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 half of the fibula and the adjacent interosseous membrane
insertion: the dorsal side of the base of the dist...
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. It is one of the extrinsic muscles of the hand.
origin: posterior ...
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 can refer to the:
extensor retinaculum of the wrist
extensor retinaculum of the foot
The extensor retinaculum of the foot is the broad ligamentous sheet 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 extensor retinaculum of the wrist is the broad ligamentous sheet located at the dorsal aspect of the wrist and functions to keep the extensor tendons in alignment and prevent bowstringing during movement.
It is obliquely oriented and attaches proximally to the lateral surface...
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 se...
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 (or outer 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 (EIA) is the larger of the two terminal branches of the common iliac artery (CIA).
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.
The posterior division of the retromandibular vein and posterior auricular vein unite within the parotid gland to form the external jugular vein, at the angle of the mandible.
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 laryngeal nerve is one of the two branches of the superior laryngeal nerve and supplies the cricothyroid muscle.
origin: arises as the smaller of the two branches of the superior laryngeal nerve at the level of the greater cornu of the hyoid bone
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...
Extradural neural axis compartment (EDNAC) exists from the tip of the coccyx all the way to the back of the globe, and yet it is relatively unknown as a concept. It is bounded externally by the periosteum of the vertebrae and sacrum inferiorly and the skull superiorly, and the visceral layer of ...
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 hand are muscles that originate outside the hand but insert into structures within the hand 1,2. Most of the extrinsic muscles have their origins within the forearm, with several solely/also originating from the humerus:
flexor carpi radialis
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 eyebrows may refer either to:
horizontal ridge where the forehead meets the superior eyelid consisting of the five layers of the scalp, i.e. skin, subcutaneous soft tissue, intertwined fibers of the orbicularis oculi and occipitofrontalis muscles, areolar layer and lastly the pericranium of...
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)
A suture is formed where two or more of the bones ar...
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 Zebras Bit My Coccyx
Ten Zebras Buggered My Car
To Zanzibar By Motor Car
Two Zombies Buggered...
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 recess of the petrous temporal bone is a small recess in the posterior wall of the mesotympanum lateral to the pyramidal eminence and stapedius muscle origin. The upper mastoid portion of the facial nerve runs immediately posterior to it, giving it its name. Medial to the pyramidal em...
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 lateral portion of 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...
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 canal or facial nerve canal refers to a bony canal through which the facial nerve traverses the petrous 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 contai...
The eponym Fallopian may refer to:
Fallopian canal (facial nerve canal)
Fallopian tube (uterine duct)
Fallopian ligament (inguinal ligament)
History and etymology
It is named after Gabriele Falloppio (also known by his Latin name Fallopius), Italian anatomist (1523-1562).
A useful mnemonic to remember the order of the five 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 (plural: falxes/falces cerebrorum) 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 m...
Fasciae (or fascias) are connective tissues found below the skin.
A consensus terminology on the components of fascia is elusive 1. Many anatomy authors in the English language separate the fascia into superficial and deep layers.
Superficial fascia refers to the loose connectiv...
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 vulva, 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 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 embedded...
The femoral canal is the medial compartment of the femoral sheath, an inverted cone-shaped fascial space medial to the common 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 expan...
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 mus...
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 an anatomical space in the anterior upper thigh that contains several palpable structures.
The major boundaries can be recalled with the mnemonic SAIL 1,2:
lateral border: medial border of sartorius
medial border: medial border of adductor lo...
A mnemonic for the boundaries of the femoral triangle is:
This should be easy to remember because the femoral triangle is shaped like a sail.
A: adductor longus
IL: inguinal ligament
Mnemonics to recall the order of the femoral vessels and nerve as they emerge from beneath the inguinal ligament into the femoral triangle are:
From lateral to medial:
N: femoral nerve
A: femoral artery
V: femoral vein
Y: "Y-fronts" (i.e. the midline)
The femoral vein is the main deep vein of the thigh and accompanies the superficial femoral artery and common femoral artery.
The term "superficial femoral vein" or its abbreviation, "SFV" should not be used as it is a misnomer (i.e. it is not a superficial vein), and can be especi...
The femoroacetabular or hip joint is a large ball-and-socket synovial joint between the femoral head and the acetabulum.
articulation: ball and socket joint between the head of the femur and the acetabulum
ligaments: ischiofemoral, iliofemoral, pubofemoral and transverse acetabular li...
The femur (plural: femora) is the longest, most voluminous and strongest bone in the human body.
It is composed of the upper extremity, body and lower extremity and provides several muscular origins and insertions.
