One who devotes himself to some specialty; as, a medical specialist, one who devotes himself to diseases of particular parts of the body, as the eye, the ear, the nerves, etc.
A skin specialist is a "dermatologist".
Myologist is the term meaning specialist in the study of muscles, but an orthopedist is the typical specialist physician who treats muscle problems.
A gerontologist is a specialist in the treatment of the elderly.
A neonatologist is a specialist in the care of the newborn.
A vocal specialist is called a Speech Therapist
A neonatologist is a specialist in the care of newborns.
A pharmacist is a specialist in dispensing and preparing medications.
neurologist
botanist
A cardiologist.
An Obstetrician or midwife.
A neurologist.