98 Proceedings of the Royal Society of Victoria. 



to the lower part of the lung, alongside the main branch of the 

 pulmonary vein. 



The pulmonaiy veins are two large vessels, each of which is 

 formed, as it leaves the lung of its own side, of two, or some- 

 times three, main vessels. The left pulmonary vein would appear 

 to be both longer and wider, as also more sloping, than the right. 

 The two unite and form a median trunk, as in Marsupials 

 generally, similar in thickness to the corresponding trunk of the 

 pulmonary artery, but at least twice as long as the latter. Each 

 pulmonary vein runs ventral and also posterior to the bronchus 

 of its own side. The division of the trachea into the bronchi 

 occurs dorsal to the anterior half of this main pulmonary venous 

 trunk. It then opens into the i-ight auricle by a wide aperture, 

 behind the emergence of the pulmonary arterial trunk, and in 

 front and slightly to the right of the entrance of the left anterior 

 vena cava into the right auricle. This is the usual arrangement 

 of these parts in Marsupials. 



Systemic Arteries. 



The aorta emerges from the base of the heart at about the 

 same level vertically, or slightly in front of the pulmonary artery, 

 curving towards the front and left, round the trachea, and then 

 backwards dorsally to the bronchus and root of the left lung. 

 From the beginning of the arch, as usual, the coronary vessels 

 are given off, one of which only can sometimes be seen with the 

 unaided eye. The relative positions of the origins of the carotid 

 and subclavian arteries vary somewhat in different individuals. 

 The two types are : (1) The two carotid arteries, left and right, 

 arise as a common trunk ^-inch in length, from the root of which 

 opens the right subelavian artery, the left subclavian leaving the 

 arch considerably to the left end of the transverse part of this 

 arch. This corresponds to the condition found in the majority of 

 Marsupials and in Choeropus in particular.-^ (2) In other speci- 

 mens again, and, so far as my material shows, most frequently, 

 the right carotid and subclavian arteries arise as a common inno- 

 minate trunk similar to that of many higher forms, including 

 Man. The left carotid artery arises close to the base of this 



1 Parsons : Jour. Linn. Soc. Lond., Zoology, vol. xxix.,No. 188, Oct. 1903, p. 64. 



