The feline arm, comprising the forelimb, is a marvel of muscular structure and flexibility, enabling cats to perform a wide range of movements from the subtlest paw adjustments to powerful leaps. Understanding the muscular anatomy of a cat’s arm requires a detailed examination of the muscles involved, their origins, insertions, and functions. The primary muscles can be categorized into those of the shoulder, upper arm, forearm, and paw, each playing a critical role in the cat’s mobility and dexterity.
Shoulder Muscles
- Trapezius Muscle: Originates from the external occipital protuberance, the superior nuchal line, and the spinous processes of the C7 to T3 vertebrae. It inserts into the spine of the scapula and the acromion process. This muscle helps in elevating the scapula.
- Rhomboid Major and Minor Muscles: These muscles connect the scapula to the thoracic vertebrae and aid in scapular rotation and elevation.
- Serratus Ventralis Muscle: Runs from the ribs to the costal surface of the scapula. It rotates the scapula and draws it forward around the thorax.
- Latissimus Dorsi Muscle: One of the largest muscles in the cat, extending from the fascia of the lumbar and sacral vertebrae to the teres major tubercle on the humerus. It adducts, extends, and rotates the shoulder joint medially.
- Teres Major Muscle: Smaller than the latissimus dorsi, originating from the caudal border of the scapula and inserting into the humerus, assisting in adduction and medial rotation of the shoulder joint.
Upper Arm Muscles
- Deltoid Muscle: Covers the shoulder joint, aiding in flexion, extension, and rotation of the shoulder.
- Supraspinatus Muscle: Originates in the supraspinous fossa of the scapula, inserting on the greater tubercle of the humerus. It helps stabilize the shoulder joint and assist in arm abduction.
- Infraspinatus and Teres Minor Muscles: Both contribute to the lateral rotation of the humerus and are located in the infraspinous fossa of the scapula.
- Biceps Brachii Muscle: Although primarily a forearm muscle, its action starts in the upper arm. It has two heads (long and short) that converge into a single muscle belly, crossing both the shoulder and elbow joints to flex the elbow and supinate the forearm.
- Triceps Brachii Muscle: Extends the elbow joint, with three heads (long, lateral, and medial) that converge to form the common tendon, inserting into the olecranon process of the ulna.
Forearm Muscles
These can be divided into the anterior (flexor) compartment and the posterior (extensor) compartment. - Anterior Compartment: Includes muscles like the Flexor Carpi Radialis, Flexor Carpi Ulnaris, Flexor Digitorum Superficialis, and Flexor Digitorum Profundus, which are responsible for wrist and finger flexion. - Posterior Compartment: Muscles such as the Extensor Carpi Radialis Brevis, Extensor Carpi Radialis Longus, Extensor Carpi Ulnaris, and Extensor Digitorum Communis are involved in wrist and finger extension.
Muscles of the Paw
- Thenar and Hypothenar Muscles: Located in the palmar surface of the paw, these muscles control the movements of the digits, enabling grasping and releasing of objects.
- Interosseous Muscles: Between the metacarpal bones, these muscles aid in finger spread and adduction, contributing to the cat’s grip and manipulation abilities.
The intricate combination of these muscles allows for an extraordinary range of motion and precision, making the cat’s arm a highly versatile and effective limb for climbing, hunting, and self-defense. The understanding of these muscles and their functions not only aids in veterinary diagnosis and treatment of feline musculoskeletal conditions but also in appreciating the evolutionary adaptations that make cats such agile and formidable predators.
