OEGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. 39 



fibres have a wavy outline, and are arranged nearly parallel to one 

 another (ligaments, tendons). In other cases they cross one another 

 at an angle in different directions (dermis), or they present a net-like 

 arrangement (mesentery). Fat tissue consists of ordinary connective 

 tissue in which the cells are for the most part round and contain 

 greater or smaller fat globules. 



If the normal fibrillse and bundles of fibrillae be treated with acids 

 and alkalies, they swell up, and a second form of fibre, which resists 

 these re-agents, comes into view. These are the elastic fibres (fig. 28), 

 so called because they preponderate in 

 tissue which is especially elastic. They 

 present a tendency to branch and to 

 form networks, and often possess great 

 strength (ligamentum nuchae, arterial 

 walls). They may also be spread out and 

 connected together so as to form a perfo- 

 rated membrane (fenestrated membrane). 



Cartilage is another form of connective 

 tissue. It is characterized by the shape 

 of its cells, which are usually spherical, 

 and its firm intercellular substance. The 

 latter contains chondrin, and determines 

 the rigidity of the tissue. Externally, 

 cartilage is covered by a vascular connective tissue -coat, known as 

 the perichondrium. When the intercellular substance is very 

 slightly developed, we get tissues which are transitional between 

 cellular connective tissue and cartilage. 



FIG. 28. -Elastic fibres, a; 

 b, network. 



FIG. 29. a, Hyaline cartilage with cells. b, Fibro-cartil i.^-e. 



According to its special constitution, three kinds of cartilage may 

 be distinguished, viz., hyaline (fig. 29, a), fibrous (fig. 29, b}, and 



