1883.] VALVES IN ECHIDNA AND ORNITHORHYNCHUS. 11 



large mass a b runs upwards to the auricular ostium from the outer or 

 free ventricular wall rather than from the ventricular septum, as in 

 Ornithorhynchus and other Mammals, appears to me to have very httle 

 importance. The moulding of the ventricular cavities may very 

 readily result in an apparent dislocation of parts, so as to give the 

 muscular upgrowths of the ventricular wall at one time a septal, at 

 another time a free-wall attachment. This variation is seen in 

 higher mammalian hearts, as for instance in the Seal {Phoca vitu- 

 lina), where important musculi papillares are attached, not (as is 

 usual) to the septal, but to the free ventricular wall. 



Lumen of the Right Ventricle iti Ornithorhynchus. — In figs. 3 and 

 4 of Plate IV. sections are represented taken across the ventricles of 

 the heart of Ornithorhynchus and Lepus. The drawings are intended 

 to show the Sauropsidan character of the heart of Ornithorhynchus, 

 in that its right ventricle appears thus in section as a crescentic sac 

 embracing the very thick-walled cylindrical left ventricle, as in Birds 

 and Reptiles, whilst in the normal Mammalia as represented by Lepus 

 the right ventricle does not embrace the left ventricle so closely, and 

 presents, instead of a strongly convex septal wall, a nearly plane one. 



Right Cardiac Valve of Echidna hystrix. — I am not acquainted 

 with any figure of the right cardiac valve of the second genus of 

 Monotreme Mammalia, Echidna. Prof. Owen, in vol. iii. of his 

 •Anatomy of Vertebrates,' p. 517, thus describes it : — " The tricuspid 

 valve is membranous and consists of one principal portion closing 

 the outer angle ; the free margin of the valve is attached to the ex- 

 tremity of a large fleshy column arising by different roots from both 

 the fixed and the free walls of the ventricle ; a short fleshy column 

 is attached to the left extremity of the valve ; some chordae tendinese 

 are fixed to its right angle." The membranous character of the valve 

 and "the large fleshy column (a) arising by different roots (^x and y) " 

 will be recognized in the drawings on Plate IV. figs. 5, 6, 7. I am 

 not able any further to identify in the hearts kindly placed at my 

 disposal by Professor Flower the other features mentioned by Pro- 

 fessor Owen. 



As compared with the hearts of Ornithorhynchus already described, 

 the two iJc/u'c^wa-hearts present one important difference. The mem- 

 branous substance of the valve is not traversed by the muscular 

 columns or musculi papillares connected with it. These muscular 

 columns are simply inserted into or fixed to the membrane, and do 

 not, as in Ornithorhynchus, pass upwards through it so as to be in- 

 serted into the auriculo-ventricular ring. Membrane alone depends 

 from that ring, as in the Marsupial and Placental Mammalia. At 

 the same time an equally important agreement with Ornithorhynchus 

 and difference from other Mammalia is presented by Echidna in a 

 leading feature of the construction of its right cardiac valve. This 

 feature is the total absence (in the two specimens studied by me) 

 of a septal flap. This character is clearly exhibited in the three 

 dissections drawn in Plate IV. figs. 5, 6, 7. 



The muscular columns (musculi papillares) agree pretty closely 

 with those of some Ornithorhynchus-h.e&rt$ in number and origin 



