Lecture+8_Skeletal

Lecture Overview

  • Title: The Skeletal System: The Forelimb

  • Instructor: Dr. Tara Gaab

  • Course: ANFS240, Spring '25

  • Date: 2/19/25

Key Terminology

  • Forelimb: The upper limb of animals, crucial for movement and manipulation.

Forelimb Anatomy

  • Components of the Forelimb:

    • Shoulder Region: Comprises scapula and clavicle.

    • Brachium (Upper Arm): Humerus.

    • Antebrachium (Forearm): Radius and ulna.

    • Carpus (Wrist): Composed of carpal bones.

    • Metacarpus: Metacarpal bones and digits (fingers).

Scapula

  • General Structure:

    • Flat, roughly triangular shape.

    • Located over the craniodorsal part of the thorax.

    • Muscle-held in place, absence of clavicle in quadrupeds.

  • Scapular Features:

    • Spine: Divides the lateral surface into supraspinous and infraspinous fossa.

    • Acromion Process: Projects laterally.

    • Glenoid Fossa: Articulates with the humerus.

    • Supraglenoid Tubercle: Muscle attachment site.

    • Scapular Cartilage: Enlarges with age for muscle attachment.

Humerus

  • Structure:

    • Long bone, obliquely positioned against the thorax.

    • Shorter and robust in cattle and horses compared to other domestic species.

  • Humeral Features:

    • Head: Articulates with glenoid fossa.

    • Greater Tubercle: Lateral process, point of shoulder.

    • Olecranon Fossa: Where olecranon fits at the elbow.

    • Deltoid Tuberosity: Attachment site, connects greater tubercle to ridge.

Ulna and Radius

  • Role:

    • Ulna is caudal to the radius.

    • Bound by ligaments; fusion possible in some species.

  • Rotation:

    • Important in species that can supinate the forearm.

  • Anatomy:

    • Ulna: Olecranon at the proximal end (elbow prominence).

    • Radius: Head articulates with humerus at the elbow.

Distal Forelimb (Manus)

  • Anatomy:

    • Similar structure to hindlimb: Carpus, Metacarpus, Phalanges, and Sesamoid bones.

Carpus (Carpal Bones)

  • Joint Composition:

    • Multiple small, cuboidal bones in two rows (proximal and distal).

    • Proximal Row: Radial, Intermediate, Ulnar, Accessory.

    • Distal Row: Carpal bones 1–4.

Metacarpus (Metacarpal Bones)

  • Structure:

    • Located distally from the carpus.

    • Number varies by species.

  • Notable Features:

    • Palpable in cats and dogs.

    • Carnivores typically possess all five metacarpal bones.

Comparative Anatomy of Metacarpals

  • Differences in Species:

    • Herbivores have reduced numbers (e.g., horses only have MCIII weight-bearing).

Phalanges (Digits)

  • Structure:

    • Each digit comprises three phalangeal bones (P1, P2, P3).

    • Carnivores typically contact the ground with 4 digits.

    • Herbivores usually have digit III and IV, or just III.

Sesamoid Bones

  • Definition:

    • Small bones within/near tendons, changing tendon direction and preventing wear.

  • Location:

    • Patella: At the knee joint.

    • Proximal Sesamoid Bones: Between metatarsals and P1 (fore and hindlimb).

    • Distal Sesamoid Bones: Between P2 and P3 (fore and hindlimb), rarely in carnivores.

Summary

  • The forelimb is a complex structure contributing significantly to movement, manipulation, and activity across different species.