Appendicularmuscle

Appendicular Muscles

1. These muscles all insert on girdles, limbs, or fins. Remember that fish use axial myomeres for locomotion; fin muscles are rather simple (levators and depressors). Appendicular muscles of tetrapods are much more complex as a consequence of terrestrial life.

2. In fish, dorsal and ventral components of embryonic muscle buds form the levators (extensors) and depressors (flexors). Paired fins operate as unjointed appendages.

3. Tetrapods have developed very complex appendicular muscles to accomplish movement at joints. Muscles are organized as opposing groups and usually classified as intrinsic or extrinsic.

4. Extrinsic muscles (most primative) originate from blastemas within the body wall and insert on a girdle or on a proximal limb bone.

Intrinsic appendicular muscles originate from blastemas located within the developing limb (aka primary).

5. Extrinsic muscles of the pectoral girdle and forelimbs:

Dorsal group: this group includes the latissimus dorsi, levator scapulae ventralis, levator scapulae dorsalis, rhomboideus, and the trapezius (which may be subdivided (cleidotrapezius, acromiotrapezius, and spinotrapezius... which you'll see on the cat). Of interest is that the trapezius originates from neural crest and is a muscle of the pharangeal arch (as is the cleidomastoideus which moves the head).

Ventral group: these are also known as the pectoral muscles. Included are the pectoralis (major and minor) and the supracoracoideus (birds). In mammals, the supracoracoideus has become an intrinsic muscle, the supracoracoid.

6. Intrinsic muscles of the pectoral girdle and forelimb:

Dorsal group: include muscles that arise on the scapula and insert on the humerus (deltoideus, teres major, teres minor, subscapularis, and long head of the triceps brachii); the supinator and brachioradialis, and extensors of the hand and digits.
Ventral group: the ventral musculature of the pectoral girdle includes the supraspinatus and infraspinatus (derivatives of the supracoracoid of reptiles). Also included are the coracobrachialis, biceps brachii, brachialis, aconeus, and the small epitrochleoanconeus. Pronators and flexors of the manus, and flexors of the digits complete the ventral group.

7. Muscles of the pelvic girdle and hind limbs: these muscles are primarily intrinsic since the pelvic girdles of amniote tetrapods do not move independently of the vertebral column. Urodeles, reptiles, and birds have an extrinsic caudofemoralis connecting some of the proximal caudal vertebrae to the femur, but it does not function in locomotion. In tetrapods below mammals these muscles are named for their attachments (ie., puboischiofemoralis) while in mammals, their names change.

Rotators and abductors: iliacus and psoas major rotate the femur. The gluteus, pyriformis, and gemelli both adbuct the thigh and rotate the femur.

Extensors and adductors: include the quadratus femoris complex (rectus femoris, vastus lateralis, v.intermedius, and v. medialis), semimembranosus, adductor femoris, adductor longus, pectineus, sartorius, and gracillis.

The obturator muscles flex, rotate, and abduct the thigh.

Flexors: biceps femoris, semitendinosus, and gastrocnemis.

8. Innervation of appendicular muscles comes from spinal nerves that originate in the same body segment that contributes the muscle buds.

9. Branchiomeric muscles: serve the pharyngeal arches of vertebrates. Basic pattern is seen in the shark. They remain the jaw muscles in tetrapods, but with the loss of gills the most posterior have acquired functions relating to movement of the head and neck.

Mandibular arch muscles: powerful muscles operating the jaw. Strongest muscle of the first arch is the adductor mandibulae which in tetrapods has split into the masseter, temporalis, and pterygoideus. The myohyoideus, digastricus, and tensor tympani of tetrapods probably arose from the intermandibular of fishes.

Hyoid arch muscles: constrict the pharyngeal cavity by elevating the hyoid arch. In tetrapods, the posterior belly of the digastricus participates in chewing. The platysma becomes the muscle of facial expression, while the stapedius acts to protect hair cells of the chochlea from loud noises.

Muscles of the remaining arches: include the trapezius, extrinsic muscles of the larynx, and neck muscles.

10. Innervation of the branchiomeric muscles in mammals is by the cranial nerves (V, VII, IX, X, and XII).

11. Integumentary muscles: well differentiated only in mammals. The panniculus carnosus and auricular muscles serve as examples.

12. Electric organs: occur in cartilaginous and bony fish. Modified muscle masses (electroplax) that can produce up to 600 V. Usually associated with the pectoral fins or hypaxial muscles of the tail.