1897 Human Embryology 18

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Minot CS. Human Embryology. (1897) London: The Macmillan Company.

Human Embryology: Introduction | The Uterus | General Outline of Human Development | The Genital Products | History of the Genoblasts and the Theory of Sex | The Germ-Layers | Segmentation | Primitive Streak | Mesoderm and the Coelom | Germ-Layers General Remarks | The Embryo | The Medullary Groove, Notochord and Neurenteric Canals | Coelom Divisions; Mesenchyma Origin | Blood, Blood-Vessels and Heart Origin | Urogenital System Origin | The Archenteron and the Gill Clefts | Germinal Area, the Embryo and its Appendages | The Foetal Appendages | Chorion | Amnion and Proamnion | The Yolk Sack, Allantois and Umbilical Cord | Placenta | The Foetus | Growth and External Development Embryo and Foetus | Mesenchymal Tissues | Skeleton and Limbs | Muscular System | Splanchnocoele and Diaphragm | Urogenital System | Transformations of the Heart and Blood-Vessels | The Epidermal System | Mouth Cavity and Face | The Nervous System | Sense Organs | Entodermal Canal | Figures | References | Embryology History
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Part V. The Foetus

Chapter XVIII. Growth and External Development of the Human Embryo and Foetus

The two sections following on the growth of the foetus and the weight at birth are taken from my article on " Growth " in Buck's "Reference Handb. Med. Sci.," III., 394. A more accurate conception of the growth of the embryo can, however, be gathered from the figures in the latter part of this chapter.

Growth of the Foetus

The difficulty of determining the age of the human foetus and of obtaining specimens certainly fresh and normal has prevented our having any definite information on this subject. Preyer has compiled the following table of the length of the human embryo in centimetres :

Embryo Length (cm)
Lunar Month. Toldt. (300 obs.) Hennig. (100 obs.) Hecker.
First 1.5 (1.8) 0.75
Second 8.5 4.0
Third 7.0 8.4 4 to 9
Fourth 12.0 16.2 10 to 17
Fifth 20.0 27. 5 18 to 27
Sixth 80.0 35. 25 28 to 34
Seventh 35.0 40. 25 85 to 38
Eighth 40.0 44.8 39 to 41
Ninth 45.0 47.2 42 to 44
Tenth 50.0 (49. 0) 45 to 47


If the absolute length at the end of each month is divided by the increase during that month we obtain what Preyer calls the relative growth. Hennig's figures give the following relative growth for each month: First, 1,000; second, 0.812; third, 0.52:J; fourth, 0.41i>; fifth, 0.410; sixth, 0.219; seventh, 0.124; eighth, 0.01)3; ninth, 0.00'J; tenth, O.o;37. All the above data ai-e obviously inexact. Toldt's are evidently cooked up and not derived from ol)servation, nor do the lengths mean the same thing, for of the early stages the head and trunk only were measure<l ; of the later stages the head, trunk, and legs. A falser and more misleading device for studying growth has never been put in practice. The foetus, t(K>, l)eing spirally coiled in early stages cannot have its length determined accurately. Far better would it be to alwaj's determine the weight. The growth of the foetus in weight has }x}en most inadequately studied, although the weight is the r>/ J?/ available measure of the growth of the foetus as a whole. Hecker's data are perhaps the best. The weights are in grammes :

Month.


Maximum. Minimum.


Third,


20 5


Fourth,


120 10


Fifth,


600 75


Sixth,


1,280 875


Seventh,


2,250 780


Eighth,


2,488 1,093


Ninth,


2,906 1,500


Tenth,


1.562


Average.

11

57

284

684

1,218

1,569

1,971


The range of the maxima and the minima suggests that errors in the determination of the ages may have occurred — such errors of a month are not rare with obstetricians.

Appended here are Hecker's data as to the weight of the placenta in grammes, and the length of the umbilical cord in centimetres :


Month.


No. of obs.


Placenta.


Cord


Third,


8


86


7


Fourth,


17


80


19


Fifth,


24


178


31


Sixth,


14


278


37


Seventh,


19


874


42


Eighth,


32


451


46


Ninth,


45


461


47


Tenth,


62


481


51


2. Weight of the New-Born Child, — It is subject to very considerable variations. For middle Europe the average may be held to be about 3,340 grammes for boys, 3,190 for girls, the latter being somewhat lighter. The variations are very great, ranging from 1,000 to 5,000 grammes. For instance, the following table is given by Pfannkuch, who unfortunately jumbles the two sexes together :


Kilos.


Ol>8.


Kilos.


ObR,


1.50 to 2.00


23


3. 00 to 3. 25


150


2. 00 to 2. 25


36


3.25 to 8.50


115


2.25 to 2.50


52


3 50 to 3.75


79


2. 50 to 2. 75


90


3.75 to 4.00


46


2. 75 to 3. 00


110


4.00 to 4.50


13


It will be noticed that the maximum number of cases (150) falls between 3.00 and 3.25 kilos., and that the further the weight is removed on either side, above or below from this mean, the fewer are the cases. ThQ tables by other authors show the same general results, with usually slight differences in the quantitative values. For the most part these tables cannot be combined with one another, for they nearly all fail to fulfil some obvious requirement of good statistics; indeed, amateur statistics are generally provoking to the expert. It is, therefore, not desirable to attempt an analysis of the recorded data. As an example of statistics at once valuable and grossly defective, the following table is given after Siebold. The author gives the weights in pounds, but has neglected to say, as is necessary' in Germany, what kind of pounds, hence the metric equivalents cannot be calculated. Moreover the number of cases weighing even pounds and half-pounds is far in excess of those weighing pounds and one-fourth or three-fourths, which shows inaccnrato weighing, of course. To correct this the (piarter-iKJund groups of original table are condensed into half-pound groups :


Weight in lbs.


