The lacrimal bone is a small and fragile
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
of the
facial skeleton
The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase.
In human anatomy and development, the facial skeleton is sometimes called the ''membranous viscerocr ...
; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
. It has two surfaces and four borders. Several bony landmarks of the lacrimal bone function in the process of lacrimation or crying. Specifically, the lacrimal bone helps form the nasolacrimal canal necessary for tear translocation. A depression on the anterior inferior portion of the bone, the lacrimal fossa, houses the membranous lacrimal sac. Tears or lacrimal fluid, from the lacrimal glands, collect in this sac during excessive lacrimation. The fluid then flows through the nasolacrimal duct and into the nasopharynx. This drainage results in what is commonly referred to a runny nose during excessive crying or tear production. Injury or fracture of the lacrimal bone can result in posttraumatic obstruction of the lacrimal pathways.
Structure
Lateral or orbital surface
The lateral or orbital surface is divided by a vertical ridge, the
posterior lacrimal crest
The posterior lacrimal crest is a vertical bony ridge on the orbital surface of the lacrimal bone. It divides the bone into two parts. It gives origin to the lacrimal part of the orbicularis oculi muscle.
Structure
The posterior lacrimal crest ...
, into two parts.
In ''front'' of this crest is a longitudinal groove, the
lacrimal sulcus
On the nasal surface of the body of the maxilla, in front of the opening of the sinus is a deep groove, the lacrimal groove (or lacrimal sulcus), which is converted into the nasolacrimal canal, by the lacrimal bone and inferior nasal concha; this ...
(''sulcus lacrimalis''), the inner margin of which unites with the frontal process of the
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
, and the
lacrimal fossa is thus completed. The upper part of this fossa lodges the
lacrimal sac
The lacrimal sac or lachrymal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It connects the lacrimal canaliculi, which drain tears from the ey ...
, the lower part, the
nasolacrimal duct
The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. The ...
.
The portion ''behind'' the crest is smooth, and forms part of the medial wall of the orbit.
The crest, with a part of the orbital surface immediately behind it, gives origin to the lacrimal part of the
orbicularis oculi
The orbicularis oculi is a muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short ...
and ends below in a small, hook-like projection, the
lacrimal hamulus
The lacrimal hamulus is a small, hook-like bony projection of the lacrimal bone. It is a continuation of the posterior lacrimal crest. It articulates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the lacrimal canal ...
, which articulates with the
lacrimal tubercle of the maxilla, and completes the upper orifice of the
nasolacrimal canal; the hamulus sometimes exists as a separate piece, and is then called the
lesser lacrimal bone.
Medial or nasal surface
The medial or nasal surface presents a longitudinal furrow, corresponding to the crest on the lateral surface.
The area in front of this furrow forms part of the
middle meatus
In anatomy, the term nasal meatus can refer to any of the three meatuses (passages) through the skulls nasal cavity: the superior meatus (''meatus nasi superior''), middle meatus (''meatus nasi medius''), and inferior meatus (''meatus nasi inferio ...
of the nose. The area behind it articulates with the
ethmoid
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
, and completes some of the
anterior ethmoidal cells
The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral e ...
.
Borders
Of the four borders:
* the ''anterior'' articulates with the frontal process of the maxilla;
* the ''posterior'' with the
lamina papyracea
The orbital lamina of ethmoid bone, (or lamina papyracea or orbital lamina) is a smooth, oblong bone plate which forms the lateral surface of the labyrinth of the ethmoid bone in the skull.
The plate covers in the middle and posterior ethmoidal c ...
of the ethmoid;
* the ''superior'' with the frontal bone.
* The ''inferior'' is divided by the lower edge of the posterior lacrimal crest into two parts:
** the posterior part articulates with the orbital plate of the maxilla;
** the anterior is prolonged downward as the descending process, which articulates with the lacrimal process of the
inferior nasal concha
The inferior nasal concha (inferior turbinated bone or inferior turbinal/turbinate) is one of the three paired nasal conchae in the nose. It extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, cu ...
, and assists in forming the canal for the nasolacrimal duct.
Development
The lacrimal is ossified from a single center, which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule.
Articulations
The lacrimal articulates with four bones: two of the cranium, the
frontal
Front may refer to:
Arts, entertainment, and media Films
* ''The Front'' (1943 film), a 1943 Soviet drama film
* ''The Front'', 1976 film
Music
*The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...
and
ethmoid
The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...
, and two of the face, the
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
and the inferior
nasal concha
In anatomy, a nasal concha (), plural conchae (), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various animals. The conchae are shaped like ...
.
Other animals
In early
lobe-finned fish
Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...
es and ancestral
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s, the lacrimal bone is a relatively large and robust bone, running from the orbit to the nostrils. It forms part of the side of the face, between the
nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose.
Eac ...
s and the maxilla. In primitive forms, it is often accompanied by a much smaller
septomaxilla bone, lying immediately behind the nasal opening, but this is lost in most modern species. The lacrimal bone is often smaller in living vertebrates, and is no longer always directly associated with the nasal opening, although it retains its connection with the orbit. The bone is entirely absent in living
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s, as well as some reptilian species.
Dinosaurs
In dinosaurs, the lacrimal bone usually defines the anterior rim of the orbit (eye socket), and the posterior rim of the
antorbital fenestra
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
. In some theropods (e.g. ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'', ''
Ceratosaurus
''Ceratosaurus'' (from Ancient Greek, Greek κέρας/κέρατος, ' meaning "horn" and wikt:σαῦρος, σαῦρος ' meaning "lizard") was a carnivorous Theropoda, theropod dinosaur in the Late Jurassic Period (geology), period (Kim ...
'', ''
Albertosaurus
''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...
'') the upper part of the lacrimal bone grew in such a manner as to form a horn on the top of the dinosaur's head, usually situated above, and anterior to the eye. In many dinosaurs, the lacrimal bone comes into contact with the nasal bone, the jugal bone, the prefrontal bone, and the maxillary and premaxillary bones. The boundaries where some of these bones meet with the others are called
sutures. Rarely, the lacrimal bones fused with the nasal bones to form a pair of "nasolacrimal" crests, which are present in dinosaurs such as ''
Dilophosaurus
''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 193 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved ...
'', ''
Megapnosaurus
''Megapnosaurus'' (meaning "big dead lizard", from Greek μεγα = "big", 'απνοος = "not breathing", "dead", σαυρος = "lizard") is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago duri ...
'' and ''
Sinosaurus
''Sinosaurus'' (meaning "Chinese lizard") is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately in length and in body mass. Fossils of the animal were found at the Lufen ...
''.
Additional images
File:Lacrimal bone - animation.gif, Position of the lacrimal bones (shown in green). Animation.
File:Lacrimal bone - animation3.gif, Animation. Some bones are removed to show the position of the lacrimal bones (shown in green).
File:Orbital bones.png, Orbital bones. Lacrimal bone shown in green.
File:Left lacrimal bone - close-up - animation.gif, A left lacrimal bone. Enlarged. Animation.
File:Orbital cavity.jpg, Lacrimal bone
File:Slide7llll.JPG, Lacrimal bone
See also
References
External links
*
*
*
Diagram at upstate.edu
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Bones of the head and neck
Irregular bones
Flat bones