Ectopic pancreatic tissue, also known as heterotopic pancreatic tissue, refers to the presence of pancreatic tissue in the submucosal, muscularis or subserosal layers of the luminal gastrointestinal tract outside the normal confines of the pancreas and lacking any anatomic or vascular connection...
An ectopic posterior pituitary reflects a disruption of normal embryogenesis of the posterior pituitary and is one of the more common causes of pituitary dwarfism. Although it can be an isolated abnormality, numerous other congenital central nervous system malformations have been identified. Whe...
An ectopic thyroid gland is one which is located in a location other than the normal position anterior to the laryngeal cartilages.
Ectopic tissue refers to the gland located outside its normal anatomical position whereas accessory tissue refers to extra tissue located remote from ...
The Edinger-Westphal nucleus is a small parasympathetic motor nucleus in the midbrain and one of the two nuclei for the oculomotor nerve. It is one of the cranial nerve nuclei.
The nucleus is located in the central midbrain at the level of the superior colliculus ventral and medi...
The ejaculatory ducts are paired structures of the male reproductive system and convey seminal fluid.
Each ejaculatory duct is formed by the union of the excretory duct of the seminal vesicle and the ampulla of the ductus deferens and is approximately 2 cm long. The ducts course ...
A useful mnemonic to remember the ejaculatory pathway of sperm is:
S: seminiferous tubules of the testes
V: vas (ductus) deferens
E: ejaculatory duct
The elbow is a complex synovial joint formed by the articulations of the humerus, the radius, and the ulna.
The elbow joint is made up of three articulations 2,3:
radiohumeral: capitellum of the humerus with the radial head
ulnohumeral: trochlea of the humerus w...
The elbow bursae are a collection of synovial-lined bursae that exist around the elbow. They can be divided into bursae around the olecranon and in the cubital fossa.
superficial olecranon bursa: lies between the olecranon and the subcutaneous tissue.
subtendinous olecranon ...
Elbow ossification occurs at the six elbow ossification centers in a reproducible order. Being familiar with the order of ossification of the elbow is important in not mistaking an epicondylar fracture for a normal ossification center.
The order of appearances of the elbow o...
The atypical 11th rib is one of two floating ribs.
The 11th rib has a single facet on its head for articulation with the T11 vertebra. It has a short neck and no tubercle. The angle is slight. Its costal groove is shallow. The internal surface of this rib faces slightl...
Elster's rule provides a guide to the expected approximate pituitary gland height in relation to age 1. The rule follows an even-numbered pattern of 6, 8, 10, and 12 1:
6 mm pituitary gland height in infants and children
8 mm pituitary gland height in men and postmenopausal women
10 mm pituit...
Emissary veins (also known as the vena emissaria) are veins which pass through foramina in the skull to provide a venous communication between the dural venous sinuses and veins of the scalp or veins inferior to the skull base (cranial-cerebral anastomosis).
They are thin-walled and valveless. ...
An empty sella, also known as an empty pituitary fossa, is a relatively common incidental finding and posed more of a diagnostic problem before modern cross-sectional imaging. In addition to being incidental, a well-established association with idiopathic intracranial hypertension is also recogn...
The endocardium defines the inner soft tissue lining oft he heart within the cardiac chambers and constitutes the superficial surface of the cardiac valves. It apparently serves as a regulatory mechanism on myocardial contractility.
The endocardium represents the inner layer of t...
Endochondral ossification describes the process of ossification from mesenchymal cells (stem cells) with a cartilaginous template and is involved in the healing process of fractures.
Bone formation occurs at ossification centers, which are either primary or secondary:
primary ossification cent...
Endolymph is one of the two types of cochlear fluids, the other being perilymph. It is located in the scala media of the cochlea.
It is secreted by the stria vascularis (also colloquially called the 'battery of the cochlea') on the outer wall of the scala media. It has a high level of potassium...
The endolymphatic duct is a small epithelial-lined channel, part of the membranous labyrinth that passes through the vestibular aqueduct in the bony labyrinth of the petrous temporal bone. It arises from the utricle and saccule via the utriculosaccule duct and drains endolymph. The distal end is...
