The endometrium refers to the inner lining of the uterine lumen, composed of endometrial glands surrounded by loose highly cellular connective tissue.
In women of reproductive age, the endometrium is composed of two layers:
stratum basale (basal layer):
describes the de...
An enthesis (pl. entheses), also known as a footprint, generally refers to the anatomic junction where connective tissue (e.g. ligaments, tendons, joint capsules) attach to bone.
Enthesis are commonly classified into two types 1:
In a fibrous enthes...
The entorhinal cortex (Brodmann area 28) is located in the mesial temporal lobe and acts as the interface between the hippocampus and the neocortex. It has been considered part of the hippocampal formation (along with Ammon’s horn, subiculum and presubiculum), but is difficult to precisely local...
The eparterial bronchus is a synonymous term for the right superior lobar bronchus. Its name is derived from the bronchus being the only one originating superior to the level of the pulmonary artery. Conversely, all other bronchi can be referred to by their anatomical relationship to the pulmona...
Ependymal cells are one of the four main types of glial cells, and themselves encompass three types of cells 1:
ependymocytes: line the ventricles of the brain and central canal of the spinal cord
tanycytes: line the floor of the third ventricle
choroidal epithelial cells: line the surface o...
Ependymocytes are one of the three types of ependymal cells, which in turn are one of the four principles types of glial cells, and are found lining the ventricular system of the brain and the central canal of the spinal cord 1.
They do not form a water-tight barrier between the cerebrospinal ...
Epididymal appendices, also known as appendix of the epididymis or appendix epididymis, are an testicular appendage found at the head of the epididymis 1. They represent a developmental remnant of the mesonephric duct (Wolffian duct). In 78% of the cases, it has a stalk configuration and is thus...
The epididymis (plural epididymides) is situated adjacent to the testis within the scrotal sac. Its primary function is the collection, maturation and transport of sperm via the ductus deferens.
The epididymis is an elongated structure, posterolateral to the testis. It can be sub...
The epidural ligaments, also known as meningovertebral ligaments, are variably thick bands of connective tissue located within the spinal epidural space attaching the outer surface of the theca to the inner borders of the spinal canal (vertebrae and ligaments).
They are somewhat variable in nu...
The epiglottis is a leaf-shaped fibrocartilaginous structure that forms part of the supraglottic larynx and defines the division of the hypopharynx from the larynx.
The epiglottis projects posterosuperiorly from its stem-like base, which is attached to the thyroid cartilage. It ...
The epiphyses (singular: epiphysis) are the rounded portions at the ends of a bone separated from the metaphysis by the physis. The epiphysis contributes to a joint, compared with an apophysis which is a site of tendon or ligament attachment. Once the growth plate has fused, the epiphysis and me...
Epiploic appendages (or appendix epiploica, plural: appendices epiploicae) are peritoneum-lined protrusions of subserosal fat that arise from the surface of the large bowel.
Epiploic appendages typically measure 1.5 x 3.5 cm but have been reported to measure up to 15 cm in lengt...
The epiploic foramen (also called the foramen of Winslow) is a passage between the greater (general peritoneal space) and lesser sac (omental bursa), allowing communication between these two spaces.
It has the following borders:
anterior: the free edge of the lesser ...
Episternal (or suprasternal) ossicles are accessory bones and a normal variant of the sternum. They result from supernumerary ossification centers and are seen in ~4% (range 1-7%) of the population.
Episternal ossicles are usually located posterior or superior to the superior bor...
The epithalamus is a dorsal posterior segment of the diencephalon which includes the habenula, stria medullar is, pineal gland and posterior commissure. Its function is the connection between the limbic system to other parts of the brain.
Epitransverse process is a rare anatomical variant of the atlas, consisting of a bony exostosis which extends cephalad from the transverse process of the atlas to articulate with the occipital bone. This process sometimes meets with a paracondylar process from the occipital bone, forming a pseud...
The epitympanum, also known as the attic or epitympanic recess, is the most superior portion of the tympanic cavity. It is that portion of the tympanic cavity superior to the axial plane between the tip of the scutum and the tympanic segment of the facial nerve 1,3.
Posteriorly the epitympanum ...
The erector spinae group is the intermediate layer of the intrinsic muscles of the back. This group is made of three subgroups, with the group divisions occurring by location. The iliocostalis group occurs most laterally, followed by the longissimus group, and finally the spinalis as the most me...
