A muscle must depend on other muscles to assist in a desired movement A muscle must depend on other muscles to assist in a desired movement. For this reason muscles are called prime movers, antagonists and synergysts.

Primer Movers Muscles that actively produce a movement

Antagonist Muscles that are in opposition to the prime movers

Synergist Muscles that contract simultaneously with the prime mover to help execute a movement or steady a part

The names of muscles are based on six points of identification The names of muscles are based on six points of identification * named for their action * named for their origin and insertion * named for their location * named for their shape or use * named for the direction of their fibers * named according to the number of their sections

Adjectives

Azygous : not paired

Bi, Tri, Quadri : two, three, four

Externus : external or outer

Gracilis : slender

Latissimus : wide

Longissimus, longus : long

Medius : intermediate

Orbicularis : surrounding

Quadratus : square

Rectus : straight

Rhomboideus : diamond shaped

Scalenus : unequally three sided

Serratus : sawtoothed

Teres : round or cylindrical

Transversus : crosswise

Vastus : great

Facial muscles There are many facial muscles that produce a variety of movement.

Orbicularis oculi

masseter

Muscles of the neck, back and thorax Muscles of the neck, back and thorax. These muscles assist in rotation of the head, flexion and extention of the head on the neck, breathing and attachment of the forelimbs to the body

Serratus muscle group

Pectoral muscle group

Latissimus dorsi broadest muscle in the back, supports forelimb and flexes shoulders

The important muscles of the dorsum include the epaxial group: iliocostalis longissimus transversosspinalis

These muscles extend the vertebral column and produce lateral movement of the trunk

Transversospinalis

Three important muscles of the thorax are. external intercostals Three important muscles of the thorax are *external intercostals *internal intercostals *diaphragm

During respiration: the external intercostals lift the ribs the internal intercostals lower the ribs the diaphragm contracts and flattens out causing the thorax to enlarge and the lungs to expand

Muscles of the forelimbs in addition to the back and upper thorax the muscles of the upper forelimbs contribute to the movement of the distal extremities. Included are triceps brachii and biceps brachii

tricep                                                                                                                         

Biceps brachii                                                                                                                         

Abdominal muscles: external oblique internal oblique rectus abdominis transversus abdominis these muscles keep the organs in place, support and compress the abdomen, contract during parturition, defecation, urination and coughing

These muscles also assist in rotating the vertebral column These muscles also assist in rotating the vertebral column. The linea alba is a fibrous band that runs the length of the center of the abdomen and is the central attachment of the abdominal muscles. This is a very important landmark for any abdominal surgery

                                                                                                                         Rectus abdominis Transversus abdominis External oblique Internal oblique

Linea alba

Muscles of the hindlimb These muscles have several functions in movement. The most important muscle groups include *gluteal group *quadricep group *semi group

gluteal Major muscles over pelvis, extends and abducts limb

Quadriceps femoris flex and extend the leg

Semi group descends the posterior hind leg and form the “hamstrings” Semi group descends the posterior hind leg and form the “hamstrings”. These muscles flex the distal extremity

                                                                                                         Gastrocnemius: flexes the leg and foot, the tendon at the insertion is commonly called the achilles tendon

Miscellaneous muscles: arrector pili These are smooth muscles attached to hair on the dorsum. When stimulated these muscles raise the hair on the back.

Cutaneous trunci: a muscle that attaches to the dermis and controls the insect twich in large animals Another large animal muscle is the cremaster, this muscle is part of the spermatic cord and attaches to the scrotum. This muscle contracts and relaxes, raising and lowering the testicles. This movement helps to regulate testicular temperature