Dissection Notes on Thoracic Wall and Muscles

Anatomical Dissection of the Thoracic Wall

Introduction to Common Integument

  • Definition: Common integument refers to the natural outer covering of the organism, acting as a protective barrier between internal and external environments.
  • Function: It protects underlying structures, helps in thermoregulation, and aids in sensory input.

Digital Pads: Comparison between Forelimb and Hindlimb

  • Definition: Digital pads are specialized soft pads located under each digit in mammals.
  • Differences:
    • Forelimb Pads: Longer and thinner, primarily supporting an animal's weight.
    • Hindlimb Pads: Broader, adapted for propulsion, and assist in shock absorption.

Digital Organs

  • Definition: Specialized sensory structures used for tactile perception found in animals like dogs and cats.

Extrinsic Muscles of the Forelimb

  • Dissection Steps:
    1. Make a skin flap around the thoracic limb at the olecranon.
    2. Perform a dorso-ventral incision at the neck and along the costal arch to expose superficial musculature.
    3. Reflect the skin flap dorsally, maintaining its attachment to protect the dissection.
  • Notes:
    • There are 7 extrinsic muscles in the forelimb.
    • These muscles are involved in locomotion and respiratory mechanics, enabling thoracic cavity volume increase during inspiration (an active process).
  • Passive expiration occurs due to elastic recoil and involves fewer muscles.

Muscle Structure and Function

  • The extrinsic muscles are crucial for mobility and shock absorption, forming a muscular sling attaching to the body without direct bone articulation.

Cutaneous Trunci Muscle

  • Observation: Embedded in superficial fascia, reflecting the muscle exposes lateral cutaneous nerves and blood vessels.
  • Function: Provides skin movement, particularly in response to irritants like flies.
  • Nerve Supply: Supplied by the lateral thoracic nerve, with roots from dorsal branches of spinal nerves.

Comparison of Muscle Attachment Types

  • The forelimb is attached to the trunk via muscles only, creating unique joint mechanics compared to bony attachments in the hindlimb or human limbs.
  • Advantages/Disadvantages: Muscle-only attachments allow greater flexibility and mobility while having less stability compared to bony joints.

Identification of Muscles

  • Extrinsic muscles include:
    • Trapezius mm.
    • Rhomboideus mm.
    • Omotransversarius mm.
    • Brachiocephalicus mm.
    • Latissimus dorsi mm.
    • Serratus ventralis mm.
    • Pectoral mm.
  • Functions: These muscles aid in the manipulation of the limb and the stabilization of the trunk.

Dissection Technique for Forelimb Removal

  1. Cut the Brachiocephalicus muscle first at the neck.
  2. Follow up by cutting the Omotransversarius and expose cervical lymph nodes.
  3. Cut through the Trapezius, exposing rhomboideus underneath.
  4. Proceed with the Latissimus Dorsi, noting the lateral thoracic nerve.
  5. Expose the Rhomboideus and further reflect to access the Serratus ventralis.
  6. Cut nerves and blood vessels close to the first rib for later dissection.
  7. Finally, remove Pectoral muscles to free the limb.

Identification of Thoracic Wall Muscles

  • Key muscles include:
    • External abdominal oblique mm.
    • Scalenus mm.
    • Serratus dorsalis mm.
    • Functions: Involved in respiration (inspiration and expiration).

Epaxial muscles (identified):

  • Spinalis and semispinalis mm.
  • Longissimus thoracis mm.
  • Iliocostalis mm.
    Function: Aid in maintaining erect posture and allowing movement of the vertebral column.

Intercostal Muscles

  • External and Internal Intercostal Muscles: Important for respiration, facilitating the mechanics of inhalation and exhalation.
  • Vascular/Nervous Supply: Intercostal vessels and nerves run near the ribs, important in surgical considerations.

Endothoracic Fascia

  • A connective tissue layer attaching the pleurae to structures within the thoracic cavity, critical for maintaining lung function and protecting thoracic organs.