The ethmoidal air cells, also known less commonly as the ethmoidal sinuses, form one of the four pairs of paranasal sinuses. They are located within the single, midline ethmoid bone.
location: between the orbit and the nasal cavity, within the ethmoid labyrinth of the ethmoid bone
The ethmoid bone is a single midline facial bone that separates the nasal cavity from the brain and is located at the roof of the nose and between the orbits. It is a cubical shape and is relatively lightweight because of its spongy construction. It contributes to the anterior cranial fossa.
The ethmoid bulla, also known as bulla ethmoidalis, is the largest and most consistent air cell of the anterior ethmoid air cells.
It is located posterior to the frontal recess and enclosed laterally by the lamina papyracea. It forms the roof of the middle meatus.
It can be clas...
The ethmoid infundibulum is a curved cleft of the ethmoid bone which leads into the anterior portion of the hiatus semilunaris. It is bordered medially by the uncinate process and laterally by the orbital plate of the ethmoid. The infundibulum is often continuous with the frontal recess into whi...
The Eustachian tube, or more appropriately the pharyngotympanic tube, is the channel through which the tympanic cavity communicates with the nasopharynx. It is approximately 36 mm in length and is directed downward, forward, and medially, forming an angle of about 45 degrees with the sagittal pl...
The Eustachian valve (also known as the "valve of the inferior vena cava") is a ridge of variable thickness in the inferior right atrium. It is a remnant of a fetal structure that directed incoming oxygenated blood to the foramen ovale and away from the right atrium.
Incomplete regression of ...
Extensor carpis radialis brevis (ECRB) is a muscle of superficial layer on posterior compartment of the forearm. It passes through the 2nd extensor compartment of the wrist. ECRB is one of the three muscles forming the mobile wad of Henry.
origin: lateral epicondyle of the humerus, ann...
Extensor carpis radialis longus (ECRL) is a muscle of the superficial layer in the posterior compartment of the forearm. It passes through the 2nd extensor compartment of the wrist. It is one of the three muscles forming the mobile wad of Henry.
origin: lateral supracondyle ridge of hu...
Extensor carpi ulnaris (ECU) is a muscle of the superficial layer of the posterior compartment of the forearm. It is separated from the extensor digitorum and the extensor digiti minimi muscles by a distinct intermuscular septum. It is the only forearm extensor that lies in its own fibro-osseous...
The extensor tendons at the level of the wrist are divided into six extensor compartments that are designated by Roman numerals from lateral to medial 1:
I: extensor pollicis brevis, abductor pollicis longus
II: extensor carpi radialis longus, extensor carpi radialis brevis
III: extensor poll...
Extensor digiti minimi (EDM) is a muscle of the superficial layer of the posterior compartment of the forearm, and with other extensor muscles arises from a common extensor tendon attached to the lateral epicondyle of the humerus. The EDM represents a medial group of superficial extensor muscles...
Extensor digitorum (ED), also known as extensor digitorum communis (EDC), is a muscle of the superficial layer of the posterior compartment of the forearm and with other extensor muscles arises from a common tendon attached to the lateral epicondyle of the humerus. ED represents a medial group o...
The extensor digitorum brevis manus (EDBM) muscle is an accessory muscle in the hand and is a normal anatomical variant.
origin: distal radius and posterior radiocarpal ligament
insertion: extensor hood of 2nd or 3rd digits (variable)
innervation: posterior interosseous nerve
The extensor digitorum brevis muscle is a muscle on the dorsal surface of the foot which helps extend digits 2 through 4.
origin: superolateral surface of calcaneus
insertion: lateral sides of the tendons of extensor digitorum longus of toes II to IV
action: extension of toes II to I...
Extensor digitorium longus (EDL) is a thin muscle situated in the anterior leg lateral to extensor hallucis longus and extends the lateral four toes.
origin: lateral tibial condyle, medial surface of the middle portion of the fibula and superior portion of the anterior surface of the i...
The extensor hallucis brevis is a muscle on the dorsal surface of the foot which helps to extend the big toe.
superolateral surface of calcaneus
base of proximal phalanx of great toe
extension of metatarsophalangeal joint of great toe
Extensor hallucis longus is a thin muscle in the anterior compartment of the leg between tibialis anterior and extensor digitorum longus.
origin: anterior surface of the middle portion of the fibula and the interosseous membrane
insertion: the dorsal side of the base of the distal pha...
