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The lungs, not having received air in respiration, are collapsed and dense, containing no more blood than is necessary for their nutrition. They are of a dark colour, like liver, and do not fill the cavities of the chest. Their specific gravity is greater than that of water, and consequently they sink in that fluid. On cutting into them, no air is emitted, and no hemorrhage follows. The absolute weight, however, of the lungs is less; no more blood, as we have seen, being sent to them than what is necessary for their nutriment; whilst, after respiration is established, the whole of the blood passes through them; the vessels are consequently filled with blood, enlarged, and the organs themselves increased in absolute weight. Ploucquet asserts, from experiments, that the weight of the lungs of a full-grown foetus, which never respired, is to that of the whole body, as 1 to 70; whilst in those, in which respiration has been established, it is as 1 to 35; the absolute weight being thus doubled. These numbers cannot, however, be considered to afford a satisfactory average; the exceptions being most numerous, but all show that, as might be expected, the absolute weight is less prior to the establishment of respiration. The subject is one of great interest, connected with infanticide, and has been treated in a competent manner by Dr. T. Beck in his Elements of Medical Jurisprudence,—decidedly, in our opinion, the best medico-legal work in existence.
It is, however, in the circulatory system of the foetus, that we meet with the most striking peculiarities. The heart is proportionably larger and more conical than in the adult. The valve of Eustachiusat the left side of the mouth of the inferior vena cava, where this vessel joins the sinus venosus, is larger than at an after period, and is supposed to direct the principal part of the blood of that cava directly through the opening which exists between the right and left auricle. This opening, which is called the foramen ovale or foramen of Botal, is in the septum between the auricles, and is nearly equal in size to the mouth of the inferior cava. It is situated obliquely, and has a membrane, forming a distinct valve, and somewhat of a crescentic shape, which allows part of the blood of A the right auricle to pass through the opening into the left auricle, but prevents its return.
The pulmonary artery, instead of bifurcating as in the adult, divides into three branches; the right and
A, A. Lungs.-B. Right auricle.-C. Left auricle.-D. Right left going to the lungs of ventricle.-E. Pulmonary artery.-F. Aorta.-a. Ductus arte- the corresponding side,
whilst the middle branch,—to which the name ductus arteriosus has been given,—opens directly into the aorta; so that a great part of the blood of the pulmonary artery passes directly into that vessel. From the internal iliac arteries, two considerable vessels arise, called the umbilical arteries. These mount by the sides of the bladder, as in Fig. 156, on the outside of the peritoneum and perforate the umbilicus in their progress to the umbilical cord and pla
The umbilical vein, which is also a constituent of the cord, and conveys the blood from the placenta to the fœtus, arises from the substance of the placenta by a multitude of radicles, which unite together to form it. Its size is considerable. It enters the umbilicus, (Fig. 156;) passes towards the inferior surface of the liver, and joins the left branch of the vena porta hepatica. Here a vessel arises called the ductus venosus, which opens into the vena cava inferior, or joins the left vena hepatica, where that vein enters the cava. A part only of the blood of the umbilical vein goes directly to the vena cava; the remainder is distributed to the right and left lobes of the liver, especially to the latter.
The digestive apparatus exhibits few peculiarities. The bowels, at the full period, always contain a quantity of greenish, or deep black, viscid fæces, to which the term meconium has been applied, owing to their resemblance to the inspissated juice of the poppy, (μn, 'a poppy.') It appears to be a compound of the secretions from the intestinal canal and bile, and frequently contains down or fine hairs mixed with it.
The liver is very large; so much so as to occupy both hypochondriac regions; and the right and left lobes are more nearly of a size than in the adult.
The urinary bladder is of an elongated shape, and extends almost to the umbilicus. The muscular coat is somewhat thicker and more irritable than in the adult, and it continues to possess more power during youth. The common trick of the schoolboy—of sending the jet over his head—is generally impracticable in more advanced life.
From the fundus of the bladder, a ligament of a conical shape, called the urachus, (Fig. 156,) ascends between the umbilical arteries to the umbilicus; becoming confounded in this place with the abdominal aponeuroses, according to Bichat, and forming a kind of suspensory ligament to the bladder. It is sometimes found hollow in the human fœtus, but such a formation Bichat considers to be preternatural. In the foetal quadruped, it is a large canal, which transmits urine to a bag, called allantois, placed between the amnion and chorion and presumed to be, in some way, inservient to the nutrition of the foetus; but the notions on this subject are extremely vague and imprecise.
Lastly, the genital organs require some notice. The succesVOL. II.
sive development of this part of the system has given rise to some singular views regarding the cause of the sex of the fœtus. During the first few weeks, the organs are not perceptible; but about the termination of the fifth week, a small, cleft eminence appears, which is the rudiment of the scrotum or the vulva, according to the sex. In the sixth week, an aperture is perceptible, common to the anus and genital organs, in front of which is a projecting tubercle. In the seventh and eighth weeks, this tubercle seems to be tipped by a glans, and grooved beneath by a channel which extends to the anus. In the eleventh and twelfth weeks, the perineum is formed and separates the anus from the genital organs. In the fourteenth week, the sex is distinct; but there still remains, for some time, a groove beneath the clitoris or penis, which becomes closed in the former, and is made into a canal in the latter.
