. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. Folivores; Forest ecology; Leaves; Mammals; Mammals. in the trunk and head. The tissue analysis of the trunk in Figure 4 shows the major differences with the agouti. Skin, truncal bone, and limb musculature are about the same in both forms except that the upper arm is a free segment in the sloth but incorporated within the trunk in the agouti. The back extensor muscles, however, are a bit over 2 percent TBW, and the flexors are rela
. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975. Folivores; Forest ecology; Leaves; Mammals; Mammals. in the trunk and head. The tissue analysis of the trunk in Figure 4 shows the major differences with the agouti. Skin, truncal bone, and limb musculature are about the same in both forms except that the upper arm is a free segment in the sloth but incorporated within the trunk in the agouti. The back extensor muscles, however, are a bit over 2 percent TBW, and the flexors are relatively large. Lucae (1883) noted this disproportion between truncal extensors and flexors. The viscera (lungs, heart, liver, guts) constitute almost 40 percent of total weight. Beebe (1926) observed that the abdominal viscera equal percent TBW in the three-toed sloth, Britton (1941a) that stomach and intestines equal 25 percent TBW. Gut size has altered lung position (Boker, 1937) and may explain the peculiarly expanded pelvic basin. The fetus and placenta were 13 percent TBW in Bradypus; a new- born, without placenta, constituted percent TBW (Britton, 1941a). In a Choloepus, the newborn, with- out placenta, was percent TBW (Britton, 1941a). A characteristic feature at the junction of trunk and proximal limb segments, the rete mirabile, forms an arteriovenous network (Straus and Wislocki, 1932) which is also found in the elbows and knees. The hair pattern is reversed on the trunk and limbs, parting ventrally and meeting dorsally. The ascribed function is water drainage to accommodate the habitual suspen- sory posture. Striking similarities with the potto and slow loris should be noted: reduced percent of body muscle; balanced proportions of forelimb and hindlimb seg- ments; reduced or vestigial tail; elevated calf and forearm weight because of the enlarged digital flexor muscle; expanded range of truncal motion, reduced vertebral spines and articular processes, and
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