ivision of the common primary vessel (bulbus arteriosus),
an arrest in the growth of the partition would leave them still as one
vessel, which (supposing the ventricular septum remained also
incomplete) would then arise from a single ventricle. 5th. The ductus
arteriosus may remain pervious, and while co-existing with the proper
aortic arch, two arches would then appear on the left side. 6th. The
systemic normal aortic arch may be obliterated as far up as the
innominate branch, and while the ductus arteriosus remains pervious, and
leading from the pulmonary artery to the descending part of the aortic
arch, this vessel would then present the appearance of a branch
ascending from the left side and giving off the brachio-cephalic
arteries. The right ventricular artery would then, through the medium of
the ductus arteriosus, supply both the lungs and the system. Such a
state of the vessels would require (in order that the circulation of a
mixed blood might be carried on) that the two ventricles freely
communicate. 7th. If the fourth arch of the right side remained pervious
opposite the proper aortic arch, there would exist two aortic arches
placed symmetrically, one on either side of the vertebral column, and,
joining below, would include in their circle the trachea and oesophagus.
8th. If the fifth arch of the right side remained pervious opposite the
open ductus arteriosus, both vessels would present a similar
arrangement, as two symmetrical ducti arteriosi co-existing with
symmetrical aortic arches. 9th. If the vessels appeared co-existing in
the two conditions last mentioned, they would represent four aortic
arches, two on either side of the vertebral column. 10th. If the fourth
right arch, instead of the fourth left (aorta), remained pervious, the
systemic aortic arch would then be turned to the right side of the
vertebral column, and have the trachea and oesophagus on its left. 11th.
When the bulbus arteriosus divides itself into three parts, the two
lateral parts, in becoming connected with the left ventricle, will
represent a double ascending systemic aorta, and having the pulmonary
artery passing between them to the lungs. 12th. When of the two original
superior venae cavae the right one instead of the left suffers
metamorphosis, the vena cava superior will then appear on the left side
of the normal aortic arch. [Footnote 2] Of these malformations, some are
rather frequently met with, others very seldom, and others c