A SYSTEMATIC STUDY OP THE MAIN ARTERIES IN THE REGION OF THE HEART. AVES XIII.

Further studies on the arrangement-pattern of the main arteries in the neck and thorax of 19 species of Ciconiiformes reveals the presence of a basic ordinal arrangement of these vessels, and further substantiates the view of Glenny (1945) that there are notable steps in the evolution of the carotids from a bicarotid to unicarotid condition. As has been shown by Garrod (1873) and Glenny (1945), union of the carotid (trunk) arteries results in the conjugate condition. Subsequent reduction of the basal portion of either side (usually the left side in the Ciconii-formes) may lead to complete loss of the reduced vessel. It may be noted that there is not any notable uniformity in occurrence of these reductions with respect to generic status at the present time. As a result, bicarotid and conjugate carotids may occur in different species of a single genus. Further-more, these variations may occur in the several families and subfamilies since they are not restricted to any single grouping of genera. The characteristic ordinal arrangement-pattern for the Ciconiiformes is as follows; bicarotidinae-normales (with variations); ligamentum aortae present; ligamentum botalli reduced or lacking; branches of subclavian artery: coracoid or sterno-clavicular, axillary, internal mammary or intercostal, two pectorals; branches of the common carotid: ductus shawi and tracheal, thyroid, superficial cervical (comes nervi vagi), vertebral, internal carotid (trunk). The following species have been studied, and differences in the arrangement-pattern noted. Unless otherwise noted, the following species present the pattern characteristic of the order