The Sacrum
Video Overview	Rotating Model
Read this description and then try to find the structures. Note, you can enlarge at any time by hitting the enlarge button (4 arrows), but you lose this text. The blue plus mark will give you a labeled picture from a posterior view and the red plus gives you labeled pictures from the anterior view. I don't suggest hitting in the enlarged view on the labed picture. It goes past the screen, at least on my computer. The sacrum started out as 5 vertebrae that eventually fused together. However, we can see remnants of typical vertebral structures on the sacrum. Start with a posterior view. You should see the numbers 5,25,26, and 27. The base is at the top of the picture and you can see the superior articulating facets from S1. Down the center of the sacrum you can see the median sacral crest. This crest is the remnants of the spinous processes of S1-S4. The number 25 marks the crest at S3. You will notice that there is no crest at S5. Instead, you will see the sacral hiatus. This hiatus is because the vertebral arch of S5 is incomplete and the trailing spinal nerves, S5 and Co1, exit here. Lateral to the median sacral crest, you will see the posterior sacral foramen. The posterior rami of sacral nerves s1-s4 will exit through these foramen. Lateral to the foramen is the lateral sacral crest. This crest is the remnant of the transverse professes. Rotate the sacrum. As you rotate, you will notice something that looks like an ear on the lateral surface. That is the auricle. This articulates with the auricle of the ileum which we will talk about in the next lab. You will notice two flared , wing like structures at the broad base, which is 21. These wing like structures are called ala. Similar to the posterior side, there are 4 anterior foramen. You can see transverse lines between the bodies of the sacral vertebrae. These lines are where the bodies of the vertebrae fused. Lastly, the sacrum ends at a point called the apex which you can see better on this side.