MUSCLES OF THE PIG

The muscles of the fetal pig are soft and delicate, easily torn apart, and therefore hard to dissect.

We will therefore only dissect a few. Also examine these same muscles in the cat, if one is available.

HEAD AND NECK REGION:

Begin with a cut through the skin (and only the skin) along the ventral midline of the throat. Create a flap my making two transverse cuts, and peel back the flap you mave made. Also palpate to locate the angle of the lower jaw (mandible). Extend the ventral incision this far and at least 1 cm further forward. Make a transverse incision near the anterior end of this ventral incision and locate the masseter muscle. Locate the several strap-like muscles located ventrally in this region.along the ventral side. Identify the following muscles:

Masseter This is the largest jaw muscle in pigs and other ungulates.

Sternohyoid This muscle originates from the sternum and inserts onto the hyoid.

Sternocleidomastoid This muscle runs diagonally toward the ear, inserting on the mastoid process.

TRUNK OF THE BODY:

Make a mid-sagittal incision along the dorsal midline of the neck, cutting only the skin. Now make two transverse incisions perpendicular to this, one arcoss the shoulders, and the other about half way from the shoulders to the pelvis. Gently pull some of the skin back in this region. Make a similar cut along the ventral midline and proceed from this dorsally. Pay attention to the fiber direction, and identify the following muscles:

Trapezius Identify this by its position and its fiber directions (converging onto the scapula).

Latissimus dorsi A very broad muscle, originating from the lumbodorsal aponeurosis, and

converging onto a tendon that inserts on the humerus.

Serratus anterior Find this muscle deep to the latissimus dorsi.

External oblique Deep to the caudal border of the latissimus dorsi. Examine its fiber direction.

Internal oblique Deep to the external oblique, with a different fiber direction.

Rectus abdominis Running longitudinally along the ventral midline, just beneath the ext. oblique.

SHOULDER AND FORELIMB:

Extend the transverse shoulder incision distally to the elbow and beyond. Make a similar incision across the chest between the forelimbs. Gently pull back some skin, and identify the following muscles:

Deltoid A very strong muscle adhering to the shoulder girdle.

Pectoralis major, minor These muscles originate ventrally and converge onto the humerus.

Triceps brachii The major extensor muscle on the caudal side of the arm.

Biceps brachii The major flexor muscle on the cranial side of the arm.

CONTINUED ON REVERSE SIDE

PELVIS AND HIND LIMB:

Beginning along the dorsal midline, gently peel away the skin over the pelvic region and hind limb. Find the fascia lata, an aponeurosis covering the cranial one-third of the thigh. Identify these:

Tensor fasciae latae: A small muscle, in series with the gluteals, that tenses the fascia lata.

Gluteus medius, gluteus maximus: Notice the position of these muscles, which are abductors in most

mammals. Also notice that the gluteus maximus is small.

Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius):

These muscles lie beneath the fascia lata and more medially, on the anterior side of the thigh.

Semitendinosus, semimembranosus, biceps femoris:

Locate these “hamstring” muscles along the posterior half of the thigh.

Gracilis (meaning “graceful”): This broad but thin muscle accompanies the hamstrings.

Adductor longus, magnus: These muscles are on the inner (medial) side of the thigh.

Gastrocnemius: This is the principal extensor of the ankle joint. Note the strong Achilles tendon.