Extensor digitorum [digitalis] lateralis muscle

The Extensor digitorum [digitalis] lateralis muscle is a muscle of the pelvic limb located laterally to the tibia. It exists in all domestic animals, but not in humans.

Conformation: This muscle consists of a fleshy, fusiform, flattened body and a tendon that starts half-way along the leg. This muscle is single in carnivores, ruminants and equines, but double in rabbits and pigs. Its tendon runs along the lateral surface of the tarsus, then over the two most lateral toes or to the most lateral toe, depending on the species.

Origin: Proximal third of the fibula.

Insertion: Depending on the species, on the phalanges of the most lateral toe, on the phalanges of both lateral toes, or in common with the insertions of the extensor digitorum longus muscle.

Relations: This muscle is covered by the crural fascia. Cranially, it is partially covered by the Fibularis longus muscle. Caudally, we find the soleus muscle and the flexor digitorum lateralis muscle. In carnivores and rabbits, the extensor digitorum lateralis muscle covers the fibularis brevis muscle, and when the latter is present, their tendons follow each other. The tendon lies caudal to that of the long fibular, and passes through a groove in the caudal edge of the lateral malleolus, then into a sheath in the dorsal fascia of hindfoot. Here, it is surrounded by a synovial sheath. It then crosses the tendon of the long fibular muscle.

Action: Extension of the toes to which it attaches. Slight abduction.

Vascularization: Branches of the cranial tibial artery.

Innervation: Superficial fibular [peroneal] nerve

Description: The Extensor digitorum [digitalis] lateralis muscle is located in the lateral part of the leg. It is single in carnivores, ruminants and equines, but double in rabbits and pigs. In both cases, it consists of a more or less flattened, fusiform fleshy body that originates on the proximal third of the fibula. It lies between the fibularis longus muscle, cranially, and the soleus muscle and flexor digitorum lateralis muscle, caudally. Its tendon starts at mid-leg height, then passes over the lateral surface of the tarsus, through a groove in the lateral malleolus, into a sheath of fascia, where it is surrounded by a synovial sheath, before joining the dorsal surface of the toes. Depending on the species, it attaches to one or both of the lateral toes. The tendon of the fibularis longus muscle passes cranially to that of the extensor digitorum [digitalis] lateralis muscle along its entire length, before crossing over after passing through the fascial sheath. In species where it exists, the fibularis brevis muscle is covered by the extensor digitorum [digitalis] lateralis muscle, and their tendons follow the same path. Vascularization is provided by branches of the cranial tibial artery. Its action is activated by the superficial fibular nerve, causing the extension of the toes to which it attaches and a slight abduction.

Variations:

• In equids, this muscle is simple, and its tendon joins that of the long extensor digitorum muscle, with which it attaches in common to the distal phalanx. There is no fibularis brevis muscle or fibularis longus muscle.