PLATE VI. 



Heart of OpJiiodon eloiigattis. 



Fig. 39 is from a photograph of the posterior half of a large OpJiiodojCs heart, 

 looking inward and caudad. This heart had previously been injected 

 with a gelatin mass and hardened in formalin, and the cut was made 

 directly between the anterior and posterior auriculo-ventricular valves. 



40. As above, is a photograph of the ventral side of a large Ophiodotis 

 heart. A portion of the ventral wall of the ventricle had been removed 

 to the depth of the central cavity to show the semi-lunar and auriculo- 

 ventricular valves. X 2. 

 Abbreviatio7is used. — Aur., Auricle. A.V.O., Auriculo-ventricular opening. 

 A.V.V., Auriculo-ventricular valves. B.Art., Bulbus arteriosus. C.Art., Conus 

 arteriosus. C.C.V., Central cavity of the ventricle. C.T., Connective tissue. 

 L.F., Longitudinal folds or ridges. M.L., Muscular layer. S.A.O., Sinu-auric- 

 ularopening. S. A. V. , Sinu-auricular valves. S.V., Semi-lunar valves. S.Ven., 

 Sinus venosus. T.C.A., Trabecule carnse auricle. T.C.V., Trabecula; carnie 

 ventricle. V.Ao., Ventral aorta. Ven., Ventricle. 



Text-fig. \. — Represents a transverse section through the auricle and ven- 

 tricle of Ophiodon elongattis. This section was made through one of the auric- 

 ulo-ventricular valves. Camera lucida. Leitz No. 2 obj. with lower lens 

 removed. 



Textfig. 2. — Camera drawing of transverse section through the region of 

 the conus arteriosus. Same obj. as above. 



Abbreviations used. — Aur., Auricle. A.V.V., Auriculo-ventricular valve. 

 C.T., Connective tissue. E.M.F., Elastic muscle fibers. End., Endothelium. 

 L.M., Longitudinal muscle fibers. S.V., Semi-lunar valves. T.^L, Transverse 

 muscle fibers. Ven., Ventricle. 



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