390 



MONOTREMATA. 



modification of the Vertebrate type as does 

 the Ornithorhynchus, is one of which it was 

 obviously most interesting to ascertain the 

 form of the blood-discs. I have made appli- 

 cations to different professional and zoological 

 correspondents in Australia on this subject, 

 for the transmission of a portion of recently 

 drawn blood thinly spread and dried on glass, 

 or preserved in its fluid state in brine and 

 other menstrua of the same density as serum, 

 and for the results of observations on the 

 blood-discs of both the Ornithorhynchus and 

 Echidna. Mr. Hobson, of Hobart Town, 

 Van Diemen's Land, an accomplished sur- 

 geon and comparative anatomist, has made 

 the required observations on the blood of 

 the Ornithorhynchus, of which he has trans- 

 mitted to me the following account: "The 

 globules of the blood of the Ornithorhyn- 

 chus are discoid, and measured about the 

 Sj&jfth of an inch, calculating two-and-a-half 

 millimetres to the line. The human blood- 

 globules were placed side by side with those of 

 the Ornithorhynchus, and both in shape and 

 size so nearly resembled each other that it was 

 impossible to say which was human and which 

 was Ornithorhynchus. These examinations 

 were made in the presence of Mr. Ronald 

 Gunn, by means of one of Oberhauser's mi- 

 croscopes; the powers used were 250, 400, and 

 800. In order to be sure that there was no 

 delusion, I placed the elliptical globules of a 

 Lizard's blood beside those of the Ornitho- 

 rhynchus. The tenacity and high florid colour 

 of the blood, together with the greater propor- 

 tional number of globules in a given quantity" 

 (in the Ornithorhynchus) " is most interesting 

 in an analogical point of view." 



From the preceding highly valuable observa- 

 tions we may infer that the Ornithorhynchus 

 resembles the Mammalia in the circular form, 

 the size, the proportional number, and florid 

 colour of its blood-discs, which correspond in 

 size with those of the only Edentate species 

 yet examined, viz. the Armadillo,* and conse- 

 quently with those of the Quadrumana and 

 of Man. 



The blood-discs of the Echidna, according 

 to the observations made by Dr. John Davy on 

 a portion of blood of that animal, transmitted 

 to England in brine, are likewise circular. 



Heart. The heart of the Ornithorhynchus 

 (fig. 187, a, b, c) presents a rounded oblong 

 form ; it is situated in the middle of the ante- 

 rior part of the chest, parallel with the axis of 

 the cavity. It is inclosed in a thin subtrans- 

 parent but strong pericardium. 



The right auricle (6) is larger and longer 

 than the left; its appendix is free and is slightly 

 bifid, as in the Marsupials. It receives the 

 venous blood, also, as in that order, by three 

 great veins; the left vena innominata (f) de- 

 scending behind the left auricle to join the 

 termination of the inferior cava (A). The coro- 

 nary vein also terminates in the auricle to the 

 riyht of the inferior cava. The right superior 



* See Medical Gazette, Nov. 18, 1840. 



cava (e) is joined to the left by a transverse 

 branch (g). Meckel found in the heart of 

 both the Ornithorhynchi dissected by him a 

 deep but closed fossa ovalis, near the upper 

 extremity of the septum. This structure would 

 indicate that the intra-uterine existence of the 

 young was of longer duration than in the 

 Marsupialia. 



The right ventricle () is capacious, with thin 

 parietes. The tricuspid valve I found to consist 

 of two membranous and two fleshy portions : 

 the smallest of the latter was situated nearest the 

 origin of the pulmonary artery, and seemed to 

 correspond with the lesser fleshy valve observ- 

 able in the heart of certain birds, as the Ostrich ; 

 it is attached to the whole of the side of the 

 first or adjoining membranous portion. The 

 second fleshy portion may be described as ana- 

 logous to the muscular valve in the Bird's heart, 

 if the lateral margin of this were detached from 

 the wall of the ventricle, and the connection of 

 its two extremities was preserved, the one to 

 the angle between the fixed and moveable wall 

 of the ventricle, the other to the auriculo-ven- 

 tricular orifice. The two edges of the lower 

 half of the second fleshy portion of the valve 

 in the Ornithorhynchus are free ; but those of 

 the upper half are attached to the two mem- 

 branous portions of the tricuspid valve ; the 

 margin of the membranous part of the valve is 

 attached to the fixed wall of the ventricle by 

 two small chordae tendinese; and the structure 

 of the valve thus offers an interesting transi- 

 tional state between that of the Mammal and 

 that of the Bird.* 



The origin of the pulmonary artery is pro- 

 vided with the three usual sigmoid valves. 



The left ventricle has very thick parietes, 

 which form the apex of the heart ; the mitral 

 valve is membranous ; the larger flap is at- 

 tached to two strong columme carnese ; the 

 smaller flap to three smaller columnse. 



The small left auricle (c) receives two pulmo- 

 nary veins. 



In the Echidna the free appendix of the 

 right auricle is slightly indented. The ter- 

 minal orifice of the superior cava is protected 

 by a membranous semilunar valve, extending 

 from its left side. The musculi pectinati di- 

 verge from a strong fasciculus, which extends 

 from the appendix to the orifice of the in- 

 ferior cava; this fasciculus bounds the left 

 side of a wide fossa ovalis, which is imper- 

 forate. The inferior cava is protected by a large 

 membranous Eustachian valve ; the left vena 

 innominata terminates by a distinct aperture to 

 the left of the preceding, and is also defended 

 by a process of the Eustachian valve. The 

 inner surface of the right ventricle is more irre- 

 gular than in the Ornithorhynchus ; the free 

 wall is attached to the fixed one by several 

 columnar carnese and short chordae tend inea?; the 

 tricuspid valve is membranous and consists of 

 one principal portion attached to the exterior 



* " Similitude quaedam cum avium valvula ve- 

 nosa dextra et propter carnositatem et propter 

 figuram minime prstervidenda adest." Meckel, 

 1. c. p. 31. 



