THE HEART. 



219 



Fig. 139- 



rod-shaped, 2'5 to 3-5 n broad and 25 to 43 p in length. The 

 ratio of length to breadth varying from i : 8 to I : 16. These 

 cells are more frequent in the right half of the base of the ven- 

 tricle than the former variety. In the trabeculae the second 

 variety is more numerous (Pohl-Pincus). 



The muscle-fibre may be simple (Fig. 141 a J/) or possess branches 

 (Fig. 138); the fibres are all more or less spindle-shaped, and 

 striated transversely and longitudinally, but possess no sarcolemma. 

 The protoplasmic contents of the cell are finely granular; the 

 nucleus much more coarsely granular and possessing one or more 

 distinctly marked nucleoli. The striations are due to the presence 

 of a network, which has been carefully described bv Messrs. B. Mel- 

 land and C. F. Marshall l , and is similar to that of ordinary 

 voluntary muscle (see histology of muscle).] 



b. The nerves of the heart. 



The nervous supply of the heart is derived from the sympathetic 

 system and from the cardiac branches of the pneumogastric nerve ; 

 the course of which has already 

 been traced (page 175) to the roots 

 of the anterior caval veins, where 

 they form a simple plexus by means 

 of a connecting link (Fig. 139). 

 The plexus possesses nerve-cells and 

 sends off two nerves into the auri- 

 cular septum ; the one (d) lies dor- 

 sally and is shorter and thicker than 

 the other (r), which lies ventrally 

 in the septum. They course back- 

 wards to the posterior border of 

 the septum, and there distribute 

 fine branches to the base of the 

 ventricle and surrounding parts. 



[In the whole of their course in 

 the heart they have numerous 

 nerve-cells, either imbedded be- 

 tween their fibres or attached to 

 the nerves and their branches. 



The nerve-fibres are both me- 

 dullated and non-medullated. The nerve-cells (Figs. 139, 140, 141) 



1 I have had opportunity of examining Mr. Marshall's glides and have convinced 

 myself of the correctness of his observations. 



Course of the cardiac nerves in the auricular 

 septum. 



d Dorsal nerve. 

 v Ventral nerve. 



