The tarsi (tarsal plates) are two comparatively thick, elongated plates of
dense connective tissue
Dense connective tissue, also called dense fibrous tissue, is a type of connective tissue with fibers as its main matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows of fibroblasts, fibe ...
, about in length for the upper eyelid and 5 mm for the lower eyelid; one is found in each
eyelid
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eye ...
, and contributes to its form and support. They are located directly above the lid margins. The tarsus has a lower and upper part making up the
palpebra
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyel ...
e.
Superior
The ''superior tarsus'' (''tarsus superior''; superior tarsal plate), the larger, is of a
semilunar
Semilunar can refer to:
* Semilunar valves
* Semilunar ganglion, or the trigeminal ganglion
* An older name for the Lunate bone
The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and ...
form, about in breadth at the center, and gradually narrowing toward its extremities. It is adjoined by the
superior tarsal muscle
The superior tarsal muscle is a smooth muscle adjoining the levator palpebrae superioris muscle that helps to raise the upper eyelid.
Structure
The superior tarsal muscle originates on the underside of levator palpebrae superioris and inser ...
.
To the anterior surface of this plate the aponeurosis of the
levator palpebræ superioris
The levator palpebrae superioris ( la, elevating muscle of upper eyelid) is the muscle in the orbit that elevates the upper eyelid.
Structure
The levator palpebrae superioris originates from inferior surface of the lesser wing of the sphenoid bon ...
is attached.
Inferior
The ''inferior tarsus'' (''tarsus inferior''; inferior tarsal plate) is smaller, is thin, is elliptical in form, and has a vertical diameter of about . The free or ciliary margins of these plates are thick and straight.
Relations
The attached or orbital margins are connected to the circumference of the orbit by the
orbital septum
In anatomy, the orbital septum (palpebral fascia) is a membranous sheet that acts as the anterior (frontal) boundary of the orbit. It extends from the orbital rims to the eyelids. It forms the fibrous portion of the eyelids.
Structure
In the u ...
.
The lateral angles are attached to the
zygomatic bone
In the human skull, the zygomatic bone (from grc, ζῠγόν, zugón, yoke), also called cheekbone or malar bone, is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is s ...
by the
lateral palpebral raphe
The lateral palpebral raphe is a ligamentous band near the eye. Its existence is contentious, and many sources describe it as the continuation of nearby muscles. It is formed from the lateral ends of the orbicularis oculi muscle. It connects the ...
.
The medial angles of the two plates end at the
lacrimal lake
The lacrimal lake is the pool of tears in the lower conjunctival cul-de-sac, which drains into the opening of the tear drainage system (the '' puncta lacrimalia''). The volume of the lacrimal lake has been estimated to be between 7 and 10 μ ...
, and are attached to 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. T ...
by the
medial palpebral ligament
The medial palpebral ligament (medial canthal tendon) is a ligament of the face. It attaches to the frontal process of the maxilla, the lacrimal groove, and the tarsus of each eyelid. It has a superficial (anterior) and a deep (posterior) layer ...
).
The
sulcus subtarsalis
Sulcus subtarsalis is a groove in the inner surface of eyelid near the eyelid margin and which is also parallel to it. This separates marginal conjunctiva
The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and cov ...
is a groove in the inner surface of each eyelid.
Along the inner margin of the tarsus are modified sebaceous glands known as tarsal glands (or
meibomian glands
Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye' ...
), aligned vertically within the tarsi: 30 to 40 glands in the upper lid, and 20 to 30 in the lower lid, which secrete a lipid-rich product which helps keep the lacrimal secretions or tears from evaporating too quickly, thus keeping the eye moist.
[Martini, 2006]
Additional images
Image:Gray379.png, Left orbicularis oculi, seen from behind
Image:Gray888.png, Sagittal section of right orbital cavity
File:Slide2www.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection.
See also
*
References
{{Authority control
Human eye anatomy