MUSCULAR CONTRACTION 



113 



But these may consist of still more delicate fibrils; in Limulus muscle, 

 for example, the myofibrils may be resolved into successively finer fibrils 

 to the limits of visibility. 



Heart muscle can be similarly, but less precisely divided, the endo- 

 cardium and epicardium corresponding to the epimysium. Fasciculi and 

 perimysium are not so readily distinguished, but the endomysium is re- 



' A' " i *C 



%...- ' 



Xoi 



FIG. 128. STRIATED MUSCLE OF A CAT SEEN IN TRANSECTION. 



The blood-vessels have been injected and are black in the figure. At a an artery is 

 contracted and empty. The heavy black vessels are veins and arterioles; the small 

 black dots are capillaries in transection. One whole fasciculus is represented and is 

 surrounded by a delicate perimysium of connective tissue. Between the muscle 

 fibers is the still more delicate endomysium. The larger vessels are almost exclusively 

 found in the perimysium. The section was not stained. X 80. 



lated to cardiac muscle in a manner essentially similar to that described 

 for skeletal muscle. 



The student should have well in hand the several criteria for the 

 differentiation of the three types of muscle, both in transverse and 

 longitudinal sections; and of smooth muscle from the dense white 

 fibrous connective tissue. In brief, cross sections of skeletal striped muscle 

 can be readily distinguished on the basis of their greater diameter and 

 the peripheral position of the nucleus. Both cardiac and smooth muscle 



