TISSUES. 



blood-vessels, lymph- vessels, large ducts of glands, 

 nipple, hair-follicles, Eustachian tube, spleen, pros- 

 tate gland, ciliary muscles, and iris of the eye. 



2. Cardiac Muscle. The heart ontogenetically is 

 a modified blood-vessel, and its muscle, therefore, 

 has the same origin as smooth muscle. Heart 

 muscle cells are oval or brick-shaped and mono- 

 nucleated, the oval nuclei occupying the center of 



Muscle nucleus. 



Connective-tissue cell. 



pig, 23. Longitudinal section of heart muscle fibers. 



the cell. Longitudinal fibrils and, in addition, a 



fine cross striation, are present in the cytoplasm, 



resembling the cross stri- 



ation of voluntary mus- 



cle. This cross striation 



is explained under Vol- 



untary Muscle, and 



therefore will not be 



given here. The cells 



are joined together, end 



to end, by delicate ce- 



ment lines and laterally 



may unite with adjacent cells by means of protoplas- 



mic processes. In the cytoplasm adjacent to the ends 



of the nuclei, normally fat is frequently present and 



Muscle nucleus. 



Fig 



54 _ Cross sec tion of heart 

 muscle fibers - 



