Huesos faciales anatomía PDF

## System Skeletal: Axial Skeleton ### Chapter 7: System Skeletal: Axial Skeleton #### 7.5 Cranial Bones - Identify the location and superficial characteristics of the following bones: frontal, parietal, temporal, occipital, sphenoid, and ethmoid. The skull is a bony framework that protects th...

## System Skeletal: Axial Skeleton ### Chapter 7: System Skeletal: Axial Skeleton #### 7.5 Cranial Bones - Identify the location and superficial characteristics of the following bones: frontal, parietal, temporal, occipital, sphenoid, and ethmoid. The skull is a bony framework that protects the brain and some of the special sense organs. It consists of 22 bones: 8 cranial and 14 facial. The cranial bones are joined by sutures, which are immovable joints, except for the temporomandibular joint (TMJ). A *cranial fossa* is a depression on the internal surface of the skull. The cranial fossae are distinguished by their relative positions, the brain structures they house, and the foramina they contain. **Cranial Bones** * **Frontal Bone** The frontal bone (front- = forehead) (Fig. 7.3), curved and shaped like a shell, forms the anterior part of the cranium. It forms the forehead, the superior part of the bony orbits of the eyes, and the roof of the nasal cavity. The frontal bone contains several foramina, the most noteworthy of which is the *foramen supraorbitarium*, located above the superior orbital margin, just medial to the supraorbital ridge. It is through this foramen that the supraorbital artery and nerve pass. * **Parietal Bones** (Fig. 7.3) Two parietal bones make up most of the roof and sides of the cranium. They are joined at the midline by the *sagittal suture*, a prominent seam visible on a skull. The point where the sagittal suture intersects with the lambdoid suture (at the posterior part of the cranium) marks the *lambda*. They join with a sphenoid bone at the *sphenoparietal suture*. Each parietal bone has a *parietal foramen* (foramen- = opening) where a small vein passes to the superior sagittal sinus. * **Temporal Bones** (Figs. 7.3 and 7.4) The right and left temporal bones are lateral to the parietal bones, forming part of the sides and base of the skull. They are located inferior to the parietal bones and anterior to the occipital bone. The *squamous suture* joins the temporal bone to the parietal bone. The *zygomatic process* of the temporal bone (zygo- = yoke) extends anteriorly to meet the *temporal process* of the *zygomatic bone*, forming the *zygomatic arch* (cheekbone). Key anatomical landmarks associated with the temporal bone include the: * **External Auditory Meatus** The external auditory meatus is an opening, or canal, that leads into the ear. * **Mastoid Process** The mastoid process is a bony prominence that is located posterior and inferior to the external auditory meatus. It serves as an attachment for certain neck muscles. * **Styloid Process** The styloid process is a sharp, slender process located anterior to the mastoid process. It serves as an attachment for several muscles and ligaments of the tongue and neck. * **Jugular Foramen** The *jugular foramen* (Fig. 7.5) is a large opening between the temporal bone and the occipital bone. The internal jugular vein, cranial nerves IX, X, and XI pass through this opening. * **Carotid Canal** (Fig. 7.5) The *carotid canal* is a passageway allowing the carotid artery to reach the brain. * **Occipital Bone** (Figs. 7.3 and 7.5) The occipital bone forms the posterior part of the skull, including the base of the skull. It is located inferior to the parietal bones. The *lambdoid suture* joins the occipital bone to the parietal bones. The occipital bone has a large hole, the *foramen magnum* (magnum = great), which is located in the posterior part of the base of the skull. It allows passage of the spinal cord. The occipital bone also contains the *external occipital protuberance*, which serves as an attachment for the *trapezius, the *semisterinalis capitis*, and the numerous ligamentous structures of the neck. The *condyles* (condyl- = knuckle) are two oval-shaped projections located on either side of the foramen magnum. They articulate with the first cervical vertebra (atlas). * **Sphenoid Bone** (Figs. 7.3 and 7.5) The sphenoid bone is located within the cranial fossa. It is shaped like a butterfly or bat, and its wings extend laterally in a butterfly shape. It is known as the "keystone" of the cranial floor because it articulates with all the cranial bones. The sphenoid bone forms part of the floor of the cranium, the sides of the skull, and the posterior wall of the orbits of the eyes. The sphenoid has a central prominence, the *sella turcica* (sella- = saddle), which is located on the superior surface of the body of the sphenoid bone. The sella turcica contains the *pituitary gland* (hypophysis). The *foramen ovale* (oval = egg-shaped) allows for the passage of the mandibular branch of the trigeminal nerve (V). The *foramen rotundum* (rotund = round) allows for the passage of the maxillary division of the trigeminal nerve (V). The *foramen spinosum* (spina = thorn) allows for the passage of the middle meningeal artery. * **Ethmoid Bone** (Fig. 7.5) The ethmoid bone is like an irregular block of sponge-like bone, which is located anterior to the sphenoid bone. It is the lightest skull bone and also the most complex in structure. It forms part of the roof of the nasal cavity, the upper part of the nasal septum, and part of the orbital walls of the eyes. The ethmoid is not a solid bone, but contains a maze of air cells, called ethmoid sinuses. The *crista galli*, a prominent thin vertical process shaped like a rooster's comb, projects upward from the cribriform plate. The crista galli serves as a point of attachment for the membranes that protect the brain. The *cribriform plate* (cribri- = sieve; form- = shape) is a part of the roof of the nasal cavity and the floor of the cranial cavity. **Clinical Correlation** **Craniosynostosis** When one or more of the cranial sutures fuses prematurely, the skull may have an abnormal shape. This condition is called craniosynostosis. Craniosynostosis is the most common type of skull abnormality in newborns that affects the shape of the skull. It occurs as a result of the suture prematurely fusing, limiting the growth of the skull in that area. The brain can continue to grow even though the skull is not expanding properly. The brain can squeeze through the opening in the skull, causing the skull to deform. Some forms of craniosynostosis can be corrected with surgery. * **Frontal bone:** Premature closure of the *metopic suture* in the frontal bone results in *trigonocephaly*, a triangular-shaped head. This condition causes a "pointed forehead" and is the most common form of craniosynostosis. In most cases, the metopic suture fuses before birth and is not considered a developmental abnormality. * **Sagittal suture:** Premature closure of the sagittal suture causes *scaphocephaly*-an elongated head due to the narrowing of the skull from side to side. * **Coronal suture:** Premature closure of the coronal suture causes *brachycephaly*-a flattened head due to a wide skull that is short from front to back. * **Lambdoid suture:** Premature closure of the lambdoid suture causes *plagiocephaly*-a head that is flat on one side because one parietal bone is growing more slowly than the other. Plagiocephaly often affects the head’s shape but not its size. The deformed skull shape is usually the result of the baby’s position in the womb and can be corrected with a helmet. **Learning Connection** **Forensic Anthropology** The bones of the skull provide a wealth of information for forensic anthropologists who study bones to determine such things as age, sex, ancestry, and the cause of death. The skull’s suture patterns, foramina, and bone densities are all useful indicators of age. The thickness of the *mandible*, the *zygomatic arches* (cheekbones), and the *mastoid process* of the *temporal bone* are useful indicators for determining sex. The *shape of the orbits*, the *nasal opening*, and the presence or absence of a *post-bregmatic depression* are all important anatomical features used in determining ancestry. Forensic anthropologists are often called on to help identify victims of accidents, crimes, natural disasters, and other situations where the identity of the victim is unknown.