but dog bites are a common cause of
human infection worldwide.
Other zoonoses are transmitted from
animals less obviously associated with
humans, usually by insect vectors. For
example, yellow feveris transmitted by
mosquito bites. (See also dogs, diseases
from; cats, diseases from; rats, dis-
eases from; insects and disease.)
zopicloneA drug used in the short-term
treatment of insomnia. It has a brief dura-
tion of action and causes little hangover
effect. Side effects include a bitter metal-
lic taste, nausea, and dry mouth.
Z-plastyA technique that is used in
plastic surgery to change the direction
of a pre-existing scar so that it can be
hidden in natural skin creases, or to
relieve skin tension caused by the con-
tractureof a scar. Z-plasty is especially
useful for revising unsightly scars on
the face and for releasing scarring across
those joints,such as on the fingers or in
the armpits, that may restrict normal
movement or cause deformity.
zygomatic archThe arch of bone,
commonly known as the cheek bone, on
either side of the skulljust below the eye
socket. The zygomatic arch is formed of
the zygomatic and temporal bones.
zygoteThe cell that is produced when a
spermfertilizes an ovum. A zygote, mea-
suring about 0.1 mm in diameter in
humans, contains all the genetic mat-
erial for a new individual. The zygote is
surrounded by a protein-rich layer
known as the zona pellucida.
ZYGOMATIC ARCHThe zygote travels down 1 of the
woman’s fallopian tubes, dividing as it
does so. After about a week, the mass of
cells (now called a blastocyst) implants
into the lining of the uterus, and the next
stage of embryological growth begins.
(See also embryo; fertilization.)
zygote intrafallopian transferA type
of in vitro fertilization, also referred to as
ZIFT, in which ovaare fertilized outside
the body and returned to a fallopian
tuberather than to the uterus.ZYGOTEZOPICLONE ZYGOTE INTRAFALLOPIAN TRANSFER
Frontal
bone
Zygomatic
bone
Parietal boneTemporal boneOccipital boneZygomatic archMandibleZona pellucida Zygote