Related Experiment Video
Updated: Apr 13, 2026

Rodent Model of Masseter Volumetric Muscle Loss for Studying Bioengineering Materials
Published on: May 31, 2024
Morphometric aspects of the facial and skeletal muscles in fetuses
Hiroshi Moriyama1, Kaori Amano2, Masahiro Itoh3
1Department of Anatomy, Showa University School of Medicine, 5-8, Hatanodai 1, Shinagawa-ku, Tokyo 142-8555, Japan.
Objectives:
There are few research reports providing a comparison of the muscle fiber morphometry between human fetuses and adults. Data on fetal and adult muscle fibers would be valuable in understanding muscle development and a variety of muscle diseases. This study investigated human muscle fiber growth to clarify the difference between the facial muscles and other skeletal muscles.
Methods:
The materials were obtained from three male fetuses (6-month-old) and 11 Japanese male cadavers aged 43-86 years (average: 71.8). Human buccinator muscles (facial muscles), masseter and biceps brachii muscles (skeletal muscles) were resected. We counted the muscle fibers and measured their transverse area. We also calculated the number of muscle fibers per mm(2) (NMF) and the average transverse area of the muscle fibers (TAMFs).
Results:
The average of the NMF of the buccinator, masseter and biceps brachii muscles in fetuses had, respectively, 19, 37, and 22 times as many fibers as those in adults. The average fetus/adult ratios of the TAMF of the buccinator, masseter and biceps brachii muscles were 4.0%, 2.4%, 4.1%, respectively.
Conclusions:
The average NMF for all kinds of muscles decreased after birth; however, the peak in life-span or decreases with the aging process tended to vary with the kind of muscles examined. The average TAMF for all kinds of muscles enlarged after birth. We considered that the enlargement of the TAMF was connected with the emergence of fetal movements and functional demands after birth.
Related Concept Videos
Muscles for Facial Expressions
Microscopic Anatomy of Skeletal Muscles
The muscle sarcolemma is a plasma membrane enclosing each muscle cell that conducts electrical signals called action potentials. The sarcolemma extends into the cell to form T-tubules, ensuring the neural impulses are uniformly distributed across the entire muscle...
Introduction to the Skeletal System
Components of the Skeletal System
Bone, or osseous tissue, is a hard connective tissue that forms an internal support structure for the human body. Bones shield vulnerable organs and soft tissue from external forces. For example, the vertebral bones protect and support the spinal cord.
Cartilage, a semi-rigid connective tissue found in regions such as...
Gross Anatomy of Skeletal Muscles
Bone Formation by Intramembranous Ossification
The process begins when mesenchymal cells in the embryonic skeleton gather together and differentiate into osteogenic cells, which then develop into ...
Naming Skeletal Muscles
The key factors used in naming muscles include:

