Arcus costalis
The costal arch is formed by the costal cartilages of the asternal (false) ribs, typically ribs 9 through 18 in the horse. These cartilages do not attach directly to the sternum; instead they overlap and join one another to create a continuous flexible arch along the ventral and caudal border of the thorax. The arch defines the transition between the thoracic and abdominal cavities and provides attachment for abdominal muscles and the diaphragm. It is palpable in lean horses and serves as a landmark for abdominal ultrasound and for assessing respiratory effort. Trauma or rib fractures can involve the contributing cartilages.
The costal arch is a useful external landmark. Displaced rib fractures or severe trauma can disrupt it. It is imaged indirectly during thoracic or abdominal ultrasound.
Pain, swelling, or asymmetry along the back edge of the rib cage after a fall or kick should be checked. Most soft-tissue bruising resolves; difficulty breathing needs prompt veterinary attention.
The costal arch is a useful external landmark. Displaced rib fractures or severe trauma can disrupt it. It is imaged indirectly during thoracic or abdominal ultrasound.
Pain, swelling, or asymmetry along the back edge of the rib cage after a fall or kick should be checked. Most soft-tissue bruising resolves; difficulty breathing needs prompt veterinary attention.
See the Costal Arch (Left) on our interactive 3D horse model. Open 3D Model