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Facial bones (viscerocranium)

The skull (cranium) is a complex bony structure composed of two distinct regions: the neurocranium and viscerocranium. The viscerocranium is a collection of bones that make up the face skeleton. It is named in contrast to the neurocranium (braincase), or the bones of the skull that accommodate the human brain

The face skeleton includes 14 facial bones (6 paired and 2 unpaired) with specific anatomical landmarks and embryological development. These bones include the paired inferior nasal conchae, nasal bones, maxillae, palatine bones, lacrimal bones and zygomatic bones, as well as the unpaired mandible, and  vomer

The main functions of viscerocranium are to give a characteristic shape to the human face and to protect the delicate organs of the face. In addition, it provides a bony surface for the attachment of the facial muscles and bears many foramina for the passage of the neurovascular structures. 

This article will discuss the anatomy and function of viscerocranium.

Key facts about the viscerocranium
Definition A collection of 14 bones that make up the human face
Paired bones Nasal concha, nasal bone, maxilla, palatine bone, lacrimal bone, zygomatic bone
Unpaired bones Mandible, vomer
Functions Forms the characteristic shape of the human face;
Provides attachment for facial muscles;
Creates a passageway for neurovascular structures;
Provides protection to the structures of the face

Bones

Maxilla

The maxilla is the central, paired bone of the viscerocranium. The left and right maxilla fuse in the midline to form the upper jaw. Between the two maxillae lies a cranial suture called the intermaxillary suture. The maxilla is made of several parts: 

  • The body
  • The zygomatic process (zygomatic arch)
  • The frontal process 
  • The alveolar process (teeth socket)
  • The palatine process (hard palate)

Important features of the maxilla include the infraorbital foramen, maxillary sinus, and incisive foramen. The main function of the maxilla is to hold the upper teeth in place. 

Zygomatic bone

The zygomatic is an irregular paired bone of the face located at the upper lateral part of the face. It is also known as the 'cheek bone' because it forms the lateral prominences of the face. The zygomatic bone has three processes that include the frontal, maxillary and temporal processes. Through its processes, the zygomatic bone articulates with the frontal bone, temporal bone, sphenoid bone, and maxilla.

The most important feature of the zygomatic bone is the zygomatic arch. This arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The main function of the arch is to protect the eyes from a direct blow and to provide attachment for the masticatory muscles (temporalis and masseter). 

Lacrimal bone

The lacrimal bone is the smallest and the most fragile bone of the viscerocranium. It is a paired oblong bone situated in the anterior part of the medial wall of the orbit. The word 'Lacrima' is Latin for 'tear', so the name of the bone corresponds with its relation to the nearby lacrimal structures.

The bone has two surfaces (lateral and medial) and four borders (anterior, posterior, superior and inferior). 

The main function of the lacrimal bone is to provide support for the structures of the lacrimal apparatus, which secretes and drains tears.

In addition, the lacrimal bone as an attachment site for the orbicularis oculi muscle.

Inferior nasal concha

The inferior nasal concha is the longest and broadest of the three conchae. In contrast to the superior and middle nasal conchae, the inferior nasal concha is a separate bone. 

The inferior nasal concha is a bony plate located on the lateral wall of the nasal cavity

The main function of the inferior nasal concha is to participate in the formation of both the middle and inferior nasal meatus. The inferior nasal meatus lies directly beneath the inferior nasal concha and is the largest space of the nasal cavity. It is responsible for the majority of airflow direction, humidification, heating and filtering of air inhaled through the nose.

Palatine bone

The palatine bone is a paired, L-shaped bone located posterior to the nasal cavity. More specifically, the bone is interposed between the maxilla and sphenoid bones. The palatine bone is primarily defined by its horizontal and perpendicular plates. Due to its many connections with the surrounding bones, the palatine bone participates in the formation of several important structures: 

  • The horizontal plate forms the posterior portion of the hard palate of the oral cavity
  • The perpendicular plate contributes to the lateral wall of the nasal cavity where it borders the pterygoid process of the sphenoid bone. 

The palatine bone also contributes to a small portion of the orbital floor, via the orbital process found at the superior end of the perpendicular plate.

Nasal bone

The nasal bone is a paired, rectangle-shaped bone located medial to the frontal processes of the maxillae. The left and right nasal bones connect in the midline via the internasal suture.

The bone has 4 borders and 2 surfaces which form a number of connections with the surrounding bones. 

The main function of the nasal bone is to form the bridge of the nose, the nasal aperture, and to protect the nasal cavity from external factors.

Mandible

The mandible is the largest bone of the viscerocranium located in the inferior portion of the face, forming the lower jaw. It is important to note that the mandible is not part of the skull, but it is attached to it via the temporomandibular joint (TMJ). Besides the bones of the middle ear (auditory ossicles), the mandible is the only mobile bone of the head. 

The mandible is composed of two main parts; a horizontal body (anteriorly) and two vertical rami (posteriorly). On each side, the body and the ramus are connected at the angle of the mandible. These parts harbor various anatomical landmarks that participate in important functions of the mandible.

The main function of this bone is to form the contours of the face (chin and jawline) and to hold the lower teeth in place. The TMJ allows the mandible to move in various directions and allows a person to speak and chew. 

Vomer

The vomer is the second unpaired bone of the viscerocranium situated in the midsagittal line. It is a flat plate of bone situated vertically in the nasal cavity. Along with the ethmoid bone, the vomer forms the bony portion of the nasal septum which separates the left and right sides of the nose. 

More specifically, the superior two-thirds of the bony nasal septum is formed by the perpendicular plate of the ethmoid bone, while the inferior third is formed by the vomer. The anterior part of the nasal cavity is formed by the nasal cartilage. 

Functions

The prime function of the viscerocranium is to shape the human face and cavities of the anterior skull including the orbit, oral and nasal cavities. It protects the delicate contents of these cavities, as well as the neurovascular structures of the face. 

The bony surface of the viscerocranium provides attachment points for the facial muscles which are important for expressing emotions and mood. The viscerocranial bones also contain sinuses (e.g. maxillary sinuses) that reduce the weight of the skull and enhance the resonance of the voice while speaking.

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