CARTILAGE 71 



Elastic Cartilage. Elastic cartilage occurs in the external ear, in 

 the auditory tube, in the epiglottis and in the cuneiform and corniculate 

 cartilages and the vocal processes of the arytenoid cartilages of the 

 larynx. It is essentially hyaline cartilage the matrix of which has 

 become permeated with delicate elastic fibers forming a dense interlacing 

 network. The large spheroidal cartilage cell lies in a lacuna bounded 

 by a capsule and surrounded by a layer of hyaline matrix free of elastic 

 fibers. The plates of elastic cartilage, like the hyaline variety, are sur- 

 rounded by a dense fibrous perichondrium. Neither blood-vessels, nerves, 

 nor lymphatics are distributed within the matrix of elastic cartilage. 



Fibrocartilage This tissue forms the interarticular cartilages of the 

 lower jaw, the clavicle, and the knee; composes the intervertebral disks 

 and the other cartilaginous symphyses of the body; lines the tendon 

 grooves of the bones, and forms the 

 glenoid ligament of the shoulder and the 

 cotyloid ligament of the hip. Fibrocar- 

 tilage is intermediate in structure between 

 hyaline cartilage and such very dense 



fibrous tissue as occurs in the tendons of , 



FIG. 84. FIBROCARTILAGE, FROM 



muscles. At the attached margins of the INTERVERTEBRAL DISK OF Ox. 

 cartilaginous plates its tissue is continued 



by imperceptible gradations into the surrounding fibrous connective tis- 

 sues. Like the other forms of cartilage, this variety is also non-vascular 

 and devoid of nerves. . 



Microscopically, fibrocartilage differs from such dense white fibrous 

 tissue as is found in the ligaments and tendons, in that the meshes of 

 the dense fibrous tissue of fibrocartilage are everywhere permeated by a 

 hyaline matrix in which here and there are small groups of ovoid car- 

 tilage cells. Each cartilage cell is occasionally surrounded by a charac- 

 teristic, concentric, lamellar appearance of the adjacent matrix, the so- 

 called 'capsule/ Plates of fibrocartilage, unlike the other varieties, are 

 not surrounded by a perichondrium. 



A peculiar sort of connective tissue of entodermal origin is found 

 in the nuclei pulposi of the invertebral disks. It is the sole adult 

 vestige of the embryonic axis, the notochord. According to Williams 

 (Amer. Jour. Anat., 8, 3, 1908), who carefully studied its cytomorphosis 

 in the pig, "It is primarily cellular and epithelial; later it becomes a 



