The tricuspid valve (TV) is one of the four cardiac valves. It is one of the two atrioventricular valves (AVs) and allows blood to flow from the right atrium to the right ventricle. It opens during diastole and closes during systole. The valve has anterior, posterior and septal leaflets (cusps),...
The trigeminal ganglion, also known as the Gasser, Gasserian or semilunar ganglion, is the large crescent-shaped sensory ganglion of the trigeminal nerve located in the trigeminal cave (Meckel cave) surrounded by cerebrospinal fluid.
The ganglion contains the cell bodies of the sensory root of ...
The trigeminal nerve is the fifth cranial nerve and its primary role is relaying sensory information from the face and head, although it does provide motor control to the muscles of mastication. It is both large and complicated and has multiple brainstem nuclei (sensory and motor) as well as man...
A mnemonic for remembering the names of the skull foramina that the division of the trigeminal nerve (CN V) pass through is:
Standing Room Only
S: superior orbital fissure (ophthalmic division of trigeminal nerve)
R: foramen rotundum (maxillary division of trigeminal nerve)
The trigone of the lateral ventricle is an area of the lateral ventricle at the confluence of the occipital and temporal horns. It refers either to the three-dimensional space at the transition between the body of the lateral ventricle and the occipital and temporal horns, in which case it is al...
The triquetrum (also known as os triquetrum or triangular bone) is one of the carpal bones and forms part of the proximal carpal row.
The triquetrum is wedge-shaped carpal bone located between the lunate and the pisiform. It has an oval facet for articulation with the ...
The triradiate cartilage is the Y- shaped epiphyseal plate that occurs at the junction where the ischium, ilium, and pubis meet in the skeletally immature skeleton.
The vertical component of the "Y" is the meeting of the ischium and pubic bone. The anterior arm is the junction of the ilium an...
The triscaphe joint is the shared joint between the scaphoid, trapezium and trapezoid bones in the wrist. This joint is also referred to by its much longer name, the scaphotrapeziotrapezoid (STT) joint.
This joint may be fused as an alternative to scapholunate fusion in treat...
Trochlea (sing., pl. trochleae) is a general term that refers to an anatomic structure that resembles the grooved part of a pulley system:
Trochlea have been described in:
trochlea of the superior oblique muscle
trochlear nerve (CN IV)
trochlea of ...
The trochlear nerve is the fourth cranial nerve and is the motor nerve of the superior oblique muscle of the eye. It can be divided into four parts:
nucleus and an intraparenchymal portion
cavernous sinus portion
Nucleus and intraparenchy...
The trochlear nucleus is a small motor nucleus in the midbrain for the trochlear nerve.
The nucleus is located in the midbrain at the level of the inferior colliculus ventral and medial periaqueductal grey and dorsal to the medial longitudinal fasciculus. It lies just caudal to ...
The true vocal cords are the thickened, free edge of the cricovocal membrane, the cricovocal ligament, lined by mucous membrane 1. Together they form part of the glottis, the V-shaped aperture through which air passes. Their primary role is in phonation where vibration of the adducted vocal cord...
Tuber cinereum is a hollow eminence of gray matter. It is a part of the hypothalamus.
It is located between mammillary bodies and optic chiasm. Devoid of the blood brain barrier, it normally enhances after contrast administration.
It is continuous:
laterally: with an...
The tuberculum sellae is the ridged process of the sphenoid bone which forms the anterior wall of the sella turcica.
The tuberculum sellae forms the anterior wall of the sella turcica, which houses the pituitary gland. It is an elongated ridge located immediately poste...
The tunica albuginea (TA) forms the fibrous covering of the testis and is itself covered by the serous layer, the tunica vaginalis. The covering is total, except for at the point of attachment of the epididymis, and a small defect posteriorly where the spermatic cord vessels enter and leave the ...
Tunica is a word used in anatomy to refer to a type of covering.
tunica adventitia (also known as tunica externa)
tunica albuginea (clitoris)
tunica albuginea (ovary)
tunica albuginea (penis)
tunica albuginea (testis)
The tunica vaginalis (TV) represents the investing serosal covering of the testis. It forms as the embryological testis descends and passes out through the superficial inguinal ring carrying its abdominal peritoneal covering with it.
The tunica vaginalis is said to consist of two layers, the pa...
The twelfth rib is an atypical rib. It is the shortest rib, and one of two floating ribs.
The 12th rib has a single facet on its head for articulation with the T12 vertebra. It has a short neck and no tubercle. It also lacks a costal groove and angle. internal surface ...
