The fabella has been mainly studied using imaging methods but there are less research reports on the gross anatomical studies. We performed this anatomical study of the fabella and its surrounding structures with functional implications using 150 heads of the gastrocnemius muscles of 75 knees from 39 Japanese cadavers. This study is the direct representation of the human fabella and its functional implications. We observed 99 fabellae (66.0%) including 44 complete bony fabellae (29.3%). Of these bony fabellae, 43 (97.7%) were located in the lateral head of the gastrocnemius muscle with its surrounding structures and were positioned only on the lateral condyle of the femur. Moreover, the cartilage and bony fabellae, especially on the lateral side, contributed to the fabella complex with its surrounding muscles and ligaments and formed small articular cavity by cooperating with the femoral condyle. Although the human fabella is considered as appearing in the fabella complex with ageing and it possibly induces clinical symptoms, the fabella may play an important role as a stabilizer between the fabella complex and the femoral condyle.

The anatomy of the brachial plexus in the common hippopotamus (Hippopotamus amphibius), which has not been previously reported, was first examined bilaterally in a newborn hippopotamus. Our observations clarified the following: (1) the brachial plexus comprises the fifth cervical (C5) to first thoracic (T1) nerves. These formed two trunks, C5-C6 and C7-T1; in addition, the axillary artery passed in between C6 and C7, (2) unique branches to the brachialis muscle and those of the lateral cutaneous antebrachii nerves ramified from the median nerve, (3) nerve fibre analysis revealed that these unique nerve branches from the median nerve were closely related and structurally similar to the musculocutaneous (MC) nerve; however, they had changed course from the MC to the median nerve, and (4) this unique branching pattern is likely to be a common morphological feature of the brachial plexus in amphibians, reptiles and certain mammals.

A detailed anatomical analysis of the left brachial plexus, composed of the fourth cervical to first thoracic spinal nerve roots, was performed in an adult male orangutan obtained from the Osaka Museum of Natural History. Although the medial and posterior cords fused into a common trunk, a nerve fibre analysis revealed that the cords were not actually connected. A superficial branch (Rs) running ventral to the musculocutaneous nerve (MC) and a deep branch (Rp) running dorsal to the MC innervated the coracobrachialis muscle, which was also innervated by coracobrachialis branches (Rmc) from the MC. Koizumi (1989: Acta Anat. Nippon, 64, 18) reported that the Rmc and Rs innervated the superficial region of the coracobrachialis muscle corresponding to superficial coracobrachialis muscle in prosimians, whereas the Rp innervated the deep region. However, the detailed innervation of the coracobrachialis muscle in orangutans was not included in Koizumi and Sakai's (1995: J. Anat. 186, 395) report. Our observations in an orangutan did not seem to support generalisation, because the common trunk of the Rp and Rmc appeared to innervate both the superficial and deep regions of the coracobrachialis muscle. Therefore, a nerve fibre analysis of the common trunk was performed as a detailed examination. The analysis confirmed that the Rp in the orangutan only innervated the deep region of the coracobrachialis muscle, similar to the innervation pattern seen in other apes and humans.

Summary: Aberrant biceps brachii muscles (BB); the right aberrant head, the left aberrant head, and the left aberrant bundle, were observed bilaterally in a 94-year-old Japanese female cadaver during a regional anatomy of the upper extremities. We examined the nerve supply as well as scrutinizing these aberrant BB.The branches to the right aberrant head and the right brachialis muscle arose as a common nerve trunk from the musculocutaneous nerve, and both branches entered each muscle from the ventral aspect. The branches to the superior portion of the left aberrant bundle and the short head of the BB arose as a common nerve trunk from the musculocutaneous nerve, and both branches entered each muscle from the dorsal aspect. The branches to the inferior portion of the left aberrant bundle and the left aberrant head arose separately from the musculocutaneous nerve, but they were found to be closely related after peeling off the epineurium.From these observations, we speculated that the right aberrant head could have differentiated from the brachialis muscle, the left aberrant head from the long head of the BB, and the left aberrant bundle aberrant head from the short and long head of the BB, based on the formation of the common nerve trunk and the close relartion of the nerve fibers.Our suggested muscular differentiation agreed with the entering aspect (ventral/dorsal aspect.) of the innervating nerve.During a regional anatomy of the upper extremities, aberrant biceps brachii muscles (BB) were encountered. According to Bergman et al. (1988), the BB is very variable and the aberrant BB has reported by many authors.Although the ontogenetic origin of the aberrant muscle has been usually determined by the innervating nerve, the origin of aberrant brachial flexor muscles can not be determined by this approach because of the same innervation in the case of brachial flexor muscles. On the other hand, several authors have pointed out that a common nerve trunk is critical for determining an ontogenetic relation between muscles (Fuchino, 1960; Honma, 1980;Yamada, 1986; Kawashima et al., 2002).As a result, we attempted to discuss the ontogenetic origin of the aberrant muscle from the viewpoint of a common nerve trunk. Materials and MethodsAberrant BB were found bilaterally in a 94-yearold Japanese female cadaver (cause of death: acute bronchiolitis) during a regional anatomy of the upper extremity. After careful examination, the muscles and their nerve supplies were excised en bloc. Bony elements were completely removed to facilitate a detailed dissection of the muscle origin and the innervating nerve. Finally, the intramuscular nerve distribution was examined under a stereomicroscope and then recorded by photographs and sketches.