66 ANIMAL PHYSIOLOGY. [LESSON 23. 



body is found to be composed of the two elements ; that is to say, 

 of the white and yellow fibrous tissues. If the areolar, or cellular 

 tissue, beneath the pectoralis major muscle (large muscle of the 

 chest) be examined, microscopically, these elements will be seen as 

 clearly as in the subjoined figure (Fig. 93) obtained from this situa- 

 tion ; a shows the white and b the yellow fibrous tissue. 



FIG % 379. The yellow, or elastic fibre, exists as 



long, branched filaments, with a dark border, 

 and always curling when not put on the stretch 

 (Fig. 94). 



380. This tissue is seen in great perfection 

 in the strong Ligamentum nuchoe of the Ox 

 (Fig. 95), and its tendency to curl at the ends is 

 well marked ; a transverse section of the same 

 tissue is shown at Fig. 96. 



LESSON XXIII. 



SIMPLE CELLS, FLOATING IN ANIMAL FLUID. 



381. If the human blood be examined by the Microscope, or, 

 still better, the circulation of the blood in the web of the Frog's foot, 

 a great number of distinct bodies, or cells, will be seen floating in an 

 invisible fluid. The cells are the red corpuscles, characteristic of the 

 blood in all the red-blooded animals ; the fluid in which they float is 

 the liquor sanguinis. 



382. The red corpuscles have been called " globules " an im- 

 proper name because untrue. Their figure differs in various animals, 

 but they are not globular in any. In man, and the mammalia, they 

 are flattened discs, slightly concave on both sides ; in all the Ovipa- 

 rous (egg-bearing) vertebrata, they are oval, and of much greater size 

 than in the mammals, or man. 



383. That the corpuscles are very elastic is proved by the alter- 

 ation of figure which they undergo in passing through narrow capil- 

 lary blood-vessels, particularly when passing the bent, or rounded 

 part of the vessel ; as soon as they have more room, they instantly 

 recover their original figure. 



384. The size of the corpuscles not only greatly differs in various 

 animals, but even in the same individual some being met with as 



