THE ELEMENTARY TISSUES 7 



(c) Adipose tissue is composed of modified connective tissue 

 cells, known as fat cells which occur in the meshes of areolar 

 tissue. Adipose tissue is essentially a '' packing substance," 

 for it accumulates in the spaces between structures of the body 

 very much as bric-a-brac is packed in excelsior. The greatest 

 quantities of this tissue occur in the lumbar region in the areolar 

 tissue around the kidneys, in the marrow of long bones, in the 

 omentum, in the subcutaneous areolar tissue, and in other 

 places. However, that lying between the skeletal muscles will 

 be most often noticed in dissecting the rabbit. 



(d) Reticular (retiform) tissue consists essentially of branch- 

 ing cells which form a network containing fluid and other 

 cellular elements. It occurs as supporting framework in lymph 

 glands, spleen, mucosa of the intestine, in interstitial tissues of 

 kidneys, Hver, and in the framework of bone marrow. 



(e) Cartilaginous tissue is nonvascular and is comparatively 

 brittle. It is usually divided into three kinds according to 

 differences in its intercellular matrix: (i) Hyahne cartilage 

 (gristle) has an opalescent blue-like tint, is brittle, and forms 

 the articular surfaces of bones, the larger cartilages of the nose, 

 larynx, trachea, and bronchi, the costal and xiphoid cartilages, 

 and enters into numerous other structures. (2) Elastic (yellow 

 elastic fibrocartilage, reticular) cartilage is yellowish in color, 

 comparatively tough and pliable, and is limited in distribution. 

 It occurs in the Eustachian tube, cartilages of the external ear, 

 epiglottis, and other parts of the larynx. (3) Fibrous cartilage 

 (white fibrocartilage) occurs mainly between articulating sur- 

 faces in certain joints, such as the knee (menisci or interarticular 

 plates), the vertebral centra (connecting fibrocartilage), as 

 lining of osseous grooves through which a tendon passes (strati- 

 form fibrocartilage), e.g., bicipital groove of humerus (Fig. 12) 

 and peroneal groove of tibiofibula (Fig. 16) and forms the 

 fibrocartilaginous rim to certain joints (circumferential fibro- 

 cartilages) such as the hip joint. 



(f) Osseous, or bone tissue is the densest and hardest tissue 

 in the body, except the dentin and enamel of the teeth. The 



