46 



PHYSIOLOGY OF MUSCLE AND NERVE 



Cardiac muscle tissue occupies a special position, because embryologically as 

 well as histologically it appears in the form of modified contractile fibers. This 

 is especially evident in the lower vertebrates in which these cells possess a spindle- 

 shape, a marked cross-striation, and a long-oval nucleus. In mammals, the cardiac 

 muscle cell appears as a short cylinder which is usually united with a neighbor- 

 ing one by an oblique process to form a muscular plexus. ^ Functionally it is of 

 interest to remember that these prolongations bring the cells of adjoining rows or 



•/'■;.' 



f' 



1\ 



Fig. 18. 

 Muscles of a Wasp, Prepared by Rollett's 



B 



Fig. 17. 



Fig. 17. — Fibrils of the Wing 

 Method. Highly Magnified. 



A, a contracted fibril; B, a stretched fibril with its sarcous elements separated at the 

 line of Hensen; C, an uncontracted fibril showing the porous structure of the sarcous 

 elements. (Schdfer.) 



Fig. 18. — Smooth Muscle Cells, Teased Apart and 

 Nuclei Surrounded by Undifferentiated Protoplasm. 



Showing Long Oval 



areas into closer relation. The oval nucleus occupies a position in the axial portion 

 of the cell which also contains much undifferentiated protoplasm, or sarcoplasm. 

 The other parts of the cell exhibit a very delicate cross-striation. 



The Action of Striated Muscle in Locomotion. — As far as the 

 mechanical properties of the resting muscle are concerned, we have 

 previously seen that it is a very yielding tissue and possesses a soft 

 consistency so that its shape may be varied with ease. The contracted 

 muscle, on the other hand, is firm to the touch and exhibits a more 

 rounded outline, because its length is diminished in favor of its breadth. 



1 Zimmermann, tJber den Bau der Herzmuskulatur, Archiv f ur mikr. Anat., 

 Ixxv, 1910. 



