696 MK. F. E. BEDDARD ON THE [June 15, 



Finally, the anterior cusp or cusps of the tricuspid valve are also 

 attached by chordfe tendinea3 to the right-hand of the two 

 papillary muscles, which are connected with the septal cusps of 

 the valve. It is to be noted that these muscles also spring from 

 the free wall of the ventricle. They correspond, I take it, with 

 those lettered " c " in Lankestei-'s figure of the human heart. 

 My illustration also shows the remainder of the papillary muscles 

 of the septal flap of the valve, of which still a,nother is attached 

 mainly to the free wall of the ventricle. It appears to me that 

 the chief features of interest in the structure of the right 

 auriculo-ventricular valve of Tamandua are, in the first place, 

 the very great amount of its attachment by papillary muscles to 

 the free wall of the ventricle, in which it contrasts very markedly 

 with such a type as Lepus * ; and, in the second place, the inser- 

 tion of papillary muscles which are fleshy throughout upon the 

 actvial collar of the annular valve — a state of affairs which is 

 closely paralleled in Ornithorhynchus, but is at least not always 

 found among the Eutherian Mammals. 



The Aorta has, at any rate, no perforate or partly perforate 

 ductus Botalli between itself and the pulmonary artery, where 

 they cross. I could, indeed, see no definite separate ligament 

 representing this former arterial connection in the specimen 

 which I dissected. On cutting open the thoracic aorta the 

 orifices of the intercostal arteries could be counted. I examined 

 nearly the whole of this region of the aorta ; but, through an 

 oversight, omitted to ascertain exactly the topographical limits of 

 the section of arteiy which I cut open. It had been already 

 removed from the body. In this section of aorta the first five 

 intercostal orifices were single apertures into the aorta, though 

 they divided at once only just below the orifice into the aorta. 

 The sixth orifices were paired. But the two intercostal arteries 

 opened into the aorta, one a little nearer to the heart than the 

 other. I have already called attention to a similar asymmetry 

 in the case of Chiromys madagascariensis t, where one of several 

 pairs of intercostals opened into the aorta a little in advance of 

 its fellow. After this pair of intercostals I counted seven single 

 orifices into the aorta. This animal, therefore, contrasts with 

 Chiromys and some other mammals, to which I have referred in 

 the memoir quoted below, in the prevalently unpaired character 

 of the intercostal arteries. The intercostal artei-ies, moreover, 

 have a relationship to the azygos vein which varies in different 

 mammals. It differs, for example, in Tamandiia very much 

 from the conditions which I have described in Chiromys already 

 referred to. In Tamandtm the right azygos vein, as in other 

 Edentates, is the onlj^ azygos, and it extends through the whole 

 of the thoracic cavity, down to nearly the diaphragm. It is a 

 large vein, and gives off" its branches, on the right side at least, 



* Lankester, loc. cit. pi, xxxviii. figs. 3, 4. 



t " Some Notes upon the Anatomj- of Chiromys, &c.," P. Z. S. 1908, pp. 698 & 699, 

 • text-fig. 152. 



