CONNECTIVE TISSUE. 67 



free from their attachments, become bent or coiled, and, when boiled, 

 yield elastin, and not gelatin, as is the case with white fibres. This 

 structure occurs in the ligamentum nuchw, ligamenta subflava, 

 walls of bronchioles and alveoli of lungs, arteries, vocal cords, and 

 in connective tissue generally. This and the preceding form of con- 

 nective tissue are intercellular in character and are, therefore, asso- 

 ciated with cells in the formation of tissues. For the practical 

 study of elastic fibres,, the ligamentum nuchw of an ox may be used. 



III. AREOLAR TISSUE. 



Areolar tissue is composed of cells and an intercellular substance 

 which consists chiefly of white and elastic fibers. It lines the un- 

 der surface of the skin, forms the muscle sheaths, and is found in the 

 mammary gland and other structures. 



IV. ADIPOSE TISSUE. 



Adipose tissue is almost wholly cellular. The cells are probably 

 formed from connective tissue corpuscles, in which fat globules ap- 

 pear, increase in size, and finally coalesce. Thus is formed one large 

 globule of fat, which distends the cell-wall, crowding the protoplasm 

 and nucleus outward. The cells are well supplied with blood capil- 

 laries. They are bound together by areolar tissue into lobules, and 

 the lobules into lobes. For practical study, a section of the tongue 

 will be found satisfactory. It is widely distributed, occurring al- 

 most everywhere that connective tissue is found. 



V. MUCOUS TISSUE. 



This occurs in the umbilical cord and comprises cells and a gel- 

 atinous intercellular substance called the jelly of Wharton. The 

 cells are stellate in form, and the protoplasmic processes anasto- 

 mose with each other, forming a mesh- work throughout the struc- 

 ture. This tissue contains but few fibrous elements, except as the 

 cord approaches full time. 



Laboratory exercise No. 18. Umbilical cord. Embed pieces of a 

 three-months' umbilical cord in celloidin. Stain with haematoxylin, 

 method No. 5. Observe (1) a thin layer of superficial cells; (2) the 

 blood-vessels, two arteries and one vein, surrounded by the mucous 

 tissue, the jelly of Wharton, or mucin, containing- the stellate cells; 

 (3) look also for white or elastic fibres. In what other structure is 

 mucous tissue found? 



