The External, Musculoskeletal and Neuro-Anatomy of Sea Turtles
57
2.4 MUSCULAR ANATOMY
The muscles are responsible for movement, modifying the action of other muscles, and
stabilizing the joints. They originate and insert via tendons. A muscle’s origin is its
fixed point, and its insertion is typically the point that moves. Muscles can attach via
tendons to bones, other muscles, other tendons, skin, or eyes. Muscle actions, as they
apply to marine turtles, include: flexion, bending one part relative to another at a joint;
extension, straightening of those parts; protraction, moving one part (usually a limb)
outward and forward; retraction, moving that part inward and back; abduction, moving
a part away from the plastron; and adduction, bringing the part toward the body’s ventral
surface. Rotation turns a structure about its axis. Depression (a special form of abduction) opens the jaws, whereas elevation closes the jaws (a kind of adduction).
Muscles are frequently grouped by their embryonic origin and position (e.g.,
hypaxial, epaxial, preaxial, or postaxial), extent (intrinsic or extrinsic), major
innervations (e.g., trigeminal, cervical plexus, or sacral plexus), actions (e.g.,
extensors, abductors), and/or position in the body (e.g., axial, appendicular, pectoral, or pelvic). Here, muscles are discussed in groups by position because those
in close proximity often act together and are often dissected and viewed by
location. Pectoral and pelvic muscles are associated with the plastron as well as
the limb girdles. Forelimb muscles are those of the flippers, pectoral girdles, and
FIGURE 2.16 The cut end of a leatherback bone shows the vascular channels embedded
within the white cartilage. (Adapted from Wyneken, J. The Anatomy of Sea Turtles, U.S.
Department of Commerce, NOAA Technical Memorandum NMFS-SEFSC-470, 2001. With
permission.)
1123_C02.fm Page 57 Friday, November 15, 2002 11:16 AM
57
2.4 MUSCULAR ANATOMY
The muscles are responsible for movement, modifying the action of other muscles, and
stabilizing the joints. They originate and insert via tendons. A muscle’s origin is its
fixed point, and its insertion is typically the point that moves. Muscles can attach via
tendons to bones, other muscles, other tendons, skin, or eyes. Muscle actions, as they
apply to marine turtles, include: flexion, bending one part relative to another at a joint;
extension, straightening of those parts; protraction, moving one part (usually a limb)
outward and forward; retraction, moving that part inward and back; abduction, moving
a part away from the plastron; and adduction, bringing the part toward the body’s ventral
surface. Rotation turns a structure about its axis. Depression (a special form of abduction) opens the jaws, whereas elevation closes the jaws (a kind of adduction).
Muscles are frequently grouped by their embryonic origin and position (e.g.,
hypaxial, epaxial, preaxial, or postaxial), extent (intrinsic or extrinsic), major
innervations (e.g., trigeminal, cervical plexus, or sacral plexus), actions (e.g.,
extensors, abductors), and/or position in the body (e.g., axial, appendicular, pectoral, or pelvic). Here, muscles are discussed in groups by position because those
in close proximity often act together and are often dissected and viewed by
location. Pectoral and pelvic muscles are associated with the plastron as well as
the limb girdles. Forelimb muscles are those of the flippers, pectoral girdles, and
FIGURE 2.16 The cut end of a leatherback bone shows the vascular channels embedded
within the white cartilage. (Adapted from Wyneken, J. The Anatomy of Sea Turtles, U.S.
Department of Commerce, NOAA Technical Memorandum NMFS-SEFSC-470, 2001. With
permission.)
1123_C02.fm Page 57 Friday, November 15, 2002 11:16 AM