THE HEART. 



221 



tissue. In the latter part the spiral valve is wholly formed of 

 this tissue. 



Fig. 141 a. 



^-. 



Small group of nerve-cells from the auricular sejitum. Stained with picrocarmine and silver 



nitrate, after Dogiel. 



E Endothelium (endocardium). 



G Nerve-ceUs. 



* M Muscle-fibres. 



N Nucleus. 



JV' Nucleolus. 



The whole of the inner surface is lined with endothelium 



Fig. 141 b. 



Isolated nerve-cells from frog's heait. 1. Usual form of nerve-cell. II. 'Twin-cell.' 



C Capsule. 



JV' Nucleus. 



N' Nucleolus. 



P Process. 



