Thoracic Articulations

The thoracic articulations may be divided as –

1. Extrinsic articulations
   • Costo-vertebral articulations between the ribs and vertebrae.
2. Intrinsic articulations
   • Costo-chondral articulations between the ribs and costal cartilages.
   • Chondro-sternal articulations between the costal cartilages and sternum.
   • Sternal articulations between the segment of sternum articulations.

Extrinsic / Costo-vertebral articulations

This articulation is formed between the ribs and vertebrae. Each rib articulates with vertebra at the following two points

1. Costo-central articulations
2. Costo-transverse articulations

Costo-central articulations

Ox

They are trochoid formed between the heads of ribs and the capitular cavities formed by two adjacent dorsal vertebrae and the inter-vertebral disc in-between.

• Ligaments
  1. Capsular ligament
  2. Radiate ligament extends from the neck of the rib to the ventral part of the body and the intervertebral discs. It consists of three parts; of these, one becomes attached to the vertebrae in front, one to the intervertebral discs and other to the vertebra behind.
  3. Conjugal ligament attached to the sulcus on head of a rib and enters the spinal canal, passes under dorsal longitudinal ligament attached itself to it and the vertebrae in front and the intervertebral disc and finally ends on the head of the corresponding rib of the opposite side. The first costo-central articulation has no conjugal ligament
  4. Ligament of the neck of the rib is a strong, flat band which begins from the neck of the rib, crosses the joint superiorly and ends on the vertebra above the costal facet.
• Motion
  1. Rotation

Costo-transverse articulations

These are gliding joints formed between the facet on the tubercle of a rib and the tubercular facet on the transverse process of the corresponding dorsal vertebra.

• Ligaments
  1. Capsular ligament
  2. Anterior costo-transverse ligament lies in front of the joint and connects the neck of the rib to the anterio-ventral part of the transverse processes.
  3. Posterior costo-transverse ligament is situated on the superio-posterior aspect of the joint connects the tubercle to the lateral part of the transverse process.
• Motion
  1. Gliding movement

Horse and Dog

No difference

Intrinsic articulations

The intrinsic articulations are as follows-

1. Costo-chondral articulations between the ribs and costal cartilages.
2. Chondro-sternal articulations between the costal cartilages and sternum. 
3. Sternal between articulations the segment of sternum. 

COSTO-CHONDRAL ARTICULATIONS

• Ox
  • These arediarthroses (arthrodia). All the ribs except the first and last two articulate with the concerned costal cartilages. The roughened end of costal cartilage is inserted in the depression at the end of the concerned rib. The perichondrium and periosteum cover the junction.
  • Ligaments : Capsular ligament.
  • Motion: Gliding (inappreciable).
• Horse
  • The costo-chondral junctions are synarthroses (gomphosis).
  • The periosteum and perichondrium of the ribs and their cartilages are continuous.
• Dog
  • No difference.

CHONDRO -STERNAL ARTICULATIONS

• First chondro-sternal articulations
  • Ox
    • They are synchondrosisbetween the ventral ends of the first pair of the ribs and the first segment of the sternum.
    • Ligaments
      • Capsular ligament is a common one for the first pair of joints
      • Cruciate ligament–the fibres are strong and extend diagonally from one joint to the opposite joint and cross at the middle.
    • Motion: Restricted.
• Other chondro-sternal articulations
  • Ox
    • They are diarthroses (trochoid) between the second to eighth cartilages of sternal ribs and the concerned concavity of the sternum.
    • Ligaments
      • Capsular  ligament
      • Dorsal and Ventral chondro-sternal extending from the cartilage to the sternum on the dorsal and ventral aspect of the joint. The fibres of the dorsal ligament also called radiate costo-sternal ligament as they pass medially to blend with the internal sternal ligament.
      • Costo-xiphoid ligament-the cartilage of the eighth rib is connected with xiphoid cartilage by this ligament.
    • Motion: Rotation around the vertical axis.
• Inter-chondral articulations
  • Ox
    • The asternal cartilages and the last two cartilages are united together by their free ends to those infront by fibrous connective tissue called interchondral ligament. These are known as interchondral articulations.
  • Horse
    • The cartilages articulate with each other medially.
  • Movements of ribs
    • The costal movements are of great importance in respiration.
    • During inspiration each rib is rotated laterally and forwards as if it was hinged in an axis passing through its head and sternal end of its cartilage.
    • There is thus a simultaneous rotation in the costo-central joints.
    • The effect being to move the midpoint of each ribs laterally and forwards from the corresponding point of the opposite ribs.
    • In this way the transverse diameter of the chest between any two opposite ribs is increased. During expiration each rib returns to its original position.
    • In each of these respiratory movements, the tubercle of rib glides on the facet of the transverse process moving in a circle whose centre is the costo central joint.
    • The ranges of motion are greater in the posterior series of ribs.

STERNAL ARTICULATIONS

• Ox
  • The first sternebra is articulated to the second forming a diarthrosis, which permits, limited movements.
  • The other sternal articulations are synchondroses.
  • The segments are connected to one another through discs of cartilages.
  • The different segments are connected on their dorsal aspect by a common internal sternal ligament which is narrow to start with from the first segment becomes wider posteriorly and ends on the last segment.
  • Motion
    • Limited lateral movement between the first and second sternebrae.
    • The remaining is immovable joint.
• Horse
  • There is no diarthrosis between the first and second segments and all joints are immovable. The internal sternal ligament consists of a central and two lateral bands.
• Dog
  • The internal sternal ligament divides into three bands.