Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Facial and Masticatory Muscles of the Pig (Sus scrofa)

Text by Lazaro Gonzales, Jr.

Jaw and Face:

As a fetus, the pig receives its nutrients via the umbilical cord from its mother.  At this stage of development, the pig does not chew food, and the muscles of mastication are not used.  However, it is important for the muscles of mastication to be functional to eat when the time comes.  The pig has few facial muscles and as a result does not communicate with facial expressions.  The facial musculature the pig does have is important.  Orbicularis oris is necessary for suckling, while the buccinator is involved in chewing.  Also, orbicularis oculi is a sphincter muscle that enables the pig to close its eye.  The adult pig is omnivorous and has an average-size masseter muscle for mastication compared to carnivores (small masseter) or herbivores (large masseter).  The pig digs for food and uses its tough, cartilaginous snout and forefeet to dig in the dirt.  The pig does not have significant musculature to the move the pinnae because it does not dig deep into the ground or submerge itself in water.  There is not a reason to close off its auditory canal for protection.

The principle muscle used in mastication is the masseter [1,2].  Another major muscle utilized in jaw closing is the temporalis [1,2].  Small pterygoid muscles aid these two major jaw muscles in closing.  The digastric muscle controls jaw opening [1,2].

General Dissection:

It was more difficult to skin the head than the body.  I made a shallow incision from the throat cranially to the lower lip.  I initially used the scalpel to separate the skin from the subcutaneous tissue.  It was easiest to clamp the skin with a hemostat and continue the separation with a blunt probe once I reflected the edge of the skin.  Another helpful technique for separating out layers or structures is using the sharp scissors closed in a scraping motion.  Segmental veins and arteries were visible deep to the skin piercing through; it is ok to cut through these.  The eyes, ears, and snout were the problematic spots.  I skinned around the ears as much as possible then cut the auditory canal as close to the skull as possible, detaching the pinna.  I carefully scraped the skin away from the eyes as keep the orbicularis oculi muscle intact.  I mostly pulled the skin off of the eye, making small cuts when the skin began to lift musculature underneath it.  The skin around the snout was very difficult to separate.  It is tough and well attached.  I was less careful with it because there are not fragile structures underneath.

Comparative:

The herbivores in the class had larger jaw muscles relative to their body size.  The pig jaw musculature was of average size comparative to body size.  The cat’s jaw musculature was smaller in comparison to the fetal pig’s ratio of jaw muscle to body size.  As a carnivore the cat has a smaller masseter and barely chews its food.  The beaver’s masseter is very large as it is important for herbivores to have powerful jaw muscles because of the sustained chewing.  The beaver had more musculature to move its ears.  This is important to the beaver for closing its auditory canal while underwater.

 Muscles of the Jaw and Face [1,2,3]:

References:

1. Odlaug, T.O.  1980.  Laboratory Anatomy of the Fetal Pig.  Wm. C. Brown Company Publishers, Dubuque, Iowa.

2. Smith, D.G.  1998.  A Dissection Guide and Atlas to the Fetal Pig.  Morton Publishing Company, Englewood, CO.

3. Moore, K.L. and Agur, A.M.R.  2002.  Essential Clinical Anatomy: Second Edition.  Lippincott, Williams, & Wilkins, Baltimore, MD.