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Mr. Shevalier Human Anatomy & Physiology Name __________________________________ Date_____________ SKULL LAB This lab is a study of the human skull. You will be using skull specimens both plastic and real bone. Please handle them with care. Be sure not to touch them with pencils or pens; use only the pointers provided. Compare the specimens with the diagrams and notice if any differences occur. The skull is composed of 22 bones divided into two major portions: the bones of the cranium (8) and the bones of the face (14). In addition, there are bones associated with the skull (7). The associated bones are the hyoid and the auditory ossicles. Try and locate all of the structures mentioned. In addition, you must answer the followup questions and correctly label the two diagrams at the end of this document. THE CRANIUM The portion of the skull that surrounds the brain is called the cranium. This is made up of the following bones: a frontal, a left and right parietal, a left and right temporal, a single occipital, a single ethmoid, and a single sphenoid. This makes a total of eight cranial bones. I. Frontal -- The anterior portion of the skull consists of the frontal bone. It forms the ridges above the eyebrows and nose. The most inferior ridge of this bone extends well into the orbit (eye socket). On the superior ridges of the orbits you will observe the supraorbital foramina. Like many bones that neighbor the nasal cavity, this bone contains paranasal sinuses. II. Parietal -- The parietals are located directly posterior to the frontal bone. They form the supeiror and lateral aspects of the cranium. A lateral view of the skull presents only one of these bones, the other obviously being on the other side. There are no significant markings on these bones. The two parietals meet on the midline of the skull, forming the sagittal suture. Between the parietals and the frontal bone you will find another suture called the coronal suture. III. Temporal -- Inferior to the parietals, you will find the temporal bones. Between the parietal and temporal bones, you will find the squamosal suture. Please locate the following points of interest on the temporal bone: the mandibular fossa (where the condyle of the mandible articulates), the external acoustic meatus which leads to the eardrum. Observe the zygomatic process whhich helps to form the zygomatic arch (the prominence of the cheek), the mastoid process, an attachment point for several neck muscles. Note the sharp styloid process which serves as an attachment point for the hyoid bone and several neck muscles. Human Anatomy and Physiology: Skull Lab Page 1 of 4 Mr. Shevalier The cranial floor has five foramina associated with the temporal bone: 1. foramen lacerum -- characterized by having a jagged margin, hence the name. Look for it at the junction of the occipital, sphenoid, and temporal bone. 2. carotid canal -- To locate this opening, carefully place a bent paper clip into the foramen lacerum and push it laterally into this foramen. It is through this canal that the internal carotid artery enters the brain. 3. jugular foramen -- Located just posterior to the carotid canal. This foramen is not located in the temporal bone. It is actually located between the temporal and the occipital bone. This foramen allows for the drainage of blood out of the brain. The jugular fossa is adjacent to it. 4. stylomastoid foramen -- A small opening at the posterior base of the styloid process. 5. mastoid foramen -- Located posterior to the mastoid process. This foramen is sometimes absent. IV. Occipital -- This bone occupies the posterior portion of the skull. Where it joins with the parietals, note the lambdoidal suture. The large foramen magnum allows for the passage of the brain stem. On either side of the foramen magnum, note the occipital condyles. These condyles articulate with the fossa of the first cervical vertebra. Near the base of each condyle are two openings. The hypoglossal canals are seen by passing a piece of paper clip wire transversely through the base of the condyle. Another canal, the condyloid canal may be visible in the condyloid fossa posterior to the occipital condyle. V. Sphenoid -- This bone is often described as being in the shape of a bat (not of the baseball variety!). The portion of this bone that is visible on the lateral aspect of the skull is called the greater wing (the greater wing composes the wing of the bat). Now find the lesser wings (they are the ears of the bat). Locate the portion of the sphenoid that is called the orbital surface. Locate the sella turcica which protects the pituitary gland. Find the anterior and posterior clinoid processes which surround the sella turcica. Now locate the lateral and medial pterygoid processes. Muscles that move the jaw and palate are attached to these pterygoid processes. The sphenoid contains several important foramina which you should now locate. 