Professor Midwestern University Glendale, Arizona, United States
Abstract Body : The Gerenuk, Litocranius walleri, is a monospecific, rare bovid, found only in the horn of Africa. Gerenuks employ a postural strategy to browse for leaves which requires that they stand on their hindlimbs and hold on to small trees using their forelimbs. This posture likely requires adapting the pectoral region to optimize this behavior. We compare the pectoral region of the Gerenuk with that of the goat (Capra hircus), another bovid that occasionally employs a similar behavior, but not exclusively so. We dissected the pectoral region of one gerenuk and three domestic goats. The Pectoralis superficialis cranialis is triangular in gerenuk but rectangular in goat. In the gerenuk, the two parts of the Pectoralis superficialis are distinct while in the goat, they are relatively convergent. The origin of Pectoralis superficialis cranialis extends to sternebra 3 in the gerenuk, but only to the first sternebra in goat. While the Pectoralis superficialis pars caudalis is similar in both, it receives some axillary nerve fibers in the Gerenuk only. The subclavius is indistinct in Gerenuk, but prominent in goat. The pectoralis profundus in both gerenuk and goats is relatively similar. However, in the gerenuk the caudal surface of the Pectoralis profundus fuses with the cranial border of latissimus dorsi. In both taxa the Pectoralis profundus inserts on the major tubercle of the humerus. In Gerenuk some of the fibers wrap around the glenohumeral joint to provide support at the joint. In goat, the muscle inserts onto the minor tubercle by a small fleshy part to the distal supraspinatus. While preliminary, these data are consistent with the hypothesis that in the Gerenuk the pectoral musculature is modified to habitually function to support the body and grasp the trees during feeding.
