Human Anatomy - Zynoviy Mirchuk, Maryna Mirchuk 2007

Axial skeleton
Bones of the neurocranium

The neurocranium is divided into the vault (roof) and the base. The Base of the Skull is further subdivided into external and internal parts. The external surface of the cranial vault is smooth and features clearly defined cranial sutures: squamous, sagittal, coronal, lambdoid, and serrated.

The surface of the external base of the skull is uneven and pierced by numerous openings, including the choanae, foramen magnum, jugular foramen, and lacerate foramen, among others. The mastoid and styloid processes are located in the lateral Regions of the skull base.

The Occipital bone forms the posteroinferior region of the neurocranium. It features the foramen magnum, which connects the cranial cavity with the vertebral canal, allowing passage for the Spinal Cord, Blood Vessels, and nerves. The bone consists of a basilar part, lateral parts, and the occipital squama. Its posterior (external) surface bears the external occipital protuberance, which is easily palpable through the Skin.

The Frontal bone contributes to The formation of the anterior cranial vault, the anterior cranial fossa of the skull base, and the orbits, which house the eyeballs and their accessory structures (Lacrimal Apparatus, Muscles, fascia). It is composed of a squama, as well as nasal and orbital parts. The external surface of the frontal bone terminates in the supraorbital margin. The nasal part of the bone contains the air-filled frontal sinus.

The Parietal bone is a paired bone that forms the superior and lateral aspects of the cranial vault. The parietal bones articulate with each other via the sagittal suture, and with the frontal and occipital bones via the coronal and lambdoid sutures, respectively.

The Temporal bone is a paired bone situated between the occipital, parietal, and sphenoid bones, contributing to the Formation of the base and lateral wall of the cranial vault. Each temporal bone forms a joint with the Mandible and articulates with the Zygomatic bone to form the zygomatic arch. The temporal bone comprises the petrous part (pyramid) with the mastoid process, as well as the tympanic and squamous parts.

Class="center">

Fig. 1. Skull

The Ethmoid bone contributes to the formation of the cranial base, the orbital walls, and the Nasal cavity. It consists of the cribriform plate, the perpendicular plate, and the ethmoidal labyrinth. The cribriform plate is visible from the internal base of the skull; it is perforated by 30-40 small openings through which Olfactory nerve fibers and blood vessels enter the cranial cavity. The perpendicular plate forms the anterosuperior part of the bony nasal septum. Inferiorly, it articulates with the Vomer—an unpaired, quadrilateral plate that forms the posteroinferior part of the nasal septum. The posterior border of the vomer is smooth and free, separating the posterior nasal apertures from one another.

Suspended downward from the margins of the cribriform plate is the ethmoidal labyrinth, which consists of numerous air-filled ethmoidal Cells. These cells are lined with mucous membrane and communicate with one another and with the nasal cavity. The lateral surface of the labyrinth, known as the orbital plate, is thin and smooth, contributing to the formation of the medial orbital wall. The Medial surface of the labyrinth is rough and projects into the nasal cavity as two processes—freely curved margins rolled outward, which are termed the superior and middle nasal conchae. Occasionally, an underdeveloped third nasal concha may also be present.