Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community. We post anatomical, medical or surgical terms, their 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


William J. Larsen, PhD

An American scientist, Dr. Larsen was a gifted scientist, consistently producing research at the forefront of cell, developmental, and reproductive biology. Early in his career he published a landmark paper that conclusively established mitochondrial fission as the mechanism of mitochondrial biogenesis. He went on to become the first to demonstrate the endocytosis of gap junctions. Moreover, his work on the hormonal regulation of gap junction formation and growth culminated in an authoritative review article in Tissue and Cell, “Structural Diversity of Gap Junctions (1988)”, which became a citation classic.

Throughout his 25 year teaching career, his sixty-seven peer reviewed publications—not to mention numerous invited reviews, abstracts, and book chapters—covered a wide range of research areas including adrenal cortical tumor cells, human ovarian carcinomas, preterm labor, cumulus expansion, oocyte maturation, ovulation, folliculogenesis, and in-vitro fertilization.

In addition to his many contributions to basic research, Dr. Larsen loved to teach and was much appreciated by his students. His exceptional ability was reflected in the four teaching awards he received as a professor at the University of Cincinnati.

Notably, he was the author of Human Embryology, a textbook for medical students that was the first to incorporate modern experimental research into a subject that had traditionally been taught in a strictly descriptive style. On its initial publication in 1998 it was hailed as, “a magnificent book…” by the European Medical Journal. With the release of the fourth edition in 2008, the book was renamed “Larsen’s Human Embryology” in recognition of Dr. Larsen's place as the originator of this revolutionary text. This book is today in it's 6th Edition.

His stellar scientific career would be enough for most people, but Dr. Larsen pursued his numerous and varied interests with such extraordinary passion, energy, and skill that he seemed to have more hours in a day than the ordinary person. He was fascinated with the American Southwest and studied and collected traditional arts and crafts of the Hopi, Zuni, and Navajo peoples. He was a woodworker who built three harpsichords and a fortepiano for his wife, and, with his two children, over 100 pieces of gallery-quality furniture. In addition, he loved to regale his friends, colleagues, and students with jokes and stories, and to share his love for gourmet cooking.

The William J. Larsen Distinguished Lecture Series

An annual lecture series was created for the Department of Cancer & Cell Biology at the University of Cincinnati to honor Dr. Larsen's research which was at the forefront of cell developmental and reproductive biology. This series recognizes forward-thinking research scientists in the field of developmental biology and asks that they share their research and findings with students and faculty of the University of Cincinnati, College of Medicine.

Personal note: I had the opportunity to meet and attend Dr. Larsen’s embryology lectures as he and I worked in the Anatomy, Embryology, and Histology program at the University of Cincinnati Medical College. Unfortunately, I never had the opportunity to have Dr. Larsen sign my personal copy of his book. He is sorely missed, Dr. Miranda


1. "The William J. Larsen Distinguished Lecture Series" University of Cincinnati, College of Medicine.
3. 2022 Larsen Lecture Series brochure (download here)
4. Dr. Larsen's family personal communications

 "Clinical Anatomy Associates, Inc., and the contributors of "Medical Terminology Daily" wish to thank all individuals who donate their bodies and tissues for the advancement of education and research”.

Click here for more information

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Vesalius' Annotated Fabrica

Image of the Annotated Fabrica 
Annotated Fabrica

UPDATED: Everybody has the hope of someday finding a treasure, and we look for it in garage sales, antique shops, anywhere and everywhere. As a book collector, I live for the day when I find a precious book that has been overlooked and that I can add to my collection. This is the story of such a find by a book collector.

No one knows exactly how many copies were printed of Andrea Vesalius' magnificent book “De Humani Corporis Fabrica, Libri Septem”. It is estimated that each run of the first (1543) and second (1555) editions were between 600 -1000 copies, maybe less.  The censuses on the surviving copies of this book published by S. Joffe, MD and V. Buchanan in 2015 tell us that less than 60 copies of each of these books exist in the USA, and the total worldwide number is unknown.

Most of the books available today are in rare book repositories at university libraries, and only a few are available to private book collectors.

The price for a good copy today is close to half a million US dollars (or more). Although some copies can be found for less, they are probably not original and could be one of the many plagiarized copies of this wonderful book.

In 2007, Vancouver pathologist and book collector Dr. Gerard Vogrincic bought a Fabrica at auction in Germany. This was not the best copy of the Fabrica. The index (an important part of the book, as it was the first anatomy book to ever have one) was missing, but most important, the book text was heavily underlined; some paragraphs were crossed out with ink, and over one thousand annotations were found on the sided of the pages, as well as in the images, a critical part of this book and the reason for its fame. As a result, the price at the auction was not too high.

