Vascular Supply of Digit III and Foraging in the Aye‐Aye ( Daubentonia madagascariensis )

The aye‐aye is an unusual primate that differs from other primates in several aspects of its anatomy and behavior. Its thin, elongated third digit serves as a tool for tap‐scanning and prey extraction during percussive foraging for wood‐boring insects. The surface temperature of digit III is higher than the other digits on the foraging hand; in contrast, digit III has a lower temperature than the other digits on the stabilizing hand and this difference has been hypothesized to relate to stenotic kinking of the palmar digital arteries during hyperextension at the metacarpophalangeal joint. Though previously described qualitatively, aye‐aye hand vasculature has never been photo‐documented or quantified. Here we describe and compare the arterial supply of the forearm and hand in Daubentonia madagascariensis and Lemur catta in the context of hand function during foraging. The forelimbs of two primates, one aye‐aye and one ring‐tailed lemur, were dissected and arterial morphology was documented and photographed. Measurements of palmar digital arteries were collected using a dissecting microscope equipped with an ocular reticle. Inter‐digit and inter‐species comparisons were made for the pattern and diameter of each vessel. Lemur catta and Daubentonia madagascariensis differ in several aspects of their forelimb vascular morphology. In L. catta , the brachial artery does not pass through the entepicondylar foramen and a superficial palmar arterial arch supplies the digits. By contrast, in D. madagascariensis the brachial artery does pass through the entepicondylar foramen and the palmar aspects of the digits are supplied by individual branches of the ulnar and radial arteries rather than an anastomotic arch. These two species also differ in terms of the diameter of the arteries leading to the digits relative to the diameter of the ulnar artery (as a way of assessing relative scale). In the aye‐aye, the arterial supply to digit III has the smallest relative diameter (digit IV has the largest). In the ring‐tailed lemur, digit V has the largest total relative diameter and digit I the smallest. These observed differences in the vascular supply of the forelimb and hand in Lemur catta and Daubentonia madagascariensis likely relate to differences in foraging and locomotor strategy. While it has been suggested that stenotic kinking is responsible for the relatively low temperature of digit III on the stabilizing hand in the aye‐aye, our study suggests that this temperature differential may instead be due to the relative under‐supply of this digit compared to the other digits of the hand.