The clavicle is known as your collar bone – it is an ‘S’ shaped bone that articulates with the sternum, specifically the manubrium, (see Day 9) in the midline and then sweeps out to connect with your scapula (shoulder blade). For its shape, the clavicle was named for the Latin word clavis, meaning ‘small key’ (Ljunggren 1979). Together with the scapula, the clavicle, forms the shoulder or pectoral girdle – which connects your axial (trunk) and appendicular (limb) skeletons, anchoring your arm and allowing for transmission of movement. In fact, the ligamentous attachments between your manubrium and clavicle, at the sternoclavicular joint, are so strong that you are more likely to break your clavicle than dislocate that joint.
Compared to other mammals, primates, including humans, have very well developed clavicles. Can you spot the tiny feline clavicle in the image below? Many of our four legged carnivorous friends, both domestic and wild, have reduced clavicles (or even no clavicle) which allows the scapula a broader range of motion across the back of the rib cage as they run – no need for broad set shoulders (Ljunggren 1979; Souza et al. 2019).
Well developed clavicles, like those seen in primates are an adaptation that allows for movements like climbing and grasping and manipulating objects (Souza et al. 2019) – objects like stone and bone tools perhaps. So next time you’re holding your phone or reaching out to grab your cup of coffee thank your clavicles for your wider set primate shoulders.
That’s all for the clavicle, tomorrow we will discuss the scapula to round out the shoulder girdle.
REFERENCES & MORE TO EXPLORE
The Clavicle. Teach Me Anatomy Series. 2020
Shoulder Girdle. Okpe & Kench. KenHub Anatomy. October 2020
Clavicle in Carnivorans: A Forgotten Bone. Souza et al. The Anatomical Record. 2019
Clavicular Function. Ljunggren, A.E, Acta Orthopaedica Scandinavica. 1979