A careful revision of the handwritten notes led Dr. Vogrincic to believe that the notes may have been written by Vesalius himself, but he had no idea of how to confirm it and he could not read Latin, the language of the annotations. There are only a few examples of Vesalius’ handwriting, as Vesalius burned many of his notes and letters, and only some survived. Dr. Vogrincic obtained a facsimile of one of Vesalius’ letters and was surprised that indeed the writings matched!

Dr. Vogrincic contacted Dr. Vivian Nutton, Emeritus Professor at the UCL Center for the History of Medicine in London. Dr. Nutton, a Latin scholar and Vesalius expert confirmed that this was a book that not only belonged to Vesalius, but that the handwriting, the style of the Latin was by Vesalius. The book includes corrections to the style, grammar, anatomy, images, and also instructions for a third edition that was never published.

The book now rests at the Thomas Fisher Rare Book Library in University of Toronto, Canada on a permanent loan, part of a 2015 exhibit, and was an important addition to the translation and annotations for the “New Fabrica” authored by Drs. M. Hast and D. Garrison. The New Fabrica is now out of print.

Following is a YouTube video by Philip Oldfield, curator of the Thomas Fisher Rare Book Library in University of Toronto, Canada, talking about this book

1. “The annotated Vesalius” Duffin, J; Duffin, J. CMAJ (2014) 186:11, 856-857
2. “A Clever Collector Makes an Astonishing Discovery” Vogrincic, Click here for the article
3. “Vesalius Revised. His Annotations to the 1555 Fabrica” Nutton, V. Med. Hist. (2012), 56(4), 415–443 Click here for the article
4. “Updated Census in USA of First Edition of Andreas Vesalius’ ‘De Humani Corporis Fabrica’ of 1543” Joffe, SN; Buchanan V. International Archives of Medicine; 2015: 8:1
5. “An Updated Census of the Edition of 1555 of Andreas Vesalius’ De Humani Corporis Fabrica in the United States of America” International Archives of Medicine; 2015: 8:1
6. “Vesalius’ notes for unpublished edition of De fabrica” Click here for the website 
7. "A Spectacular New Arrival" Oldfield, P; The Halcyon, Issue 49, June 2012 Click here for the article


vine tendril
Vine tendril. Image courtesy of Jon Sullivan


The term [pampiniform] comes from the Latin term [pampinus] meaning "a vine tendril". It refers to a twisted, curved structure as seen in the accompanying image.  The second portion of the word also comes from Latin, [forma] means "shape" or "in the shape of".

Pampiniform then means "in or with the shape of a vine tendril"

Although mostly associated with the pampiniform plexuses found in both the testicular veins in the spermatic cord and the ovarian veins found within the infundibulopelvic ligament, the term is also used to denote the coiled aspect of the organ of Rosenmuller, also known as the pampiniform body or paraovarium.

The pampiniform body is a non-functional embryological remnant of the development of the female reproductive system. It is composed of a blind longitudinal duct and 10-15 transverse smaller ducts. It is located in the mesosalpinx, an extension of the broad ligament related to the uterine tube (Fallopian tube).

Thanks to David Van Tol for suggesting this article!

Image courtesy of Jon Sullivan, Public domain, via Wikimedia Commons


Brachial plexus (
Brachial plexus

UPDATED: The term [plexus] comes from the Latin term [plectere] meaning " to twine, or to braid". In anatomy, the term [plexus] refers to a group of structures that are intertwined or form a meshwork.  The plural form is [plexuses], although the Latin plural form [plexi] is also correct. Gabrielle Fallopius used the term to denote "a tangle of nerves"

There are many plexuses described in the human body. Most are formed by nerves, but there are many that are lymphatic or vascular. The best known are the plexuses of nerves formed by the ventral rami of the spinal nerves. These are the cervical plexus, the brachial plexus, the lumbar plexus, and the sacral plexus. The image depicts the brachial plexus. For a larger version, click on the image, and for further information on the cervical and brachial plexuses, click here

Images and links courtesy


Left Atrial Appendage

Left atrial appendage. Image modified from Gosling 1996
Left atrial appendage

The left atrial appendage (LAA) is an embryological remnant of the development of the heart. It represents the primitive left atrium (LA) which is then “pushed to the side” by the development of the final (adult) stage of the LA. While the LAA is thin, tubular, tortuous, and presents with convoluted muscular walls, the adult LA has smooth walls and is considered to be a dilation of the terminal portion of the veins that enter the LA, hence the name “sinus venarum”, another term for the atria. The LAA is also known as the "left atrial appendix", or the "left auricle".

