During a routine dissection in the anatomy laboratory at The University of North Texas Health Science Center, the left leg of an 84-year-old female cadaver was found to have an additional muscle belly and tendon slip originating from the deep muscles of the posterior compartment. The small accessory muscle had two separate heads (medial and lateral) that arose in the lower third of the leg from the posterior deep fascia covering the flexor digitorum longus, tibialis posterior, and flexor hallucis longus muscles.
The accessory muscles tendon bifurcated near its terminus, and then inserted on the fascia between the deep surface of the abductor hallucis and the quadratus plantae muscles. The surrounding muscular, vascular and nervous structures followed the typical course described in standard anatomical texts.
