zygolabialis 
zygolabialis (zi-go-la-bi-a'lis), n.; pi. zygolaU- 
ales (-lez). [NL., < :!/(jo{ma) + labialis, labial.] 
The lesser zygomatic muscle ; the zygomaticus 
minor. C'oM««, 1887. See first cut under wjiscfel. 
zygoma (zi-go'ma), w. ; pi. zygomata (-ma-ta). 
[NL., < Gr. Ci'y^fa, the zygomatic arch, also a 
yoke, bolt, bar, < fijoi'p, yoke, join, < Cvydv, 
a yoke, joining: see yoke^.'] 1. The bony arch 
or arcade of the cheek, formed by the malar or 
jugal bone and itsconnections:socalled because 
it serves to connect bones of the face with those 
of the skull about the ear. in mammals, including 
man, tlie zygoma consists of a malar bone connected be- 
hind with the squamosal bone, usually by a zygomatic pro- 
cess of the latter, and abutting in front against a protuber- 
ance of the superior maxillary bone, or of the frontal or 
the lacrymal bone, or any of these. It is usually a stout 
Skull of Mylodon, a gigantic extinct sloth, showing the massive 
zygoma X, with strong superior and inferior processes a, a". (Great- 
ly reduced.) 
l>ony arch, sometimes with a strong descending process, 
giving principal origin to a niasseter muscle, and bridging 
over the tenii>oraI muscle. It is sometimes a slender rod, 
and may be imperfect, as in shrews. The part taken in its 
formation by the malar bone is very variable in extent. 
(.See cut under gkuU.) Below mammals the construction 
of the zygoma iwsteriorly is entirely altered. In birds the 
arch is articulated there with the (juadrate bone, or sus- 
pensohum of the lower jaw, representing the malleus of a 
mammal, and an additional bone, the qiiadratojugal, inter- 
venes between the quadrate and the malar proper. In such 
cases the anterior connection is more particularly witli 
the maxillary bone, or with this and the laciymal, and the 
zygoma is generally a slender rod-lil<e structure. (See cut 
under Qatliiix.) In reptiles further modifications occur, 
suchaa the completion of the arch behind by union of the 
jugal bone with the postfrontal and squamosal ; or there 
may be no trace of a structure to which the term zygoma 
is properly applicable, as in the Ophidia, in which there 
is no jugal or quadratojugal lK>ne. Among batrachiaiis. 
as the frog, a zygomatic arch is represented by the con- 
nection of the maxillary bone, by means of a quadratojugal 
bone, with a bone called temporoniastoul (see cuts there 
and under Anura). In any case a zygoma consists of a 
suborbital or postorbital series of ossihcations in mem- 
brane, or raembrane-lH>nes, developed on the outer side 
of the maxillary arch of the embryo (the same that gives 
rise to the pterygopalatine bar), and when best differen- 
tiated is represented by lacrymal, maxillary, jugal, and 
quadratojugal liones; and its connection with ttte sphe- 
noid, as occurs In man, is quite exceptional. 
2. The malar or jugal bone itself, without its 
connections. [Rare.] — 3t. The cavity under 
the zygomatic process of the temporal bone ; 
the zygomatic fossa. Brande. 
zygomatic (zi-go-mat'ik), a. [< XL. sygomati- 
ctiD, < zygoma, q. v.] In zoiil. and aiiat., of 
or pertaining to the malar or jugal bone, or 
this bone and its connections; constituting or 
entering into the formation of the zygoma; 
jugal — Zygomatic apophygls. .Same as zngnmatic 
process.- zygomatic arch, the zygoma. See cut under 
»*««.— Zygomatic l)one, the malar.— ZyKomatlc ca- 
nallL two canals in the malar bone of man, through which 
pass branches of the superior maxillary nerve; thetempo- 
romalar canals : (a) the zyoomatico/acial, or malar, running 
between the oridtal and anterior surfaces ; (b) the zygomati- 
cotemitoral, or Umi>oral, riiiinInK between the orbital and 
temporal surfaces. — Zygomatic crest, that edge of the 
human alisphen'jid wlii^-h articuhites with the malar. — 
Zygomatic diameter, the greatest distance between the 
zygomatic- anhis ..( the skull.— Zygomatic fOSsa, See 
/'jsjrai. — Zygomatic glands, lymph-nodes found along 
the course of the internal maxillary artery. — Zygomatic 
muscle. Same as z,i/3o?na«<-Hji.— Zygomatic process. 
