Deltoid muscle: a proposed classification system on human foetuses

BACKGROUND: The deltoid muscle originates from the spine of the scapula, the lateral border of the acromion, and the lateral third of the clavicle. It inserts on the deltoid tuberosity. It is divided into three parts: spinal, acromial, and clavicular. Our research shows that each part of the deltoid muscle can have up to three bellies during prenatal life. MATERIALS AND METHODS: The material included 80 upper limbs of spontaneously-aborted human foetuses (32 male, 48 female; Central European population), 18–38 weeks of gestation at the time of death. RESULTS: Each part had one (Type I), two (Type II) or three (Type III) bellies. In all parts, the most common form was Type I: it was present in 81.25% of cases in the clavicular part, 73.75% in the acromial part, and 57.5% in the spinal part. In contrast, Type III was the rarest form in all parts: it was present in 3.75% of cases in the clavicular part, 12.5% in the acromial part, and 7.5% in the spinal part. CONCLUSIONS: The deltoid muscle is characterised by morphological variability, even in foetuses.