The striking similarity between the male and female organs has led Tiedemann to conclude, that the female sex is the male, arrested at an inferior point of organization. In his view, every embryo is originally female; the cleft, described above, being the vulva, the tubercle, the clitoris; to constitute the male sex, the cleft is united so as to form a raphe, the labia majora are joined to form the scrotum, the nymphæ to form the urethra, and the clitoris is transformed into a penis. In support of this opinion Tiedemann asserts, that the lowest species of animals are almost all females; and that all the young acephali and aborted fœtuses, which have been examined, are of that sex.
Others again, have affirmed, that the sexes are originally neuter, and that the future sex is determined by accidental circumstances, during the first week of foetal life; whilst Geoffroy St. Hilaire maintains, that the difference of sex is owing to the distribution of the two branches of the spermatic artery. If they continue in approximation, proceeding together, the one to the testicle, the other to the epididymis, the individual is male; if they separate, the one going to the ovary, the other to the cornua of the uterus,—the individual is female. The degree of predominance of the cerebro-spinal system, he thinks, determines the approximation or separation of the two arterial branches. This predominance being greater in the male, the spermatic arteries are more feeble and consequently in greater proximity; and vice versa.
Leaving these phantasies of the generalizing anatomist, on a subject on which we must, probably, ever remain in the dark, let us inquire into the phenomena of the descent of the testes in the fœtus. In the early months of fœtal life, the testicle is an abdominal viscus, being seated below the kidney. About the middle of the third month of utero-gestation, it is about two lines long, and is situated
behind the peritoneum, which is reflected over its ventral surface. At this time, a sheath of peritoneum may be observed, passing from the abdominal ring to the lower part of the testicle, and containing a ligament, called gubernaculum testis, which is considered to be formed of elastic cellular tissue, proceeding from the upper part of the scrotum, and from the part of the general aponeurosis of the thigh near the ring, and of some muscular fibres coming from the internal oblique and transversalis muscles.
Peritoneum of the loins.-D. Pe
The head of the foetus in utero being the lowest part, the testis has necessarily to ascend into the scrotum, and consequently some force must be exerted upon it. This is supposed to be effected by the contraction of the gubernaculum testis. About the Seventh month the testes are in pro- A. Testicle.-B. Peritoneal covering or tunica gress towards the Scrotum. Fig. 158 ritoneum descending before the testicle.-F. Peexhibits one about to leave the ab-ritoneum lining abdomen. domen and enter the scrotum, into which it generally passes about the eighth month. In this descent, the organ successively abandons one portion of the peritoneum to pass behind another immediately below, until the lowest part of the pouch, formed by the peritoneum, around the testicle, as in Fig. 159, becomes the tunica albuginea or first coat; whilst the portion of peritoneum, that descended before the testicle, becomes, when the testicle has fully descended, the second coat or tunica vaginalis.
As soon as the testicle has reached the lower part of the Dscrotum, the neck of the pouch approaches a closure, and this
is commonly effected at birth. A. Testicle in the scrotum.-B. Prolongation of the Sometimes, however, it re- of the peritoneum.-F. Kidney. peritoneum.-C. Peritoneum lining the abdomen.-D. mains open for some time, the
intestines pass down, and congenital hernia is thus induced.
Physiology of the Fœtus.
In investigating this interesting point of human physiology, we shall inquire into the functions, in the order of the classification we have adopted of the functions of the adult. Over many of the topics that will have to engage attention, the deepest obscurity rests; whilst the hypotheses, indulged regarding them, have been of the most fanciful and mystical character.
I. Animal functions.—The external senses in general are manifestly not in exercise during foetal life: of this there can be no doubt, as regards the sense of sight; and the same thing probably applies to the taste, smell, and hearing. With regard to tact, however, we have the best reason for believing that it exists, particularly towards the latter periods of utero-gestation. The cold hand, applied over the abdomen of the mother, will instantly elicit the motions of the child. The brain and nervous system of the foetus must, therefore, have undergone the development, necessary for the reception of the impression made through the medium of the mother, to convey such impression to the percipient organ, and to accomplish perception.
The existence of most of the internal sensations or wants would of course be supererogatory in the factal state, where the functions, to which they excite after birth, are themselves wanting. It is probable, that there is no digestion except of the mucous secretions of the tube; no excretion of fæces or urine, and certainly there is no pulmonary respiration. It is not improbable, however, that internal impressions, originating in the very tissue of the organs, may be communicated to, and appreciated by, the brain. We have strong reason for believing, that pain may be experienced by the fœtus; for if it be destroyed by any sudden influence, in the latter periods of pregnancy, death will generally be preceded by irregular movements, which are manifest to the mother, and frequently lead her to anticipate the result. Adelon asks, whether it may not be affected, under such circumstances with convulsions, similar to those that animals experience when they die suddenly, especially from hemorrhage? It is impossible to reply to this question, but that the child suffers appears evident.
The most elevated of the functions of relation—the mental and moral faculties—would seem to be needless to the foetus, and consequently little, if at all, exercised. Bichat and Adelon, considering that its existence is purely vegetative, are of opinion that they are not exerted at all. Cabanis, however, suggests, that imperfect essays may, at this early period, be made by virtue of the same instinct that impels animals to exercise their organs prior to the period at which they are really able to derive service from them; as in the case of the bird, which will shake its wings before they are covered with feathers, and when yet incapable of bearing them.