A Twig-like middle cerebral artery or rete mirabile anomaly is a term to describe a discontinuity of a single trunk of the middle cerebral artery with several small vessels reconstituting the artery and giving it a twig-like appearance. Distally, normal vascular anatomy of the MCA branches need ...
The tympanic annulus is the thickened edge of the pars tensa of the tympanic membrane, anchoring it in the tympanic sulcus 3.
The tympanic annulus is formed by a fibrocartilaginous thickening of the edge of the pars tensa and has a horseshoe-shaped configuration. It is deficient ...
The tympanic membrane is a thin membrane that separates the external ear from the middle ear. It acts to transmit sound waves from air in the external auditory canal (EAC) to the ossicles of the middle ear.
The tympanic membrane is shaped like a flat cone pointing into the middle...
The tympanic part of the temporal bone is situated inferiorly to the squamous part and anteriorly to the mastoid part.
The tympanic part surrounds the external auditory meatus, forming the anterior wall, floor and some of the posterior wall of the bony external acoustic meatus. The lateral bord...
The tympanomastoid fissure is one of the intrinsic fissures of the temporal bone, located parallel and posterior to the bony external auditory canal, dividing the tympanic part of the temporal bone and mastoid process. Its radiological significance is as a fracture mimic (pseudofracture) 1. Its ...
The tympanosquamous fissure separates the tympanic part of the temporal bone from the squamous part. It is parallel and anterior to the bony external auditory canal and divides medially into the petrotympanic fissure and petrosquamous fissure.
Of the seven cervical vertebrae, C3 through C6 have typical anatomy, while C7 looks very similar. C1 (atlas) and C2 (axis) have very distinct anatomical features. For a basic anatomic description of the structure a generic vertebra, see vertebrae.
small, oval-shaped vertebral bod...
Typical ribs are those numbered 2 to 10 with ribs 1, 11 and 12 considered atypical.
A typical rib is long and flat. They contain a:
Ribs have a rounded, smooth superior border. The inferior border is thin and sharp.
Given the twelve thoracic vertebrae are largely similar, most are considered typical thoracic vertebrae with the exceptions T1 and T9 to T12. For a basic anatomic description of the structure of typical vertebrae, see vertebrae.
In medical English, some doctors and texts refer to t...
The ulna (plural: ulnae) is one of the two long bones of the forearm, located medially in the supinated anatomic position. It has a larger proximal end and tapers to a smaller distal end (opposite to the radius).
Prominent features of the ulna include:
The ulnar artery is a terminal branch of the brachial artery, arising at the proximal aspect of the forearm. Along with the radial artery, it is one of the main arteries of the forearm.
origin: terminal branch of the brachial artery
location: inferior aspect of the cubital fossa
The ulnar nerve is one of the terminal branches of the brachial plexus and has motor and sensory supply to the forearm and hand.
The ulnar nerve originates as a terminal branch of the medial cord of the brachial plexus with nerve root fibers from C8-T1.
The ulnar vein is one of the two major deep veins of the forearm, along with the radial vein. As is usual in the upper and lower limbs, there are often two veins (venae comitantes) that run on either side of the ulnar artery and anastomose freely with each other.
It forms in the hand from the d...
The ulnomeniscal homologue (UMH) is an obliquely oriented, fibrocartilaginous structure, that forms part of the ulnar collateral ligament complex (ULC) of the wrist.
The UMH is located between the ulnar styloid process and the triquetrum. It adheres to the ulnar joint capsule and...
The umbilical artery gives rise to both a nonfunctional remnant of the fetal circulation and an active vessel giving supply to the bladder. In the adult, the obliterated area of the vessel is identifiable as the medial umbilical ligament and the patent segment is the superior vesical artery.
The umbilical cord is a fetal organ that connects the placenta to the developing fetus and is a vital passage for nutrients, oxygen and waste products to and from the fetus.
The umbilical cord inserts into the center of the placental bulk and into the fetus at the umbilicus. Vari...
The umbilical folds are a series of 5 folds of parietal peritoneum on the deep surface of the anterior abdominal wall and consist of:
a single midline median umbilical fold,
bilateral medial umbilical folds, and
bilateral lateral umbilical folds
The umbilical vein is the conduit for blood returning from the placenta to the fetus until it involutes soon after birth.
The umbilical vein arises from multiple tributaries within the placenta and enters the umbilical cord, along with the (usually) paired umbilical arteries. Once it enters the...
The umbilicus is the fibrous remnant of the fetal attachment of the umbilical cord after birth.
