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Equine Reciprocating Systems: Examining the Shoulder to Thorax Junction

In the fourth in this series, Dr. Deb Bennett illustrates the relationship between the horse’s forelimb and the body.

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Cross sections of the equine thorax cut through the body at the level of the withers. The bones and muscles are labeled. In View A, muscles are in various shades of red and orange, loose connective tissue is gray, bones are yellow, nuchal ligament is gold, scapular cartilages are green and the DSL is in blue. View B is a simplification, with bones in dark brown for emphasis, and only those muscles that attach to the DSL are colored. Note how the forelimbs hang off the DSL. The plane where “bubble wrap” fascia is found is marked.

A cross-section cut through the horse’s thorax reveals that the equine rib cage is far from being a round barrel (Figure 1). Instead, it is shaped like a peach leaf: pointed at the bottom, with rather flattened sides. Slapped up against the flattened surface formed by the rib cage is the scapula, and the junction so formed is the connection between the horse’s forelimb as a whole and its body.

Farrier Takeaways

  • The shoulder to thorax junction constitutes the upper end of the forelimb reciprocating system.
  • Horses lack collar bones and there is no socketed joint between the rib cage and forelimb.
  • The dorso-scapular ligament (DSL) anchors the top of the forelimb, while the serratus ventralis and pectoral muscles form the thoracic sling. Together they substitute for a socketed joint.

I say “junction” rather than “joint” because we normally think of joints as relating bones to each other by means of some…

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Dr deb bennett

Deb Bennett

Dr. Deb Bennett has studied classification, evolution, anatomy and biomechanics of the horse. She worked at the Smithsonian Institution, until founding the Equine Studies Institute. She is an author who has published four books on horse-related topics, in addition to articles in most major equine magazines in North America.

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