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Related Concept Videos

Muscles of the Thorax01:25

Muscles of the Thorax

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The thorax muscles are central to the body's respiration and provide essential support and movement for the upper body. They are intricately designed to facilitate the complex breathing process while also contributing to the structural integrity and mobility of the chest and upper limbs.
The diaphragm is at the core of thoracic musculature, the primary muscle involved in breathing. This expansive, dome-shaped muscle marks the division between the thoracic and abdominal cavities. It...
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Mechanism of Breathing III: The Accessory Muscles01:21

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The Role of Accessory Muscles in the Respiratory System
The respiratory system is a complex network that relies on primary respiratory muscles like the diaphragm, but also involves accessory muscles to enhance lung expansion and airflow during both inhalation and exhalation.
Enhancing Inhalation with Accessory Muscles:
Accessory muscles such as the sternocleidomastoid, scalene, intercostal, and abdominal muscles are crucial when additional respiratory effort is required, such as during deep...
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Axial and Appendicular Muscles01:18

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Skeletal muscles, the key players in our body's movement, can be classified into two groups based on their location and function: axial muscles and appendicular muscles. These classifications reflect the primary roles the muscles play in the body's structure and movement.
Axial Muscles
Axial muscles, situated along the body's midline, are intricately connected to the axial skeleton, which includes the skull, spine, ribs, and sternum. These muscles facilitate facial expressions and...
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Muscles of the Anterior Neck01:26

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The anterior neck muscles are the group of muscles covering the front part of the neck. These muscles are classified into three subgroups. The first one is the superficial muscles, the most visible muscles in the front of the neck. It includes the platysma and sternocleidomastoid. The second group is the suprahyoid muscles, located above the hyoid bone. This group comprises the digastric, mylohyoid, geniohyoid, and stylohyoid. Lastly, the infrahyoid muscles are found below the hyoid bone and...
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Muscles of the Shoulder01:23

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The muscles surrounding the shoulder girdle, including the clavicle and scapula, primarily stabilize the scapula. This stable base allows other muscles to move the humerus effectively. Scapular movements often mirror those of the humerus and extend its range of motion. For instance, raising the arm above the head would not be feasible without simultaneous upward rotation of the scapula.
Anterior Thoracic Muscles
The anterior thoracic muscles include the serratus anterior, subclavius, and...
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Muscles that Move the Head01:19

Muscles that Move the Head

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The muscles that move the head are a dynamic and complex group of structures that work together to facilitate a wide range of head movements, including rotation, flexion, extension, and lateral bending.
The bilateral sternocleidomastoid, or SCM, and the suprahyoid and infrahyoid muscles are significant head flexors. The SCM muscles originate at the sternum and clavicle and attach to the mastoid process of the temporal bone. The SCM contracts bilaterally to bend the head forward, whereas...
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Updated: Jun 22, 2025

Continuous Telemetric In Utero Tracheal Pressure Measurements in Fetal Lambs
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Published on: December 22, 2023

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Accessory thoracic muscles in human foetuses.

Nicol Zielinska1, Marta Pośnik2, Krzysztof Koptas2

  • 1Department of Clinical Anatomy, Masovian Academy in Plock, Płock, Poland.

Folia Morphologica
|July 4, 2024
PubMed
Summary

Accessory pectoral muscles, like the pectoralis quartus, occur in 16% of human fetuses. Understanding these anatomical variations is crucial for surgeons.

Keywords:
axillary arch musclechondrocoracoideus musclehuman foetusespectoral regionpectoralis major musclepectoralis minor musclepectoralis quartus musclesternalis muscle

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Area of Science:

  • Anatomy
  • Embryology
  • Morphology

Background:

  • Anterior thoracic wall musculature typically includes pectoralis major and minor muscles.
  • Embryological development from a common pectoral mass can lead to accessory muscles.
  • Aberrant muscle development may result in variations of pectoral muscles.

Purpose of the Study:

  • To identify and classify accessory muscles in the pectoral region of human fetuses.
  • To document the morphology, origins, insertions, and morphometric details of these accessory muscles.

Main Methods:

  • Examination of 50 human fetuses (25 male, 25 female) aged 18-38 weeks.
  • Specimens fixed in 10% formalin solution.
  • Assessment of pectoralis major and minor morphology, and identification of accessory pectoral muscles.

Main Results:

  • Pectoralis major and minor muscles were present bilaterally in all fetuses.
  • Accessory pectoral muscles were identified in 16% of cases (16 out of 100 sides).
  • Four types of accessory muscles were differentiated: pectoralis quartus (8 cases), axillary arch (3 cases), chondrocoracoideus (3 cases), and sternalis (2 cases).

Conclusions:

  • The thoracic region exhibits numerous morphological variations, present in both fetuses and adults.
  • The pectoralis quartus was the most frequent accessory muscle variation observed.
  • Knowledge of accessory pectoral muscles (sternalis, chondrocoracoideus, pectoralis quartus, axillary arch) is clinically significant for surgeons.