ap-worksheet-axial-skeleton

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Apr 3, 2024

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Lab: Axial Skeleton Source: Cynthia Harley, Ph.D. Name: __________________________ Required Materials Variety of animal skulls, including both prey animals and predators Variety of hominid skulls A male and a female skeleton Several skulls of differing racial backgrounds Skull Anatomy For today’s lab, we are going to look at the axial skeleton. Specifically, we are going to look at the bones of the skull and hopefully get a better understanding of the different bones and their names. 1. In the following figures, label the skull bones (you may use Visible Body’s Human Anatomy Atlas or notes to help you). 1
2. The plates of the skull are joined by several sutures that allow the skull to flex so it can fit out of the birth canal and to grow so it can accommodate a growing brain. In the following figures, label the sutures. 2
3. What skull bones are not illustrated in any of the previous pictures? 3
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Comparing Skulls Well, that was fun. Now, we are going to look at many skull replicas of different hominids (prehistoric humans) and some animals. This kind of comparative anatomy study gives a lot of information about evolution. It can tell us how an animal moves and reproduces, what it eats, etc. We have a number of skulls around the room. You will look at features of these skulls to try to determine things about these animals. Feature Details Brain Case How big is the brain case? In general, a bigger brain case will allow for greater intelligence. Snout A smaller snout moves the molars under the rest of the skull. This allows for flexibility in chewing and grinding food and points to a more varied diet. Location of the Orbits If the eyes are in front, both eyes can see some parts of the visual field. This binocular overlap allows for depth perception (3D vision). However, if the eyes are on the side of the head, they can see more of the stuff around them. This is great for prey animals. Foramen Magnum Foramen means hole and magnum means big. Can you find a big hole on the skull? This is where the spinal cord enters the head. If the foramen magnum is at the bottom of the skull, the animal could walk erect (standing up like humans). If it is at the back of the skull, it is more indicative of a four-legged lifestyle. Masseter Muscle Attachment Points One end of this muscle attaches to the mandible and the other end attaches to the zygomatic bone. This muscle brings the molars together in a grinding motion and can indicate chewing. An indicator of the strength of this muscle would be the size of the zygomatic bone. This muscle would be bigger in herbivores. Temporalis Muscle Attachment Points The temporalis passes between the zygomatic arch and the rest of the skull. One end attaches to the temples, the top of the skull, or the cranial ridge (when present) and the other end attaches to the back of the mandible. This muscle is used for biting and tearing food. It is better for meat eaters. 4
Teeth Canine teeth, or pointy teeth, are used for tearing and ripping food, whereas molars are used for grinding. This is why they are commonly associated with carnivores and herbivores, respectively. Questions on the Animal Skulls 1. Which skulls belong to four legged animals? How can you tell? 2. Which skulls belong to prey animals? How can you tell? 3. Which skulls belong to herbivores (plant eaters)? How can you tell? 4. Which skulls belong to carnivores (meat eaters)? How can you tell? 5. Which skulls belong to omnivores (plant and meat eating)? How can you tell? 5
Question on the Early Hominid Skulls Which structures are different between the early and modern hominids? (give 5) Be specific about the bones and how they look different. Examine each skull individually and compare it to the human skull (meaning, don’t just say bone X is thicker. I want to hear that bone X is thicker in these hominids and bone Y is bigger in these.) Determining the Sex and Race of the Skeletons in Class Your instructor has several skulls and two skeletons. We want to identify each of them. The following traits can be indicative of ethnic background, but one trait is not enough to identify a person. Instead, humans are more of a collection of traits. This is especially true of those of a mixed-race background. Determining Sex Females have a smooth external occipital protuberance, whereas males have a prominent external occipital protuberance. Protuberance means bump. Females have a more vertically oriented frontal bone, whereas males have a sloping frontal bone. Males have a squarer mandible than females. Males have a more pronounced temporal suture than females. Males have a more prominent and wider mastoid process . The female pelvic inlet is larger than that of the male, and it is circular, whereas the male pelvic inlet is more heart shaped. Also, the angle between the left and right ischium is narrower in males. The female iliac crest is more outwardly flared than that of the male. Determining Race 6
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The palatine bone has a transverse suture that is straight in Native Americans, curved in African Americans, and jagged in Caucasians. Incisors are scoop shaped in Native Americans and Asians and flat in African Americans and Caucasians. The shape of the mastoid process is indicative of race. In Caucasians, it is narrow and pointed. African-Americans have a wider mastoid process. Asians and Native Americans have a secondary projection at the back of the mastoid (making a second bump). Caucasians tend to have smaller teeth, often with significant crowding and impacted third molars, and frequently exhibiting an overbite. African Americans rarely have crowding, and the upper teeth often project outwards (prognathism) due to the angled shape of the maxilla . The nasal bone provides multiple race indicators. The nasal aperture is the opening of the nose between the nasal and maxillary bones). In Caucasians, the nasal aperture is long and narrow, with a high bridge, a sharp nasal sill (the lower edge of the nasal aperture projects sharply outwards), and a long nasal spine. In African Americans, this is wider than it is in Caucasians. The nasal bridge in Asians is medium sized and has a heart- like shape (the African American nasal aperture often looks like a wider smushed heart in comparison.) The eye orbit shape can also aid in racial determination. Caucasians have sloping circular orbits which are squared at the edges. These look a little like aviator sunglasses. Native American and Asian orbits are rounded, and African American orbits have a rectangular shape. Keep in mind while making your determinations that each of these traits is suggestive of race. This is an inexact science. Furthermore, some of your samples could be of mixed ancestry giving them more ambiguous features. 7
1. Based on the information above, what can you tell me about the skulls/skeletons that you were given to identify? Include your reasoning in your answer. 2. What would your skeleton look like given your heritage and gender? Vertebrae There are three different kinds of vertebrae (we will skip the sacral ones, because those are all fused anyway). Your instructor has placed a number of vertebrae on the table. 1. Examine these vertebrae and draw a representative image from each of the three types. 2. How many vertebrae fit into each of the three types? 8
3. Read the following information on the three types of vertebrae, and then use this information to label the images you drew previously as cervical, thoracic, or lumbar. Most cervical vertebrae have transverse foramina located on them. These are holes through which the vertebral arteries and veins pass. Thoracic vertebrae articulate with the ribs. They have costal facets or costal demifacets on the lateral side of the body (the fat part of the vertebrae), which is where they join with the ribs. Lumbar vertebrae bear the weight of the body and have thick spinous processes (processes that look like spines) for attaching to back muscles. 9
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