14 ELEMENTS OF MAMMALIAN ANATOMY. 
nervous system and making up cartilage and ligaments 
(Fig. 11); muscular, composing the greater part of the 
muscular system; and nervous, constitut- 
6 8 a. ing the nervous system (Fig. 97). 
e uy =) The naked eye is unable to distinguish 
OO 18 Ps the elements of the tissues, but the micro- 
o. @ scope reveals the fact that each kind of 
Fic. 9. Cetrs or tissue is formed of either cells or fibers 
ee * or, as is most frequently the case, a com- 
bination of both. 
The different relative arrangements of these anatomic 
elements, together with their morphology, permit one to 
know from what organ any particular section of tissue 
under consideration has been taken. 
These ultimate units of structure are still further resolved 
into parts by the chemist, who has shown that they are 
composed largely of carbon, hydrogen, oxygen, and nitro- 
gen. Since there can be no energy developed in the body 
without the disintegration and consequent death of some of 
the particles composing the millions of tiny cells, it is plain 
that they must have their losses replaced in order to con- 
tinue their existence. Therefore a method of preparing the 
‘food for the use of the cells, and a way of transporting it 
to each of them are necessary. 
The former is accomplished by the digestive system, 
which, through the agency of the salivary, gastric, pan- 
creatic, and other glands, transforms the food into a special 
liquid state capable of being absorbed by the millions of 
minute finger-like villi of the small intestine (Fig. 63). 
Thence it is transferred by the lacteal vessels and veins to 
the heart, whence it is conveyed by the arteries to their 
capillary distribution in the neighborhood of every cell in 
the body. 
The dead matter or waste material resulting from the 
