Medical Terminology Daily - Est. 2012

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

Jean George Bachman

Jean George Bachmann
(1877 – 1959)

French physician–physiologist whose experimental work in the early twentieth century provided the first clear functional description of a preferential interatrial conduction pathway. This structure, eponymically named “Bachmann’s bundle”, plays a central role in normal atrial activation and in the pathophysiology of interatrial block and atrial arrhythmias.

As a young man, Bachmann served as a merchant sailor, crossing the Atlantic multiple times. He emigrated to the United States in 1902 and earned his medical degree at the top of his class from Jefferson Medical College in Philadelphia in 1907. He stayed at this Medical College as a demonstrator and physiologist. In 1910, he joined Emory University in Atlanta. Between 1917 -1918 he served as a medical officer in the US Army. He retired from Emory in 1947 and continued his private medical practice until his death in 1959.

On the personal side, Bachmann was a man of many talents: a polyglot, he was fluent in German, French, Spanish and English. He was a chef in his own right and occasionally worked as a chef in international hotels. In fact, he paid his tuition at Jefferson Medical College, working both as a chef and as a language tutor.

The intrinsic cardiac conduction system was a major focus of cardiovascular research in the late nineteenth and early twentieth centuries. The atrioventricular (AV) node was discovered and described by Sunao Tawara and Karl Albert Aschoff in 1906, and the sinoatrial node by Arthur Keith and Martin Flack in 1907.

While the connections that distribute the electrical impulse from the AV node to the ventricles were known through the works of Wilhelm His Jr, in 1893 and Jan Evangelista Purkinje in 1839, the mechanism by which electrical impulses spread between the atria remained uncertain.

In 1916 Bachmann published a paper titled “The Inter-Auricular Time Interval” in the American Journal of Physiology. Bachmann measured activation times between the right and left atria and demonstrated that interruption of a distinct anterior interatrial muscular band resulted in delayed left atrial activation. He concluded that this band constituted the principal route for rapid interatrial conduction.

Subsequent anatomical and electrophysiological studies confirmed the importance of the structure described by Bachmann, which came to bear his name. Bachmann’s bundle is now recognized as a key determinant of atrial activation patterns, and its dysfunction is associated with interatrial block, atrial fibrillation, and abnormal P-wave morphology. His work remains foundational in both basic cardiac anatomy and clinical electrophysiology.

Sources and references
1. Bachmann G. “The inter-auricular time interval”. Am J Physiol. 1916;41:309–320.
2. Hurst JW. “Profiles in Cardiology: Jean George Bachmann (1877–1959)”. Clin Cardiol. 1987;10:185–187.
3. Lemery R, Guiraudon G, Veinot JP. “Anatomic description of Bachmann’s bundle and its relation to the atrial septum”. Am J Cardiol. 2003;91:148–152.
4. "Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje" Icilio Cavero and Henry Holzgrefe Advances in Physiology Education 2022 46:4, 549-579.
5. Knol WG, de Vos CB, Crijns HJGM, et al. “The Bachmann bundle and interatrial conduction” Heart Rhythm. 2019;16:127–133.
6. “Iatrogenic biatrial flutter. The role of the Bachmann’s bundle” Constán E.; García F., Linde, A.. Complejo Hospitalario de Jaén, Jaén. Spain
7. Keith A, Flack M. The form and nature of the muscular connections between the primary divisions of the vertebrate heart. J Anat Physiol 41: 172–189, 1907.


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Mandibular Canal. Image provided by M. Fernanda Cortes, DDS, MsC.
Click for a larger image


The mandibular canal is a long, bilateral canal which runs along and within the mandible. This canal transports the inferior alveolar neurovascular bundle. The mandible is known vernacularly as the “jawbone” or “lower jaw”.

The mandibular canal starts on the medial surface of the mandibular ramus at the mandibular foramen (Figure A, arrow) descends anteroinferiorly through the body of the mandible until it ends in the mental foramen at the buccal (anterior) surface of the mandible, usually in the area between the premolars (Figure B, arrow).

Before exiting, the canal forms an “anterior loop” projected anterior to the mental foramen prior to changing its direction back and outwards in direction to the buccal plate (Figure C, red line). This last portion of the canal is called the “mental canal”.

A frequent anatomical variation is the presence of a bifid mandibular canal (recent studies indicate it has a prevalence of around 16%).

Different anatomical studies show that the mandibular canal not only finishes at the mental foramen, but it could divide itself giving an incisive canal which runs anteriorly onto the incisal region (Figure C, yellow line). When it doesn’t continue as an incisal canal, the neurovascular elements go anteriorly through the cells of the spongy bone tissue.

The presence of this Incisal canal has surgical relevance, and knowledge of its exact location and anatomical parameters has a high importance on reducing complications of surgical procedures in the mental area such as dental implants, bone lesions removal and bone harvesting among others, all which could damage the incisal canal and the neurovascular bundle inside it.

With the latest use of CBCT (Cone Beam Computed Tomography) technology to evaluate anatomical structures, the presence of this canal has showed to be high (92-100%) and its length can vary from reaching only the premolar area or even the central mandibular incisors in the least of cases.

Sources:
1. Haas LF, Dutra K, Porporatti AL, Mezzomo LA, De Luca Canto G, Flores-Mir C, Corrêa M. Anatomical variations of mandibular canal detected by panoramic radiography and CT: a systematic review and meta-analysis. Dentomaxillofac Radiol. 2016;45(2):20150310.
2. Kong N, Hui M, Miao F, Yuan H, Du Y, Chen N. Mandibular incisive canal in Han Chinese using cone beam computed tomography. Surg Radiol Anat. 2016 Nov 11. [Epub ahead of print] Int J Oral Maxillofac Surg. 2016 Sep;45(9):1142-6.
3. Rouvierre H, Delmas A. Anatomía humana: Descriptiva, topográfica y funcional. Cabeza y cuello. Volumen 1. 11° ed. España: Masson, S.A.;2005. P. 114.
4. Von Arx T, Lozanoff S. Clinical Oral Anatomy: A Comprehensive Review for Dental Practitioners and researchers. Switzerland: Springer; 2016. P 323- 390
 
Article and image provided by Prof. M. Fernanda Cortes, DDS, MsC.