Skull Anatomy PDF

SKULL Skull is formed by 17 different types of bones. Most of the bones of skull are flat type. The bones of skull can be classified as cranial and facial bones as well as paired and single bones. Cranial Bones Facial Bones 1. Occipital (Single)...

SKULL Skull is formed by 17 different types of bones. Most of the bones of skull are flat type. The bones of skull can be classified as cranial and facial bones as well as paired and single bones. Cranial Bones Facial Bones 1. Occipital (Single) 1. Nasal (Paired) 2. Parietal (Paired) 2. Zygomatic / Malar (Paired) 3. Interparietal (Single) 3. Lacrimal (Paired) 4. Temporal (Paired) 4. Maxilla (Paired) 5. Sphenoid (Paired) 5. Premaxilla (Paired) 6. Ethmoid (Single) 6. Palatine (Paired) 7. Frontal (Paired) 7. Pterygoid (Paired) 8. Turbinate / Conchae (Paired) 9. Vomar (Single) 10. Mandible (Single) Frontal Bone : It is a paired cranial type of bone. It forms the forehead part of the skull. It also forms the roof of the cranial cavity. The dorsal border in its middle presents elevated area called as frontal eminence or torus frontalis. The dorsal border at its corner, presents projection called as corneal process, which represents the horns. Laterally, its presents a frontal crest, which distally continue to form orbital processes and joins with the frontal process of malar or zygomatic process. It also forms part of orbital rim. Above the orbital rim presents a canal called as supraorbital canal. Inside this canal, there is a foramen called as supraorbital foramen. It gives a passage to the supraorbital nerve. The frontal bone joins with the malar, lacrimal, nasal, parietal and interparietal bone. Occipital Bone : It is a single cranial type of bone. It forms caudoventral part of cranial cavity. Little above the middle part, it presents a rough protruded area called as external occipital protruberance. It gives attachment to the ligamentum nuchae. Just below the external occipital protruberance, there is a foramen called as foramina magnum, which gives passage to spinal cord. On either side of foramen magnum, there is an oval smooth articular area called as occipital condyle, which articulates with cranial articular areas of atlas to form occipitoatlantal joint. Lateral to the occipital condyles, there is projection on either side called as paramastoidprocess or jugular process. In between condyle and paramastoid process, there is depression called as condyloid fossa. Inside the condyloid fossa there are two foramina. The cranial foramina is called as hypoglossal foramen and the caudal foramen is called as condyloid foramen. Ventrally there is rough area called as occipital tubercle. Parietal Bone : These are paired cranial type of bones. It forms the dorsolateral part of the cranial cavity. Along with, temporal bone, it helps in formation of temporal fossa. Interparietal Bone: It is single cranial type of bone and is interposed in between the two parietal bones. Temporal Bone: It is paired cranial type of bone and forms the ventrolateral part of the cranial cavity. It has two parts, the petrous and the squamous part. The squamous part of temporal bone consists of body and a zygomatic process. The body along with the parietal bone forms the temporal fossa. The zygomatic process of squamous part of temporal bone is directed cranially and joins with the zygomatic process of malar bone. The petrous part of temporal bone has got glenoid cavity, external auditory meatus, tympanic bulla and hyoid process. The glenoid cavity articulates with the condyloid process of mandible and forms temporo-mandibular joint. Laterally there is external auditory meatus, which represents the opening for middle and internal ear. Medially the temporal bone presents a hollow protruded area called as tympanic bulla. It gives accommodation to the tympanic membrane of ear. Adjacent to the tympanic bulla, there is stump like structure called as hyoid process. Sphenoid Bone : It is a single cranial type of bone. It forms most of the part of the floor of cranial cavity. It has two parts, the presphenoid and the postsphenoid. Both the parts have wings termed as wings of presphenoid and wings of postsphenoid. At the junction of the presphenoid and postsphenoid wings, there is foramen called as foramina orbitorotandum. In the wings of postsphenoid bone, there is a foramen called as foramina ovale. On the cranial surface of the sphenoid bone, there is depression called as pituitary fossa or sella turcica, which gives accommodation to the pituitary gland. Cranially, it is attached with the ethmoid bone and caudally with the occipital bone. Ethmoid Bone : It is single cranial type of bone and helps in the formation of cranial part of floor of cranial cavity and also forms the partition between nasal cavity and cranial cavity. In the middle of the ethmoid bone, there is crest called as crista galli. On either side of crista galli, there is depression called as olfactory fossa, which gives accommodation to olfactory bulbs of the brain. The fossa is porous and gives out bony plates inside the nasal passage called as cribriform plate. FACIAL BONES Lacrimal Bone : It is paired facial type of bone. It helps in formation of orbital rim. The rim of the orbit laterally presents a depression called as lacrimal fossa, which gives accommodation to the lacrimal sac. Nasal Bone : Nasal bone is paired facial type of bone. It forms the roof of the nasal cavity. It has got two surfaces and two extremities. The dorsal surface is smooth and convex. The inner or caudal surface is concave. The proximal extremity is pointed, while distal extremity is notched. Malar / Zygomatic Bone : It is paired facial type of bone. It forms the cranio-lateral part of the face. It also helps in formation of rim of the orbit. It consists of two projections. The projection, which is directed upward is called as frontal process, which joins with the orbital process of the frontal bone. The other process which is directed caudally is called as zygomatic process of malar and joins with the zygomatic process of temporal bone. In between zygomatic process and frontal process, there is an arch called as zygomatic arch. Maxilla : It is a paired facial type of bone. It is the largest bone of the upper jaw. It forms the roof of the mouth cavity