HISTOLOGY OF THE FROG 101 



stood. They are often called fixed corpuscles, in opposition to 

 intrusive leucocytes which are frequently found in the areolar 

 tissue. But it seems probable, from the analogy of lower 

 animals, that some, at least, of the connective tissue cells may 

 have a migratory character. 



Tendons and ligaments are a modified form of connective 

 tissue, known as white fibrous tissue. In them the bundles of 

 white fibres run in parallel courses instead of crossing one 

 another irregularly, and are greatly preponderant over the 

 elastic fibres. The corpuscles of fibrous tissue are all of the 

 flat or lamellar variety, and tend to be disposed in rows or 

 chains following the parallel arrangement of the bundles. 



Some ligaments, such as the ligamentum nuchae of the 

 ox and other mammals, are composed almost entirely of 

 yellow elastic tissue, and they are very elastic and extensible. 

 Ordinary white tendons, on the other hand, are scarcely 

 extensible. 



It is clear that the bulk of a connective tissue consists of an 

 intercellular substance which has been formed by the activity 

 of the cells contained in it. In the course of development, 

 connective tissue appears as an accumulation of amoeboid 

 undifferentiated cells, which presently send out ramifying 

 processes which become united with one another to form a 

 network. The meshes of the network are occupied by an 

 albuminous fluid, which afterwards becomes changed to form 

 the ground substance. The ground substance is at first homo- 

 geneous, but presently fibres are formed in it ; how they are 

 formed is not clear. Some think that they are the result of 

 the actual conversion of cells into bundles of fibres ; others 

 think that the substance of the fibres is simply deposited in 

 the matrix, the cells contributing the material without being 

 themselves converted and used up in the process. The latter 

 view is more probably correct, though there is little positive 

 evidence on the subject. 



The substance popularly known as gristle, but scientifically 

 named cartilage, has many features in common with connec- 

 tive tissue. Like the latter, it consists of a homogeneous 

 matrix in which cells are imbedded. If a thin slice of the 

 white or pearly and translucent cartilage from the articular 

 head of a bone or from the hyoid, sternum, or supra-scapula of 

 a frog be examined under the microscope, it is seen to consist 



