Forelimb - Anatomy & Physiology

BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY

Common structures of the Proximal Forelimb and Shoulder

Scapula

The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk.

In ungulates, the dorsal border is extended by a scapular cartilage, which enlarges the area for muscle attachment. This ossifies with age.
The bone is roughly triangular, with a prominent spine that can be palpated through the skin
The spine defines Infraspinous and Supraspinous Fossae, inhabited by muscles accordingly
The spine serves as a point of attachment for the trapezius muscle
The spine culminates in the acromion in all but the horse and pig
Medial muscle attachment comprises mostly of the subscapularis, with the serratus ventralis attaching dorsally
The Scapula articulates with the Humerus at the Glenoid cavity

Clavicle

The Clavicle is all but absent in most domestic species, with the notable exception of the avian skeleton. In the dog and cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus, which may prove misleading in radiographic images.

Humerus

The Humerus is the long bone of the forearm, articulating with the Scapula to form the Shoulder Joint and the Radius and Ulna to form the Elbow Joint. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.

The head of the humerus comprises greater and lesser tubercles, separated by an intertubercular groove through which runs the tendon of the biceps brachii
The shaft of the humerus takes on a characteristically twisted shape via a groove carrying the brachialis and radial nerve
Laterally, the deltoid tuberosity is palpable through the skin and connects to the head of the humerus via a ridge and merges distally with the crest of the humerus
Distally, the humerus culminates in a condyle which articulates to form the elbow
- In large animals, it meets the radius via a trochlea
- In dogs and cats, it articulates with the radius medially via a trochlea and the ulna laterally via a capitulum
- Caudally, all species show an olecranon fossa which articulates with the olecranon of the ulna
Medial and lateral epicondyles provide attachment for flexors and extensors of the carpus and digits