Skeletal Muscles of a Toad/Frog

SKELETAL MUSCLES  – consists of the origin and the insertion - taper at their ends into the tendons TENDONS  – tough white cords of connective tissue - serve to attach SM to bones or other M ORIGIN – ORIGIN – fixed end INSERTIONINSERTION- movable end HEADS – HEADS – end with more than one origin SLIPS – more than one point of insertion BELLY – fleshy middle portion ACTION – movement of effect caused by M *Each SM has a characteristic origin, insertion and action. *They are arranged in antagonistic pairs/groups that have opposing actions *Effective study: time, patience & good dissection technique General Classes of SM accdg. to Action: 1. EXTENSORS –straighten EXTENSORS –straighten or extend a part 2. FLEXORS-bend FLEXORS-bend one part toward another  part 3. ADDUCTORSADDUCTORS- pull a part back toward the axis of the body. 4. ABDUCTORSABDUCTORS- draw a part away from Axis of the Body Skinning the Toad  Ventral surface up Cut along midventral line from anterior tip of   jaw to region of cloaca Transverse cut thru skin Loosen skin with blunt instrument FASCIAFASCIA- thin white sheets of C.T. between the skin and muscles Subcutaneous lymph sacs- large areas where skin is not attached to muscles and where colorless fluid collects in a living toad. Turn skin inside out Carefully free & separate M with blunt probe Follow direction of muscle fibers in separating In exposing deeper muscles, reflect covering muscle by cutting it thru its belly • •

• • •

•

• • • •

THE PRINCIPAL MUSCLES 

A. Abdominal  – contract the body cavity B. Pectoral or Chest - inserted on ventral side of humerus - draw the arm toward the chest and expand abdominal activity C. Lower jaw D. Dorsal side of Head & Trunk E. Ventral surface of Thigh (upper leg) F. Dorsal side of Thigh G. Shank (lower leg) A. ABDOMINAL MUSCLES 1. Rectus Abdominis - occupy mid-ventral part - divided longitudinally by LINEA ALBA - Transversely by INSCRIPTIONES TENDINAE 2. External Oblique - cover sides of the body from the ilium & inserts on the Linea Alba 3. Internal Oblique/Transversus - beneath external oblique - forms innermost layer of abdominal muscles B. PECTORAL MUSCLES - anterior to abdominal muscles - inserted on the ventral side of humerus 1. Pectoralis Epicoracoidea - arises from coracoid & epicoracoid 2. Pectoralis Sternalis - arises from sternum & xiphisternum 3. Cutaneous Pectoralis - pocket-shaped M. covering Pectoralis sternalis 4. Pectoralis Abdominis - arises from anterior half of Rectus abdominis C. LOWER JAW MUSCLES 1. Mylohyoid - superficial M. originating from medial surface of  mandible & inserted on the median raphe 2. Geniohyoid - lateral, underlying muscle w/c originates from tip & border of lower jaw & inserts onto the processes & body of the hyoid & a more medial Hyoglosus 3. Genioglosus – Genioglosus  – anterior anterior to the Hyoglosus Hyoglosus 4. Submentalis – Submentalis – small muscle muscle at tip of of lower jaw 5. Sternoradialis – Sternoradialis  – lies posterior posterior to Geniohyoid Geniohyoid & partly covered by Mylohyoid. - originates from sternum & inserts on to radius. 6. Deltoid/Scapulo-humeralis -postero-lateral -postero-lateral to mylohyoid w/c originates originates from scapula & inserts onto the humerus - it extends the arm. D. Dorsal side of Head & Trunk

1. Pterygoideus – Pterygoideus  – at eye eye level - from middorsal line of the cranium 2. Temporalis - large muscle posterior to the eyes at the level of the tympanic membrane - from middorsal line of cranium & extends ventrally passing bet. the eyes and the eardrums 3. Depressor mandibulae  – posterior posterior to the temporalis temporalis 4. Masseter  - short M. wedged bet. temporalis and depressor  mandibulae inserted on the mandible 5. Dorsalis scapulae - large broad muscle posterior to Depressor  mandibulae - from dorsal surface of suprascapula & scapula, extends ventrally & inserts on lateral side of humerus.

6. Latissimus Dorsi - large flat muscle posterior and partly covering Dorsalis scapulae - from lumbo-dorsal fascia & inserts on lateral side of the proximal end of humerus. 7. Longissimus Dorsi - mass of muscles that tapers posteriorly & posterior to Latissimus Latissimus dorsi - from anterior third of urostyle extending anteriorly 8. Iliolumbaris - lateral to longissimus dorsi w/c came from anterior  part of ilium - inserts onto transverse processes of the trunk vertebrae. 9. Coccygeosacralis - small V-shaped m. posterior to Longissimus dorsi 10. Coccygeoiliacus - bigger V-shaped m. posterior to Coccygeosacralis

E. Ventral surface of Thigh (upper leg) 1. Triceps femoris - large muscle covering entire of lateral surface of  the thigh - its 3 heads: a.) outer  Vastus externus w/c arises from posterior  end of the crest of the ilium

b.) middle Rectus femoris anticus w/c arises from ventral border of the posterior third of the ilium in front of the acetabulum c.) inner Vastus inner Vastus internus w/c arises from the inner  border of acetabulum

2. Sartorius - slender muscle transversing the thigh obliquely w/c arises from lower end of ilium & inserted on the proximal end of the tibio-fibula

3. Adductor longus

- partly covered by Sartorius whose small portion is exposed along the pre-axial side of the Sartorius. 4. Adductor magnus - stout muscle lying behind Sartorius crossing it as its distal end. - arises from the ischium & pubis and inserts at the distal end of the femur. 5. Gracilis major  - large muscle at the posterior margin of the thigh w/c bears an oblique marking near its posterior portion. 6. Gracilis minor  - slender m. closely attached to Gracilis majorw/c runs along the inner margin of the thigh. 7. Semitendinosus - slender shiny m. that can be seen by pushing aside the gracilis major and originated by two heads from the ischium.

F. Dorsal side of Thigh 1. Gluteus - medial & anterior to the triceps femoris - orig. from ilium & inserted on the femur  2. Biceps femoris - long slender m. partly covered by the triceps’ Vastus externus - originating from posterior end of the dorsal crest of  the ilium & inserting into the proximal end of the fibula 3. Semimembranosus - large muscle posterior to biceps femoris with an oblique marking across it. 4. Piriformis - small muscle near the cloacal opening, between the biceps femoris & the semimembranosus

G. Shank (lower leg) 1. Gastrocnemius - biggest muscle at the medial surface of the shank - has two heads & is inserted by means of the tendon of Achilles 2. Peroneus - lateral to & partly covered by the Gastrocnemius 3. Tibialis posticus - long narrow muscle beneath the gastrocnemius & posterior to the tibio-fibula