BIO 342
Comparative Vertebrate Anatomy
Lecture Notes 6 - Muscular System

Vertebrate muscles:

Skeletal muscle (left) & Smooth muscle (right)

Skeletal muscle = muscles attached to the skeleton that are striated & voluntary

Non-skeletal muscle = muscles not attached to the skeleton; most are smooth & involuntary

Vertebrate Muscles:

Skeletal muscles have muscular & tendinous portions:

Used with permission of John W. Kimball

Names of skeletal muscles are based on:



Axial Muscles:


Axial musculature of an aquatic salamander, Necturus maculosus. The layers of lateral hypaxial musculature are exposed from superficial to deep in the cranial to caudal direction. The number of external oblique layers varies between one and two in this species (the figured specimen exhibits two). Abbreviations: oes, M. obliquus externus superficialis; oep, M. obliquus externus profundus; oi, M. obliquus internus; ta, M. transversus abdominis (Brainerd and Simons 2000).

Trunk & tail muscles of fish:

Trunk & tail muscles of tetrapods

Epaxials of tetrapods:

Hypaxials of tetrapods:

Oblique & transverse muscles:

1 - External intercostal muscles, 2 - Internal intercostal muscles, 3 - Ribs, 4 - Intercartilaginous muscles,
5 - Sternum, 6 - Subcostal muscles, & 7 - Vertebral column

Rectus muscles:

Subvertebral muscles:



 Diagram showing the onset and duration of lateral hypaxial muscle EMG activity relative to maximum body bending in two Ambystoma tigrinum during swimming. Values are means ± S.D. for alpha-burst (filled bars) and beta-burst (open bars) onset and duration times. OES, m. obliquus externus superficialis; OEP, m. obliquus externus profundus; OI, m. obliquus internus; TA, m. transversus abdominis. *Denotes the side of the body on which the electrodes were implanted (Bennett et al. 2001).


Hypobranchial & tongue muscles:

The neck muscles ending in "hyoid" are associated with the hyoid apparatus, whereas those
beginning or ending with "thyro" are attached to the larynx. These muscles are hypobranchia
and function in movement of the hyoid apparatus, larynx and/or floor of the mouth.

Appendicular muscles - move fins or limbs

Extrinsic appendicular musculature

The 'muscular sling' of tetrapods. Appendicular muscles of the forelimbs suspend the anterior body of tetrapods from the shoulders. Some of these muscles are axial muscles (rhomboideus & serratus ventralis), some are branchial muscles (trapezius), & some arise from the forelimb musculature itself (pectoralis).

The pelvic girdle requires no such muscular anchoring because it is attached directly to the vertebral column. As a result, the volume of extrinsic muscle is relatively small in posterior limbs.

Extrinsic appendicular muscles:

Intrinsic appendicular muscles:

Appendicular muscles:

Branchiomeric muscles:

Integumentary muscles:

Electric organs:

Several species of fish have evolved an electric organ in their tail that produces a continous electric signal
that propogates through the water. These fish have specialized receptors on their skin surface that can "feel" electricity.
Objects in their environment, such as rocks, plants and pirhanas disturb the flow of their electric signal through the water.
This disturbance will affect how strong the electric field is on a patch of skin near the object. In other words, a non-conductive
object such as a rock will cast an electric "shadow" on the skin. The skin receptors near the object sense these disturbances
and then increase or decrease their signal rate (depending wether the local electric field increased or decreased in intensity). These
signals are then sent up to specialized regions of the brain that collate all the information and compute a coherent "picture" of the
fish's environment (see

Functions of electric organs:

Related links:

Muscles and Electric Organs

Musculature of Chordate Taxa

Literature cited:

Bennett, W. O., R. S. Simons, and E. L. Brainerd. 2001. Twisting and Bending: The Functional Role of Salamander Lateral Hypaxial Musculature During Locomotion. Journal of Experimental Biology 204:1979-1989.

Brainerd, E. L. and R. S. Simons. 2000. Morphology and Function of Lateral Hypaxial Musculature in Salamanders. American Zoologist 2000 40: 77-86

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