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The branching patterns in the blood vascular system in the avian hind limb have been studied comparatively in 43 species representing 16 orders of the class Aves.

Six main arterial patterns are distinguishable in the upper part of the limb. Interspecific variations in the patterns include differences in the origin of three larger arteries (a. femoralis caudalis, a. genicularis medialis and a. cruralis medialis) and the differences in the size relationships of a. femoralis and a. ischiadica. The last artery constitutes the main supply to the leg in most birds, except Spheniscus, Musophaga, Chiroxiphia, Procnias and Pipra where the entire hind limb is supplied by the a. femoralis. This is made possible by the presence of an anastomosis between the distal part of the a. ischiadica and a. femoralis medialis.

Six arterial patterns are distinguishable in the feet of birds, which could all be derived from a basic, hypothetical pattern. The interspecific differences in the pedal arterial pattern include differences in the number of dorsal metatarsal arteries and differences in the origin of the digital arteries.

The variability of the venous system is treated more superficially.

The findings are discussed and compared with analogous differences in the branching pattern in the vascular system in the head of birds. The significance of the leg vasculature in phylogenetic studies is briefly discussed.

Summary

Patterns in the hind-limb vascular system were studied in 43 species of birds, using plastic corrosion casts and dissection of Indian ink injected legs.

The sciatic artery was the main artery of the leg, except in Spheniscus, Musophaga, Procnias and Pipra, wherein the hind limb is supplied by the femoral artery through a highly developed anastomosis between the a. femoralis medialis and the distal part of the a. ischiadica. The following arteries are branches either of the femoral artery system or of the ischiadic-popliteal system: a. circumflexa femoris, a. nutricia femoris proximalis, a. femoralis caudalis, a. genicularis medialis and a. cruralis medialis. On the basis of these differences, six arterial patterns are distinguishable in the upper part of the avian hind limb.

Differences in the six main pedal arterial patterns are determined by the number of dorsal metatarsal arteries and the point of origin of the digital arteries. One dorsal metatarsal artery is present in most birds, two such occur in penguins, and three in the pigeon and owl.

The main pedal vein is a large medial metatarsal vessel in all species, except in the penguin where a large vein has evolved on the dorsal aspect of the foot.

Vascular interspecific differences are discussed and their significance in phylogenetic studies is assessed. A haemodynamic principle may explain some of these differences.

Sincere gratitude is tendered to Professor J. J. Baumel, Department of Anatomy, Creighton University, Omaha, Nebraska, who willingly read the manuscript and gave many helpful comments and to Professor K. G. Wingstrand for his interest in the work and for his critical reading of the manuscript. Thanks are also due to Mrs Nyhave Kristiansen, who skillfully prepared the drawings, and to Mrs Ursula Früs for typing the manuscript.