To assess the prevalence and role of the arterial duct in hearts with incomplete development of the aorticopulmonary septum, 110 autopsy specimens, comprising 100 examples of common arterial trunk and 10 cases with aorticopulmonary window, were studied. In addition to intracardiac malformations, these specimens were analyzed to determine the side of the aortic arch, the presence and location of any interruption of the arch, the presence of any anomaly of origin and course of the subclavian arteries, and the status of the arterial duct. The arterial duct was present in 33 cases, absent in 63 cases and undetermined in four cases with common arterial trunk. The duct provided an essential pathway for flow in the 20 cases with interrupted aortic arch, and in two cases with interruption of the proximal portion of the left pulmonary artery. The presence of the duct in 11 cases, in functional terms, was not essential. In the 10 hearts with aorticopulmonary window, the duct was present in eight. It was an obligatory part of the circulatory pathways in three cases where the aortic arch was interrupted. The prevalence of non-obligatory ducts was 71% in hearts with aorticopulmonary window compared to 15% in hearts with common arterial trunk. The prevalence of the duct in cases with aorticopulmonary window suggests this lesion is a later developmental defect. The functional role of an arterial duct in these hearts should be properly assessed in the clinical situation.

A total of 112 human embryos (224 upper limbs) between stages 12 and 23 of development were examined. It was observed that formation of the arterial system in the upper limb takes place as a dual process. An initial capillary plexus appears from the dorsal aorta during stage 12 and develops at the same rate as the limb. At stage 13, the capillary plexus begins a maturation process involving the enlargement and differentiation of selected parts. This remodelling process starts in the aorta and continues in a proximal to distal sequence. By stage 15 the differentiation has reached the subclavian and axillary arteries, by stage 17 it has reached the brachial artery as far as the elbow, by stage 18 it has reached the forearm arteries except for the distal part of the radial, and finally by stage 21 the whole arterial pattern is present in its definitive morphology. This differentiation process parallels the development of the skeletal system chronologically. A number of arterial variations were observed, and classified as follows: superficial brachial (7.7%), accessory brachial (0.6%), brachioradial (14%), superficial brachioulnar (4.7%), superficial brachioulnoradial (0.7%), palmar pattern of the median (18.7%) and superficial brachiomedian (0.7%) arteries. They were observed in embryos belonging to stages 17–23 and were not related to a specific stage of development. Statistical comparison with the rates of variations reported in adults did not show significant differences. It is suggested that the variations arise through the persistence, enlargement and differentiation of parts of the initial network which would normally remain as capillaries or even regress.