The extensor indicis muscle is an accessory extensor of the 2nd digit. It is located in the deep layer of the posterior compartment of the forearm and its tendon passes through the 4th extensor compartment of the wrist.
origin: posterior surface of the ulna (distal to extensor pollicis...
The extensor mechanism of the knee comprises:
medial patellar retinaculum
lateral patellar retinaculum
extensor mechanism of the knee injuries
Extensor pollicis brevis (EPB) is one of the muscles of the deep layer of the posterior compartment of the forearm, inserting into the base of the proximal phalynx of the thumb. Along with extensor pollicis longus, it is responsible for extension of the thumb. Along with abductor pollicis longus...
Extensor pollicis longus (EPL) is a muscle of the deep compartment in the posterior compartment of the forearm. It passes through the 3rd extensor compartment of the wrist, then continues laterally towards the thumb around Lister's tubercle. The tendon of EPL defines the ulnar border of the Anat...
The extensor retinaculum is located at the dorsal aspect of the foot and consists of the superior and inferior extensor retinacula.
The superior extensor retinaculum is located proximally to the dorsal aspect of the ankle joint and houses the tibialis anterior, extensor digitoru...
The external auditory canal (EAC) or external auditory meatus (EAM) extends from the lateral porus acusticus externus medially to the tympanic membrane.
As the term external auditory meatus (EAM) is variably used to refer to the canal or the porus acusticus externus (the round late...
The external capsule is a series of white matter tracts in the brain situated between the putamen and claustrum. It is composed of claustrocortical fibers dorsally and the combined mass of the uncinate fasciculus and inferior frontal occipital fasciculus ventrally.
The putamen s...
The external carotid artery (ECA) is one of the two terminal branches of the common carotid artery. The other terminal branch is the internal carotid (ICA), which is somewhat larger than the ECA.
origin: bifurcation of the common carotid artery
course: under the submandibular gland an...
The external ear comprises the auricle (or pinna), the external auditory meatus, and the tympanic membrane (eardrum). The auricle concentrates and amplifies sound waves and funnels them through the outer acoustic pore into the external auditory meatus to the tympanic membrane.
The external iliac artery is the larger of the two terminal branches of the common iliac artery.
The common iliac artery bifurcates into the internal iliac artery and external iliac artery at the level of the pelvic brim anterior to the sacroiliac joint.
The external iliac lymph nodes can be found surrounding the external iliac artery and act as the draining nodes for several regions of the pelvis and lower limb.
The external iliac lymph nodes lie anterior to the internal iliac lymph nodes and usually form three separate subgrou...
The external iliac vein (EIV) is located along the pelvic brim between the inguinal ligament and the sacroiliac joint.
posterior to inguinal ligament within lacuna vasorum 1 as continuation of femoral vein
The external iliac vein unites with the internal il...
The external (or outermost) intercostal muscles are important muscles of respiration. They number eleven on each side and are located in the intercostal space, expanding the transverse dimension of the thoracic cavity during inspiration.
The external intercostal muscles are the o...
The external jugular vein (EJV) drains the head, face, and part of the pectoral region.
Origin and course
The posterior division of the retromandibular vein and posterior auricular vein unite to form the external jugular vein at the angle of the mandible.
It courses inferiorly ...
A mnemonic to remember external jugular vein (formed by the retromandibular and posterior auricular veins) tributaries is:
P: posterior external jugular vein
A: anterior jugular vein
S: suprascapular vein
T: transverse cervical vein
The external oblique muscle (EOM) is one of the muscles that forms the anterior abdominal wall. Its free inferior border forms the inguinal ligament, and its aponeurotic part contributes to the anterior wall of the inguinal canal.
origin: outer surface of the shaft of the lower 8 ribs...
The external petrosal nerve is one of the three branches from the geniculate ganglion. It carries sympathetic fibers to the middle meningeal artery.
The extraconal orbital compartment or extraconal space is the space within the orbit outside the musculofascial cone. The base of which is anterior and is formed by the orbital septum that surrounds the equator of the globe. The external sides are formed by the bones of the orbit and their perio...
The extradural (epidural) space is a potential space between the cranial bones and the endosteal layer of the dura mater, which is otherwise adherent to the cranial bone.
The extradural space is a potential space inside the cranial vault and is not normally appreciable unless th...
An extramural air cell is one that is not contained within its named parent bone. So, the infraorbital ethmoidal air cells that lie within the maxilla rather than the ethmoidal bone are an example of extramural air cells.