1. optic foramen - located just beneath the lesser wings. 2. superior orbital fissure - elongated opening between the greater & lesser wings. 3. foramen rotundum - located just inferior to the medial portion of the fissure. 4. foramen ovale - located on the inferior surface, it is somewhat oval in shape. 5. foramen spinosum - a small foramen just lateral to the foramen ovale. 6. pterygoid canal - located just medial to the foramen rotundum. VI. Ethmoid -- Locate the orbital surface on the medial aspect of the orbit. You should also locate its perpendicular plate which makes up the superior portion of the nasal septum. The superior and middle nasal conchae are processes of this bone. Try to locate them by looking into the nasal passage. One other feature of interest that this bone has is the cribiform plate. This plate is characterized by tiny foramina which allow for the passage of olfactory neurons. Also locate the crista galli which extends upwards like the comb of a rooster serving as an Human Anatomy and Physiology: Skull Lab Page 2 of 4 Mr. Shevalier attachment place for membranes of the brain. (Since the Egyptians removed the brain through the nose, mummification destroyed this bone) THE FACE The face is made up of 13 or 14 bones (depending on the book being used). If 13 facial bones are being studied, six bones are paired and one, the vomer is unpaired. The unpaired mandible would be the 14th bone in some references. I. Vomer -- This bone is visible in the inferior aspect of the nasal cavity where it makes up the inferior part of the nasal septum. The foot of this bone is visible on the base of the central floor where it articulates with the sphenoid bone. II. Maxillae -- The upper set of teeth are set into alveoli of this bone. The alveolar processes are distinct on its surface. The palatine process makes up a majority of the hard palate. A portion of this bone is located on the orbital floor. Foramina of note that are associated with this bone are the infraorbital foramen and the anterior palatine foramen (a.k.a. incisive foramen). III. Palatines -- The base of this bone makes up the posterior portion of the hard palate. A small portion of it is visible in the orbit. The greater palatine foramen and two lesser palatine foramina (sometimes absent) are found in this bone. IV. Zygomatics -- Also known as the malar bones, these form the prominence of each cheek. They make up the lateral part of the lateral surface and part of the inferior surface of the orbits. A small zygomatic foramen may be visible. They combine with the temporal bones to form the zygomatic arch, a prominent cheek feature. V. Lacrimals -- These are located in the orbit between the maxillary and ethmoid bones. Each has a groove which allows the tear ducts to pass down the into the nasal cavity via the nasolacrimal canal. IV. Nasals -- These two small bones form the bridge of the nose. VII. Inferior Nasal Conchae -- Curved bones attached to the lateral walls of the nasal cavity. Like the other conchae, the function is to create turbulence for the inspired air. VIII. Mandible -- (Some books do not count this bone as a face bone) Important features of the mandible include: The coronoid process, the mandibular condyle, the mental foramen on the external surface and the mandibular foramen on the medial aspect, the mandibular notch, and the mental protuberance. Human Anatomy and Physiology: Skull Lab Page 3 of 4 Mr. Shevalier BONES ASSOCIATED WITH THE SKULL I. II. Auditory ossicles- Within the temporal bones are located the auditory ossicles. You will not be able to see these on the skull models but be sure to see the individual ossicles (malleus, incus, and stapes) on display. Hyoid- This bone is shaped like a horseshoe. It lies behind the mandible and is positioned just superior to the larynx. It serves as an attachment point for several muscles that move the tongue and larynx. Review Questions Be sure to label the four figures that follow and answer the following questions. 1. What purpose do the foramina of the skull serve? 2. Name all of the bones of the cranium. 3. Name all of the bones of the face. 4. List all of the bones that make up the orbit. 5. What is the function of the auditory ossicles? 6. Explain why the terms skull and cranium are not synonymous. Human Anatomy and Physiology: Skull Lab Page 4 of 4