The thymus is a T-cell producing lymphoid organ in the anterior mediastinum that plays a role in the development of the immune system, particular the maturation of T-cells. It typically has a retrosternal location and hence can mimic retrosternal pathology.
It is relatively large...
The thyrocervical trunk is one of the 3 branches of the first part of the subclavian artery and gives off numerous branches to supply viscera of the neck, the brachial plexus, neck muscles and the scapular anastomosis.
The trunk arises lateral to the vertebral artery from the anterosuperior wal...
The thyroglossal duct is an epithelium-lined connection between the foramen caecum and the thyroid that develops during the descent of the thyroid. It usually involutes in the 8th-10th week of gestation.
The thyroglossal duct arises from foramen caecum located at the junction of...
The thyrohyoid muscle is an infrahyoid muscle of the neck that is innervated by the ventral ramus of C1. The primary function of the thyrohyoid muscle is to depress and fix the hyoid bone and larynx though it may also raise the larynx when the hyoid bone is fixed.
origin: oblique line ...
The thyroid cartilage is the largest of the cartilages of the larynx, with its superior pole sitting at the level of the C4 vertebrae.
The thyroid cartilage consists of two laminae that are fused anteriorly in the median plane to form the laryngeal prominence. Each laminae posses...
The thyroidea ima artery is an uncommon variant of the blood supply to the inferior aspect of the thyroid gland. It is reported in ~7.5% (range 1.5-12.2%) of individuals and can arise from:
right common carotid artery
internal thoracic artery
The thyroidea ...
The thyroid gland is an endocrine organ in the neck which is completely enveloped by pretracheal fascia (middle-layer of the deep cervical fascia) and lies in the visceral space.
The thyroid extends from C5 to T1 and lies anterior to the thyroid and cricoid cartilages of the lar...
The tibia (plural: tibiae) is the largest bone of the leg and contributes to the knee and ankle joints. (shin- or shank-bone are lay terms). It is medial to and much stronger than the fibula, exceeded in length only by the femur.
The tibia has a prismoid shaft, expande...
The tibialis anterior muscle is one of the muscles of the anterior compartment of the leg involved in dorsiflexion and inversion of the foot.
origin: body of the tibia
insertion: medial cuneiform and first metatarsal
action: dorsiflexion and inversion of the foot
arterial supply: an...
The tibialis posterior muscle is one of the small muscles of the deep posterior compartment of the leg.
origin: inner posterior borders of the tibia and fibula
insertion: navicular and medial cuneiform
the tendon splits into two slips after passing inferior to plantar calcaneonavicu...
The tibial nerve is one of two terminal branches of the sciatic nerve and supplies the leg and foot with motor and sensory supply.
origin: the terminal branch of sciatic, at or above the popliteal fossa
course: courses straight down the popliteal fossa, passing deep to gastrocnemius t...
The tibial plateau is the proximal articular surface of the tibia.
The tibial plateau is composed of two parts:
concave articular surfaces of the oval-shaped medial and circular-shaped lateral tibial condyles (medial and lateral tibial plateaus)
the medial tibial plateau is lar...
The tibiofemoral joint is a modified hinge synovial joint between the distal femur and the proximal tibia.
articulation: modified hinge joint between the medial and lateral condyles of the femur and the tibial condyles
ligaments: transverse ligament of the knee, medial an...
The tibioperoneal or TP trunk, which occasionally referred to as the tibiofibular trunk is the direct continuation of the popliteal artery in the posterior upper leg after the anterior tibial artery origin. It is a short trunk that bifurcates into two terminal branches.
The tongue is a complex, principally muscular, structure that extends from the oral cavity to the oropharynx. It has important roles in speech, swallowing and taste.
The tongue has a tip, ventral surface, dorsal surface and root. The tongue is made of a midline lingual septum an...
Torus ethmoidalis, also known as torus lateralis, is the term given when there is no air cell in the ethmoid bulla (failure of pneumatisation). It is encountered in 8% of subjects.
Torus tubarius or cushion of the auditory canal is a mucosal elevation in the lateral aspect of the nasopharynx, formed by the underlying pharyngeal end of the cartilaginous portion of the Eustachian tube. The opening of the Eustachian tube is anterior to the torus tobarius. Immediately posterio...
The trachea, known colloquially as the windpipe, connects the upper respiratory tract to the lungs via the tracheobronchial tree, enabling gas exchange.
The trachea is a tube-shaped structure consisting of 15-to-20 D-shaped cartilage rings anterolaterally bridged by annular ligam...
A tracheal bronchus (with some variations also known as a pig bronchus) is an anatomical variant where an accessory bronchus originates directly from the supracarinal trachea. The latter term (pig bronchus or bronchus suis) is often given when the entire upper lobe (usually right side) is suppli...
Tracheobronchial branching anomalies can be seen as an isolated finding or accompanying heterotaxy syndromes, pulmonary sling, and conditions associated with pulmonary underdevelopment (agenesis and aplasia), including the scimitar syndrome.
Abnormal branching patterns include:
right sided iso...
