THE BLOOD, LYMPH, AND HISTOLOGY OF THE VESSELS. 265 



(Miiller). The walls of the hearts are formed of three layers ; an 

 external^ compared by Waldeyer to an adventitia, a muscular layer, 

 and an endothelial lining". The muscular fibres form a close inter- 

 lacing- mass, the fibres being small, branched (Leydig"), and pos- 

 sessed of many nuclei. Among the muscular fibres are pigmented 

 corpuscles, together with medullated and non-medullated nerve- 

 fibres, but no ganglion-cells (Volkmann, Waldeyer, Priestley). 

 The adveiditia is a connective-tissue layer with many pigment 

 cells (Leydig, Hyrtl, Waldeyer).] 