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...
The endopelvic fascia is the enveloping connective tissue network for the pelvic viscera, suspending, supporting and fusing the pelvic organs to the arcus tendineus fasciae pelvis, which itself inserts onto the pelvic sidewalls and pubic bones.
The major anterior component is the pubovesical li...
The enteric nervous system (ENS) is a general term that refers to the vast network of neurons that supply the gastrointestinal system. It is part of the autonomic nervous system and allows the gastrointestinal system to act independently from the brain and spinal cord.
An enthesis (plural: entheses), also known as a footprint, generally refers to the anatomic junction where connective tissue (e.g. ligament, tendon, joint capsule, bursa or a combination thereof) attach to bone.
Enthesis are commonly classified into two types 1:
The entorhinal cortex (plural: cortices) (a.k.a. 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 di...
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 overlying the median eminence of the hypothalam...
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 ...
The epicardium is the visceral part of the serous pericardium and forms the outer layer of the cardiac wall.
The epicardium is the visceral part of the serous pericardium, envelopes the heart, contains a variable amount of epicedial fatty tissue adjoining the myocardium at its ou...
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 su...
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 single midline 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...
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 sac (peritoneal cavity proper) and the lesser sac (omental bursa), allowing communication between these two spaces.
anterior: the free edge of the lesser omentum, known as the h...
Epipyramis also knows as os epitriquetrum is an accessory ossicle of the wrist. It is a small pyramidal shaped ossicle seen in the medial intercarpal space between lunate, triquetral, capitate and hamate bones. It is one of the rare accessory ossicles of the wrist and can be mistaken for a fract...
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 that includes the habenula, stria medullaris, 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.
iliocostalis subgroup is the most lateral
longissimus subgroup is between iliocostalis and spinalis
There are multiple handy mnemonics to recall the erector spinae muscles. They usually describe the position from lateral to medial.
I Like Standing
I Love Sex
I Long for Spinach
I Like Siri
Esophageal lymph node stations are those nodal stations in the neck, chest, and abdomen considered regional (rather than distant) for the purpose of esophageal cancer staging. This list reflects the map provided in the 8th edition of the American Joint Committee on Cancer (AJCC) Cancer Staging M...
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, also known as the pharyngotympanic tube or auditory tube, is the channel via which the tympanic cavity communicates with the nasopharynx.
It is ~36 mm in length and is directed downward, forward, and medially, forming an angle of about 45 degrees with the sag...
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) muscle is a muscle of the superficial layer of the posterior compartment of the forearm. It passes through the 2nd extensor compartment of the wrist. Extensor carpi radialis brevis muscle is one of the three muscles forming the mobile wad of Henry. It is on...
Extensor carpis radialis longus (ECRL) muscle 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. It is one of the extrinsic muscles of the h...
Extensor carpi ulnaris (ECU) muscle 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-...
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) muscle 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 ...
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 digitorum longus (EDL) is a thin muscle situated in the anterior leg lateral to extensor hallucis longus and extends the lateral four toes.
origin: upper two thirds of anterior shaft of fibula, superior portion of the anterior surface of the interosseous membrane, superior tib...
Extensor digitorum (ED) muscle, also known as extensor digitorum communis (EDC) muscle, 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. It is one of the...
The extensor expansions (also known as the extensor hood or dorsal digital expansion) are triangular aponeuroses by which the extensor tendons insert onto the phalanges.
On the dorsal aspect of the fingers, the tendons of the long extensor muscles of the posterior forearm (exten...
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 (EI) 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.
The extensor mechanism of the knee comprises:
medial patellar retinaculum
lateral patellar retinaculum
extensor mechanism of the knee injuries
Extensor pollicis brevis (EPB) muscle 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...
Extensor pollicis longus (EPL) muscle 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 t...
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 is variably used to refer to the canal itself or the porus acusticus externus (the round lat...
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 scapular 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 muscle
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 eyelids cover the eyes, with an upper and lower eyelid on each side, and are covered in front with loose skin and behind with adherent conjunctiva. The lower lids possess very little mobility; lids are closed gently by levator palpebrae superioris muscle fibers and forcefully by the orbicula...