A mnemonic to remember the nerve supply to the extraocular muscles:
LR6SO4O3 (mock 'chemical formula')
The letters represent the extraocular muscles and numbers represent their respective cranial nerve supply:
LR6: lateral rectus, innervated by the 6th (abducens) nerve
The extraocular muscles are the six muscles that insert onto the eye and hence control eye movements:
superior rectus: elevation
superior oblique: intorsion
medial rectus: adduction
lateral rectus: abduction
inferior oblique: extorsion
inferior rectus: depression
The extrapyramidal system is the part of the motor system involved in modulation and regulation of movement. As its name suggests, it is distinct from the motor fibers that are relayed through the pyramids of the medulla oblongata (corticospinal and corticobulbar tracts).
It is composed of nerv...
Extrarenal pelvis refers to the presence of the renal pelvis outside the confines of the renal hilum; it is a normal anatomic variant.
It is found in ~10% of the population 2.
An extrarenal pelvis usually appears dilated, erroneously suggesting...
The extreme capsule is a series of white matter tracts in the brain that run between the claustrum and insular cortex.
The extrinsic muscles of the tongue are a group of 4 muscles of the tongue. They all arise outside the tongue, which is in comparison to the intrinsic muscles of the tongue which are entirely within the tongue with no external attachments. They act to alter the position of the tongue where as th...
The extrinsic muscles of the tongue can be remembered with the following mnemonic:
Paris St Germain's Hour
Paris St. Germain's Hour
The eyelid covers the eye and is covered in front with loose skin and behind with adherent conjunctiva. The lower lid possesses very little mobility; lids are closed gently by palpebral fibers and forcefully by orbicularis oculi.
The eyelid comprises of a number of key features ...
Eye movements are a complex set of movements of the globe that are performed by the extraocular muscles that are grouped by the muscles that perform particular movements:
ocular internal rotators
ocular external rotators
The fabella is an accessory ossicle typically found in the lateral head of the gastrocnemius. It occurs in ~20% (range 10-30%) of the population 1.
The fabella can also be fibrocartilaginous in nature and is occasionally found in the medial head of the gastrocnemius. The fabella articulates wi...
A faceless kidney refers to one in which the normal appearance of the renal sinus on cross-sectional imaging is absent. It was initially described as a sign of duplication of the collecting system 1 (a slice obtained between the two collecting systems will not demonstrate the normal components o...
Facet joints, also known as apophyseal or zygapophyseal joints, are the articulations of the posterior arch of the vertebrae and form part of the posterior column.
They are symmetrical synovial-lined joints with a fibrous capsule that connect the articular facets of the vertebra...
Facet joint capsules are the fibrous capsule that surround the vertebral facet or zygapophyseal joints. They are particularly thin and loose, attached to the margins of articular facets on adjoining articular processes. The capsules merge medially with the ligamentum flavum.
In the cervical re...
The facial artery is one of the branches of the external carotid artery and supplies blood to the structures of the face.
origin: branch of the external carotid artery a little above the level of the lingual artery, in the carotid triangle of the neck
course: passes deep to the poster...
The facial bones comprise a set of bones that make up the face:
inferior nasal concha
zygoma (zygomatic bone)
Where these bones join each other, sutures occur.
The facial-cavernous anastomoses are the communications of the facial and deep facial veins with the cavernous sinus.
At the medial canthus of the eye there is a communication with the ophthalmic veins, which drain into the cavernous sinus. Blood from the frontal scalp normally f...
The facial colliculus is an elevation on the floor of the fourth ventricle and is not formed by the facial nerve nucleus, but by the fibers of the facial nerve arching backwards around the abducens nerve (CN VI) nucleus before turning forwards once more in the caudal pons.
The facial muscles (also known as the muscles of facial expression or mimetic muscles) enable facial expression and serve as sphincters and dilators of the orifices of the face. These muscles differ from those of other regions in the body as there is no fascia deep to the skin of the face; many ...
The facial nerve is one of the key cranial nerves with a complex and broad range of functions.
Although at first glance it is the motor nerve of facial expression which begins as a trunk and emerges from the parotid gland as five branches (see facial nerve branches mnemonic), it has taste and p...
There are many mnemonics to recall the branches of the facial nerve (superior to inferior) as they exit the anterior border of the parotid gland. Examples include:
Tall Zulus Bear Many Children
Two Zulus Bit My Cat
Two Zebras Bit My Coccyx
Ten Zebras Buggered My Car
To Zanzibar By Motor Car...
