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 



Musck nucleus. 



Muscle nucleus. 



Sl:-B!*S_ Connective-tissu 



Fig. 53. 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 



Fig. 54. Cross section of heart 

 muscle fibers. 



