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Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community, medical students, and the medical industry. We will post a workweek daily medical or surgical term, its meaning and usage, as well as biographical notes on anatomists, surgeons, and researchers through the ages. Be warned that some of the images used depict human anatomical specimens.

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A Moment in History

Thomas Willis, MD
Thomas Willis
(1621-1675)

An English physician and anatomist, Willis was born on his parents' farm in Great Bedwyn, Wiltshire, where his father held the stewardship of the Manor. He was a kinsman of the Willys baronets of Fen Ditton, Cambridgeshire. He graduated M.A. from Christ Church, Oxford in 1642. In the Civil War years he was a royalist, and was dispossessed of the family farm at North Hinksey by Parliamentary forces. In the 1640's Willis was one of the royal physicians to Charles I of England. He obtained his medical degree in 1646.

Thomas Willis might well be one of the greatest physicians of the 17th century.He is one of the founders of the Royal Society of London. He is remembered by his many publications, especially "Cerebri Anatome: Cui accessit Nervorum Descriptio et Usu", where he describes the arterial anastomoses at the base of the brain. This work is also the first detailed description of the vasculature of the brain. Willis described nine cranial nerves.

He is considered as the father of Neurology as a discipline. He used the term "neurology" for the first time in 1664. He described several neurological conditions

The Arterial Circle of Willis is a famous eponymous structure found at the base of the brain. It represents an anastomotic roundabout that connects the right and left sides as well as the carotid and vertebral arterial territories that supply the brain. Named after Thomas Willis, this structure was known well before him, but it was Willis who described its function.  If you click on the image or here, you will be redirected to a detailed description of this structure.

Sources:

1. "The legendary contributions of Thomas Willis (1621-1675): the arterial circle and beyond" Rengachary SS et al J Neurosurg. 2008 Oct;109(4):765-75
2. "Thomas Willis, a pioneer in translational research in anatomy (on the 350th anniversary of Cerebri anatome)" Arraez-AybarJournal of Anatomy, 03/2015, Volume 226, Issue 3
3. " The naming of the cranial nerves: A historical review" Davis, M Clinical Anatomy, 01/2014, Volume 27, Issue 1
4. "Observations on the history of the circle of Willis". Meyer A, Hieros, R.Med Hist 6:119–130, 1962


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Crus / crura

The word [crus] is Latin (cruris) and refers to the leg, or region of the shin. It is commonly used to mean "leg" or "pillar". The plural form is [crura].

Several authors suggest a relation of [crus] with another Latin term [crux] meaning "cross" as if a cross is formed by two [crura] (legs).

The term crus is widely used in human anatomy:

- crus cerebri: there are two crus cerebri in the anterior aspect of the mesencephalon
- crura of the penis: the posterior aspect of the corpora cavernosa firmly attached to the ischiopubic rami
- crura of the clitoris:  the posterior aspect of the corpora cavernosa firmly attached to the ischiopubic rami
- crura fornix cerebrii: the posterior converging bands that form the fornix of the cerebrum

Special mention is deserved by the crura of the diaphragm. There are two pairs of diaphragmatic crura. The esophageal crura (right and left) which bound the passageway of the esophagus from the thorax into the abdomen, the esophageal hiatus. The esophageal crura have a muscular structure. The aortic crura (righ and left) allow for passage of the aorta into the abdomen, and although muscular superiorly, they are mostly tendinous. The accompanying image shows an anteroinferior view of the respiratory diaphragm. Click on the image for a larger picture.

Respiratory diaphragm - anteroinferior view (modified from bartleby.com) 1. Right tendinous aortic crus 2. Left tendinous aortic crus IVC=Inferior Vena Cava

1. Right tendinous aortic crus 2. Left tendinous aortic crus IVC= Inferior vena cava. Modified from the original image. Courtesy of www.Bartleby.com