VARIETIES OF THE AORTA. 



385 



2. A very remarkable malformation of the descending aorta consists in the greater or less 

 division of the vessel through a part or the whole of its channel into two closely united 

 tubes, by a median septum running from before backwards, or slanting from side to side, 

 which, when not due to pathological changes, may admit of explanation on the supposition 

 of the fusion of the original double embryonic aorta having remained incomplete. 



3. The Varieties of the Stems, or of the ascending aorta and pulmonary trunk, are inti- 

 mately connected and usually associated with malformations of the heart, and frequently 

 with persistence of the ductus arteriosus. These first parts of the two great arteries, specially 

 enclosed by the pericardium, are derived from the aortic bulb of the foetal heart, and are liable 

 to variations which may be traced to deviations from the natural mode of their septal 



EXT. CAR. 



EXT. CAR. 



DESC. AORTA 



EXT. CAR. 



PULM./ 

 TRUNK 



DESC, AORTA 



DESC. AORTA 



PULM...' 

 TRUNK 



DESC, AORTA 



ASC V 

 AORTA 



PULM... 

 TRUNK 



DUCT. ART. 

 \ 



PULM. 



E 



DESC. AORTA 



ASC. 

 AORTA 



PULM.. 

 TRUNK 



OESC, AORTA 



Fig. 333. DIAGRAMS SHOWING THE MODE OP DEVELOPMENT OP THE GREAT ARTERIES IN THE 

 NORMAL AND IN SOME ABNORMAL CONDITIONS. (After Eathke and Turner, with modifications and 



additions. Gr. D. T.) 



A, the normal arrangement ; B, double aortic arch ; C, dorsal origin of the right subclavian artery, 

 with ventral origin of the right vertebral ; D, simple transposition, as in situs inversus ; E, right aortic 

 arch, with a left innominate artery ; F, right aortic arch, with dorsal origin of the left subclavian and 

 vertebral arteries. 



division, and of their union with the left or right ventricles of the heart respectively. Thus, 

 these two arterial trunks may be transposed, or each one may be connected with the ventricle 

 to which it does not naturally belong, i.e., the pulmonary artery with the left, and the aorta 

 with the right ventricle. Or the arterial trunks may communicate together more or less 

 freely by deficiency of the septum between them. Or one of the vessels may be nearly or 

 entirely obliterated ; while the other, from unnatural openings left between them, serves as 

 the channel for the stream of blood belonging to both vessels. Or the aorta and pulmonary 



