SMOOTH MUSCLE TISSUE 



55 



variable. Its greatest diameter in the region of the centrally sit- 

 uated nucleus is from 5 to 10 /A, about the diameter of a red blood 

 corpuscle. The length of the cell varies from 50 to 500 /A. As 

 seen in transverse section these fibres vary in size from a mere 



FIG. 56. SMOOTH MUSCLE FIBRES FROM THE WALL OF THE HUMAN INTESTINE. 

 Longitudinal section. Hematein and eosin. x 665. 



point up to their maximum diameter, according as the section hap- 

 pens to pass through the end or through the middle of a fibre. 

 Because of its central location, the nucleus is onlv found in the 

 larger transections. 



Smooth muscle fibers may be joined together in interlacing 

 groups as in the wall of the uterus or bladder; or they may form 

 broad membranous layers as in the wall of 

 the alimentary tract ; or again, they may $ 



form small isolated bundles, as in the skin. & 9 * 



In any case, the muscle bundles are united 9 



by a delicate network of connective tissue. $ 



Smooth muscular tissue occurs chiefly in 



the walls of the hollow or tubular viscera. 



Its distribution may be classified as follows : jtr 



(1) In the alimentary tract: lower por- 

 tion of the esophagus, stomach, small and 

 large intestines. 



(2) In the respiratory system : trachea 

 and bronchial tubes. 



(3) In the genito-urinary system : ureter, 



bladder, urethra, penis, prostate, vagina, uterus, oviduct, and ovary. 



(4) In the vascular system : arteries, veins, and the larger 

 lymphatic vessels. 



(5) In the ducts of all secreting glands : gall ducts and gall 

 bladder, and the ducts of the pancreas, salivary glands, testicle, etc. 



(6) It is also found in the capsules of the spleen and lymphatic 

 nodes, in the skin, and in the intrinsic muscles of the eye. 



FIG. 57. SMOOTH MUSCLE 

 FIBRES FROM THE WALL 



OF THE HUMAN INTES- 

 TINE. 



Transection. Hcmatein 

 and eosin. x 750. 



