The thorax is another name for the chest - sort of. Generally, the word chest has come to mean the front breathing part in ordinary language. Most folks wouldn’t call a tennis ball impact on ribs between the back wing bones as hit in the chest. Thorax is a cover-it-all front-to-back designation for the chest region, the part of the body with ribs.

The back side of the body is also called dorsal. As a dorsal fin on a shark is on the back of the shark or its dorsal side. The front is called ventral.  Want more words? OK.

If lying supine (belly side up) then ventral side is up. If lying prone, belly side down, then dorsal side is up. Got it?

This actually simplifies things. Now we can talk about the dorsal spine and know we are talking about the part we see from the back. The ventral spine is the big column seen only from the front (or side views).

Let’s look at a thoracic vertebrae This is T-1 :

T1 is the top thoracic vertebra. It has all the components of the group. At the top the vertebrae look a bit like the cervical. At the bottom end nearing T-12 the vertebrae are looking closer to lumbar as the bodies and discs get bigger. In transition the facets are very much like shingles lying near flat on one another. At the lumbar region the facets are more like hands holding a goblet, no longer lying flat but curling up.

Above, we are looking down the spinal canal of the thoracic T1 vertebra. The floor of the spinal canal is the large kidney bean shaped vertebral body (and the discs adjacent). The roof of the canal, called “posterior elements” is bumpy. Shark fins at each level - spinous process - are the bumps you feel on someone’s back when you run your finger down their spine. But there are other deeper more covered bumps as well (upholstered by muscle) and boney arms sticking to the sides called transverse processes. Like handle bars on a bicycle, these give good grip to steering and supporting muscles.

Looking from the back, each posterior element looks like a - what? An elephant head with trunk hanging down? On x-rays more like butterflys. They overlap as shingles on a roof. Butterflys with shark fins? Hmmm.

The small joints where overlapping vertebral parts articulate have small facing surfaces (small = ette and facing = fac) called facets (Feh-set). The top two (R&L) of a single vertebra are the superior and the lower two are the inferior. In medicine superior and inferior mean upper and lower. At a facet joint, an inferior facet of the superior vertebra overlies a superior facet of the vertebra below, the inferior vertebra. Got that?

Looking from the side, (peeking between ribs) the discs bulge out and the vertebral bodies scallop inward. Segmental arteries and veins coming off the aorta and vena cava travel out sideways on the concavities of the vertebral bodies. Nerves exiting the foramena skirt the under edge of the ribs.

Chest organization:

There are twelve vertebrae that normally sport ribs. They attach to the vertebrae in the back and the top seven attach to the chest “bone” in front. That chest bone has 3 parts: the top is the manubrium, the main central bone is the sternum, and the small stickie-down bottom piece is the xiphoid (because it looks like a xiph).

The 8^th rib attaches to the rib above as does numbers 9 & 10. Rib nine is easy to locate from the front because the rectus (6-pack) muscle outer edge ends on it. Inside the diaphragm attaches along this periphery and balloons into the chest cavity. When the diaphragm muscle pulls tight it flattens and thus travels downward creating vacuum behind it - causing the lungs to fill.

Ribs 11 & 12 float (no bone connections in front).

Looking at those ribs from the side we see that the attachment to the vertebrae is by two joints each. The tip of the rib sits on the vertebral body anchored by ligaments. As it sweeps around it touches the transverse process of the rib where more ligaments secure it. Around this axis the ribs pivot as a handle on a bucket. As the ribs are interconnected by muscle they move in unison. Up is also out and down is also in. Up & out is taking a breath and down and in is exhaling.

A rib is cut away to better show the two points of rib attachment to the vertebrae. One thoracic vertebra is shown in light blue because it likes to show off - no - because it helps show the segmental nature of this.

One of the nice things about the chest cavity is that it is a cavity. By collapsing lungs (we have ways), it is a short unobstructed path through just air to get to the front of the spine. Certain kinds of extensive surgeries to the spine can be done with little exposure when the thorax is involved.

As with everything, there are advantages and there are disadvantages. The surgeon juggles many things in making choices.