536 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 



The right auricle is thin-walled and capacious, the large triangular appendix pro- 

 truding well forward. There is no internal valve at the opening of the inferior vena 

 cava ; but the aperture, nevertheless, may be influenced or diminished in circumference 

 by what appears to be an oblique or spiral band of supernumerary fibres, situate near 

 the orifice in question. The tuberculum Loweri is an unusually thick and deep free 

 crescentic fold, such as must divert the current of the blood returned by the inferior 

 cava. The fossa annulus ovalis is deep, but perfectly closed. The margins of the wide- 

 mouthed coronary vein are thickened by an addition of fibro-elastic tissue ; the approxi- 

 mation of which no doubt partially if not entirely closes the opening during contraction 

 of the auricle. Delicate but numerous musculi pectinati are confined to the auricular 

 appendix ; otherwise the internal walls are smooth. The auriculo-ventricular opening 

 has a diameter of 1^ inch. The right anterior segment of the tricuspid valve is by far 

 the largest of the three. Its thick flat columnee carnese spring chiefly from the apical 

 portion of both walls of the cavity ; and there is moreover a strong broad inter- 

 twined transverse band, reaching from the median to the anterior -^rall at their middles. 

 The pulmonary veins, above eight in number, unite so as to pour the blood by four 

 channels into the left auricle. This cavity is smaller-sized than the right ; and the only 

 peculiarity possessed is a small semilunar valvular fold overarching the closed foramen 

 ovale. The lower thickened border of the obliterated foramen also exhibits traces of a 

 similar fold. From these it may be inferred that during the foetal condition the san- 

 guineous current would be directed downwards into the auricle or even at times checked 

 in its flow. The mitral and semilunar valves present nothing remarkable. 



2. Arterial iJistribution. 



a. Aorta and branches to Neck and Head. 



Immediately above its commencement from the left ventricle, and having given ofi' 

 the coronary arteries, the aorta has a circumference of 4^ inches ; its calibre continues 

 about the same to the hollow of the arch. From the summit of the vessel and 5 inches 

 distant from its origin, the innominate artery is given off; to the left of this, rather 

 behind, but in close proximity, the left carotid is derived ; one tenth of an inch further 

 to the left springs the wider left subclavian artery. Directly beneath this last, at the 

 concavity of the arch towards its front edge, is the ductus arteriosus. Beyond the deri- 

 vation of the above vessels, where the aorta bends downward, it narrows considerably ; 

 and a few inches below, as the thoracic aorta, it is barely over 2 inches in circumference. 

 Thus the arch presents a considerable relative dilatation to its descending trunk, as occurs 

 in other Pinnipedia. 



The arteria innominata is 1 inch in length, and about 2 in girth ; it splits, as normally 

 is the case in Man, into the right carotid and right subclavian, the latter being about 

 twice as wide as the former. The common carotid artery of the right side of the neck 



