
The Scalenus Posterior is one of three Scalenus muscles (the s. anterior, the s. medius being the other two). It is the most deeply seated of these muscles, that is, it's overlapped by the others and would be impossible to find by flexing your neck muscles. But if you pulled it, you would not be able to tilt your head to the same side, or only with pain and difficulty. Also, breathing would perhaps be just a tad more labored and you'd feel it with every breath, as the muscle is attached to your second highest rib at one end (the other end is attached to the knobs coming off your lowest two or three vertebra in the back of your neck).

