Medical illustration of free nerve endings. The terminal filaments of sensory nerve fibers end freely in the tissue. Labeled structures include the myelin sheath, free nerve endings, epidermis, and epithelial cells.

Medical illustration of free nerve endings. The terminal filaments of sensory nerve fibers end freely in the tissue. Structures shown include the myelin sheath, free nerve endings, epidermis, and epithelial cells.

Medical illustration showing the spinal nerves C6 and C7 innervating the opponens pollicis muscle of the hand. Seen here is the left palm.

Medical illustration showing the spinal nerves C6 and C7 innervating the opponens pollicis muscle of the hand. Seen here is the left palm.

Medical illustration of a nerve pathway originating in the peripheral nerves of the arm, side, and leg, and terminating in the contralateral cerebral cortex. Labeled structures include the cerebral cortex, thalamocortical fiber, thalamic nucleus, spinothalamic tract, peripheral nerve fibers, and spinal cord nucleus.

Medical illustration of a nerve pathway originating in the peripheral nerves of the arm, side, and leg, and terminating in the contralateral cerebral cortex. Structures shown include the cerebral cortex, thalamocortical fiber, thalamic nucleus, spinothalamic tract, peripheral nerve fibers, and spinal cord nucleus.

Medical illustration of the equine female reproductive tract, showing the uterus, ventral view, with vagina cut open to show the cervix, urethral opening, and urine pool.

Medical illustration of the central and autonomic nervous systems, seen in a female figure, sagittal view. Shown here are the central nervous system (yellow) and the autonomic (involuntary) nervous system, which is split into sympathetic (red) and parasympathetic (blue) divisions.

Medical illustration of the female reproductive tract, sagittal view. Structures shown include the uterus, fallopian tube, vagina, cervix, and ovary.

Medical illustration of the male reproductive organs, sagittal view. Structures shown include the penis, prostate gland, testicle, corpus spongiosum, epididymis, and urethra.

Special effects of a red human heart showing arteries on a black background and a star on the surface.

Computer graphics showing blood cells flowing through a blood vessel.

Computer graphics showing normal lungs.

Illustration of the heart and major blood vessels within a transparent figure, set before a background of cells.

Illustration of a human figure, showing the circulatory system. (c) Duval

Female genital system.

Normal uterus in the female reproductive system.

Side cutaway view of human head and torso.

Illustration of a heart.

Illustration of the frontal anatomy of normal heart.