The upper extremity is composed of the head, neck, greater tr...
Fetal circulation differs from the adult circulation due to the presence of certain vessels and shunts.
These shunts close after birth, and most of the fetal vessels are visible as remnants in the adult circulation. The function of these shunts is to direct oxygen-rich venous blood to the syst...
There are four sutures in the fetal skull vault of obstetric importance:
1. frontal suture: it lies between the two frontal bones
2. sagittal suture: it lies between the two parietal bones
3. coronal suture: it lies between the parietal and frontal bones
4. lambdoid suture: it lies between t...
Fibrous joints are a type of joint where the bones are joined by strong fibrous tissue rich in collagen. These joints allow for very little movement (if any) and are often referred to as synarthroses.
cranial sutures between bones of the skull
gomphosis joints between teeth and alveo...
The fibula (plural: fibulae) is the smaller of the two bones of the leg. It is not directly involved in the transmission of weight but is important for ankle stability and acts as a source for numerous muscle attachments. It is commonly raised as a flap for reconstructive surgery.
The fibular or peroneal artery is one of the three arteries of the leg, along with the anterior and posterior tibial arteries.
Origin and course
arises from the tibioperoneal trunk approximately 2.5 cm distal to popliteus and passes obliquely to the fibula, descending along its ...
The fifth lumbar vertebra (L5) is the largest of the five lumbar vertebrae and is considered an atypical vertebra due to its shape.
L5 is the largest, most inferior lumbar discovertebral unit in the vertebral column, and participates in forming the lumbar lordosis (from L1 to L5...
The fifth ventricle has historically been used to refer to either the:
cavum septum pellucidum
The filum terminale is a filament of connective tissue that extends inferiorly from the apex of the conus medullaris.
The filum terminale is continuous with the pia mater and is described as having two sections:
filum terminale internum: upper three quarters of the filum; covere...
The first rib is the most superior of the twelve ribs. It is an atypical rib and is an important anatomical landmark and is one of the borders of the superior thoracic aperture.
Compared to a typical rib, the first rib is short and thick and it has a single articular f...
Fishtail pancreas (also known as pancreas bifidum or bifid tail of the pancreas) is a rare anatomical variant of the pancreas produced by a branching anomaly during its development. It is named as such due to the fishtail-like appearance of the pancreas.
It is a rare anatomical an...
The fissula ante fenestram (FAF), also known as the cochlear cleft, is a small connective tissue-filled cleft located where the tendon of the tensor tympani muscle turns laterally toward the malleus. It is situated immediately anterior to the oval window, and posterior to the cochleariform proce...
Flat bones are 1 of the 5 types of bones in the body and represent a group of bones (predominantly of the cranium) that have a relatively flat shape and form from intramembranous ossification.
Flexor carpi radialis (FCR) is a muscle found in the first layer of the anterior compartment of the forearm. It does not pass through the carpal tunnel, but rather by itself in a small separate tunnel between the superficial and deep layers of the flexor retinaculum along the scaphoid and trapez...
Flexor carpi ulnaris (FCU) is a muscle of the first layer of the anterior compartment of the forearm. It is one of the extrinsic muscles of the hand.
humeral head: medial epicondyle of the humerus
ulnar head: medial border of olecranon and posterior border of ulna
The flexor digiti minimi brevis of the foot lies under the 5th metatarsal bone.
origin: base of metatarsal V and related sheath of fibularis longus tendon
insertion: lateral side of base of proximal phalanx of 5th toe
action: flexes 5th toe at metatarsophalangeal joint
The flexor digiti minimi brevis muscle of the hand lies lateral to the abductor digiti minimi, within the hypothenar eminence, and is one of the intrinsic muscles of the hand.
origin: hook of the hamate and flexor retinaculum
insertion: proximal phalanx of 5th digit
action: flexes 5t...
The flexor digitorum brevis muscle lies immediately superior to the plantar aponeurosis and inferior to the tendons of the flexor digitorum longus in the sole of the foot.
origin: medial process of calcaneal tuberosity and plantar aponeurosis
insertion: sides of plantar surface of mid...
The flexor digitorum longus (FDL) muscle is located on the tibial side of the leg within the deep posterior compartment of the leg. At its origin it is thin but as it descends, the muscle increases in size.
origin: medial side of posterior surface of the tibia
insertion: plantar surfa...
Flexor digitorum profundus (FDP) makes up the third layer of the anterior compartment of the forearm along with flexor pollicis longus. It passes through the carpal tunnel. It is one of the extrinsic muscles of the hand.
origin: proximal, anterior surface of ulna and adjacent interosse...