ORGANIZATION 



237 



by connective tissue. The microscope informs us that 



each fiber is itself a bundle of smaller fibers; and when 



one of these is more closely exam- 



ined, it is found to consist of a 



delicate, smooth tube, called the sar- 



co lemma, which is filled with very 



minute, parallel fibrils, averaging 



lowo f an m h m diameter, the 



whole having a striated aspect and 



containing numerous nuclei. Tissue 



of this description constitutes all 



ordinary muscle, or "lean meat," 



and is marked by regular cross FlG 



lines, or s trice. 



Besides this striated 



muscular tissue, there 



exist, in the coats of 



the stomach, intestines, 



blood vessels, and some 



other parts of verte- 



brates, smooth muscular fibers, which show 



a single nucleus under the microscope, and 



do not break up into fibrils (Fig. 319). 



The gizzards of fowls exhibit this form. 

 All muscle has the property of shorten- 



ing itself when excited; but the contraction 



of the striated kind is under the control of 



the will, while the movement of the smooth 

 - fibers is involuntary. 72 Muscles are well 



Man, divided by * 



transverse septa supplied with arteries, veins, and nerves ; 



into separate nu- , , . . . ' 



portions; but the color is due to a peculiar pigment, 



208. Voluntary 

 Muscle, portions of two 

 fibers showing the char- 

 acteristic transverse mark- 

 ings; the lighter band is 

 divided by the row of 

 minute beads constituting 

 the intermediate disk: 

 a, termination of muscular 

 substance and attachment 

 of adjoining fibrous tissue; 

 , nuclei of muscle fibers. 



much magnified. 



Muscular tissue is found in all animals from the coral 

 to man. 



(8) Nervous Tissue. Nervous Tissue consists of large, 



