Objective The purpose of this study was to determine whether high amounts of fast/type II myosin heavy chain (MyHC) in the superficial as compared to the deep temporalis muscle of adult female and male baboons(Papio anubis) correlates with published data on muscle function during chewing. Electromyograpic (EMG) data show a regional specialization in activation from low to high amplitude activity during hard/tough object chewing cycles in the baboon superficial temporalis (Wall et al., 2007, 2008). A positive correlation between fast/type II MyHC amount and EMG activity will support the high occlusal force hypothesis. Design Deep anterior temporalis (DAT), superficial anterior temporalis (SAT), and superficial posterior temporalis (SPT) muscle samples were analyzed using SDS-PAGE gel electrophoresis to test the prediction that SAT and SPT will show high amounts of fast/type II MyHC compared to DAT. Serial muscle sections were incubated against NOQ7.5.4D and MY32 antibodies to determine the breadth of slow/type I versus fast/type II expression within each section. Results Type I and type IIM MyHCs comprise nearly 100% of the MyHCs in the temporalis muscle. IIM MyHC was the overwhelmingly predominant fast MyHC, though there was a small amount of type IIA MyHC (≤5%) in DAT in two individuals. SAT and SPT exhibited a fast/type II phenotype and contained large amounts of IIM MyHC whereas DAT exhibited a type I/type II (hybrid) phenotype and contained a significantly greater proportion of MyHC-I. MyHC-I expression in DAT was sexually dimorphic as it was more abundant in females. Conclusions The link between the distribution of IIM MyHC and high relative EMG amplitudes in SAT and SPT during hard/tough object chewing cycles is evidence of regional specialization in fiber type to generate high occlusal forces during chewing. The high proportion of MyHC-I in DAT of females may be related to a high frequency of individual fiber recruitment in comparison to males.

Galago senegalensis is a habitual arboreal leaper that engages in rapid spinal extension during push-off. Large muscle excursions and high contraction velocities are important components of leaping, and experimental studies indicate that during leaping by G. senegalensis, peak power is facilitated by elastic storage of energy. To date, however, little is known about the functional relationship between epaxial muscle fiber architecture and locomotion in leaping primates. Here, fiber architecture of select epaxial muscles is compared between G. senegalensis (n = 4) and the slow arboreal quadruped, Nycticebus coucang (n = 4). The hypothesis is tested that G. senegalensis exhibits architectural features of the epaxial muscles that facilitate rapid and powerful spinal extension during the take-off phase of leaping. As predicted, G. senegalensis epaxial muscles have relatively longer, less pinnate fibers and higher ratios of tendon length-to-fiber length, indicating the capacity for generating relatively larger muscle excursions, higher whole-muscle contraction velocities, and a greater capacity for elastic energy storage. Thus, the relatively longer fibers and higher tendon length-to-fiber length ratios can be functionally linked to leaping performance in G. senegalensis. It is further predicted that G. senegalensis epaxial muscles have relatively smaller physiological cross-sectional areas (PCSAs) as a consequence of an architectural trade-off between fiber length (excursion) and PCSA (force). Contrary to this prediction, there are no species differences in relative PCSAs, but the smaller-bodied G. senegalensis trends towards relatively larger epaxial muscle mass. These findings suggest that relative increase in muscle mass in G. senegalensis is largely attributable to longer fibers. The relative increase in erector spinae muscle mass may facilitate sagittal flexibility during leaping. The similarity between species in relative PCSAs provides empirical support for previous work linking osteological features of the vertebral column in lorisids with axial stability and reduced muscular effort associated with slow, deliberate movements during anti-pronograde locomotion.

The predominance of Type 2 fibers in G. senegalensis epaxial muscles facilitates rapid muscle excursion and spinal extension during leaping, and is consistent with their relatively long muscle fibers. The predominance of Type 1 fibers in N. coucang epaxial muscles may aid in maintaining stable postures during bridging and cantilevering behaviors characteristic of slow-climbing. These histochemical characteristics highlight the major divergent locomotor repertoires of G. senegalensis and N. coucang.

Variations in branching patterns of the sciatic nerve are thought to be clinically significant because of the nerve’s extensive distribution area. Here we report a rare and unusual branching pattern of the sciatic nerve which was observed in a male cadaver. Sciatic nerve underwent a high division inside the pelvic cavity, and entered the gluteal region as separate tibial and common fibular nerves. Subsequent distal courses of both nerves into the leg were normal. Knowledge of sciatic nerve variations is useful in treating lower limb neuropathies, such as piriformis syndrome, which tends to be caused by the compression of the sciatic nerve by the piriformis muscle.Keywords: Sciatic nerve bifurcation; sciatic nerve anomalies; piriformis syndrome