A Closer Look at the
The ribcage is an important structure, determining the room available for heart and lungs. There are 13 pairs of ribs, pivoting where they join the spine, and connected to the sternum by cartilage. The first nine pairs connect by cartilage directly to the sternum, the next three pairs are connected by cartilage to the cartilage of the rib in front, whilst the final pair are 'floating ribs' with no connection to the cartilage of the other ribs. These joints (bone/cartilage or cartilage/cartilage) allow the ribcage to expand outward with each breath, increasing lung capacity. The heart rests between the lungs on the sternum between the 3rd and 8th ribs. The ribs are set against the ribs and against the diaphragm - the muscle which runs diagonally from the loin vertebrae, down the rib walls, to the 7th rib and the sternum, separating thorax from abdomen. The action of the diaphragm creates a vacuum behind the lungs, greatly assisting breathing.
The standard recognises the need for plenty of heartroom by requiring 'well sprung ribs, deep brisket'. The ribs should spring out in their initial curve away from the spine, but then flatten and lengthen slightly to deepen the chest, the length of rib and depth of chest best increases heart and lung room. If slab-sided, with little or no spring of rib from the spine and flat sides to the ribcage, room is restricted. Rounded, 'Barrel ribs' offer an illusion of room, but adequate depth of brisket could only be obtained with a disproportionately large ribcage. As well as depth and width, the ribcage should also be sufficiently long, so the brisket line should not cut up before the 7th or 8th rib. If the brisket line rises immediately behind the elbows, at the 3rd or 4th rib, the heart is pressed upwards, reducing lung room. Depth of brisket should be measured through the tip of the sternum, not merely between the foreigns.
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Reproduced from the British Chihuahua Club Handbook 1987