Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/369/
AVES. 
357 
miliary pile (cumulus) of white granular sub¬ 
stance, which is surrounded by a whitish zone, 
and is continuous with the granular stratum 
applied to the internal surface of the membrana 
vitelli, but not adherent to that membrane. 
The common envelope of the germinal vesi¬ 
cle, cicratricula, and yolk, is called the mem¬ 
brana vitelli. It is extremely delicate and 
transparent, without any perceptible organi¬ 
zation, and forms an entire or shut sac. It is 
at first scarcely distinguishable from the stra¬ 
tum of granules forming the periphery of the 
yolk, and at this period the germinal vesicle 
closely adheres to it. Subsequently, however, 
a separation is effected by an interposed stra¬ 
tum of granules. The external membranes of 
the ova are thick in proportion to the vitelline 
membrane, and can with difficulty be detached 
from without lacerating it. 
The part of the ovary in which the ovum is 
lodged is termed the calyx (a, d, fig. 185). 
It consists of two membranes; the external 
one is highly vascular; the internal one is 
somewhat smooth and pellucid, and is beset 
with equidistant, minute, and apparently glan¬ 
dular bodies. 
As the ovarian ovum advances to maturity, 
a pedicle is developed from which the calyx 
with its contained ovum depends, and which 
permits it to be brought in contact with the 
infundibular orifice of the oviduct (e,fig. 185). 
The external vascular tunic of the calyx 
then becomes covered with a rich profusion 
of vascular twigs (b,fig. 185) distributed in a 
pectinated manner, and converging towards a 
vyhite transverse line, called the stigma (c, 
Jig. 185). This stigma begins to appear when 
the ova have attained the diameter of an inch, 
in the form of a whitish streak, which con¬ 
tinues to increase in breadth, and the 
membranes at that part to be thinned by 
absorption until they readily yield, and are 
rent by the compressing force of the infun¬ 
dibular opening of the oviduct, when the 
ovarian ovum escapes, and is received into the 
efferent passage. 
The membrana vitelli is at this period 
sufficiently strong and ductile to permit the 
ovum being compressed into an elliptical 
form to facilitate its passage through the con¬ 
tracted part of the oviduct (J), but during 
this process Purkingé conjectures that the 
germinal vesicle of the cicatricula is ruptured 
and its pellucid contents diffused. It is 
certain at least that it can no longer be de¬ 
tected either in the cicatricula of the ovum of 
the oviduct, or in that of the excluded egg. 
The further changes which take place in the 
generative product, now no longer forming a 
part of the maternal system, will be described 
in the article Generation; and we resume 
the consideration of the female organs. 
The calyx of the ovum, when emptied of its 
contents (d,fig. 185) collapses, shrinks, and is 
ultimately absorbed, not forming a permanent 
corpus luteum, as in Mammalia. 
In Birds that have but few young at a brood, 
as the Eagles or Doves, the number of enlarged 
yolks is correspondingly small; but in the more 
prolific species, as the Common Fowl, they are 
more numerous. The number of young pro¬ 
duced may be, by this means, in some degree 
inferred, if the female of a rare species happen 
to be killed during the breeding season. 
The oviduct commences by the infundibular 
orifice, where its parietes are very thin ; as it 
descends, these increase in thickness, and the 
efferent tube gradually acquires the texture and 
form of an intestine. Like this, it is attached 
to and supported by a duplicature of perito¬ 
neum called the mesometriwn, but which also 
includes muscular fibres, to be presently de¬ 
scribed. 
The oviduct in the quiescent state is generally 
straight, but at the period of sexual excitement 
it is augmented in length as well as capacity, 
and describes three principal convolutions be¬ 
fore reaching the cloaca. The lining membrane 
presents a different character in different parts 
of the oviduct; at the infundibular extremity it 
is something like the mucous coat of the intes¬ 
tine, then it becomes rugous, and afterwards, 
at the part where the egg is detained and the 
chorion calcified, it presents a number of long 
close-set villi (k,fig. \Q5>). This part is by 
some anatomists termed the uterus, but by a 
loose analogy, as the ovum is developed out 
of the body of the parent. The rest of the 
canal, which, pari modo, is termed vagina, 
opens into the urethro-sexual segment of the 
cloaca, anterior to the termination of the left 
ureter, and its termination (f,fig- 164, 176) 
is provided with a sphincter. 
The mesometry (m, fig. 185) differs most 
from the mesentery when the female organs are 
in full sexual action. It presents at that period 
a true muscular structure. It is divided into 
two parts, one superior, the other inferior. 
The inferior mesometry has its point of attach¬ 
ment at the lower part of the uterine portion 
of the oviduct, and forms a somewhat dense 
and cruciform plexus of muscular fibres ra¬ 
diating from that part. The transverse fasci¬ 
culi are spread out on either side and around 
the uterus. The lower fasciculus surrounds 
the vagina more laxly, and contributes to the 
expulsion of the ovum. The upper fasciculus 
spreads out like a fan upon the oviduct from 
its insertion into the uterine portion to the com¬ 
mencement of the infundibulum. 
The superior mesometry commences by a 
firm elastic ligament, which is attached to the 
root of the penultimate rib of the left side, 
whence the muscular fibres are continued to 
the upper part of the oviduct, upon which 
they form a delicate muscular tunic, whose 
fibres embrace the oviduct for the most part 
in the transverse or circular direction, except 
at the infundibular aperture, where they affect 
the longitudinal direction, which enables them 
to dilate that orifice. Longitudinal muscular 
fibres begin again to be distinctly seen in the 
uterine portion of the oviduct, whence they are 
continued along the so-called vagina. An in¬ 
ternal stratum of circular fibres is also situ¬ 
ated immediately behind the calcifying mem-
        

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