External Anatomy, Skin, and Skeleton

Integument

(Skin) The largest body organ; separates the animal's internal environment from the outside world.

Rostral Bone

A flat, disk-shaped bone at the end of a pig's snout (not present in humans).

Stratum Corneum

A horny layer of dead skin cells at the integument surface that reduce the loss of body water. Loses cells rapidly, which are replaced by the remaining cells in the stratum basale.

Keratin

A horny protein that binds with lipids to make a cell impermeable.

Umbilical Vein

A large, thin-walled, irregularly shaped blood vessel that brings oxygen-rich blood and nutrients from the placenta to the fetus (found in the umbilical cord).

Scapular Spine

A long ridge along the lateral surface of the scapula.

Elastin

A more elastic protein found in some intercellular fibers.

Styloid Process

A pointed bump of bone that extends ventrally from the external acoustic meatus; in life, attachment for ligament that supports the hyoid bone.

Collagen

A relatively noncompliant protein found in most intercellular fibers.

Allantoic Stalk

A remnant of the allantois found in the umbilical cord; a small, hard cord of tissue.

Scrotum

A sac of skin that will receive the testes in a mature male; developed caudal to the hind legs and ventral to the tail in a pig fetus.

Hair Shaft

A shaft of cornified epithelial cells that is continually generated by the mitotic division of the hair bulb; surrounded by the hair follicle.

Hair Follicle

A sheath found around hair; extends into the dermis from the epidermis. Consists of a stratified epithelium that is continuous with the epidermis and is supported by connective tissue.

External Acoustic Meatus

A short canal from outside the ear to the tympanic membrane.

Endoskeleton

A skeletal structure that develops within the body wall or in deeper tissues.

Sacrum

A structure made of fused sacral vertebrae; section for the attachment of the pelvic girdle.

Nictitating Membrane

A third eyelid which can move across the rostral part of the eyeball to distribute (vestigial in humans).

Vertebral Body

Also called centrum; the ventral part of a vertebra. A large, solid disk of bone.

Internal Nostrils

Also called choanae; lie dorsal to the hard palate and connect the nasal cavities with the pharynx.

External Nostrils

Also called nares; paired external olfactory openings in the rostral plate.

Auricle

Also called pinna; the part of the ear that is a fleshy flap.

Tympanic Membrane

Also known as the eardrum; the membrane in the ear that vibrates to sound.

Tympanic Cavity

Also known as the middle ear; separated from the external acoustic meatus by the tympanic membrane. Houses the auditory ossicles.

Milk Set

An early set of teeth that is lost as mammals mature; replaced by permanent teeth.

Umbilical Cord

Attached to the ventral surface of the abdomen; connects the fetus with the placenta.

Dermal Bone

Bone that develops directly within connective tissue in or just beneath the dermis; occurs only as part of the somatic skeleton.

Cartilage Replacement Bone

Bone that forms as bone replaces embryonic cartilaginous skeletal elements; occurs as part of both the somatic and visceral skeleton.

Metacarpals

Bones in the palm.

Carpals

Bones in the wrist.

Phalanges

Bones supporting the free parts of the fingers and toes (digits).

Sternum

Breast bone.

Arrectores Pili Muscles

Bundles of smooth muscle fiber attached to hair follicles; extend towards integument surface. Contract and stand up hair when body temperature drops.

Intervertebral Disks

Cartilaginous disks filled with a fibrous gelatin material; separate successive vertebral bodies.

Thoracic Vertebrae

Caudal to the cervical vertebrae; vertebrae to which ribs attach.

Clavicle

Collar bone; extends from the acromion on the scapular spine to the manubrium of the sternum.

Auditory Tube

Connects the tympanic cavity to the pharynx.

Melanin

Dark pigment granules produced by specialized cells within the deepest layer of the epidermis; absorbs some light energy and helps to protect deeper tissue from damaging UV radiation.

Vertebral Arch

Dorsal to the vertebral body; surrounds the vertebral canal. Also called a neural arch.

Coccyx

Fused caudal vertebrae to which certain anal muscles attach.

Sebaceous Glands

Glands that secrete oil and are attached to the hair follicle; conditions and keeps hair healthy.

Scapula

Large, blade-shaped, triangular bone connected to the vertebral column by muscle and connective tissue.

Anus

Located directly ventral to the base of the tail; end of digestive tract.

Sweat Glands

Long, coiled, tubular glands made of myoepithelial cells surrounded by cuboidal epithelial cells; secrete water and some salts and excretory products.

Mandible

Lower jaw bone.

Pig Teeth

On each side of the jaw there are three incisors, one canine, four premolars, and three molars.

Ulna

One of the two bones of the forearm; lines up with the pinky.

Radius

One of the two bones of the forearm; lines up with the thumb.

Transverse Processes

Paired projections of the vertebrae that flank the spinous process; serve as sites for muscle attachment. Serve as attachment sites for ribs in some vertebrae.

Hair Papilla

Protrudes in the the hair bulb; contains many capillaries and nourishes the dividing cells of the developing hair.

Cervical Vertebrae

Seven vertebrae located in the neck; include the atlas and axis.