and floor of the nasal cavity. It consists of infraorbital foramen, facial / maxillary tuberosity, alveolar border and palatine process. The infraorbital foramen is located at the level of first cheek tooth or first premolar tooth. Through this foramen, the infraorbital nerve passes which, innervates to the upper jaw cheek teeth. Above the infraorbital foramen, there is rough protruded area called as facial / maxillary tuberosity, which gives attachment to the muscles of lip and nostrils. At the border of maxilla, there are alveoli for implantation of six cheek teeth (3 premolar and 3 molars). The palatine process of one side of maxilla joins with the palatine process of other side of maxilla and helps in formation of part of hard palate. Premaxilla : It is the paired facial type of bone. It forms the distal part of the upper jaw. It consists of nasal process, palatine process and palatine fissure. The nasal process runs backward and upward in direction and joins with the nasal bone. The palatine process runs in backward direction and helps in formation of cranial part of hard palate. In between the nasal and palatine process, there is fissure called as palatine fissure. Palatine bone : It is a paired facial type of bone. It consists of two parts, the horizontal part and the perpendicular part. The horizontal part forms the caudal part of the hard palate and presents a foramen called as anterior palatine foramen. The horizontal part continue behind as perpendicular part and forms the lateral wall of caudal part of nasal cavity. Vomar Bone : It is a single facial type of bone. It is cartilaginous in nature. It extends from premaxilla to presphenoid It acts as partition between the nasal cavity and forms two passages. Turbinate Bone : It is paired facial type of bone. They are two in number placed one above the other on each side of the nasal passage. The turbinates are also called as conchae. They are bony net like structures, present in the form of scroll or roll one above the other. They are named as dorsal turbinate / conchae and ventral turbinate / conchae. Due to presence of two turbinate bones, each nasal passage is divided in to three passages. These passages are named as dorsal nasal meatus, middle nasal meatus and ventral nasal meatus. These three meatuses meet with each other caudally. Pterygoid : It is paired facial type of bone. It forms the caudal part of the lateral wall of nasal cavity. Distally it has a hook like projection termed as hamulus. Mandible : Mandible is a single facial type of bone. It forms the skeleton of the lower jaw. It is formed by the fusion of two halves. The mandible has got two parts, the body of mandible and ramus of mandible. The body of mandible has two parts, the cranial incisivus part and caudal molar part. The incisivus part of body of mandible has two surfaces. The dorsal surface is concave and is called as lingual surface while the ventral surface is convex and is called as labial surface. In between lingual and labial surface, there are alveolar sockets for implantation of eight incisor teeth. Caudally the incisivus part continues in to two halves. Each halve is known as molar part of body of mandible. The molar part is having two surfaces, two borders and two extremities. The lateral surface is smooth and cranially presents a foramen called as mental foramen through which the mental nerve passes. The mental foramen caudally communicates with mandibular foramen. Dorsal border is concave and presents alveolar sockets for implantation of six cheek teeth (3 premolars and 3 molars). The ventral border is thick and convex. Cranial extremity continues as incisivus part and caudal extremity joins with ramus of mandible. The vertical ramus of mandible is having two surfaces, two borders and two extremities. The lateral surface is rough and gives attachment to the massater muscle. The medial surface has a foramen called as mandibular foramen, which cranially communicates with mental foramen. It gives passage to the mental nerve, which innervates to the lower jaw teeth. The cranial border is thin while the caudal border is thick. Distal extremity joins with the molar part of body of mandible. The proximal extremity presents two processes, the condylar process and the coronoid process. The condylar process is caudally placed and articulates with glenoid cavity of temporal bone of skull to form temporo-mandibular joint. The coronoid process is cranially placed and is non articular and remains hanging in the temporal fossa. Skull of Horse : 1. It is elongated and four sided. 2. Cornual processes are absent. 3. Parietal bones forms roof of the cranial cavity 4. Rim of the orbit is complete and circular 5. Premaxilla or incisivus bone part has alveolar sockets for implantation of incisor teeth 6. At the junction of the maxilla and premaxilla, a pair of alveolar socket is present for implantation of canine teeth. 7. Symphysis mandibuli is complete. 8. The zygomatic process of temporal and malar are completely fused. Skull of Dog: 1. The size and shape of the skull varies from breed to breed.  2. Cornual processes are absent 3. Rim of the orbit is incomplete 4. Zygomatic process are wide 5. Massateric fossa is present on the lateral surface of the ramus of mandible. 6. Parietal bones forms the roof of cranial cavity 7. Mandibular symphysis is incomplete. 8. Mandible caudally presents an additional projection, the angular process and a notch. Skull of Pig: 1. The skull is elongated in shape. 2. Basilar part of occipital bone is hexagonal in shape and depressed 3. Orbital ring is not complete 4. Canine teeth are well developed. 5. Paramastoid processes are long and extended downward. 6. Coronoid process of the mandible is short but pointed. 7. The angle between two rami are comparatively wide 8. Cranial cavity is comparatively small. 9. It has visceral bone at rostral aspect of the nasal septal cartilage known as osrostrale. Skull of Fowl : 1. Most of the bones are fused with each other. 2. Orbit is larger as compared with the size of the skull. 3. Teeth are absent. 4. Mandible is not a single bone but it is formed by 5 segments 5. Only one occipital condyle is present. Upper jaw is movable due to presence of naso- frontal hinge. Naso-frontal hinge is useful for movements of upper beak.