All layers of the anterior abdominal wall fuse at the umbilical ring, a small round defect in the linea alba located just inferior to the midpoint between the xiphoid process of the st...
The uncinate fasciculus is a white matter tract that connects the uncus (Brodmann area 35), the anterior temporal areas (temporal pole; Brodmann area 38), the amygdala and the hippocampal gyrus (Brodmann areas 36 and 30) with areas of the frontal lobe (polar and orbital cortex); runs - forming a...
The uncinate process of the ethmoid bone is a thin hook-like osseous structure of the wall of the lateral nasal cavity.
Together with the ethmoid bulla, it forms the boundaries of the hiatus semilunaris and ethmoid infundibulum.
The course of the free edge of the uncinate proces...
The uncinate process of the cervical spine is a hook-shaped process found bilaterally on the superolateral margin of the cervical vertebral bodies of C3-C7.
The uncinate processes are more anteriorly positioned in the upper cervical spine and more posteriorly location in the lower cervical spin...
Uncovertebral joints, also called Luschka’s joints, are seen bilaterally between adjacent cervical vertebrae, identified by the cat ear shaped uncinate processes of the C3-7 vertebrae (C1 and C2 have no uncinate processes).
The articulation forms between the uncina...
The uncus (plural: unci) is the innermost part of the anterior parahippocampal gyrus, part of the mesial temporal lobe.
The uncus is the most anterior portion of the medial parahippocampal gyrus. It belongs to the limbic system. Housing the primary olfactory cortex, it is part o...
Unfused spinous process, which is really failure of fusion of the neural arch, is a relatively common anatomical variant and is part of the spectrum of spina bifida occulta.
This should be differentiated from accessory ossicles of the spinous process, which appear after non-fusion of the secon...
Fusion of sternal body segments is usually complete by 25 years of age. But non-fusion of sternal body segments can be seen in older age group.
A unicornuate uterus or unicornis unicollis is a type of Müllerian duct anomaly (class II) characterized by a banana-shaped uterus usually draining into a single Fallopian tube.
This type can account for ~10% (range 6-13%) of uterine anomalies and infertility is seen in ~12.5% (ra...
Upper limb anatomy encompasses the anatomy of the shoulder, arm, elbow, forearm, wrist and hand.
This anatomy section promotes the use of the Terminologia Anatomica, the international standard of anatomical nomenclature.
The upper subscapular nerve, also known as the short or superior subscapular nerve, arises from the posterior cord of the brachial plexus and supplies the subscapularis muscle.
The upper subscapular nerve branches from the posterior cord of the brachial plexus with fibers...
The upper T sign is one of the features useful in identifying the central sulcus of the cerebral cortex on cross-sectional imaging.
It relies on identifying the superior frontal sulcus which intersects the precentral sulcus in a "T" junction, thus defining the precentral gyrus. The central sulc...
The urachus (plural: urachuses or urachi ref) is the fibrous vestigial remnant of the embryonic allantois.
The lumen of the urachus usually obliterates after birth and it becomes known as the median umbilical ligament, which is covered by a midline linear fibrous fold of parietal peritoneum (ca...
The ureter is a paired fibromuscular tube that conveys urine from the kidneys in the abdomen to the bladder in the pelvis.
The ureter is 25-30 cm long and has three parts:
abdominal ureter: from the renal pelvis to the pelvic brim
pelvic ureter: from the pelvic brim to the bla...
Ureteral duplication is the most common congenital abnormality associated with the urinary tract, and occurs in ~1% of the population.
Duplication can occur unilaterally or bilaterally, and may be partial or complete:
partially duplicated ureters fuse into a single ureter proxim...
The ureteric bud (also known as the metanephrogenic diverticulum) is a protrusion of the mesonephric duct that appears during the embryological development of urogenital organs. It will eventually form the urinary collecting system (i.e. collecting tubes, calyces, renal pelvis, ureter) of the ki...
The urethra is the terminal segment of the genitourinary system. Because of vastly different anatomy between the sexes, male and female urethras are discussed separately:
NB: At present (2020) there is no standardized universal terminology for the post-operative ur...
The urinary bladder (more commonly just called the bladder) is a distal part of the urinary tract and is an extraperitoneal structure located in the true pelvis. Its primary function is as a reservoir for urine.
The bladder has a triangular shape with a posterior base, an anteri...
The urinary system consists of the kidneys, ureter, bladder and urethra. With the exception of the urethra, this is the same in both males and females. It spans the abdomen and pelvis, from the upper abdomen to the extreme pelvis, being inextricably linked with the genital system.
