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L i s te n to T h e A B M P Po d c a s t a t a b m p.co m /p o d c a s t s o r w h e reve r yo u a cce s s yo u r favo r i te p o d c a s t s 59 bone, travels distally to cross the knee joint posteriorly, but then returns to the anterior side of the body for its distal attachment onto the tibia. No other muscle in the human body has such an unusual path. The natural question is why? The answer lies in evolution. If we look at many quadrupeds (e.g., dogs, cats) who have a fl exed position to their back legs, we see that the sartorius travels in a straight line. But when humans stood up to be bipedal, the fascia that held the sartorius in place continued to hold the fascia down against the body such that it now travels from anterior to posterior, and then back to anterior again. Cool! 4. BRACHIALIS The brachialis is a simple muscle. It attaches proximally onto the humerus and distally onto the ulna. In doing so, it crosses the elbow joint anteriorly. And because the elbow joint is a uniaxial hinge joint, the action of the brachialis is simply fl exion at the elbow joint, nothing more. For this reason, I love to start teaching muscle function by using the brachialis. Simple and elegant. And this is part of its coolness. But much of what makes me love the brachialis so much is its location, which (from an anterior perspective) is deep to the much-more-famous biceps brachii. Because the biceps brachii is more superfi cial, it gets most of the fame. But the brachialis is usually considered to be the stronger prime mover of elbow joint fl exion. I always like to say: "Behind every great biceps brachii is a great brachialis." (Note—the more superfi cial gastrocnemius and the deeper soleus of the lower extremity have a similar relationship.) Brachialis: Behind every great biceps brachii is a great brachialis. a) Anterior view. b) Lateral view. a 4 b Coracobrachialis Deltoid (cut) Brachialis Acromion process of scapula Clavicle Deltoid Biceps brachii Brachialis Brachioradialis Extensor carpi radialis longus Extensor digiti minimi Extensor carpi ulnaris Anconeus Triceps brachii Lateral epicondyle of humerus Lateral intermuscular septrum Extensor digitorum Extensor carpi radialis brevis Biceps brachii