232 MR HAROLD AXEL HAIG ON 



emerging from) the upper lobes, the bronchi being dorsal to the pulmonary arteries, 

 although the left bronchus is much closer to the artery than the left. 



(ii.) The heart (PL XX. fig. 2 and text-fig. l). — All four cavities of the heart 

 contain firm clot, which extends into the auricular appendices ; on section in the 

 coronal plane, the cavities of the auricles appear to be larger than those of the 

 ventricles, whilst the auricular appendices add considerably to the auricular capacity. 

 Moreover, although from the ventral aspect the right ventricle appear larger than 

 the left, there is not the same relative difference between the capacities of the 

 ventricles, both appearing to possess much the same size in median coronal section ; 

 the thickness of the myocardium is rather greater in the left than in the right 

 ventricle, that of the auricles being about equal on both sides. The aortic bulb is 



Fig. 1.— Dissection to show the relations of the aortic trunk, pulmonary trunk, and ductus arteriosus. 



R.S. Right subclavian. 

 AO. Aorta. 



P. A. Pulmonary artery. 

 D.A. Ductus arteriosus. 



L.V. Left ventricle in section. 

 R.V. Right ventricle in section. 

 B.AO. Aortic trunk and bulb. 

 IN. Innominate trunk. 

 R.C. Right common carotid. 



The dotted lines show the connection of the pulmonary trunk with the right ventricle ; 

 the lumen of the aortic bulb is opened, and two semilunar valves are seen. 



full of firm clot, and passes at once into a relatively short but thick aortic arch ; the 

 pulmonary trunk shows the same relations to the aortic trunk as it does in the case 

 of the human foetus of a corresponding stage of development, whilst the ductus 

 arteriosus is relatively wide and is a continuation of the main pulmonary trunk after 

 the latter has given off the two branches to the lungs (see fig. 2). The ductus joins 

 the arch of the aorta close to the origin of the latter from the bulbus aortse. 



The cardiac valves are well developed, the semilunar valves consisting of thin 

 plates of fibrous tissue, the free edges of which project into the aortic and pulmonary 

 trunks, whilst the mitral and tricuspid valves have their free edges projecting into 

 the ventricular cavities. The columnse carnse are not marked features, nor do the 

 chordae tendinse appear to be strongly developed at this stage. 



