Lacrimal bone
Encyclopedia
The lacrimal bone, the smallest and most fragile bone
of the face, is situated at the front part of the medial wall of the orbit
. It has two surfaces and four borders.
, into two parts.
In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla
, and the lacrimal fossa
is thus completed. The upper part of this fossa lodges the lacrimal sac
, the lower part, the nasolacrimal duct
.
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 and ends below in a small, hook-like projection, the lacrimal hamulus
, 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.
The area in front of this furrow forms part of the middle meatus
of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells.
and ethmoid
, and two of the face, the maxilla
and the inferior nasal concha.
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
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
s, as well as some reptilian species.
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
of the face, is situated at the front part of the medial wall of the orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
. It has two surfaces and four borders.
Lateral or orbital surface
The lateral or orbital surface is divided by a vertical ridge, the posterior lacrimal crestPosterior lacrimal crest
The lateral or orbital surface of the lacrimal bone is divided by a vertical ridge, the posterior lacrimal crest, into two parts.In front of this crest is a longitudinal groove, the lacrimal sulcus , the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is...
, into two parts.
In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
, and the lacrimal fossa
Lacrimal fossa
Located on the inferior surface of each orbital plate of the frontal bone, is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa , for the lacrimal gland....
is thus completed. The upper part of this fossa lodges the lacrimal sac
Lacrimal sac
The lacrimal 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...
, the lower part, the nasolacrimal duct
Nasolacrimal duct
The nasolacrimal duct carries tears from the lacrimal sac into the nasal cavity. Excess tears flow through nasolacrimal duct which drains into the inferior nasal meatus...
.
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 and ends below in a small, hook-like projection, the lacrimal hamulus
Lacrimal hamulus
The posterior lacrimal crest, with a part of the orbital surface immediately behind it, gives origin to the lacrimal part of the Orbicularis oculi and ends below in a small, hook-like projection, the lacrimal hamulus, which articulates with the lacrimal tubercle of the maxilla, and completes the...
, which articulates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the nasolacrimal canal
Nasolacrimal canal
The canal containing the nasolacrimal duct is called the nasolacrimal canal.It is formed by indentations in the inferior nasal conchae, maxilla and lacrimal bone...
; 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
Meatus
In anatomy, a meatus is a natural body opening or canal .Examples include:* the external acoustic meatus, the opening of the ear canal...
of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells.
Borders
Of the four borders:- the anterior articulates with the frontal process of the maxilla;
- the posterior with the lamina papyracea 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, and assists in forming the canal for the nasolacrimal duct.
Ossification
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 frontalFrontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
and ethmoid
Ethmoid bone
The ethmoid bone is a bone in the skull that separates the nasal cavity from the brain. As such, it is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that makes up the orbit of the eye...
, and two of the face, the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
and the inferior nasal concha.
In other animals
In early lobe-finned fishes and ancestral tetrapodTetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
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
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 form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
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
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, as well as some reptilian species.