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

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.


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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Combining root terms

Most medical words have only one root term and do not require combination as in the word [colectomy]. The situation arises when there is more than one organ or structure that is influenced by the suffix and the prefix (when present), such as [coloproctectomy]. Following are the basic rules for root terms combination:

  1. - Place an [-o-] between the root terms being combined. The combining vowel  [o] means "and". The word [gastroenterology] means "study of the stomach and the small intestine"
  2. - Organize the root terms using their proximal to distal relationship. For a better explanation, click here
  3. - If the first root term ends in a vowel, the combining vowel [-o-] is not needed. An example are the root terms [-chole-], meaning "bile or gall". and [cyst], meaning "bladder or sac". The word [chole-cyst-ectomy] does not have an [-o-] between the root terms
  4. - If the proximal to distal relationship does not apply, then the words should be ordered in a way that is euphonic
  5. - The only time a hyphen should be used is the rare case when using an [o] is not possible. Based on this rule, the word [salpingooophorectomy] is correct, the word [salpingo-oophorectomy] is not. An example of this is the word [cross-section].

An example of rule #5 is the word co-author. Since adding an [o] as a combining vowel would give us the word cooauthor (which is not correct), a hyphen must be used.

In the case of the word [coloproctectomy] the word can be divided into these components" The first root term [-col-], meaning "colon", the combining vowel [-o-], meaning "and", the second root term [-proct-], meaning "rectum", and the suffix [-ectomy], meaning "removal of". Properly read, the word means "removal of colon and rectum]. The proper term is [coloproctectomy], please do not use the terms [proctocolectomy] or worse, [protocolectomy], because they are incorrect usage of medical terminology.

For information on how to read medical words, click here.

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