AVES. 



357 



millary 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 atlyx (a, d, jig. 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 

 white 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 (f), but during 

 this process Purkinge 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,fg. 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 mesometrium, 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,fg. 185). 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,Jjg- 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- 



