CHARACTERISTICS OF CONNECTIVE TISSUES 659 



The amorphous ground substance or chondrin is reinforced by fibers of the 

 collagenous (white) variety, but the quantity of fiber present is much less 

 than in fibrous or elastic cartilage. The chondrocytes (i.e., the cartilage cells) 

 lie within capsules. Canaliculi apparently do not connect one capsule with 

 another. This type of cartilage forms a considerable part of the temporary 

 axial and appendicular skeleton of the developing organism and remains as 

 the adult axial and appendicular skeleton in cyclostomatous and elasmobranch 

 fishes. In the adults of other vertebrates, it is supplemented to various degrees 

 by bone. 



b. Fibrocartilage 



Fibrocartilage (fig. 313E) is a transitional form between white fibrous 

 connective tissue and cartilage. It contains bundles of collagenous fibers, placed 

 parallel to each other. Between the fibrous bundles, cartilage capsules are 

 present, containing cartilage cells (chondrocytes). A small amount of amor- 

 phous ground substance or chondrin is present, particularly around the cell 

 capsules. Some types of fibrocartilage contain more of the amorphous ground 

 substance than other types. Fibrocartilage is found in the intervertebral discs 

 between the vertebrae, in the area between the two pubic bones in mammals, 

 and in certain ligaments, such as the ligamentum teres femoris. 



c. Elastic Cartilage 



Elastic cartilage (fig. 313F) differs from the hyaline variety by the pres- 

 ence of an interstitial substance which contains branching and interlacing 

 fibers of the elastic variety. The elastic fibers penetrate through the amorphous 

 substance in all directions. While hyaline cartilage is bluish in color, the color 

 of elastic cartilage is yellowish. It is found in the external ear of mammals, 

 in the mammalian epiglottis. Eustachian tubes, the tubes of the external 

 auditory meatus, etc. 



3. Bone 



a. Characteristics of Bone 



Bone forms the greater part of the adult skeleton of all vertebrates above 

 the cyclostomatous and elasmobranch fishes. In teleost fishes and in land- 

 frequenting vertebrates, it tends to displace most of the cartilaginous sub- 

 stance of the skeleton. The interstitial substance of bone is composed of a 

 fundamental fibrous material similar to that of connective tissue. These fibers 

 are called osteocollagenous fibers. A small amount of amorphous ground 

 substance also is present. The interstices of this fibrous and amorphous sub- 

 strate are infiltrated with mineral salts, particularly calcium salts, to form 

 the bony substance. The latter is formed in layers, each layer constituting a 

 lamella. The bone cells or osteocytes are present in small cavities or lacunae 

 between the lamellae. The lacunae are connected with each other by small 