The anatomy of the LAA is presented in the video included at the end of the article, but there are some details that are important to discuss in the involvement of the LAA in the creation of thrombi and emboli in the presence of atrial fibrillation (AFib).

LAA shape and size

The LAA has important anatomical variations, with different shapes that anatomists and physicians have tried to consolidate in groups such as: chicken wing, cactus, windsock, cauliflower, etc. The fact is that recording the shape of the LAA is subjective. as the evaluation depends completely on the observer.

Researchers have tried to determine what shape can lead to a higher potential for stroke-producing emboli when AFib is present. A recent study by Dudzińska-Szczerba (2021) and an editorial by Yong Shin (2021) states that the shape itself is not a good predictor, but the distance between the LAA ostium and the first bend of the LAA is indeed a good predictor. The longer the distance there is increased potential for thrombus and emboli formation.

The size of the LAA has been studied in detail and it ranges ranging from 0.3 cm to 2.0 cm in males, and 0.3 to 1.8 cm in females. (Venoit, 1997), as shown in this table.

LAA Venoit 97

The LAA ostium

The LAA ostium is the communication between the LA and the LAA, it is generally oval in shape and its size is variable. The ostium is in some cases slit-like, or an elliptical-shaped variant, “smiley”, and even small circular (DeSimone, 2015; Cabrera, 2014). A study by Wang (2010) classified the LAA ostium into five types: oval (68.9%), foot-like (10%), triangular (7.7%), water drop-like (7.7%), and round (5.7%). It is interesting that devices that are used to occlude the LAA ostium are round and that is only 6% of the population reported in the Wang (2010) study. In a study by Su (2006) it was found that 100% of the specimens studied the LAA ostium had an oval shape with the mean diameter of the opening of 17.4 mm with a range between 10-24.1 mm).

In reference to LAA ostium occluders Su (2006) states that "These percutaneous devices / systems,however, have a round shape to fill or cover the LAA ostium. A previous study and our study show that the shape of the LAA ostium is consistently elliptical rather than round. This suggests that to seal the LAA orifice adequately without oversizing, devices may need to be elliptical for a snug fit. A round implant over an oval-shaped orifice may leave crevices on either side of the implant, leading to incomplete sealing of the orifice."


The LAA can also present with different dilations called “lobes” these can range from zero to three or four.

Muscular Wall Structure

Cow heart left atrial appendage trabeculations
Cow LAA internal structure

The LAA has internal ridges that form a muscular meshwork. The term used to describe these is “trabeculated”. It makes sense that in the case of atrial fibrillation, the slow to non-existent flow of blood within the deep recesses of the trabeculated muscular wall of the LAA will cause blood to pool and coagulate, forming thrombi. The presence of these LAA trabeculations have been found to be associated with stroke risk by Dudzińska-Szczerba (2021). The accompanying image shows the trabeculations in a cow's LAA. They are not as deep or as convoluted as those found in a human heart.


This is a rarely used term. It is a pattern along the top of a fortified wall, as in a castle, forming multiple, regular, rectangular spaces. These crenellations are found in the edge of the LAA compounding the irregularity of the wall and increasing the chance for thrombus formation and stroke-inducing thrombi. Crenellations are shown by yellow triangles in the first image in this article.

Function of the LAA

As stated, the LAA is an embryological remnant, but it does have a function in the adult. It generates a peptide involved in the control of salt in the circulatory system. This is the atrial natriuretic peptide (ANP), a hormone that is secreted by both  the right and left atria and their appendages in response to circulatory volume and pressure changes. ANP helps the elimination of excess sodium through the kidneys (natriuresis), control of urine elimination (diuresis), and antifibrotic and antihypertrophic effects within the heart (Sandeur, 2023)

While removing both the right and left atrial appendages could cause ANP deficiency, surgical removal or exclusion of only the LAA does not cause an ANP problem (8).

Involvement of the LAA in AFib

The LAA is an electrically active structure. The cardiomyocytes that form its walls have automatic activity and it has been described as an area that can trigger AFib. The accompanying video shows an LAA that has been separated from the heart (in this case using a surgical stapler) and it can be seen how the LAA continues fibrillating on its own. Video courtesy of Dr. Randall K. Wolf

This is the why LAA exclusion is a must in the case of AFib and potentially in any cardiovascular procedure where the pericardial sac is opened (this is a subject for discussion). The problem is that devices that only occlude the LAA ostium do not disconnect the LAA wall from the LA wall, leaving this potential AFib-producing connection intact.

A future article on abnormally large LAA and LAA aneurysms is forthcoming.


