![]() ![]() On the interior of the skull, the ethmoid also forms a portion of the floor of the anterior cranial cavity. The ethmoid bone is a single, midline bone that forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and contributes to the medial wall of the orbit. Two major passageways in the sphenoid are the optic canal (passageway for the optic nerve (CN) II) and the superior orbital fissure (passageway for cranial nerves (CN) III, IV, V (part), and VI) The greater wing is best seen on the outside of the lateral skull, where it forms a rectangular area immediately anterior to the squamous portion of the temporal bone. The greater wings of the sphenoid bone extend laterally to either side away from the sella turcica, where they form the anterior floor of the middle cranial fossa. The sella turcica (“Turkish saddle”) is located at the midline of the middle cranial fossa and houses the pituitary gland. Inside the cranial cavity, the right and left lesser wings of the sphenoid bone, which resemble the wings of a flying bird, form the lip of a prominent ridge that marks the boundary between the anterior and middle cranial fossae. The sphenoid forms much of the base of the central skull and also extends laterally to contribute to the sides of the skull. It serves as a “keystone” bone because it joins with almost every other bone of the skull. The sphenoid bone is a single, complex bone of the central skull. Carotid canal-The carotid canal is a zig-zag shaped tunnel that provides passage through the base of the skull for the internal carotid artery.This is the point of exit for the cranial nerve that supplies the facial muscles. Stylomastoid foramen-This small opening is located between the styloid process and mastoid process.Mastoid process – The inferior portion of the mastoid portion is an area for muscle attachment (sternocleidomastoid muscle).This structure serves as an attachment site for several small muscles and for a ligament that supports the hyoid bone of the neck. Styloid process-Posterior to the mandibular fossa on the external base of the skull is an elongated, downward bony projection called the styloid process, so named because of its resemblance to a stylus (a pen or writing tool).The mandible (lower jaw) joins with the skull at this site as part of the temporomandibular joint, which allows for movements of the mandible during the opening and closing of the mouth. Mandibular fossa-This is the deep, oval-shaped depression located on the external base of the skull, just in front of the external acoustic meatus.External acoustic meatus (ear canal)-This is the large opening on the lateral side of the skull that is associated with the ear.Important landmarks of the temporal bone include the following: ![]() ![]() Temporal Bone A lateral view of the isolated temporal bone shows the squamous, mastoid, and zygomatic portions of the temporal bone. The 22nd bone is the mandible (lower jaw), which is the only moveable bone of the skull. In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The rounded cranium of the cranial bones surrounds and protects the brain and houses the middle and inner ear structures. ![]() The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. It is subdivided into the facial bones and cranial bones. The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. In the lecture videos, I walk through the bones of the cranium and face and highlight the key features/landmarks. Remember – the learning objective is to list the bones and identify key features/landmarks. * NOTE – Most of the reading about the cranial and facial bones is very in-depth.
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