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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Pectoralis major

The pectoralis major muscle is the largest muscle in the anterior aspect of the thorax. It is thick and fan-shaped.  It attaches superiorly to the medial half of the clavicle, and medially to the anterior aspect of the sternum and cartilage of the first to sixth or seventh rib, extending inferiorly to attach to the aponeurosis of the external oblique muscle. Laterally, this muscle attaches to the lateral lip of the intertubercular groove (bicipital groove) of the humerus by a two-layered tendon which inserts each of the two heads of the muscle.

The superficial tendon attaches the clavicular head (red in the accompanying image), which extends between the intertubercular groove of the humerus and the clavicle. The deep tendon attaches the sternocostal head (purple in the accompanying image), which extends between the humeral intertubercular groove and the attachments in the sternum, costal cartilages, and the aponeurosis of the external oblique muscle. There is usually a well-defined interval between the two heads of the pectoralis major.

The pectoralis major is innervated by the medial (C8-T1) and lateral pectoral nerves (C5-C7).

This muscle is covered by the pectoral fascia which extends in different directions. An extension of this fascia is the clavipectoral fascia. In both male and female, the mammary gland is situated anterior to and anchors in the pectoral fascia.

Pectoralis major muscle - Red: clavicular head. Purple: Sternocostal head - Image modified from the original by Henry VanDyke Carter, MD. Public domain
Pectoralis major muscle - Red: clavicular head. Purple: Sternocostal head
Click on the image for a larger depiction 
The word pectoral arises from the Latin term "pectum" meaning "chest, breast". In its true meaning, pectoral or pectoralis refers to a "chest plate" or an "adornment of the chest".

1. “Gray’s Anatomy” Henry Gray, 1918
2. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
3. "Gray's Anatomy" 38th British Ed. Churchill Livingstone 1995
4. “An Illustrated Atlas of the Skeletal Muscles” Bowden, B. 4th Ed. Morton Publishing. 2015

Image modified from the original by Henry VanDyke Carter, MD. Public domain