pl. fossae [L. fossa, ditch]
A furrow, recess, or shallow depression.

acetabular fossa

The rough-surfaced fossa in the center of the acetabulum (femoral socket) of the hipbone. The fossa is deeper than the actual joint articulation, does not directly contact the head of the femur, and contains the ligament of the head of the femur.

antecubital fossa

The triangular fossa in the forearm on the anterior (flexor) surface of the elbow. Bounded laterally by the brachioradialis and medially by the pronator teres, the fossa contains the tendon of the biceps brachii, the brachial artery and the median nerve. The floor is formed by the brachialis. The roof is formed in part by the bicipital aponeurosis, over which the median cubital is found (and a common site for drawing blood).
SYN: SEE: cubital fossa

anterior cranial fossa

The anterior third of the floor of the cranial cavity, formed from the orbital part of the frontal bones, the cribriform plates of the ethmoid bone, and one third of the anterior sphenoid bones. The olfactory lobes and the inferior surfaces of the cerebral hemispheres lie in this fossa.

articular fossa of mandible

SEE: Mandibular fossa.

articular fossa of temporal bone

SEE: Mandibular fossa

axillary fossa

The armpit; axilla.

canine fossa

On the skull, the vertical fossa along the surface of the maxilla beginning between the upper canine tooth and the first premolar tooth and extending up toward the orbit.

central fossa of tooth

The front-to-back (anterior-posterior) midline fossa along the upper (occlusal) surface of a postcanine tooth.
SEE: central fissure

cerebral fossa

SEE: Cranial fossa.

Claudius fossa

SEE: Claudius fossa

condylar fossaof occipital bone

On the base of the occipital bone of the skull along the lateral edge of the foramen magnum, a prominent fossa behind the occipital epicondyle that articulates with the atlas.

coronoid fossa

On the anterior surface of the lower end of the humerus, a fossa proximal to the trochlea and between the lateral and medial epicondyles; it is analogous to the olecranon fossa on the opposite side of the humerus. During full flexion of the forearm, the coronoid process of the ulna fits into the coronoid fossa of the humerus.

cranial fossa

One of the three floor levels (anterior, middle, and posterior cranial fossae) of the interior surface of the cranial cavity. Each level contains the impressions of surface features of corresponding brain regions.
SYN: SEE: cerebral fossa; SEE: hypophyseal fossa

cubital fossa

SEE: Antecubital fossa.

digastric fossa

A small fossa in the mandible behind its lower margin at either side of the midline (symphysis menti). The anterior belly of the digastric muscle attaches in this fossa.

epigastric fossa

The fossa immediately inferior to the xiphoid process of the sternum on the anterior body wall.
SYN: SEE: epigastric region

ethmoid fossa

SEE: Olfactory groove.

glenoid fossa

1. The shallow ovoid fossa on the top of the lateral side of the scapula that articulates with the head of the humerus. The acromion of the scapula overhangs the glenoid fossa.
SYN: SEE: glenoid cavitySEE: 2. Mandibular fossa.

hyaloid fossa

The fossa on the anterior surface of the vitreous body of the eye. The lens is located there.

hypophyseal fossa

SEE: Cranial fossa.

iliac fossa

On each hip bone, the smooth, concave upper surface of the ilium, which makes a shelf that gently slopes downward and inward from the iliac crest and serves as the proximal attachment of the iliacus muscle.

implantation fossa of sperm

On a spermatozoon, the small segment behind the head to which the internal filaments of the tail attach.

incisive fossa

The vertical fossa along the surface of the maxilla beginning between the lateral upper incisor and the canine tooth and extending up toward the anterior nasal aperture.

fossa incudis

In the tympanic cavity of the middle ear, a small fossa inside the epitympanic recess, in which the short process of the incus fits and is attached by tiny ligaments.

infraspinous fossa

On the dorsal (posterior) surface of the scapula, the broad, shallow, triangular fossa filling the area below the scapular spine. The infraspinatus muscle is attached to and covers most of this fossa.

infratemporal fossa

On the lateral surface of the skull, an irregular fossa formed largely by the concave outer surface of the greater wing of the sphenoid bone as it curves into the lateral pterygoid plate of the sphenoid. This fossa is deep (medial) to the zygomatic arch and is continuous with the bottoms of both the temporal fossa and the inferior orbital fissure. The medial wall of the infratemporal fossa is split vertically by the pterygomaxillary fissure, which leads into the pterygopalatine fossa.

inguinal fossa

One of two vertical fossae in the peritoneum along each side of the anterior abdominal wall. The medial inguinal fossa is the depression between the medial and lateral umbilical folds; direct inguinal hernias typically protrude through the abdominal wall in the lower end of this fossa. The lateral inguinal fossa is the depression lateral to the lateral umbilical fold; the lower end of this fossa becomes the deep inguinal ring, the internal end of the inguinal canal.

