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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The ribs form the lateral bony wall of the thorax.  The ribs are paired and there are 12 pairs of ribs in the human thorax, most of them connecting the thoracic spine with the sternum. They are numbered from superior to inferior.

Ribs have different anatomical characteristics depending on their level. A typical rib has the following characteristics from posterior to anterior:

• Head: The head of each rib articulates with one or two ribs depending on their level. Typically ribs number 1,2, 10, 11, and 12 articulate with one vertebra, while the rest articulate with two vertebrae.

Thoracic rib, Posteroinferior view

Thoracic rib - Posteroinferior view.
Click on the image for a larger version.

Facets: These are the articular surfaces found in the head of each rib. They are covered by hyaline cartilage and form part of the costovertebral synovial joints. In the case of ribs 3 to 9, since they articulate with two vertebrae, they have two facets, each one called a demifacet, with an interarticular crest between them.

• Neck: A short, somewhat narrower portion of the rib that projects straight posterolaterally.

• Costal tubercle: A bony protuberance, usually with two components, one articular and one non-articular. The articular part of the costal tubercle presents with a facet that articulates with the transverse process of a thoracic vertebra.

• Costal angle: A sharp posterior curvature of the rib. The body when supine rests of these costal angles which deflect pressure from the thoracic spine.

• Costal body: The area of the rib anterior to the costal angle. In most ribs this oval-shaped region of the rib presents with an inferior and internal groove. This is the costal groove or costal sulcus. The corresponding level intercostal artery, vein, and nerve are found in the costal sulcus.

• Costal cartilage: All ribs have an anterior fibrocartilaginous component. Some of them attach directly to the sternum (chondrosternal joints), while some of them attach only to other costal cartilages (chondrochondral joints).

The 12 pairs of ribs are divided as follows:

• True ribs: Ribs 1-7, which attach by way of their costal cartilage directly to the sternum

• False ribs: Ribs 8-10, whose costal cartilage attach only to the cartilage of the superior rib, creating a lower border for the thoracic cage known as the costal margin.

• Free or "floating" ribs: Ribs 11 and 12. Their anterior cartilaginous end does not attach to sternum or other cartilage, so the end is free. The term "floating" although used, is a misnomer as these ribs do attach posteriorly to the thoracic spine.

There can be anatomical variations to the ribs, including the existence of extra cervical or lumbar ribs.

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