THE BLOOD, LYMPH, -VXD HISTOLOGY OF THE VESSELS. 265 



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

 external, compared by "VValdeyer to an tufoetttitia, a muscular layer, 

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

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

 i of many nuclei. Among the muscular fibres are pigmented 

 corpuscles, together with medullated and non-medullated nerve- 

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

 The ail cent ilia is a connective-tissue layer with many pigment 

 cells (Leydig, Hyrtl, Waldeyer).] 



