Axial Skeleton System
There are 22 bones of skull. They lie on the superior end of vertebral column. These bones are divided in 2 groups: Cranial bones- which forms the cranial cavity are eight in number; Facial bones- these are 14 and forms the face.
1. FRONTAL BONE
Frontal bone forms the forehead, the anterior part of cranium, roofs of the orbits. It also forms prominent ridges above the eyes known as supraorbital margins. Just above these margins, inside the bone, are the two air-filled cavities. These cavities are also known as sinuses and opens into nasal cavity.
The coronal suture joins the frontal and parietal bone. Other sutures are formed with sphenoid, zygomatic, lacrimal, nasal and ethmoid bone.
2. PARIETAL BONE
These are present in pairs and forms the side and roof of the skull. They articulate with each other and forms sagittal suture, parietal bone and frontal bone forms coronal suture, occipital bone and parietal bone forms lambdoidal suture and with temporal bone the parietal bone forms squamous suture. The inner surface is concave and is used to accommodate the brain and blood vessels.
3. TEMPORAL BONE
There are two temporal bones and lies one on each side of the head and forms sutures with parietal, sphenoid, occipital and zygomatic bone. The squamous part of temporal bone is a thin fan-shaped area that articulates with the parietal bone. The mastoid part contains the mastoid process:- a thickened region present behind the ears. these processes contains large number of air sinuses that communicate with the middle ear.
The petrous portion forms part of the base of skull and also contains organs having receptors for hearing and balance(organ of corti , vestibule and semicircular canals). The temporal bone articulate with the mandible and forms temporomandibular joint; It is the only movable joint of skull. The styloid process of temporal bone supports hyoid bone and muscles of tongue and pharynx.
4. OCCIPITAL BONE
this bone forms the back of head and also the part of base of the skull. It articulates with parietal, sphenoid and temporal bone. The inner surface is concave in shape and contains occipital lobes of cerebrum and cerebellum. this bone have 2 condyles which forms condyloid joint with atlas(1st bone of vertebral column); this joint allows the nodding movement of head. Between the condyles is the foramen magnum through which the spinal cords passes into the cranial cavity.
5. SPHENOID BONE
This bone forms the Middle part of base of the skull. This bone links the cranial and facial bones. In the middle of the bone, on the superior surface is a depression known as hypophyseal fossa, where the pituitary gland lies. It also contains large number of small air sinuses which opens into the nasal cavity. The optic foramina of sphenoid bone forms a passage for the optic nerve to reach the brain.
6. ETHMOID BONE
This bone forms the anterior part of base of skull. It helps to form orbital cavity., the nasal septum and lateral walls of nasal cavity. On each side of the bone are the projections known as middle or superior conchae. It is a very delicate bone and contains small air sinuses with opening into nasal cavity. The cribriform plate forms the roof of nasal cavity nd contains large no. of small foramens through which the nerve fibers of olfactory nerve passes and leads to brain.
Our face is formed by a group of 14 bones. some of these bones are present in pairs and others are single.
there are two zygomatic bones. Each bone earlier originate as 2 bones and later fuse after birth. The bones form prominences of the cheek and the part of floor and lateral walls of orbital cavities.
this is the upper jaw bone and forms the anterior part of the roof of the mouth, the upper jaw, part of orbital cavities and walls of nasal cavity. the alveolar process carries the upper teeth. On each side of the bone is the sinus known as maxillary sinus which opens into nasal cavity.
The two nasal bones meet at the midline and form the bridge of the nose. The rest of the supporting tissue of the nose consist of cartilage.
The two lacrimal bones are thin and are like fingernail in size as well as in shape. These are the smallest bones of face and forms a part of medial wall of each orbit. It contains lacrimal fossa that stores lacrimal sacs; the structures that gathers tears and passes into nasal cavity.
These are two L-shaped bones form the posterior portion of hard palate, floor of nasal cavity and some portion of floor of orbits. The horizontal plates form the posterior portion of hard palate.
Inferior Nasal conchae
There are two inferior nasal conchae, which are inferior to the middle nasal conchae of the ethmoid bone. These are separate bones. All the three nasal conchae(superior, inferior and middle) increase the surface area of the nasal cavity, to filter the air as it passes into the lungs. Only the superior nasal conchae are involved in sense of smell.
Vomer is a triangular bone on the floor of nasal cavity that articulates superiorly with the ethmoid bone and inferiorly with maxillae and palatine bone. It also forms inferior portion of nasal septum.
It is the lower jaw bone; It is the largest and strongest facial bone. It is the only skull bone which is movable. It consist of a curved horizontal portion, the body and two perpendicular portions known as rami. Each ramus has a posterior condylar process that articulates with the mandibular fossa and articular tubercle of temporal bone; and forms temporomandibular joint. The depression between coronoid process and condylar process is known as mandibular notch. The alveolar process contains the alveoli for lower teeth. The mental foramen is the one near which the dentist reach the mental nerve before injecting anesthetics.
Multiple choice questions(MCQs)
1. How many bones come together to form skull?
A. 20 B. 22
C. 25 D. 14
2. Which is the smallest facial bone?
A. vomer B. zygomatic
C. mandible D. lacrimal bone
3. Which is the only movable joint of skull?
A. sagittal suture B. coronal suture
C. temporomandibular joint D. lambdoidal suture
4. The frontal bone articulates with which bone?
A. temporal B. parietal
C. sphenoid D. all of the above
5. Which of the following statement is NOT true?
A. palatine bones are L-shaped bones
B. maxilla is the lower jaw bone
C. zygomatic bone is a cheek bone
D. Vomer forms inferior portion of nasal septum
6. Which part of temporal bone contains organs for hearing and balance?
A. mastoid process B. petrous portion
C. squamous part D. styloid process
7. Which bone links the cranial and facial bone?
A. sphenoid bone B. ethmoid bone
C. nasal bones D. zygomatic bone
8. Which bone is roughly triangular in shape?
A. nasal bones B. inferior nasal conchae
C. lacrimal bone D. none of the above
9. Match the following-
1. ethmoid bone a. forms middle part of skull
2. sphenoid bone b. forms most of the base of skull
3. frontal bone c. forms anterior part of base of skull
D. occipital bone d. forms the forehead
10. Which bone forms the posterior portion of hard palate?
A. nasal bones B. palatine bone
C. vomer D. zygomatic bone
2. lacrimal bones
3. temporomandibular joint
4. all of the above
5. maxilla is the lower jaw bone
6. petrous portion
7. sphenoid bone
8. none of the above; it is vomer
9. 1 – c 2 – a 3 – d 4 – b
10. palatine bones
1. Ross and Wilson-Anatomy and physiology in health and illness; 12th edition; page no.-: 396-401.
2. Gerard J. Tortora -Principles of anatomy and physiology; edition twelfth ; page no.-: 202-212.