See procfsn, and cuts under ghtUt ana tfrn/toral'-^. — ZygO- 
nuiUc suture, the squamozygomatic suture ; the immov- 
able connection of the squamosal, usually (if its zygomatic 
process, with the malar or jugal i>one. — Zygomatic tu- 
berosity, that protut>erance of the superior maxilla which 
articulates with the malar. 
zygomatics, «. Plural of zyfiomatieiis: 
zygomatico-atiricular (zi-go-mat'i-ko-ii-rik'u- 
fiir), a. 1. In anal, and ztiol., of or pertaining to 
tte zygoma and the auricle: as, a zygomatico- 
auricular muscle. See zygomatico-auricularin. 
— 2. In ernniom., noting the ratio between 
the zygomatic and auricular diameters of the 
skull, called the zygnmutico-auriciilar iiidtx. 
zygomatico-auricularis (zi-go-mat"i-k6-a-rik- 
u-Ia'ris), «. A muscle of the external ear of 
some animals, which arises from the zygoma 
and is inserted in the aurirle; in man, the at- 
trahens aurem. 
A strong zygomalico^auricularU Is also seen as we re- 
move the Integuments of the head [of the reindeer]. 
Froc. Acail. Nat. Sci. Phila., 18!il, p. 232. 
70-45 
zygomaticofacial (zi-go-mat'i-ko-fa'shal), a. 
In anat., of or pertainijig to the zygoma aiid the 
face : specifying («) the anterior connections 
of the zygoma, and (6) the anterior one of the 
two zygomatic canals which traverse the malar 
bone of man. See zygomatic canals, under zy- 
gomatic. 
zygomaticotemporal (zi-go-mat"i-k6-tem'po- 
ral), a. In anat., of or pertaining to the zygo- 
ma and the temporal bone or fossa : specifying 
(a) the posterior connections of the zygoma 
with any element of the temporal bone, as the 
squamozygomatic of a mammal, and (i) the 
posterior one of the two zygomatic canals 
which traverse the malar bone of man. See 
zygomatic canals, under zygomatic. 
zygomaticus (zi-go-mat'i-kus), ».; pi. zygo- 
matici (-si). [NL.: see zygomatic.'] One of 
several small subcutaneous muscles arising 
from or in relation with the zygoma, or malar 
bone — Zygomaticus auricularis, a muscle of the ex- 
ternal ear, ttie attrahens aurem of man, commonly called 
zygoinatico-auricidaris (which see). — ZygomatiCUS ma- 
jor, zygomaticus minor, two muscles of the face, aris- 
ing from the malar bone, inserted into the orbicularis 
oris at the corner of the mouth, and serving to draw the 
corner of the mouth upward and outward, as in the act of 
laughing. The former is sometimes called distortor ori^, 
and the latter zygolabialis. See first cut under muscle^. 
Zygomaturus (zi'go-ma-tu'rus), «. IJNL., < 
(ir. si-ju/ia, tlie zygomatic arch, -t- ohpa, tail.] 
1. A genu.s of large fossil marsupials from the 
Post-tertiary deposits of Australia. — 2. [/. c] 
A member of this genus. Imp. Diet. 
zygomorphic (zi-go-m6r'fik), a. [< zygomor- 
7*«-<)!/.s- + -If.] In Lot., same as zyyomorphous. 
zygomorphism (zi-go-mor'fizm), «. [< zygo- 
inorph-oii-1 + -ism.] The character of being 
zygomorphous. 
zygomorphoUS (zi-go-mor'fus), a. [< Gr. >; (if, 
yoke, -f- /io/xpf/, form.] Yoke-shaped: specifi- 
cally applied to flowers which can be bisected 
into similar halves in only one plane; mono- 
symmetrical. Sachs extends the term to cases where 
bisection into similar halves is possible in two planes at 
right angles to one another, the halves of one section be- 
ing different from the halves of the other. Goebel. Com- 
pare actiiwmorphoiui. 
zygomorphy (zi'go-ra6r-fl), n. [< zygomor- 
]iTi-iin.i + -.'/>'•] In hot., same as zygomorphism . 
zygomycete (zi-go-mi'set), «. In bot., a fungus 
belonging to the group Zygomycetes. 
