous 

 tissue teased apart to 

 show the individual 

 fibrils. 



Fig. 59. 



Fig. 60. 



4* 



<P,)ii4t 



fca 



mmsmm 



Elastic fibres. 



Pig. r>9.— From the subcutaneous areolar tissue of the rabbit. (Schafer.) 



Fig. 60.— Section of ear. (Hertwig.) The intercellular substance contains a reticulum of 



coarse anastomosing elastic fibres. (See Fig. 53.) 

 Fig. 61.— Fenestrated membrane from a branch of human carotid artery. (Triepel.) 



meshes of which may be large, as is the case in areolar tissue, or so 

 small and bounded by such broad fibres that the network resembles 



