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

Johann Gottfried Zinn

Johann Gottfried Zinn

Anatomist and botanist, Johann Gottfried Zinn was born on December 6, 1727 in the city of Ansbach, Germany. He started his medical studies in his native city, becoming later a student of Dr.  Albrecht von Hallers at the University of Göttingen, and received his MD in 1749.

He left for Berlin to continue his studies but came back shortly thereafter. He became a professor of anatomy at the University of Göttingen and in 1753 he also became the director of the botanical garden in the same city.

He is known for his anatomical treatise on the anatomy of the human eye: “Descriptio anatomica oculi humani iconibus illustrata”. Because of this, his name has become an eponym in the “Zonule of Zinn”, a ring of strands that forms a fibrous band connecting the ciliary body with the capsule of the lens of the eye. Zonule of Zinn is sometimes referred to as the suspensory ligaments of the lens, or the “ligament of Zinn”. His name is also attached to the anular ring tendon found in the posterior aspect of the eye, the "anular tendon of Zinn". This ring serves as attachment for all the extraocular muscles of the eye and the optic nerve passes through the center of the ring.

Carol Linné (Carolus Linneaus) named a genus of flowers in the family Asteraceae known vernacularly today as “Zinnia” in his honor. Hover your cursor over his portrait to see the flower.

The chapter on orbital anatomy of his anatomy book, taken from the second edition in 1780, has been translated and the first of three parts is published in an issue of “Strabismus”

His book "Catalogus Plantarum Horti Academici Et Agri" can be seen online here.

His life was short, dying at the early age of 32, but his name lives on in the name of a beautiful flower.

1. “Johann Gottfried Zinn" Simonz, HJ Strabismus – 2004, Vol. 12, No. 2, p. 125 
2. "Anatomical Description of the Human Eye" Zinn, JG Strabismus, 13:45–52, 2005 
Images: Public Domain by Wikipedia Commons. 1. Own work I_am Jin, and H. Wilhem Dietz

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The prefix [pre-] has its origin in the Latin preposition [prae] meaning "anterior", "in front of", or "before". 

Applications of this prefix include:

precordial: anterior to the heart, as in "precordial pain"
preoperative: before the operation
preperitoneal: anterior to the peritoneum, referring to the region found outside and anterior to the peritoneal sac, an area containing fat, and important for preperitoneal laparoscopic surgery
presystolic: before systole
• preaortic: anterior to the aorta

Posterior interventricular artery

The right coronary artery usually bifurcates in an area of the posterior aspect of the heart known as the "crux cordis" giving origin to two terminal branches: the posterior interventricular artery (anatomical term) and the posterolateral artery. The posterior interventricular artery is better know to clinicians as the "posterior descending artery" or PDA.

The PDA descends towards the apex cordis where it ends. It gives off several small ventricular branches, but its most important branches are the septal perforators. These branches dive deep and provide blood supply to the posterior 1/3rd of the interventricular septum.

The AV node artery, which provides blood supply to the AV node (a component of the conduction system of the heart) may arise from the PDA instead of arising from the right coronary artery.

The PDA may present with a number of anatomical variations, including:

Posteroinferior view of the heart. IVC=inferior Vena Cava

• arising from the circumflex artery (and absence of the posterolateral artery)
• arising from the first septal perforator of the anterior interventricular artery
• arising from the second diagonal artery
• arising from anterior interventricular artery
• being double, with one PDA arising from the circumflex artery, and another from the right coronary artery, etc.
Image property of: CAA.Inc. Photography: Efrain Klein

Sunao Tawara, M.D.

This article is part of the series "A Moment in History" where we honor those who have contributed to the growth of medical knowledge in the areas of anatomy, medicine, surgery, and medical research.To search all the articles in this series, click here.
Sunao Tawara, M.D. (1873 - 1952) Sunao Tawara was born in the prefecture of Ooita, Kyushu, Japan. Adopted by an uncle (and physician), Tawara studied English and German, and went on to the University of Tokyo medical school, where he graduated an MD in 1901.

In 1903 he traveled to Marburg, Germany, where he started working with Dr. Karl Albert Ludwig Aschoff (1866-1942), a noted pathologist. Tawara’s work led him to the discovery of what today we call the “atrioventricular node” (AV node) and the connections of the AV node and the Bundle of His (the right and left bundle branch). His work with Aschoff led to the eponym of “node of Aschoff-Tawara” for the AV node. Tawara’s work also led to the understanding of the function of the Purkinje fibers. Tawara gave the entire system the name “Reitzleitungssytem” or the “conduction system” of the heart.

In 1906 Dr. Tawara published his discoveries in a German-language article entitled “The Conduction System of the Mammalian Heart — An Anatomicopathological Study on the Atrioventricular Bundle and the Purkinje Fibers”. The same year he returned to Japan and in 1908 became Professor of Pathology at the University of Kyushu until his retirement in 1933.