Zygomycetes (zi"g()-mi-se'tez), n. pi. [NL., < 
Gr. iv)6v, yoke, + i^ihrig, pi. fivnij-fr, a mush- 
room.] A group of fungi characterized by the 
production of zygospores. It embraces tlie 
Mucoriui, Entomophthoreie, Chytridiaceie, I'sti- 
lagincee, etc. 
zygomycetous (zi"go-nu-se'tus), a. In bot., 
of or pertaining to the Zygomycetes. 
zygon (zi'gon), «. [NL., < Gr. Cvyuv, a yoke, 
cross-bar: see yoke^.] 1. A connecting rod or 
bar ; a yoke in general. 
Zygal fissures are de6ned as "H-shapedor(iuadradiate, 
presenting a pair of brjiuches at either end of a connecting 
bar or yoke, the zygon." A zygal fissure contains a bar or 
zygon, a yoke in the most general sense. B. G. Wilder. 
2. In anat., an H-shaped fissure of the brain, 
as the paroccipital fissure, it consists of anterior 
and posterior stipes, anterior and posterior rami, and the 
connecting bar (the zygon in strictness). B. G. Wilder. 
Zygonectes (zi-go-nek'tez), n. [NL. (Agassiz, 
1854), so called because said to swim in pairs; 
< Gr. Zi'^ov, yoke, -1- I'r/KTT/^, swimmer.] A large 
genus of small carnivorous American cyprino- 
donts; the top-minnows. They are closely related 
to the killiflshes (Fundtdus), the technical difference be- 
ing chiefly in the smallness and backwardness of the dor- 
sal fin, which has usually less than ten rays and is com- 
monly inserted behind the front of the anal fin. The 
top-minnows are on the average smaller than the killi- 
flshes, being usually only 2 or 3 inches long. They arc 
surface swimmers, and feed on insects. The species are 
numerous, and individuals abundant. One of the best- 
known is Z. notatue, common in ponds from Michigan to 
Alabama and Texas. 
Zygopetalum (zi-go-pet'a-lum), «. [NL. (Hook- 
er, lHi;7), so called with ref. to the union of the 
perianth with the foot of the column; < Gr. 
CtJjiJi', yoke, + -f-a'/.uv, leaf (petal).] A genus 
of epiphytic orchids, of the tribe Vandae and 
subtribe t'yrtopodieie. It is characterized by showy 
solitary or loosely racemed flowers with spreading sepals, 
the lateral oin-s united to the short foot of the incurvctl 
column ; by a fiattish lip, bearing a transverse crest at its 
base; and by an anther with four obovoid pollen-nia8se.s, 
attached bya ratherliroud stalk or gland. Tliere are about 
50 species, natives of tropical America from the West In- 
dies and Mexico to Briizil. They are handsome plants 
with short leafy stems finally thicltened into pseudobulbs. 
Their leaves are two-ranked, membranous or somewlijit 
rigid, and slightly plicate or with elevated veins. They 
are highly prized in cultivation under glass, especially Z. 
Mackaii, the original species. 
zygosphene 
Zygophyceae (zi-go-fis'e-e), n.pl. [NL., < Gr. 
iv}uv, yoke, -t- (pvKoc, seaweed, -f- -ese.J A group 
or order of unicellular or multicellular fresh- 
water algse, not now generally accepted, with 
the cells single, or segregate, or geminate, or 
united in a series. Multiplication is effected by divi- 
sion in one direction, and by means of zygospores result- 
ing from the conjugation of the cells. It embraces the 
families Desinidiacex, Zygneinacese, etc. 
Zygophyllacese (zi-'go-fi-la'se-e), «. pi. [NL., 
< Zygophyll-um -I- -aceee.] iiame as Zygophyl- 
lea?. 
Zygophylleae (zi-go-fll'e-e), ». pi. [NL. (R. 
Brown, 1814), < ZygophyU-um -¥ -ese.] An order 
of polypetalous plants, the bean-caper family, 
belonging to the series Discifloree and the co- 
hort Geranialcs. It is characterized l)y flowers which 
usually bear a fleshy disk, five free glandless sepals, fila- 
ments augmented each by a small scale, and a furrowed 
angled or lol)ed ovary witli two or more tilifoi-m ovules in 
each of the four or five cells. It includes about 110 species, 
clas.sed in 18 genera, natives of tropical and warm cli- 
mates, especially north of the equator. They are com- 
monly shrubs or herbs with a woody base, bearing divari- 
cate branches jointed at their nodes. Their leaves are 
usually opposite and pinnate or composed of two entil-e 
leaflets ; the twin persistent stipules are sometimes de- 
veloped into spines. The flowers are white, red, or yel- 
low, very rarely blue, usually solitary in the axils of the 
stipules. The principal genera are Zygopliyllum (the type), 
Trilnilus, Guaiacum, and Fagonia; lU genera are raono- 
typic; two species of Guaiacum (lignum-vitai) become 
moderate trees. The woody species are remarkable for 
the extreme hardness of their wood, and several, as Guai- 
acum, produce a bitter and acrid bark. Their detersive 
foliage is used in the West Indies to scour floors. Some 
of the family are so abundant in the Egyptian desert as to 
coustitute a characteristic feature of its vegetation. 
