HISTOLOGY OF THE FROG 111 



The looser tissue of the lymphatic glands is called adenoid 

 ( ) and is composed of an irregular network of sheets 



and strands which forms a fine meshwork of supporting cells. 



The various ligaments uniting the bones are formed of a dense and 

 non-elastic variety of white fibrous tissue. It is also found in the cutis 

 of the skin, the submucosa of the alimentary canal, in the walls of the 

 blood vessels, in the substance of glands, and in the capsules covering 

 various organs. 



Adipose tissue is regarded as a form of connective tissue in which 

 the cells have enlarged by being gorged with fat. The nucleus here lies 

 toward one side of the cell, while the cell-wall and a thin pellicle of pro- 

 toplasm surround the fat globule. 



Cartilage is a dense and massive variety of connective tissue. The 

 predominant type in the frog is known as hyaline ( ), 



the matrix of which appears transparent and homogeneous ( ), 



although it really consists of numerous fibers of different types which 

 can only be observed after various chemical experiments have been per- 

 formed upon it. The cells in this type of tissue are contained in little 

 rounded spaces or lacunae scattered quite irregularly through the mat- 

 rix. There may be two or more cells in one lacuna, causing us to believe 

 that the cells may have quite recently been formed by a division of the 

 parent cell. An intercellular substance is deposited around each cell, 

 there being a sort of partition grown between each of the cells which 

 gradually increases in thickness and presses them farther and farther 

 apart. The outer surface of the cartilage is covered by a thin layer 

 called the perichondrium ( ). 



Hyaline cartilage is found at the ends of the bones of the limbs, 

 between the spinal vertebrae and the ends of their transverse processes 

 at the tip of urostyle, in the pubis of the pelvic girdle, in the hyoid, and 

 the cartilage of the larynx and of both ends of the sternum. It also 

 forms the basis of the cranium and the central axis of the lower jaw. 



Calcined cartilage is that which contains a deposit of lime salts in 

 the matrix. It is found in the pelvis of old frogs, in the suprascapula 

 and at the ends of the larger bones in the limbs such as the head of the 

 humerus and femur. 



Bone structure is quite similar to that of cartilage and also contains 

 cells embedded in a solid matrix. In bone, however, the matrix is made 

 more firm by a deposit of carbonate and sulphate of lime. If the bone 

 is immersed in acid the lime solids are removed, the histological struc- 

 ture of bone is quite like that of cartilage. It does not follow from this, 

 however, that bone is merely calcified cartilage, for bone and cartilage 

 differ from each other both histologically and chemically. Cartilage 

 often is followed by bone, but when it is, the cartilage has been broken 

 down and the bony tissue has taken its place. We speak of two types 

 of bone, namely, compact, and spongy or cancellous. The former is firm 



