An arch worth revisiting: A study on the feline humeral supracondylar foramen and its evolutionary significance

Abstract

The supracondylar foramen with a seemingly osseous peripheral arch noticed on the medio-distal feline humeri had remained disputed among anatomists. Some scholars have argued in favor of homology between this foramen and the supracondyloid foramen formed in the presence of the ligament of Struthers in humans. Other theories include its presence as a retinaculum holding the median nerve and brachial artery to their anatomical position in a flexed elbow. Unfortunately, these theories lack investigative rigor. The emergence of non-invasive imaging modalities, such as micro-computed tomography, has enabled researchers to inspect the internal anatomy of bones without dismantling. Thus, a micro-computed tomographic investigation was conducted on three feline humeri specimens while the internal anatomy of the supracondylar foramina was examined. Unlike the humerus, the thin peripheral arch of the feline supracondylar foramen failed to elicit any osseous trabeculae or foci of calcification. While adhering to the humeral periosteum at its origin, the non-osseous arch, typical of a muscular tendon or a ligament, inserts into a bony spur attached to the medial humeral epicondyle suggestive of a ligament or aponeurotic extension of a (vestigial) brachial muscle, with the coracobrachialis longus emerging to be the most likely candidate.