Fox brachium
Text and photos: Nick Zolkowski and Elizabeth Farrell
Canids have developed elongated limb bones relative to their body size as compared to other mammals. This adaptation has led to greater stride length. [1]. Additional specializations for increased stride length are a reduced coracoid process and clavicle, resulting in an expanded anterior range of motion in the shoulder joint. One advantage of this adaptation would be an improved ability to hunt and to evade predators. Although presently the fox does not have a wide range of predators, it is still vulnerable to attack by the golden eagle and other large birds of prey [1].
Foxes are quite similar to other canids in the structure of their long bones, differing marginally in the structure of the scapula and olecranon process of the ulna. Otherwise, canids of equivalent size cannot be differentiated from foxes based on their bone structure [2]. Accordingly, we found the dissection of Vulpes vulpes to closely follow the referenced atlas of the anatomy of the dog.
On the lateral aspect of the brachium we first removed fascia to expose the muscles. The triceps brachii muscle is the largest and most visible structure, with the lateral and long heads easily defined and separated. The long head of the triceps is the most medial, and passes inferior to the teres minor muscle to reach its attachment site on the scapula. The lateral head of the triceps, as the name implies, runs lateral to the long head and attaches on the humerus, which is partially visible between these heads. Less prominent, the brachialis muscle runs deep to the lateral head of the triceps muscle, and the biceps brachii muscle runs superior to the lateral head. Following the lateral head distally leads to the anconeus muscle.
On the medial side of the brachium, the tensor fascia muscle, a thin layer of muscle, is the most superficial structure. We cut and reflected this layer to reveal the medial head of the triceps brachii muscle. The long head of the biceps muscle and the triceps brachii muscle were also visible, with the biceps muscle cranial to the triceps brachii muscle. An accessory head of the triceps brachii muscle is also present, but as it lies deep the medial head of the triceps brachii, it was not visible without further dissection.
| Muscle | Origin | Insertion | Action |
| Tensor fasciae antebrachii | lateral side of latissimus dorsi | antebrachial fascia and olecranon | extend the elbow |
| Triceps | |||
|
Long head
|
caudal border of the scapula | olecranon | extend the elbow |
|
Lateral head
|
deltoid tuberosity of the humerus | olecranon | extend the elbow |
|
Medial head
|
lesser tubercle of the humerus | olecranon | extend the elbow |
|
Accessory head
|
neck of humerus | olecranon | extend the elbow |
| Anconeus | medial and lateral supracondylar ridge of humerus | proximal end of ulna | extend the elbow |
| Brachialis | musculospiral groove of the humerus | ulnar tuberosity | flex the elbow |
| Biceps brachii | scapular tuberosity | ulnar tuberosity and radial tuberosity | flex the elbow |
Adapted from Miller [3]
1.Alderton, David. 1994. Foxes, Wolves, and Wild Dogs of the World. Facts on
File,
New York.
2. Evans, Howard E., 1993. Miller's Anatomy of the Dog. (3rd Ed.) W.B. Saunders
Co., Philadelphia.
3. Miller, Malcolm E. 1952. Guide to the Dissection of the Dog. (3rd Ed.). Edward
Brothers Inc., New York.
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