The urinary ...
The urogenital triangle forms the anterior half of the diamond-shaped perineum. The triangle's corners are defined by the pubis symphysis anteriorly and the ischial tuberosities anterolaterally. The anterolateral borders are the ischiopubic rami and the posterior border is the transverse perinea...
The U sign denotes the characteristic U-shaped appearance of the subcentral gyrus which surrounds the inferolateral end of the central sulcus and abuts the lateral (Sylvian) fissure. It has been found, at least in one study, to be the most reliable anatomical feature to identify the central sulc...
Uterine agenesis is the extreme of Mullerian duct anomalies (Class I) where there is a complete absence of uterine tissue above the vagina.
The uterine agenesis-hypoplasia spectrum accounts for ~10-15% of all Müllerian duct anomalies.
The uterine artery is seen bilaterally and is a branch of the anterior division of the internal iliac artery.
It runs medially in the pelvis, within the base of the broad ligament, to the outer surface of the uterus. From lateral to medial it has a descending, transverse ...
Uterine duplication anomalies are a group of Müllerian duct anomalies where fusion of the Müllerian duct associated structures fail to some degree:
uterus didelphys: class III
bicornuate uterus: class IV (second commonest duplication anomaly)
septate uterus: class V (commonest duplication ano...
The uterine tube, also known as the Fallopian tube or less commonly the oviduct, is a paired hollow tube that bridges between each ovary and the uterus and functions to convey the mature ovum from the former to the latter. If conception occurs, it normally does so within the tube. It can be affe...
The uterine venous plexus is a network of veins surrounding the uterus and has extensive anastomoses with the vaginal venous plexus inferiorly and ovarian venous plexuses laterally.
The uterine venous plexus lies along the lateral aspects and superior angles of the uterus within ...
The paired uterosacral ligaments are one of the supporting structures of the uterus. Uterosacral ligaments are not infrequently affected in cases of deep infiltrating endometriosis.
The paired uterosacral ligaments are extraperitoneal structures which extend posteriorly from the ...
The uterus is a hollow, thick-walled, muscular organ of the female reproductive tract that lies in the lesser pelvis.
The uterus has an inverted pear shape. In the adult, it measures about 7.5 cm in length, 5 cm wide at its upper part, and nearly 2.5 cm in thickness. It weighs ...
The utricle may refer to:
utricle of the inner ear
utricle of the prostatic urethra
The utricle is a small membranous sac (part of the membranous labyrinth) and paired with the saccule lies within the vestibule of the inner ear. It has an important role in orientation and static balance, particularly in horizontal tilt.
The vestibule is located within the bony l...
The uvea (plural: uveas), also called the uveal layer or vascular tunic, is the middle of the three layers that make up the eye. It is the pigmented layer and its main function is of nutrition and gas exchange. It sits between the retina (innermost layer) and sclera.
It is traditionally split ...
The vagina is a midline fibromuscular tubular organ positioned in the female perineum extending superiorly from the vulva, to the cervix and uterus in the pelvis.
The vagina is 8-10 cm in length, extending posterosuperior from the vestibule through the urogenital diaphragm to th...
The vaginal artery is a branch of the anterior division of the internal iliac artery, and should not to be mistaken with the vaginal branch of the uterine artery. It is often considered to be a homolog of the inferior vesical artery, which is present only in males.
origin: anterior div...
The vaginal opening, is also known as the introitus (plural: introituses), vaginal orifice, or ostium vaginae (plural: ostia vaginarum) (TA) .
The entrance to the vagina lies in the vestibule of the vulva in the median plane. It has an anteroposterior orientation and is partially...
The vagus nerve is the tenth (X) cranial nerve and provides the bulk of the parasympathetic input to the gastrointestinal system and to the heart. It is a complex mixed sensory, motor and parasympathetic nerve.
The vagus nerve arises as multiple rootlets at ...
The epiglottic valleculae are paired depressions in the oropharynx located anterior to the epiglottis and posterior to the base of tongue. They are located between the lateral glossoepiglottic folds and the median glossoepiglottic fold.
Vallecula is Latin for "small valley", a combi...
The valveless veins are veins that lack venous valves. Most veins contain valves (known as the valvula venosa in the TA) to prevent backflow, i.e. ensuring that blood flow is always towards the heart 1.
Recent evidence shows that veins that were previously thought to be valveless, are now known...
