Situated on the side of the chest. The serratus anticus consists of a number of fleshy slips, whose fibres are directed backwards and end above in a flat aponeurotic tendon.

Origin. - From the 2nd to the 13th dorsal spines.

Insertion. - Into the anterior borders and outer surfaces of all the ribs from the 5th to the 13th.

Action. - By drawing the ribs forwards and upwards it enlarges the chest and assists in inspiration.