The tracheobronchial tree is the branching tree of airways beginning at the larynx and extending inferiorly and peripherally into the lungs as bronchioles. The luminal diameter decreases as the branching increases more peripherally into the lungs. The walls of the airway down to the level of the...
Transitional vertebra is one that has indeterminate characteristic and features of vertebrae from adjacent vertebral segments. They occur at the junction between spinal morphological segments:
atlanto-occipital assimilation: complete or partial fusion of C1 and the o...
The transition zone of a nerve describes a region of a few millimetres where the myelin sheath changes from central to peripheral type. This zone is susceptible to mechanical irritation and is implicated in neurovascular compression syndromes such as trigeminal neuralgia (CN V), hemifacial spasm...
Transposition of inferior vena-cava (also known as left-sided IVC) refers to a variant course of the inferior vena cava. It is the most common anomaly of IVC and occurs due to persistence of left supracardinal vein.
Diagnosis of left sided IVC is important for:
planning of vascular procedures ...
The transpyloric plane, also known as Addison's plane, is an imaginary axial plane located midway between the jugular notch and superior border of pubic symphysis, at approximately the level of L1 vertebral body. It an important landmark as many key structures are visualised at this level, altho...
Transversalis fascia is the lining fascia of the anterolateral abdominal wall which lies between the transversus abdominis muscle and peritoneum.
The transversalis fascia, inferior diaphragmatic fascia, pelvic fascia and iliacus fascia form a continuous lining of the abdominal a...
The transverse acetabular ligament is part of the labrum but has no cartilage cells. Its strong, flat fibres cross the acetabular notch forming a foramen through which vessels and nerves enter the joint.
The transverse arch of the foot is an arch in the coronal plane formed by the three cuneiforms, the cuboid, and the bases of the five metatarsals. They are held together by the deep transverse metatarsal ligaments. The peroneus longus and tibialis posterior tendons assist in maintaining the curv...
The transverse cervical artery, also known as the cervicodorsal trunk, is 1 of the 4 branches of the thyrocervical trunk (off the first part of the subclavian artery).
It is a short artery that bifurcates into the superficial and deep branches, both which course superficially and laterally acro...
The transverse cervical nerve, also known as the superficial cervical nerve, cutaneous cervical nerve or anterior cutaneous cervical nerve of the neck, is a cutaneous branch of the cervical plexus that innervates the skin covering the anterior cervical region.
The transverse colon is the longest and most mobile part of the large intestine. It measures up to 45 cm in length.
The transverse colon is the continuation of the ascending colon from the right colic flexure. It passes from the right to left hypochondrium in a downward convex p...
The transverse ligament of the hip bridges the acetabular notch (located anteroinferiorly along the margin of the acetabulum) and joins the two ends of the acetabular labrum, thus forming a complete ring. Beneath it (through the acetabular foramen) pass nutrient vessels which enter the ligamentu...
The transverse ligament of the knee is a ligament within the anterior aspect of the knee joint.
The transverse ligament is a variable band-like intracapsular knee ligament. It attaches transversely across the anterior aspects of the convex margins of the medial and lateral menisci.
The transverse mesocolon is a broad, meso-fold of peritoneum, which connects the transverse colon to the posterior wall of the abdomen.
It is continuous with the two posterior layers of the greater omentum, which, after separating to surround the transverse colon, join behind it, and are contin...
The transverse muscle of the tongue is one of the 4 intrinsic muscles of the tongue which alters the shape of the tongue mass, being entirely confined to the tongue without an attachment outside the tongue (like the extrinsic muscles of the tongue).
The muscles fibres attach prox...
The transverse pancreatic artery, also known as the inferior pancreatic artery, is a branch of the splenic artery that supplies the pancreatic tail and body.
It arises from the proximal splenic artery and descends a short distance to run to the left along the posterior margin of the pancreas ne...
The transverse pericardial sinus is the transverse communication between the left and right parts of the pericardial space proper behind the two outflow arteries of the heart.
It is superior to the left atrium and posterior to the intrapericardial parts of the pulmonary trunk a...
The transverse sinus is one of the dural venous sinuses and drains the superior sagittal sinus, the occipital sinus and the straight sinus, and empties into the sigmoid sinus which in turn reaches the jugular bulb.
The two transverse sinuses arise at the confluence of the three aforementioned s...
Transverse vaginal (transvaginal) septum (TVS) is a type of rare congenital uterovaginal anomaly (class II under the Rock and Adam classification).
It is rare with a frequency of 1 in 70,000 females.
In the case of a complete septum, patients commonly prese...
The transversospinalis group is the deep layer of the intrinsic back muscles. These muscles lie between the transverse and spinous processes and are grouped by length of the fascicles, as well as region covered. The groups are rotatores, multifidus, and semispinalis.
The transversus abdominis muscle, named according to the direction of its muscle fibres, is one of the flat muscles that form the anterior abdominal wall. It is deep to the internal oblique muscle and ends in the anterior aponeurosis, which ultimately blends with the linea alba.
