Anatomy of the Orbit, Eyeball, and Mammary Gland
Anatomy of the Orbit
The orbit is the pyramidal bone cavity of the face’s skeleton. It contains and protects the eyeball along with most of the lacrimal apparatus.
Orbit Limits:
- Roof: Frontal and sphenoid bones.
- Medial Wall: Sphenoid, ethmoid, frontal, and lacrimal bones.
- Floor: Maxilla, zygomatic, and palatine bones.
- Lateral Wall: Sphenoid and zygomatic bones.
- Apex: Optic canal.
Orbit Content:
The orbit contains the eyeball, optic nerve, eye muscles, fascia, nerves, vessels, fat, lacrimal glands, and lacrimal sacs.
Muscles of the Orbit:
The muscles of the orbit include the levator palpebrae superioris (upper eyelid lifter), superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique.
Nerves of the Orbit:
The nerves of the orbit include the optic nerve, oculomotor nerve, abducens nerve, trochlear nerve, and trigeminal nerve.
Vessels of the Orbit:
The vessels of the orbit include the ophthalmic artery and ophthalmic vein. Lymphatic vessels drain into the cavernous sinus of the brain.
Anatomy of the Eyeball
Outer Layer:
The outer layer is fibrous, supportive, and avascular.
Sclera:
The sclera is the opaque portion, also known as the white of the eye.
Cornea:
The cornea is the transparent, circular portion responsible for the refraction of light entering the eye. It is sensitive to touch, innervated by the ophthalmic nerve, and nourished by the aqueous humor.
Aqueous Humor:
The aqueous humor provides nutrients to the cornea and lens, both of which are avascular. It drains into the venous sinus of the sclera.
Crystalline Lens:
The crystalline lens is biconvex, transparent, and encapsulated. It is posterior to the iris and anterior to the vitreous humor. The curvature of the anterior surface varies to accommodate near or distant objects. The shape of the lens changes via the ciliary muscle.
Middle Layer:
The middle layer is vascular and pigmented.
Choroid:
The choroid is a dark brown membrane between the sclera and retina to which it is firmly attached.
Ciliary Body:
The ciliary body connects the choroid and iris. The ciliary processes secrete aqueous humor.
Iris:
The iris is anterior to the lens. It is a contractile diaphragm with a central aperture called the pupil, which transmits light. Two muscles control the size of the pupil: the sphincter pupillae and the dilator pupillae.
Inner Layer:
The inner layer is nervous.
Retina:
In the background of the retina is the optic disc, where the optic nerve enters the eyeball. The disc is insensitive to light. Lateral to the optic disc is the macula lutea (yellow spot), which is the area of sharpest vision. The retina is irrigated by the central retinal artery and vein.
Anatomy of the Mammary Gland
The mammary gland appears as a prominence of varying size and firmness, featuring structures such as the nipple and areola. Internally, it consists of adipose tissue (90%) which gives it bulk, integrated with ducts and the mammary gland itself, responsible for both milk production and secretion. The mammary glands are distributed throughout the breast, with most of the glandular tissue located near the base of the nipple. They drain into the nipple via ducts, each with its own opening.
The mammary gland consists of two components:
- Glandular acini: Where milk-producing cells are located.
- Ducts: A set of hollow tubular structures, branching tubules converge, thickening towards the vertex called lactiferous.
Myoepithelial cells around the nipple-areola cause nipple erection in response to stimuli such as suckling, touch, and cold, facilitating the output of milk stored in the lactiferous sinuses. The rest of the breast is composed of connective tissue (collagen and elastin) and adipose tissue, supported by Cooper’s ligaments.
The breasts are positioned on the pectoralis major muscle, supported by tissues and ligaments that allow normal breast movement over the underlying muscle layers.
Arterial Supply:
The arterial supply comes from the internal thoracic, lateral thoracic, intercostal, and thoracoacromial arteries.
Venous Drainage:
The venous drainage occurs via the axillary vein, but can also involve the internal thoracic and intercostal veins.
Men and women have a high concentration of vessels and nerves in the nipples.
Lymphatic Drainage:
Approximately 75% of lymph from the breast drains to the lymph nodes in the armpit on the same side. The remainder travels to parasternal nodes, to the opposite breast, and to the abdominal lymph nodes. The axillary nodes include the lower group (draining deep and transmuscular areas), the internal group (draining internal areas), and the external group (draining the outer edge of the breast).