Morphological Changes on the Axillary Border of the Scapula with Special Reference to the Neandertal Problem

This study is an effort to determine the causes of the various morphologies of the axillary border of the modern human scapula and to relate the results to the unusual morphology of Neandertal scapulae.

Two-thirds of known Neandertal scapulae exhibit a dorsal sulcus on the axillary border: the remainder have a double sulcus (Chancelade pattern) and only one exhibits a ventral sulcus. The ventral sulcus is predominant on the scapulae of anatomically modern hominids where the Chancelade pattern is also present in varying frequencies.

Quantitative and qualitative analyses were performed on data derived from skeletal material of five modern human groups in order to determine the causes of morphological changes on the axillary border of the scapula. The groups are: blacks and whites from a documented hospital collection (Terry Collection); Alaskan Eskimos; Southeastern American Indians of the Mississippian period, and of the Archaic period. The groups varied with respect to race, time and technological level.

Greater frequencies of the Chancelade pattern were found with advancing age and on the right side in these groups. It is suggested that, in modern humans, increased muscular stress, resulting from increased use of the upper limb, promotes greater development of the teres minor muscle as seen in the Chancelade morphology. Additionally, in modern hominids, the Chancelade pattern is positively associated with more curved clavicles (indicating a slightly rounder thorax) and with more cranially deviated humeral heads. Thus, it is further suggested that the rounder thorax of Neandertals may have caused their scapulohumeral-musculoskeletal relationships to be different from those of modern hominids. This effect together with the more strenuous use of the upper limbs (due to greater demands of the cultural level) may have caused enlargement of the teres minor muscle, thus creating a dorsal sulcus on most Neandertal scapulae.

Other factors contributing to the morphological changes from Neandertals to modern hominids may have been cultural changes which produced differences in tool and weapon handling, and/or genetic selection.