intercondyloid fossa

The fossa on the inferior surface of the femur between the femoral condyles. The cruciate ligaments pass through it.

interpeduncular fossa

On the anterior (ventral) surface of the midbrain, a trapezoidal depression behind the mammillary bodies and between the cerebral peduncles. The oculomotor nerve (CN III) leaves the midbrain through this fossa, and a number of separate branches of the posterior cerebral arteries enter the midbrain through the base of the fossa, in an area called the perforated substance.

ischioanal fossa

SEE: Ischiorectal fossa.

ischiorectal fossa

A wedge-shaped region just under the skin on either side of the lower end of the rectum and anal canal. The fossa is bounded laterally by the obturator internus muscle and the tuberosity of the ischium, medially by the levator ani and coccygeus muscles, and posteriorly by the gluteus maximus muscle. The ischiorectal fossa contains fat, connective tissue, blood vessels, and nerves.
SYN: SEE: ischioanal fossa

jugular fossa

On the base of the skull, a kidney bean-shaped depression in the undersurface of the petrous portion of the temporal bone. The fossa is behind the carotid canal, from which it is separated by a ridge of bone, and it forms a pocket for the superior bulb of the jugular vein, just after the vein has exited the skull through the jugular foramen.

lacrimal fossa

A shallow depression in the lateral side of the roof of the orbit, just inside the upper orbital margin, into which the lacrimal gland fits.

lenticular fossa

The depression in the anterior surface of the vitreous for reception of the crystalline lens.

mandibular fossa

In the skull, the depression in the temporal bone into which the condyle of the head (condylar process) of the mandible fits; the condyle of the mandible sits on an interposed articular disk when the mandible is fully elevated (teeth clenched). The fossa, a part of the temporomandibular joint, is a horizontal furrow lying underneath and behind the zygomatic process of the temporal bone.
SYN: SEE: articular fossa of mandible; SEE: glenoid fossa (2)

mastoid fossa

The small triangular area between the posterior wall of the external auditory meatus and the posterior root of the zygomatic process of the temporal bone.

middle cranial fossa

The middle one third of the floor of the cranial cavity. It is deeper and wider than the anterior cranial fossa. It is formed from the posterior two thirds of the sphenoid bones (the greater wings, the dorsum sellae, and the clinoid processes) and the petrous and squamous portions of the temporal bones. The middle cranial fossa contains the superior orbital fissures, optic canals, foramina rotundum, foramina ovale, foramina spinosum, and foramina lacerum. It contains the temporal lobes of the cerebral hemispheres, the optic chiasm, the hypophysis (pituitary), the internal carotid arteries, the cerebral arterial circle (of Willis), and the cavernous sinuses.

nasal fossa

The cavity between the anterior opening to the nose and the nasopharynx.

nasolacrimal fossa

A bony fossa in the lower medial corner of the front of the orbit of the eye.

navicular fossa

1. In the female perineum, the recess at the posterior end of the vaginal vestibule. This fossa is posterior to the vaginal opening and anterior to the fourchette, i.e., the frenulum, where the labia minora join posteriorly.
SYN: SEE: fossa of the vaginal vestibule; SEE: navicula
2. The boat-shaped terminus of the male urethra. It is typically lined with squamous epithelium.

obturator fossa

In surgical explorations of the pelvis for diseased lymph nodes, a space defined anteriorly by the obturator blood vessels and nerves; medially by the hypogastric artery; and laterally by the external iliac vein, and the obturator internus muscle and its fascia.

olecranon fossa

On the posterior surface of the lower end of the humerus, a depression proximal to the trochlea and between the medial and lateral epicondyles; it is analogous to the coronoid fossa on the opposite side of the humerus. During full extension of the forearm, the olecranon process of the ulna fits into the olecranon fossa of the humerus

fossa ovalis cordis

The remnant of the embryonic foramen ovale in the right cardiac atrium.

fossa ovalis of heart

An oval fossa in the septal wall of the right atrium, having a raised rim along its top and front edges (limbus of the fossa ovalis). In the embryo, the floor of the fossa ovalis is a flap valve (the primary atrial septum or septum primum) that lets blood flow from the right atrium to the left atrium, bypassing the lungs. If the flap valve fails to seal after birth, the heart can have an atrial septal defect.

ovarian fossa

A shallow fossa in the wall of the pelvis behind the lateral ends of the broad ligament; the ovary lies in this fossa covered by the parietal peritoneum.

piriform fossae

Any of the fossae in the lateral walls of the laryngopharynx.

pituitary fossa

SEE: Sella turcica.