Zygophyllum (zi-go-firum), n. [NL. (Linuffius, 
1737), < Gr. Cf/O"; yoke, + (jivMov, leaf.] A ge- 
nus of plants, type of the order Zygophyllese. 
It is characterized by opposite hifoliolate leaves, flowers 
with four or flve petals, and a sessile ovary with the ovules 
fixed upon the axis. Theie are about 60 species, natives 
of the Old World and of Australia. They are diminutive 
.shrubs, often prostrate, and witli spinescent branches. 
The leaves are opposite, usually composed of two fleshy 
leaflets armed at the base with spines which represent stip- 
ules. The flowers are white or yellow, usually marked 
near the base with a purple or red spot. Z. Fahago is the 
bean-caper of the Levant ; its flower-buds are used as ca- 
pers. The aromatic seeds of Z, coccineum are used by 1 he 
Arabs as pepper. Several species are of local medicinal 
repute — 2r. Fahago as a vermifuge, and Z. trimjilex, an 
Arabian plant of nauseous odor, as a remedy for diseases 
of the eye. 
zygophyte (zi'go-fit), n. [NL., < Gr. Ci'/Oi', 
yoke, 4- (^iTtir, plant.] A plant characterized 
by the production of zygospores; a plant in 
whicli reprodtiction consists in a confluence 
of two similar protoplasmic masses. See cut 
under conjugation. 4. 
In most of these zygophijtes there is no plain distinction 
of sex. G. L. Goodale, Physiol. Bot., p. 4a9. 
Zygopleural (zi-go-plo'ral), a. [< Gr. (;v}6v. 
yoke, + ~'/evpa, side.] Bilaterally symmetrical 
in a strict sense. Zygopleural forms are dis- 
tinguished as diplcnral and tetrapleiiral. 
ZygOSaUTUS (zi-go-sa'rns), n. [NL. (Eichwald, 
1848), < Gr. (v}dv, yoke, + naipo^, lizard.] A 
genus of labyrinthodonts, based on Z. lucins 
from tlie Middle Permian of Perm in Russia. 
zygose (zi'gos), a. [< Gr. fwjfif, yoke, -I- -ose 
after zygosis.] In boL, pertaining to or cli.ar- 
aeteristic of zygosis or conjugation. 
Zygoselmidse (zi-go-sel'mi-de), n.pl. [NL., < 
Zygoselmis + -idsp.] A family of dimastigiite 
eustomatous flagellate iiifusorians, named from 
the genus Zygosclmis. Tliey have two similar 
vibratile flagella, and the endoplasm includes 
no {ligraentary bands. 
Zygoselmis (zi-go-sel'mis). n. [NL., < Gr. Cv}6v, 
yoke, + ae'/.fii(, noose.] The typical genus of 
Zygoselmidse. These animalcules are highly plastic and 
variable in form, with two unetiujil flagella from the fore 
end, at the base of which are the month and pharynx. 
Z. iiebulosa and Z. injequatis inhabit fresh water. 
zygosis (zi-go'sis), n. [NL., < Gr. i;iiyuaii; a 
.loming (used in sense of balancing), < C"}oi;r, 
join, yoke : sevzygoma.] 1. Asexual intercourse 
of protoplasmic bodies, resulting in their con- 
fluence and coalescence; the process and re- 
sult of conjugation in protozoans or other of 
tlie lowest organisms. See conjugation, 4. — 2. 
[cap.] [NL. (Porster, 1869).] Agenus of hyine- 
nopterous insects. — 3. In hot., conjugation; 
the fusion or union of two distinct cells or pro- 
toplasmic masses for reproduction. See con- 
jugation, 4. 
zygosperm (zi'go-spenn), n. [NL., <Gr. ^vjtw, 
yoke, -t- njTt'piia, seed.] In hot., same as zygo- 
sjiore. 
zygosphene (zi'go-sfen), n. [< Gr. Ci'}(ii', yoke, 
-I- cipiiv, wedge] In herj>et., tlie wedge-shaped 
Ijrocess from the fore part of tlie neural arch 
