Examville.com - Anatomy - Skull Dycondylic

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(a) Cranium (Brain Box, 8 bones). It is the bony structure that encloses the brain and protects it. It is hollow and nearly rounded. Bones constituting the cranium are called cranial bones. They are eight in number. (i) Frontal-1 (ii) Parietal-2 (iii) Occipital-l (iv) Temporal-2 (v) Sphenoid-l (vi) Ethmoid-l. Cranial bones are flattened bones. They are jointed with each other by fixed interdigited joints called sutures. At the base of skull occipital has a large opening called foramen of magnum. Through foramen of magnum brain communicates with spinal cord. There are two lateral protuberances or occipital condyles, one on each side of foramen magnum. Because of the presence of two occipital condyles, human skull is called dicondylic. The two occipital condyles are articulated with atlas vertebra by hinge joints for performing nodding movements. Each temporal bones bear opening of external auditory meatus. Skull bones also posses fontanelles. Fontanelles are the soft areas present in foetal cranium. An infant may have many fontanelles at birth but generally six are recognized. Anterior fontanell or Frontal fontanell is largest and it closes by 18 to 24 months of age. Neurocranium is part of skull having brain and sensory capsules. Temporal bone has styloid process, zygomatic process and mastoid process. It also posses an external auditory meatus. (b) Ear Ossicles (6 bones). Each side or temporal region contains an auditory capsule or middle ear. It has three bones. These bones are small in size and named as ear ossicles or ear bones. They are outer malleus (hammer shaped), middle incus (anvil shaped) and innermost stapes (stirrup shaped). These bones are helpful in the amplification of sound 20-22 times. (c) Facial Bones (14 bones). Facial bones constitute front part of skull alongwith skeleton of lower jaw, hard palate and nose. They are fourteen in number. (i) Nasals-2 (ii) Maxillae-2 (iii) Zygomatic (cheek bones)-2 (iv) Lacrimals-2 (v) Palatines-2 (vi) Inferior nasal conchae-2 (vii) Vomer-1 (viii) Mandible-1. Frontal is common bone to both cranium and face. Maxillae form the upper jaw whereas mandible forms the lower jaw. Upper jaw is fused with cranium. Lower jaw or mandible is horse-shoe shaped bone which bears two processes on each side, a pointed one named coronoid and a rounded one called condyloid. Mandible is strongest and largest bone of face. Movable mandible helps in the mastication of food as well as speech. Jaws have sockets for the fixation of teeth.

(d) Hyoid Bone (Tongue Bone, 1 bone). It lies at the base of tongue and above the larynx. It is not joined to the rest of skeleton except to styloid process of temporal bone by muscles with the help of certain muscles. It is horse shoe-shaped slender bone. Upper portion of hyoid bone has a swelling known as the greater cornu. The lower portion has small projection known as lesser cornu. Hyoid bone and the tongue together form the hyoid apparatus. Hyoid bone is fractured during strangulation.