Helpful mnemonics for remembering the segments of the facial nerve include:
I Love Going To Makeover Parties 1
I Love Grinning, Then Making Pouts
both grinning and pouting are performed by muscles which are innervated by the facial nerve
I Must Learn To Make (facial) Expressions
The facial vein (previously known as the anterior facial vein) is the continuation of the angular vein and joins the anterior branch of the retromandibular vein to form the common facial vein 1-3.
At the level of the lower margin of the orbit, the angular vein becomes the facial ...
The falciform artery, also known as the hepatic falciform artery (FHA) is an uncommon vascular anatomic variant that most commonly arises as the terminal branch of the middle hepatic artery which courses anteriorly through the falciform ligament into and supplying the supraumbilical anterior abd...
The falciform crest, also known as the crista falciformis, is a horizontal ridge that divides the internal acoustic meatus (IAM) into superior and inferior portions.
The facial nerve (VII) and superior vestibular nerve (SVN) travel in the superior portion of the IAM with the facial ne...
The falciform ligament is a broad and thin peritoneal ligament. It is sickle-shaped (Latin: "falciform") and a remnant of the ventral mesentery of the fetus.
It is situated in an anteroposterior plane but lies obliquely so that one surface faces forward and is in contact with the peritoneum beh...
The Fallopian (facial) canal refers to a bony canal through which the facial nerve traverses the temporal bone, from the internal acoustic meatus to the stylomastoid foramen. There are three segments of the canal, corresponding to the segments of the facial nerve they contain: labyrinthine, tymp...
A useful mnemonic to remember the order of the 5 segments of the Fallopian tube, from lateral to medial, the direction an ovum would pass following ovulation, is:
Four INches Across IS IMpossible
Four inches (10 cm) is the approximate length of the Fallopian tube.
The false vocal cords (vestibular folds, ventricular folds, ventricular bands) are paired shelf-like structures located within the supraglottic larynx that divide the vestibule above from the ventricle below.
The vestibular ligaments are the ligamentous component of the false vo...
The falx cerebelli is a small infolding of the dura in the sagittal plane over the floor of the posterior cranial fossa. It partially separates the two cerebellar hemispheres 1.
The falx cerebelli is attached posteriorly in the midline to the internal occipital crest of the occip...
The falx cerebri is the largest of the four main folds (or septa) of the intracranial dura mater, separating the cerebral hemispheres 1.
The falx cerebri is a double-fold of dura mater that descends through the interhemispheric fissure in the midline of the brain to separate the...
The fascia lata is part of the deep fascia, and envelopes the thigh analogous to a stocking, but with an over large proximal end.
The female reproductive system (or tract) comprises the vagina, uterus, uterine tubes and ovaries.
It can be imaged using a wide range of imaging modalities but ultrasound and MRI are most useful.
The female urethra is a simple short tube, that transports the urine out of the body, extending from the internal urethral orifice of the bladder to the external urethral orifice in the vestibule of the vagina.
The female urethra measures approximately 4 cm in length. It is embe...
The femoral canal, or the medial compartment of the femoral sheath, is the inverted cone-shaped fascial space medial to the femoral vein within the upper femoral triangle. It is only 1-2 cm long and opens superiorly as the femoral ring. It serves two purposes:
allows the femoral vein to expand ...
The femoral nerve is a large nerve arising from the lumbar plexus and one of two major nerves supplying the lower limb.
It arises from posterior divisions of L2-L4 roots of the lumbar plexus.
emerges from the lateral border of the psoas muscle to descend between ...
The femoral ring is the superior opening of the femoral canal. Its boundaries are:
medial: lacunar ligament
anterior: medial part of the inguinal ligament
lateral: femoral vein within the intermediate compartment of the femoral sheath
posterior: pectineal ligament overlying the pectineus and...
The femoral sheath is the funnel-shaped fascial space that extends from the abdomen, inferior to the inguinal ligament, into the femoral triangle. It has variable length and terminates by blending in with the adventitia of the femoral vessels. It is formed from the transversalis and psoas fascia...
The femoral triangle is found in the anterior upper thigh.
The major boundaries can be recalled with the mnemonic SAIL 1,2:
lateral border: medial border of sartorius
medial border: medial border of adductor longus
superior border: inguinal ligament