medial view of the fox antebrachium; anterior (cranial) is to the right of the photo

lateral view of the fox antebrachium; anterior (cranial) is to the left of the photo

For comparison, see antebrachial dissections of a bat, a cat, a ferret, a rabbit, and a tree shrew.

Function:

The fox is cursorial and digitigrade, meaning that it locomotes on its toes. This form of movement allows for a longer stride length, as well as greater speed in covering ground. The fox's antebrachium has extremely strong ligaments, which stabilize the wrist and restrict lateral movement. In addition, the ulna and radius are held tightly together, further restricting such movement. The manus possesses partially fused central supporting pads on the sole, which provide cushioning while running. The fox has five digits, each of which contain a claw that provides traction while running. The first digit has migrated proximal to become a dew claw. The dew claw is sharper than the other four because it is not in constant contact with the ground [1]. In addition to locomotion, the foreleg is used to pin prey to the ground when hunting. The claws may also play a role here, holding the prey in place more effectively.

Dissection:

We began the dissection by removing layers of fascia on the lateral side of the forelimb. The deep antebrachial fascia is extremely tough, and was difficult to remove, as it adhered very tightly to the muscles [2]. When we observed the muscles, they were difficult to distinguish based on anatomical relationships alone. The muscles were of comparable size, and were tightly compacted in the compartment. The muscle bellies were shorter in length than their tendons, concentrating the actual muscle around the elbow joint. Typical of cursorial mammals, this allows the distal segments of the limb to be swung forward with less weight attached, thereby conserving energy.

We followed the muscle bellies to their tendons in the wrist, where we removed layers of the extensor retinaculum. We then traced the tendons, noting the insertions on the phalanges. The muscles in this lab are difficult to distinguish at times because of the multiple tendons that insert in the manus and digits. While the tendons are tough and tight, the further distal you go the thinner the tendons become. As a result they are easy to break, particularly as they split to the digits.

We were able to identify the muscles once we located their insertions. Identification was also made easier by the fact that the muscles are compartmentalized, with the extensor muscles on the cranial aspect of the antebrachium, and the flexor muscles on the caudal face.

The extensor digitorum communis muscle has tendons inserting on each of the digits. The individual tendons can be traced proximally to a point where they join together. Cranial to the extensor digitorum communis is the extensor carpi radialis muscle. Caudal to the extensor digitorum communis is the extensor digitorum lateralis muscle. We did not see the individual tendons splitting from a common tendon in the extensor digitorum lateralis because the distal portion was deep to the extensor retinaculum and the extensor digitorum communis. Caudal to the extensor digitorum lateralis is the extensor carpi ulnaris muscle, and further caudally is the flexor carpi ulnaris muscle, marking a change in compartments and function.

We abducted the limb to observe the medial side of the antebrachium. There was still antebracial fascia to be removed, but we were able to identify the muscles based on anatomical positions more easily. The flexor carpi ulnaris muscle, which we had already observed, was the furthest caudal structure. Cranial to it is the flexor digitorum superficialis muscle. It can be distinguished from the other muscles in this compartment because its belly is much thicker. Deep to the flexor digitorum superficialis muscle is the flexor digitorum profundus muscle. Both are used to flex the digits. Cranial to the digitorum flexors is the flexor carpi radialis muscle. Similar to the extensor muscles we had seen on the lateral view, these muscles had muscle bellies that were located proximally and became tendinous the further distally they proceeded.

Muscle Origin, Insertion, and Function

Adapted from Miller (1952) [2]

Sources:

1. Alderton, David. 1994. Foxes, Wolves, and Wild Dogs of the World. Facts on File, New York.

2. Miller, Malcolm E. 1952. Guide to the Dissection of the Dog. (3rd Ed). Edward Brothers Inc., New York.

Links

to Comparative Mammalian Anatomy home

to mammalian antebrachium

to fox brachium