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CHAPTER 8 The SKELETAL SYSTEM OVERVIEW OF THE SKELETON The Skeleton is divided into axial and appendicular portions. 1. The axial skeleton consists of the skull, middle-ear bones, the hyoid bone, rib cage, vertebral column and sternum. 2. The appendicular skeleton consists of the upper and lower extremities and the pectoral and pelvic girdles. Bones of the Skeletal System 1. There are 270 bones in a newborn, but only about 206 in an adult because many fuse during growth and development. 2. The number of bones varies even among adults, because of the development of sesamoid and sutural or wormian bones. Surface Features of Bones It is important to know the names of the various surface markings of bones. THE SKULL Cranial Bones 1. The skull (cranium) bones are locked into position with sutures. 2. Several large cavities occur in the skull: the cranial cavity, orbits, nasal cavity, buccal cavity, middle-and inner ear cavities, and paranasal cavities. 3. Four bones contain paranasal sinuses: frontal, sphenoid, ethmoid, and maxillary. 4. Bones of the skull have foramina, which are holes that allow for the passage of nerves and blood vessels. The spinal cord connects with the brain through the foramen magnum. 5. The cranium consists of two major parts, the calvaria and the base. a. The calvaria, of skull cap forms the roof and walls of the brain. b. The base of the brain is divided into three fossae that correspond to its contours: the anterior cranial fossa, middle cranial fossa, and posterior cranial fossa.
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2. Eight cranial bones directly contact the meninges around the brain. a. The frontal bones feature the supraorbital margin, supraorbital foramen, and frontal sinus. The coronal suture marks the edge of the frontal bone. b. The two parietal bones extend from the coronal suture to the lambdoidal suture. The sagittal suture separates the two parietal bones at the top of the skull. c. The temporal bones form the lower lateral walls of the cranium. i. Features of the temporal bone include: zygomatic process, zygomatic arch, mandibular fossa, external auditory meatus, styloid process, mastoid process, stylomastoid foramen, mastoid foramen, carotid canal, and jugular foramen. d. The features of the occipital bone at the posterior base of the cranium are: pharyngeal tubercle, occipital condyle, hypoglossal canal, condylar canal, external occipital protuberance, and the superior and inferior nuchal lines. e. The sphenoid is a butterfly – shaped bone that lies at the anterior base of the brain. i. It has greater and lesser wings, the latter of which forms part of the orbit. ii. The pituitary gland lies within the sella turcica of the sphenoid. iii. Several foramina are found within the sphenoid: foramen ovale, foramen rotundum, foramen spinosum and foramen lacerum. iv. Nasal choanae, or internal nares, and the sphenoidal sinus,
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This note was uploaded on 04/17/2008 for the course BIOL 211 taught by Professor Wilson during the Fall '07 term at Winona.

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