The valvulae conniventes, also known as Kerckring folds/valves, plicae circulares or just small bowel folds, are the mucosal folds of the small intestine, starting from the second part of the duodenum, they are large and thick at the jejunum and considerably decrease in size distally in the ileu...
Variant anatomy of the aortic arch occurs when there is failure of normal aortic development. It results in a number of heterogenous anomalies of the aorta and its branch vessels.
Normally, the aorta ascends in the superior mediastinum to the level of the sternal notch before arc...
Variation in hepatic arterial anatomy is seen in 40-45% of people. Classic branching of the common hepatic artery from the celiac artery, and the proper hepatic artery into right and left hepatic arteries to supply the entire liver, is seen in 55-60% of the population.
There can be several variations in placental morphology. These include:
single lobed discoid placenta (single disc): most common scenario
bilobed placenta: two near equal size lobes
succenturiate lobe(s): one of more smaller accessory lobes
circumvallate placenta: rolled placental edges with...
Vascular anatomical variants are common:
SVC and IVC - caval variants
intracranial arteries - variants
The vastus intermedius muscle is one of the four quadriceps muscles in the anterior compartment of the thigh. The others are the vastus medialis, the vastus lateralis, and the rectus femoris.
origin: upper two-thirds of the anterior and lateral surfaces of the femur
The vastus lateralis is largest of the four quadriceps muscles in the anterior compartment of the thigh. The others are the rectus femoris, the vastus intermedius, and the vastus medialis.
lateral part of intertrochanteric line
margin of greater trochanter
The vastus medialis muscle is one of the four quadriceps muscles in the anterior compartment of the thigh. The others are the rectus femoris, the vastus intermedius, and the vastus lateralis.
medial part of intertrochanteric line
medial lip of the linea ...
The vein of Galen, also known as the great cerebral vein or great vein of Galen, is a short valveless trunk formed by the union of the two internal cerebral veins and basal veins of Rosenthal.
It lies in the quadrigeminal cistern and curves backward and upward around the posterio...
The vein of Marshall, oblique vein of Marshall or the oblique vein of the left atrium is a small vein that descends on and drains the posterior wall of the left atrium. It drains directly into the coronary sinus at the same end as the great cardiac vein, marking the origin of the sinus.
The velum interpositum is a small membrane containing a potential space just above and anterior to the pineal gland which can become enlarged to form a cavum velum interpositum.
The velum interpositum is formed by an invagination of pia mater forming a triangular membrane the ap...
The vena caval foramen is one of the three major apertures in the diaphragm. It is the highest of the three and situated at the level of T8-9. It is quadrilateral and placed at the junction of the right and middle leaflets of the central tendon.
It transmits several structures between the thora...
The venae cordis minimae (singular: vena cordis minima), meaning "smallest cardiac veins", also known as thebesian veins (as these are eponymous, they are sometimes capitalized as Thebesian veins) are a small group of valveless myocardial coronary veins within the walls of each of the four cardi...
The anastomotic venous circle of the base of the brain 1, also referred to as the venous circle of Trolard 2,3,5, is an inconsistently found venous homologue of the better-known arterial circle of Willis.
It should not be confused with other venous structures also described by Trolard such as t...
The anatomy of the venous drainage of the lower limbs is extremely variable. However, there is order in the variability. The veins of the lower extremities are arranged in three systems: the superficial, the deep, and the perforating venous systems. These are located in two main compartments: th...
The venous drainage of the thoracic wall drains deoxygenated venous blood from the peripheries of the thoracic cage back into systemic circulation.
Anterior thoracic wall
Anterior intercostal veins
The anterior intercostal veins originate from the intercostal space just inferio...
Venous lakes in the skull are an anatomical variant of enlarged emissary veins within the diploic space.
Venous lakes appear as round-to-oval lucencies, often in the inner table, that demonstrate vivid post-contrast enhancement 1.
The ventral horn of the spinal cord is one of the grey longitudinal columns found within the spinal cord. It contains the cell bodies of the lower motor neurons which have axons leaving via the ventral spinal roots on their way to innervate muscle fibers.
On transverse section of...
The ventricular system in the brain is composed of CSF-filled ventricles and their connecting foraminae. CSF is produced by ependymal cells which line the ventricles. They are continuous with the central canal. Ventricles contain around 1/5 of normal adult CSF volume, which is around 20-25 ml.
The ventriculus terminalis or terminal ventricle of Krause, also known as the 5th ventricle, is an ependymal-lined fusiform dilatation of the terminal central canal of the spinal cord, positioned at the transition from the tip of the conus medullaris to the origin of the filum terminale. This di...