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Morphological variability of the pectoralis major muscle in human fetuses
Nicol Zielinska1, Kacper Ruzik1, Michał Podgórski2
1Department of Anatomical Dissection and Donation, Medical University of Lodz, Poland; Department of Radiology, Diagnostic Imaging and Interventional Radiology, Medical University of Lodz, Poland.
Insights
Pectoralis major muscle anatomy shows significant variability in human fetuses, with most displaying two bellies (clavicular and sternal heads). This study classifies five morphological types based on the number of muscle bellies observed during dissection.
Area of Science:
- Anatomy
- Embryology
- Morphology
Background:
- The pectoralis major muscle is a key anterior chest muscle.
- Typically consists of clavicular, sternal, and abdominal heads.
- Variability in its structure is common.
Purpose of the Study:
- To document and categorize the morphological variations of the pectoralis major muscle.
- To analyze the number and arrangement of muscle heads in human fetuses.
- To classify observed anatomical differences.
Main Methods:
- Anatomical dissection of 35 human fetuses (18-38 weeks gestation).
- Examination of 70 sides (17 female, 18 male).
- Assessment of pectoralis major morphology, accessory heads, absent heads, and morphometric measurements.
Main Results:
- Five distinct morphological types of the pectoralis major muscle were identified.
- Type II (two bellies: clavicular and sternal) was most common (37.1%).
- Variations included single belly (Type I), three bellies (Type III), four bellies (Type IV), and five bellies (Type V).
Conclusions:
- Embryological development leads to significant pectoralis major muscle variability.
- The two-belly configuration (clavicular and sternal heads) is the most prevalent.
- Findings align with previous studies on pectoralis major muscle anatomy.
Background:
The pectoralis major muscle is located in the anterior chest wall. In most cases, it is divided into clavicular, sternal (sternocostal) and abdominal heads. The aim of this study is to demonstrate and classify the morphological variability of the pectoralis major muscles in human fetuses.
Material And Methods:
Classical anatomical dissection was performed on 35 human fetuses aged 18-38 weeks of gestation at death were examined. (17 female, and 18 male, 70 sides; fixed in 10% formalin solution). The fetuses were obtained from spontaneous abortion after informed consent of both parents and through deliberate donation to the Medical University anatomy program. Upon dissection, the following morphological features were assessed: the morphology of the pectoralis major, the possible occurrence of accessory heads, the possible absence of some head, and morphometric measurements of each head of the pectoralis major muscle.
Results:
Five types of morphology (based on number of bellies) were observed in the fetuses. Type I was characterized by a single claviculosternal belly (10% of all samples). Type II comprised the clavicular and sternal heads (37.1%). Type III comprised three clavicular, sternal and abdominal heads (31.4%). Type IV (17.2%) was characterized by four muscle bellies and was divided into four subtypes. Type V (4.3%), was represented by five parts, and was divided into two subtypes.
Conclusions:
Due to its embryological development, the PM demonstrates great variability in the numbers of its parts. The most common type was the PM with two bellies, in line with previous studies which also distinguished only clavicular and sternal heads.
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