38 AN INTRODUCTION TO ZOOLOGY 



intercrossing through the matrix in all directions. White fibres, 

 so called from their colour, appear as fairly large bundles of smaller 

 parallel fibres running together and having an undulating course. 

 These do not branch, and fibres from one bundle do not join with 

 those from another. On boiling they yield gelatin, and the addition 

 of a drop of acetic acid while they are still fresh causes them to 

 swell up and dissolve. The yellow elastic fibres differ from the 

 former in a number of ways. Their course is nearly straight, or only 

 in very shallow curves, and they branch frequently, the branches 

 anastomosing with neighbouring fibres. They are yellow in colour, 



x 



- 



FIG. 10. Areolar connective tissue of the frog. From Borradaile. 

 c., cells ; ./., elastic fibres ; './., white fibres. 



and their cut ends curl up, indicating their elastic nature. Acetic 

 acid has no effect on them, and when boiled they give elastin and 

 not gelatin. 



Various modifications of this tissue occur to meet different 

 requirements. In tendon and ligament the white fibres run parallel 

 with one another and nearly straight, and they form practically the 

 whole of the structure, the other elements being correspondingly 

 reduced. In the mammals a strong ligament, the ligamentum nuchee, 

 runs along the anterior part of the backbone and is attached to the 

 head, which it helps to hold up. This consists of yellow elastic 

 tissue, in which the elastic fibres form the major part. 