Dr. Sunao TawaraOriginal imagecourtesy of Wikipedia.
1. "Sunao Tawara" Suma, K. Clin Cardiol (1991) 14; 442-443
2. "Sunao Tawara, A Cardiac Pathophysiologist" Loukas, M. et al Clinical Anatomy 21:2–4 (2008)
3. "Sunao Tawara: A Father of Modern Cardiology" Suma, K. J Pacing Clin Electrophysiol (2001) 24:1; 88- 96

Conduction system of the heart

The conduction system of the heart is formed by a group of specialized cardiac muscle structures that serve as pacemakers and distributors of the electrical stimuli that make the heart beat coordinatedly. It is important to stress the fact that the "conduction system of the heart" is not formed by nerves.

Components of the conduction system of the heart:

• SA node: The sinuatrial (SA) node is a small nodule of cardiac muscle tissue, somewhat horseshoe-shaped that is found at the junction of the superior vena cava and the right atrium. It receives blood supply from the SA node artery, a branch of the right coronary artery. It receives innervation from both sympathetic and parasympathetic nerves

Conduction system of the heart

• AV node: The atrioventricular (AV) node is found at the junction of atria and ventricles in an area known as the "Triangle of Koch". Its function is to delay the electrical impulse passing from the atria to the ventricles by 1/10th of a second, enabling the sequential pumping action of the heart. The eponymic name for the AV node is "node of Aschoff-Tawara", and it receives its blood supply by way of the AV node artery, a branch that usually arises from the right coronary artery

• AV bundle: Also known as the "Bundle of His", this thick bundle of specialized myocardial cells is found in the interventricular septum. It divides into the right and left bundle branches

• Bundle branches: Sometimes known as the "crura" of the Bundle of His, these two divisions of the AV bundle help distribute the electrical stimuli to the ventricular walls. The right bundle branch has an extension that crosses the lumen of the right ventricle, from the base of the anterior papillary muscle to the interventricular septum, forming a cord of tissue known as the "moderator band" or "septomarginal trabecula"

• Purkinje Fibers: These thin fibers are the terminal end of the conduction system of the heart and finish the distribution of the electrical stimuli to all parts of the ventricular walls

Although the structural components of the conduction system of the heart were known, it was Dr. Sunao Tawara (1873-1952) who discovered the AV node and described the connections between the components of what he called the "Reitzleitungssytem" (conduction system) of the heart.

Click on the image for a larger version. Image modified from the original: "3D Human Anatomy: Regional Edition DVD-ROM." Courtesy of Primal Pictures

Circumflex artery

The [circumflex artery]  (CFX) is one of the two branches of the left coronary artery, the other one being the left anterior descending artery (LAD), also known as the anterior interventricular artery.

The prefix [circum-] means "around", while the root term [-flex-] means "to bend". This describes quite well the circumflex artery, which "bends around" the obtuse margin of the heart passing from the anterior surface to the posterior surface of the heart.

The circumflex artery lies deep to the epicardium in the subepicardial fatty layer. It gives off several branches, including small left atrial branches and one or two obtuse marginal arteries (OM1 and OM2)that provide blood supply to the left ventricle in its obtuse margin and posterior ventricular region, as well as a portion of the anterior papillary muscle related to the mitral valve.

Coronary Arteries. The [*] indicates the left coronary artery
There can be interesting anatomical variations in the coronary arteries of the heart. For a detail on these anatomical variations, click here. Heart and coronary artery anatomy is one of the many lecture topics presented by CAA, Inc.

Image property of: CAA.Inc.Artist: Victoria G. Ratcliffe


The prefix [post-] has its origin as a Latin adverb meaning "after". There are two variations in the use of this Latin adverb. The first is in its use as "after" referring to the position of a structure. This use is limited and is the root for the term "posterior". The most common usage is for [post-] to be used in its true meaning of "after" referring to time.

Applications of this prefix include:

postoperative: after the operation
postmortem: from the Latin word [mortis] meaning "death". After death
postpartumfrom the Latin word [partum] meaning "birth". After birth
postprandial: [prandium] is a Latin word meaning "a midday meal". Used to denote "after a meal"
• posthumous: from the Latin word [humus] meaning "ground". Refers to activities performed after burial
• postbellum: after a war

When using pure Latin terms, the word can be used as shown in the listing above, or they can be used as separate entities, such as "post partum", "post mortem", "post bellum", etc. (no hyphens). This leads to interesting facts, such as the pharmacological abbreviation "p.c." which stands for "post cibum"; the meaning of [cibum] is similar to [prandium], so "p.c." means "after a meal"