Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

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Weigert-Meyer law

The Weigert-Meyer law describes the relationship of the upper and lower renal moieties in duplicated collecting systems to their drainage inferiorly. Weigert-Meyer law With duplex kidney and complete ureteral duplication, the upper renal and lower renal moiety have their own ureters with each ...

Wernicke's area

Wernicke's area (Brodmann area 22) is an area of the posterior temporal lobe in the dominant hemisphere concerned with the receptive components of speech. Gross anatomy Wernicke's area is located in the superior temporal gyrus, posterior to the posterior commissure line. Relations It is boun...

Wharton jelly

Wharton jelly refers to the gelatinous substance within the umbilical cord. Gross anatomy Wharton jelly is derived from extra-embryonic mesoderm and is largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulphate) while containing smaller amounts of fibroblasts and macropha...

White matter tracts

White matter tracts, also known as white matter fibres, are classified into three categories: Projection tracts tracts connecting the cortex with other area in the CNS, e.g. deep nuclei, brainstem, cerebellum or spine may be efferent (motor) or afferent tracts (sensory) white matter tracts t...

White matter tracts of the spinal cord

The spinal cord has numeorus white matter tracts that ascend and descend in the peripheral substance of the cord. They can be divided by their location and function: anterolateral columns anterior corticospinal tract medial longitudinal fasiculus spinothalamic tracts lateral spinothalamic t...

Wolffian duct

The Wolffian duct (also known as the mesonephric duct) is one of the paired embryogenic tubules that drain the primitive kidney (mesonephros) to the cloaca. In both the male and the female the Wolffian duct develops into the trigone of the urinary bladder. Development Female In the female, in...

Wormian bones

Wormian bones are a subset of the small intrasutural bones that lie between the cranial sutures formed by the bones of the skull vault. The title Wormian bones is reserved for abnormal intrasutural bones that are typically found around the lambdoid suture. Some consider them abnormal only if gr...


The xiphisternum (also known as the xiphoid process or simply the xiphoid) is the smallest of the three parts of the sternum (manubrium, body or gladiolus and xiphisternum). It arises from the inferior and posterior margin of the sternal body and projects inferiorly. It is a small cartilaginous ...

Zona orbicularis

The zona orbicularis are circular fibres of the hip joint capsule and form a collar around the femoral neck. Though partly blended with the pubofemoral and ischiofemoral ligaments, these fibres are not directly attached to bone. 

Zuckerkandl tubercle

Zuckerkandl tubercle is a normal variant of the thyroid. It may be mistaken for a thyroid nodule or mass or lymph node.  Zuckerandl tubercle is a projection of normal thyroid tissue from the posterior aspect of the lateral lobes of the thyroid gland.  It is also an important surgical landmark ...


The zygoma (or zygomatic bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape. Gross anatomy Zygoma has three surfaces, five borders, and two processes. Surfaces anterolateral surface is convex, pierced at its orbital border by the zy...

Zygomatic arch

The zygomatic arch is formed by the union of the temporal process of the zygomatic bone and the zygomatic process of the temporal bone at the zygomaticotemporal suture.  Related pathology Le Fort type 3 fracture zygomaticomaxillary complex fracture

Zygomatic nerve

The zygomatic nerve is a main branch of the maxillary division of the trigeminal nerve. It should not be confused with the zygomatic branch of the facial nerve. Gross anatomy The zygomatic nerve divides off the maxillary division just after emerging from the foramen rotundum to enter the ptery...

Zygomaticofacial foramen

The zygomaticofacial foramen is a small foramen in the mid lateral surface of the zygomatic bone that transmits the zygomaticofacial nerve (a branch of the zygomatic nerve from the maxillary division of the trigeminal nerve) and zygomaticofacial vessels.

Zygomaticofacial nerve

The zygomaticofacial nerve is the smaller of the two branches of the zygomatic nerve, from the maxillary division of the trigeminal nerve. It is sometimes referred to as the malar branch of the zygomatic nerve. It leaves the inferolateral aspect of the extraconal space of the orbit through the z...

Zygomaticomaxillary suture

The zygomaticomaxillary suture is between the zygomatic process of the maxilla and the maxillary margin of the zygomatic bone.

Zygomaticotemporal foramen

The zygomaticotemporal foramen is a small foramen in the anteromediall surface of the zygomatic bone that transmits the zygomaticotemporal nerve (a branch of the zygomatic nerve from the maxillary division of the trigeminal nerve) and zygomaticotemporal vessels.

Zygomaticotemporal nerve

The zygomaticotemporal nerve is the larger of the two branches of the zygomatic nerve, from the maxillary division of the trigeminal nerve. It is primarily sensory but also relays parasympathetic fibres to the lacrimal nerve from the pterygopalatine ganglion which reach the lacrimal gland. It le...

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