Labia

Skin folds that bound the urogenital orifice laterally (female pigs); converge ventrally to form the genital papilla.

Intervertebral Foramina

Spaces between vertebrae through which spinal nerves pass; located laterally between the vertebral arches.

Spinous Process

Spike-like part of a vertebra located dorsally; serves as a site for muscle attachment.

Genital Papilla

Spikelike; formed by the ventral convergence of the labia (female pigs).

Vertebral Canal

Surrounded by the vertebral arch; space through which the spinal cord passes.

Preputial Orifice

Surrounds the penis in male pigs; found directly caudal to the umbilical cord on the abdomen.

Vulva

The body region of female pigs that includes the urogenital orifice, the labia, and the genital papilla.

Humerus

The bone of the upper arm.

Hyoid Bone

The bone that anchors the tongue.

Auditory Ossicles

The bones in the tympanic cavity (hammer, anvil, stirrup).

Urogenital Orifice

The common orifice of the urinary tract an the vagina in female pigs; located directly ventral to the anus.

Lumbar Region

The dorsal region of the caudal part of the trunk (underneath the thorax).

Hair Bulb

The enlarged base of the hair shaft whose cells are continually undergoing mitotic division.

Atlas

The first cervical vertebrae; occipital condyles of the skull rest on this vertebra.

Rostral Plate

The flat, disk-shaped section at the end of a pig's snout (not present in humans).

Hard Palate

The hard roof of the mouth; separates the air and food passages from each other and allow a mammal to manipulate and chew food within the mouth cavity while still breathing.

Orbits

The holes in the skull that hold the eyes.

Dermis

The inner, much thicker layer of skin.

Mastoid Process

The large bump of bone in the human skull caudal to the external acoustic meatus; attached to neck muscles that help support and balance the head.

Cranial Cavity

The large open area in the skull whose shape closely follows that of the brain.

Foramen Magnum

The large opening at the caudal end of the cranial region through which the spinal cord enters the skull to connect with the brain.

Stratum Basale

The layer of the epidermis next to the dermis; consists of cuboidal cells. Also known as the stratum germinativum.

Pubis

The lower central part of the pelvic bone; ventral and cranial to the acetabulum. The two sides of this structure join together to form the pubic symphasis.

Manubrium

The most cranial segment of the sternum, wider.

Epidermis

The outermost layer of skin; made of stratified squamous epithelium.

External Acoustic Meatus

The paired openings in the skull that lead into the tympanic cavity.

Facial Region

The part of the brain containing the eyes and nose and forming the upper and lower jaws.

Cranial Region

The part of the skull that houses the brain and the inner and middle ear.

Acromion

The process by which the scapular spine terminates near the shoulder joint.

Axis

The second cervical vertebrae on which the atlas vertebrae rotates.

Somatic Skeleton

The section of the skeleton that contains the axial and appendicular skeletons.

Visceral Skeleton

The section of the skeleton that includes the hyoid bone, auditory ossicles, and laryngeal cartilages; best developed in fishes.

Thorax

The section of the trunk encased by the rib cage and housing the heart and lungs.

Axial Skeleton

The skeletal section along the midsagittal axis of the body; includes most of the skull, vertebral column, ribs, and sternum.

Appendicular Skeleton

The skeletal section comprised of the bones of the forelimb (pectoral appendages) and hindlimb (pelvic appendages), as well as the shoulder and hip bone (pectoral and pelvic girdles).

Acetabulum

The socket of the ball-shaped head of the femur.

Mammary Papillae

The teats of the pig fetus (both male and female); they become part of the mammary glands in mature females. Extend along abdominal surface; usually 5-6 pairs.

Femur

The thigh bone.

Ischium

The two looped lobes to the back of the pelvic bone; ventral and caudal to the acetabulum.

Nasal Cavity

The two passages into the skull from the external nostrils.

Pubic Symphasis

The two pubic bones join together to form this structure.

Abdomen

The ventral region of the caudal part of the trunk (underneath the thorax). Houses the liver, stomach, and intestines. In the fetal pig, the umbilical cord is attached to this section of the body.

Ilium

The wider top lobes of the pelvic bone; extends dorsally and attaches directly to the sacrum.

Connective Tissue

Tissue characterized by an extensive extracellular matrix that has been secreted by the cell; the dermis consists of this type of tissue.

Occipital Condyles

Two rounded bone structures that flank the foramen magnum; part of the skull that articulates with the first vertebrae of the vertebral column.

Umbilical Arteries

Two thick-walled blood vessels that carry oxygen-depleted blood and waste products from the fetus to the placenta (found in umbilical cord).

Sacral Vertebrae

Vertebrae caudal to the lumbar vertebrae; fused together to form a sacrum.

Caudal Vertebrae

Vertebrae that are dorsal to the sacrum; support a tail.

Lumbar Vertebrae

Vertebrae that lie caudal to the thoracic vertebrae; have large transverse processes with which embryonic ribs have fused.

Myoepithelial Cells

When these cells contract, they compress the glandular tubules and assist in the discharge of sweat.