1903.] ANEURYSM IX A POLAR BEAR. 349 



On opening the Thorax an enormous quantity of recent blood 

 was found filling both pleurse. 



The Lungs were collapsed owing to the lai'ge effusion, but 

 showed no signs of any disease, nor was there any sign of 

 pleurisy. 



It was interesting to note that the lungs showed almost as 

 much anthracosis as is found usually in the lungs of human city- 

 dwellers. 



The Heart and the Aorta to within a few inches of the 

 diaphragm were found to be perfectly normal ; however, the 

 latter part of the dorsal aorta was found to be bound down by 

 recent adhesions to the vertebral column and on its antero-mesial 

 surface to be fused to a structui-e about the size of a hen's 

 Qgg. On removing the latter six inches of the dorsal aoi-ta and 

 the new fibrous structures above described, it was found that the 

 aorta was ruptured on its anterior sui-face, forming a hole (|" in 

 diameter) which led into a cavity contained within the above 

 fibrous mass. This cavity had a volume equal ,to that of the egg 

 of a blackbird ; it was filled with greyish and red laminated clot. 

 The walls of the cavity consisted therefore of clot and of fibrous 

 tissue on the outer, left, and anterior surfaces, whilst on the 

 mesial surface the laminated clot came into direct contact with 

 the bodies of the vertebrae, which were slightly eroded. At its 

 posterior extremity this sac had ruptured into the thoracic cavity. 

 There was evidence that there had been some slight leakage at 

 any rate some hours before the fatal haemorrhage, as there was 

 found on the posterior surface of the left lung a blood-stained 

 roughened area which corresponded in life to the position of 

 the sac. 



We have therefore to deal with an aneuiysm of the aorta, itself 

 perfectly healthy except for the small rupture which forms the 

 aperture into this aneurysmal cavity. No part of the aortic wall 

 has shared in the formation of the aneurysm, which therefore 

 falls into the group known as " false aneurysms." 



The aetiology of the morbid process remains obscure, and, not- 

 withstanding the fact that the oesophagus was without obvious 

 lesion, it is conceivable that, at some time previous, some sharp 

 bone, penetrating the oesophageal wall, may have lacerated the 

 aortic wall, and thus been the starting-point of leakage fi-om the 

 latter and formation of a " false aneurysm." 



I am indebted to Professor M'^Fadyean for having kindly 

 informed me that aneurysm is, so far as he knows, an unknown 

 condition in wild animals and excessively rare in the domestic 

 carnivora. 



The aneurysms in horses are examples of dilatation of the 

 aorta, and are quite distinct from the aneurysm found in this 

 case. 