popliteal fossa

A rhomboid fossa, just below the skin, behind the knee. Its edges are defined by muscles: laterally, the biceps femoris and the lateral head of the gastrocnemius; medially, the semitendinosus, the semimembranosus, and the medial head of the gastrocnemius. This fossa contains the popliteal vessels and the tibial and common fibular nerves.

posterior cranial fossa

The posterior third of the floor of the cranial cavity. It is larger and deeper than the anterior and middle cranial fossae. The posterior cranial fossa is formed from the posterior surface of the body of the sphenoid bone (the dorsum sella), the posterior surfaces of the petrous and mastoid portions of the temporal bones, and the inner surfaces of the occipital bones. The posterior cranial fossa contains the internal auditory canals, the foramen magnum, and the jugular foramina. The brainstem, the cerebellum, and the transverse and sigmoid sinuses lie in the posterior cranial fossa.

pterygoid fossa

The vertical fossa between the medial and lateral pterygoid plates of the pterygoid process of the sphenoid bone. This fossa is on the deep, basal surface of the skull, just outside (lateral to) the nasopharynx.

pterygopalatine fossa

A thin wedge-shaped space posterior to the nasal cavity, bounded anteriorly by the posterior border of the maxilla, superiorly by the greater wing of the sphenoid and posteriorly by the pterygoid process of the sphenoid. Laterally it is continuous with the infratemporal fossa at the pterygomaxillary fissure. The pterygopalatine fossa contains the pterygopalatine ganglion. The maxillary branch of the trigeminal nerve (CN V) enters the fossa from behind, through the foramen rotundum, and the nerve of the pterygoid canal enters the fossa via the pterygoid canal.
SYN: SEE: sphenomaxillary fossa

radial fossa of humerus

A small fossa in the distal humerus on its anterior surface proximal to the capitulum. When the elbow is in complete flexion, the proximal end (the head) of the radius slides up along the capitulum and one edge of the head of the radius fits into the radial fossa.

rhomboid fossa

In the brainstem, the floor of the fourth ventricle, which runs along the dorsal surface of the pons and part of the medulla.

Rosenmüller fossa

SEE: Rosenmüller, Johann Christian

scaphoid fossa of auricle (pinna)

In the auricle of the ear, the C-shaped fossa between the helix and the antihelix.

sphenomaxillary fossa

SEE: Pterygopalatine fossa.

subarcuate fossa

In the posterior cranial fossa, a variably shaped small fossa in the petrous portion of the tympanic bone superior and lateral to the internal acoustic foramen. The subarcuate fossa leads into the subarcuate canal, which contains the subarcuate artery, a main blood supplier to the bony labyrinth, facial canal, and mucosa of the mastoid antrum.

sublingual fossa

A shallow fossa on the inner surface of the body of the mandible superior to the anterior part of the mylohyoid ridge. It is occupied by the sublingual gland.

submandibular fossa

An oblong fossa between the mylohyoid ridge and the inferior border of the medial surface of the body of the mandible. It is occupied by the submandibular gland.

subpyramidal fossa

A fossa in the inferior wall of the middle ear. It is inferior to the round window and posterior to the pyramid.

supraclavicular fossa

The fossa that can be felt below the skin at the base of the neck behind the clavicle and extending from the attachment of the sternal head of the sternocleidomastoid muscle medially to the medial edge of the deltoid muscle laterally.

supraspinous fossa

The sloping, triangular concave fossa above the spine on the dorsal (posterior) side of the scapula. The supraspinatus muscle attaches to and fills most of this fossa.

fossa supratonsillaris

SEE: Supratonsillar fossa

supratonsillar fossa

A slit-like fossa extending into the upper part of the palatine tonsil. This fossa is a remnant of the embryological second pharyngeal pouch.
SYN: SEE: intratonsillar cleft; SEE: fossa supratonsillaris

supravesical fossa

On the internal surface of the anterior abdominal wall, a fossa in the parietal peritoneum between the middle (median) and medial umbilical folds.

temporal fossa

On the side of the skull, a large fan-shaped fossa containing the temporalis muscle. The upper edge of the fossa forms a broad crescent (the temporal lines) along the frontal, parietal, and temporal bones, from the upper outer edge of the orbit to the most posterior edge of the zygomatic arch. From the crescent, the fossa gradually deepens toward the “handle” of the fan, which lies inside the zygomatic arch.

tonsillar fossa

A fossa between the glossopalatine and pharyngopalatine arches along the lateral wall of the oropharynx and containing the palatine tonsil.
SYN: SEE: tonsillar recess.

trochanteric fossa

At the proximal end of the femur, an irregular fossa along the upper inner (proximal medial) surface of the great trochanter, where the medial edge of the greater trochanter overhangs the neck of the femur.

fossa of the vaginal vestibule

SEE: Navicular fossa.