94 



MUSCULAR TISSUE. 



[CH. VI. 



In addition to these physiological distinctions, there are histo- 

 logical differences between them and ordinary striped muscle. 

 These histological differences are the following : 



1. Their muscular fibres are thinner. 



2. They have more sarcoplasm. 



3. Longitudinal striation is more distinct. 



4. Transverse striation is more irregular than usual. 



5. Their nuclei are situated not only under the sarcolemma, 

 but also in the thickness of the fibre. 



6. The transverse loops of the capillary network are dilated 

 into little reservoirs, far beyond the size of ordinary capillaries. 



Cardiac Muscle. 



The muscular fibres of the heart, unlike those of most of the 

 involuntary muscles, are striated ; but although, in this respect, 



they resemble the skeletal mus- 

 cles, they have distinguishing 

 characteristics of their own. The 

 fibres which lie side by side are 

 united at frequent intervals by 

 short branches (fig. 113). The 

 fibres are smaller than those of the 

 ordinary striated muscles, and their 

 transverse striation is less marked. 

 No sarcolemma can be discerned. 

 One nucleus is situated in the 

 middle of the substance of each 

 fibre. At the junctions of the fibres 

 there is a certain amount of ce- 

 menting material, stainable by silver 



Fig. 113. Muscular fibre cells from 

 the heart. (E. A. Schafer.) 



nitrate. 



Plain Muscle. 



Plain muscle forms the proper muscular coats (i.) of the digestive 

 canal from the middle of the oesophagus to the internal sphincter 

 ani; (2.) of the ureters and urinary bladder; (3.) of the trachea 

 and bronchi ; (4.) of the ducts of glands ; (5.) of the gall-bladder; 

 (6 ) of the vesiculse seminales; (7.) of the uterus and Fallopian 

 tubes ; (8.) of blood-vessels and lymphatics ; (9.) of the iris, and 

 ciliary muscle of the eye. This form of tissue also enters largely 

 into the composition (10.) of the tunica dartos, the contraction of 