The transversus thoracis muscle is the most anterior muscle of the inner layer (external intercostal, internal intercostal and transversus thoracis) of the thoracic wall.
The transversus thoracis is a thin band of muscle and tendon arising from the lower posterior surface of th...
The trapezium (greater multangular) is one of the eight carpal bones of the hand. It is the most lateral (radial) bone of the distal row, located between the scaphoid and the first metacarpal bone . It articulates with the scaphoid proximally, the trapezoid medially, and the thumb and index meta...
The trapezium secondarium (or trapezium secundarium or secondary trapezium) is an accessory ossicle of the wrist. It can be seen adjacent to the tubercle of the trapezium superomedially 1,2.
According to Pfitzner, the trapezium secondarium is one of four potential secondary ossifica...
The trapezius muscle is a large, broad superficial muscle of the posterior neck and back. It gains its name from its diamond shape. Along with sternocleidomastoid muscle, it is invested by the superficial layer of the deep cervical fascia, which splits around it.
origin: superior nuch...
The trapezoid bone (also known as the os trapezoideum or the lesser multangular) is the smallest carpal bone in the distal row, sitting lateral to the capitate.
The trapezoid is an irregular, boot-shaped bone. The dorsal surface is larger than the palmar surface and i...
The trapezoid ligament is one of two components forming the coracoclavicular (CC) ligament. The conoid ligament is the other component.
The trapezoid ligament is a broad quadrilateral ligament that is quite thin. Its positioned almost horizontally. It is the anterolateral part of...
The triangle of Guillain and Mollaret, also known as the dentatorubro-olivary pathway, has three corners 1:
inferior olivary nucleus
contralateral dentate nucleus
Rubro-olivary fibres descend from the parvocellular division of each red nucleus along the central tegmental tracts t...
The triangle of safety is an anatomical region in the axilla that forms a guide as to the safe position for intercostal catheter (ICC) placement. With the arm abducted, the apex is the axilla, and the triangle is formed by the:
lateral border of the pectoralis major anteriorly
lateral border o...
The triangles of the neck are surgically focussed divisions of the neck, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on cross-sectional imaging (see deep spaces of the neck).
The neck can be divided into anterior and...
The triangular fibrocartilage complex (TFCC) is a complex structure that is a major contributor to the stability of the wrist.
The TFCC is located on the ulnar aspect of the wrist joint between the ulna and the lunate and triquetrum of the proximal carpal row. It has an elongate...
The triangular ligament may refer to a component of the triangular fibrocartilage complex (TFCC). It is commonly grouped with the ulnar collateral ligament and meniscal homologue, together comprising the ulnar-sided components of the TFCC. The triangular ligament attaches from the distalmost uln...
Triangular space of cruciate ligaments (TSC) is defined as the potential extrasynovial space between anterior and posterior cruciate ligaments of the knee joint.
anteriorly: anterior cruciate ligament
posteriorly: posterior cruciate ligament
inferiorly: tibial plate...
A useful mnemonic to remember the tributaries of the inferior vena cava is:
I Like To Rise So High
I: common iliac veins
L: lumbar veins
T: right testicular (gonadal) vein
R: renal veins
S: suprarenal veins
H: hepatic veins
The triceps brachii, which often referred to simply as the triceps is a three-headed muscle in the posterior compartment of the arm.
long head: infraglenoid tubercle of the scapula
medial head: posterior humerus, inferior to the radial groove, medial intermuscular septum
The triceps coxae is the tricipital (three headed) collection of 3 of the muscles in the posterior hip which act together on the hip, primarily to laterally rotate the extended thigh. It comprises (in order from superior to inferior) the superior gemellus, obturator internus and inferior gemellu...
Triceps surae is another term used for the calf muscles, more specifically two of the three muscles of the superficial posterior compartment of the leg:
medial and lateral heads of the gastrocnemius muscle
The group of muscles are innervated by the tibial nerve and form the Achi...
The tricuspid valve is one of the four cardiac valves. It is the atrioventricular valve that 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 bases of which at...
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
standing: superior orbital fissure (ophthalmic division of trigeminal nerve)
room: foramen rotundum (maxillary division of trigeminal nerve...
The trigone of of lateral ventricle, also known as the atrium, is a triangular area at the floor of the lateral ventricle that forms the transition point between the occipital and temporal horns.
It is the classic location for intraventricular meningioma.
The triquetrum (os triquetrum) 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 pisiform.
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 and...
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 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 (ovary)
tunica albuginea (penis)
tunica albuginea (testis)
tunica vaginalis (ovary)
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 ...
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 tympanosquamosal suture or fissure separates the tympanic part of the temporal bone from the squamous part. It is parallel and anterior to the bony external auditory meatus and medially continuous with 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-sized vertebral bodi...
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.
Relative to cervical and lumbar vertebrae, thoracic...
The ulna (plural: ulnae) is one of the two long bones of the forearm. It is 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 fibres 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 centre of the placental bulk and into the fetus at the umbilicus. Variations in inse...
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 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 is the innermost part of the anterior parahippocampal gyrus, part of 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 of the olfactory sys...
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...