Sentence:  And they could n't have entrusted Henri to better hands because `` le professeur '' knows his muscles from the <WSD>sterno-cleido</WSD> mastoideus of the neck right down to the tibialis anticus of the leg - and better still , he knows just what exercises work best for them and what Weider principles to combine them with for fast , fast muscle growth . 
Meaning of the word marked with <WSD> tags:  one of two thick muscles running from the sternum and clavicle to the mastoid and occipital bone; turns head obliquely to the opposite side; when acting together they flex the neck and extend the head