1. “Anatomy of the Normal Left Atrial Appendage: A Quantitative Study of Age-Related Changes in 500 Autopsy Hearts: Implications for Echocardiographic Examination” Veinot, JP; et al. 1997 Circulation; 96:3112–3115
2. “A Review of the Relevant Embryology, Pathohistology, and Anatomy of the Left Atrial Appendage for the Invasive Cardiac Electrophysiologist” De Simone, CV, et al. J AFib 2015; 8:2 81-87
3. “Left atrial appendage: anatomy and imaging landmarks pertinent to percutaneous transcatheter occlusion” Cabrera,JA; Saremi, F; Sanchez-Quintana, D. 2014 Heart 2014 100:1636-1650
4. Left Atrial Appendage Studied by Computed Tomography to Help Planning for Appendage Closure Device Placement” Wang Y. et al. J Cardiovasc Electrophyisiol 2010 21:9 973-982
5. Is the Left Atrial Appendage (LAA) anatomical shape really meaninglessmeasure for stroke risk assessment?
6. “Assessment of the left atrial appendage morphology in patients after ischemic stroke” Dudzińska-Szczerba, K. et al. Int J Cardiol 2021 330:65-72
7. “Atrial Natriuretic Peptide” Sandeur, CC; Jialal, I. Stat Pearls 2023. StatPearls
8. Personal communication, Dr. R. Wolf 2023
9. "Slide Atlas of Human Anatomy" Gosling, J.A.; Whitmore, I; Harris, P.F.; Humpherson, J.R., Et al; ISBN: 0723426570 Hong Kong: Times Mirror, 1996
10. "Atrial and brain natriuretic peptides: Hormones secreted from the heart" Nakagawa Y, Nishikimi T, Kuwahara K.  Peptides. 2019 Jan;111:18-25.
11. "Occluding the left atrial appendage: anatomical considerations" Su, P; McCarthy, KP; Ho, SY. 2008 Heart 94:1166–1170

Personal note: In November 7, 2023 Dr. Randall K. Wolf invited me to a seminar where we reviewed the anatomy of the left atrial appendage, the problems it can cause in atrial fibrillation leading to stroke, and the reasons for its exclusion in AFib surgery. Dr. Miranda.


Normal electrocardiogram - sinus rhythm
Sinus rhythm electrocardiogram

A contraction, from the Greek [διαστολη] (systolí) meaning “expansion, dilation, drawing out, or prolongation”, also [διαστέλλειν] (diastéllein) meaning “to open, expansion”. When used in music, it means "a pause".

It refers to the dilation of the heart. If you analyze a normal heartbeat (sinus rhythm), there are two diastoles: an atrial diastole and a ventricular diastole. The term diastoleis usually used in reference to the ventricular diastole.

Diastole was first recognized and named by Herophilus of Alexandria (325-255BC), most probably trough animal vivisection. Herophilus was accused of animal vivisection and the dissection of human cadavers. Because of this, some call Herophilus "The Father of Anatomy".

Galen of Pergamon (129AD - 200AD) used the term [διαστέλλεσθαι] (diastéllesthai), also meaning “expansion”.

The word in English was first used in the 16th century. The modern pronunciation in English follows the Greek pronunciation by ending the word in a long “e” as in “to be”.

1. "The Origin of Medical Terms" Skinner, HA 1970 Hafner Publishing Co.
2. "Medical Meanings - A Glossary of Word Origins" Haubrich, WD. ACP Philadelphia
3. "Dorlands's Illustrated Medical Dictionary" 26th Ed. W.B. Saunders 1994
4. "Greek anatomist Herophilus: the father of anatomy" Si-Yang, N. Anat Cell Biol. 2010; 43(4): 280–283

Note: Google Translate includes the symbol (🔈). Clicking on it will allow you to hear the pronunciation of the word.

Conduction system of the heart

Cardiomyocyte-based conduction system of the heart
Conduction system of the heart

[UPDATED] The conduction system of the heart a binary system that includes a cardiomyocyte-based component which acts as an automatic base, and an autonomic nervous system component which acts as a modulator.

The classic description of the conduction system of the heart emphasizes only the cardiomyocyte-based component and refers to 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 this primary "conduction system of the heart" is not formed by nerves but rather by specialized cardiac muscle cells.

Components of the cardiomyocyte-based conduction system of the heart:

• SA node: The sinoatrial (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. Later research indicates that the pacemaker function of the SA node includes areas of the lateral wall of the right atrium which are involved in different heart rate speeds.

• 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.

A separate article on the secondary conduction system of the heart will be published shortly

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