The rib cage is more like an egg shape the top is narrower than the bottom. the egg shape formed of planes. It has clear front, side, and back planes. The front plane is composed of the sternum and costal cartilage.
The front plane is composed of the sternum and costal cartilage.
The front plane transitions to side plane right where the costal cartilage connects to the ribs. From there the ribs continue backward in a subtle convex curve. Then they reach the angle of the ribs where they take a sudden turn medially for the back plane.
The back plane actually has a concave wedge where the ribs curve forward to connect to the spine. This is unique to humans, allowing us to lie on our backs comfortably.
In the front, from the bottom of the sternum, the costal cartilage angles outward creating the upsidedown V shape called the thoracic arch. The cartilage of the 10th rib has a sharp “corner of the ri cage”, which you can see and feel on the surface.
The Rib Cage is made up of the thoracic vertebrae, which we already covered, twelve pairs of ribs, each connected to a vertebra
From the back, the ribs angle down slightly. As they reach the side plane, they dive diagonally at about 45 degrees and stay at that angle until they reach the costal cartilage in the front. The costal cartilage of the top half stays close to horizontal. The bottom half curve upward toward the sternum.
we see some of the lower ribs in the front and also in the back.On a lean person it doesn’t take much of a stretch to reveal the ribs in the front and back, and they’re much more obvious.
The lower front edge of the rib cage is the Thoracic Arch. It’s made up of the cartilages from the 7th to 10th ribs. Starting from where the Costal Cartilages of the 7th ribs attach to the Sternum, down to the corner of the 10th rib. This corner often stands out in the figure,especially when the model is inhaling or leaning back. the figure, especially when the model is inhaling or leaning back.
Artists tend to idealize this shape to be 90 degrees on males and a narrower 60 degrees on females.
The top corners of the Manubrium are where the clavicles attach, forming the pit of the neck. The body of the sternum is the longer bone, thinner at the top and thicker at the bottom.
At the lower tip of the Sternum is the Xiphoid Process, or the dagger! It’s about the size of the tip of your thumb. Sometimes the xiphoid process sticks out from the surface, and sometimes it digs in and makes a depression, surrounded by thick costal cartilage.