Boys.


OirlK.


4.0 to 4.5


4


10


4.5 to 5.0


19


24


5.0 to 5.5


44


58


5.5 to 6.0


172


195


6.0 to 6.5


220


285


6.5 to 7.0


858


858


7.0 to 7.5


286


240


Weight in lbs.


Boys.


Girl&


7.5 to 8.0


286


200


8.0 to 8.5


101


44


8.5 to 9.0


79


42


9.0 to 9.5


15


14


9.5 to 10.0


7


2


10.0 to 10.5



1


10.5 to 11.0



1


The extremes recorded in medical literature are very far apart, and statements of excessively large size are by no means rare, but can be received with incredulity only, as, for instance, the case reported of a still-bom child weighing 8,250 gms. {Berlin, klin. Wochenschr,^ 1878, No. 14) I Vierordt gives as the accredited extremes 717 gms. (Riter), and 6,123 gms. (Wright.)

The factors which determine the weight at birth are very obscure. It is, of course, safe to say vaguely that it depends on the nutrition of the foetus ; it is probable that individual differences in the rate of growth exist before as well as after birth, and it is probable that the length of gestation is the most influential single factor, to judge from my own experiments on the growth of mammals.

It has been demonstrated that the variations in the weight of the child depend upon various maternal circumstances. .

First, It is correlated with the age of the mother, as is shown in the following table, giving the weight of the children in grammes according to three observers :


Age of mothw.


Ingersley.


15 to 19 years


8,241


20 to 24 "


8.299


25 to 29 "


8,342


30 to 84 "


8,875


85 to 39 "


8,428


40 to 44 •


8,326


Fassbender.

8,271 3.240 3.388 3,367

j 3, 292


I


s


Petersson. 8,451 3,485 3, 591 4,062 3,591 3,676


From such tables we learn that very young mothers have the smallest children, and those of about thirty-five years the heaviest. It is much to be regretted that the tables do not show the correlation by single years and also the number of observations.


Second, The weight of the child increases with the weight (Gassner) and length (Frankenhauser) of the mother. Qassner states that the weight of the child is to that of the mother as 1 to 19.13, or 5.23 per cent of the maternal weight. Frankenhauser states that if the height of the mother is less than 4 feet 6 inches the child weighs 6 lb. 15 oz. ; if it is 4 feet G inches to 4 feet 11 inches, the child weighs G lbs. 25 oz. ; if it is more than 4 feet 11 inches, the child weighs 7 lb. 3 oz.

Th ircl. The weight of the child increases according to the number of previous pregnancies, as indicated by the following table :

Number of pregnancies.

One,

Two,

Three,

Four,

Five,

Six,


Hecker.


Ingersley.


(Grms.)


(Grms.)


8.201


8,254


3,380


8,891


8,353


8,400


8,860


8,424


8,412


8,500


8,858


Here again we encounter faulty statistics, for it is not shown that we have any other effect than that of age, for the conclusion claimed cannot be established until it is proved that primiparse have smaller children than multipane of the same age.

Fourth, Negri has maintained {Annali di Obstetrica 1885) that the compilation of three hundred and thirty-three observations show that the children of women whose first menstruation is early are larger than the children of those whose first menstruation is late.

Fifth and Sixth, The influence of race and climate, which have not yet been subjected to any proper exact study.

In conclusion I may add that it seems to me probable that all these influences produce their effect principally by prolonging or abbreviating the period of gestation. In other words, the variations in the weight of children at birth are to be referred immediately to two principal causes: 1, Differences in the age at birth; 2, individual differences of the rate of growth in utero.

Measuring the Length of Embryos

Owing to many changes in the curvatures of the longitudinal axis of the human embryo it is impracticable to employ any one system of measurement, to obtain comparable results for all ages. On this account I have adopted the system of giving in all cases the greatest length along a straight line, the embryo being measured in its natural attitude — excluding, however, the limbs from the measurement.

His adopts for embryos of four to ten weeks what he calls the Nackeuldnge ("Anat. menschl. Embryonen," Heft II., 5) or the distance in a straight line from the nock bend to the caudal l>end, but as this cannot be measured accurately in later stages I have thought it best to give up this measure. Hence it results that the length of an embryo as given by His is often different from that given in this work.

Embryos ot Known Ages

As already pointed out, we have to reckon from tho last day of the menstrual period as the date of conception, but this date is never quite certain, hence there is always some doubt as to the age of every embryo. We owe to Professor His most of our information in regard to the form and size of the embryo at successive ages during the first two months, see his ** Anatomio menschl. Embryonen," Heft II., 1882, especially pp. 25 and T2, also Heft I., lOr,, Heft III., 236-254, and Taf. X., which gives figures at a uniform scale of twenty-five embryos of the first two months.


The development of the embryo during the first three wci^ks has already been described and illustrated. Up to the end of tlio ninth week the form and size of the embryo undergo a correlated development, so that generally an embryo, at a given stage of development in form, will agree with its fellows in size; but to this rule there are not infrequent exceptions, and sometimes an embryo is found much larger than others at the same stage (His, /.c. Heft III., 240). Moreover the variability of embryos is very great, for in si>ecimons otherwise alike we find this or that organ retiirded (n* advancinl in development, as compared with the embryo as a whole. Neverth(^less it is possible with the information at present at command to determine the age of an embryo within two days plus or minus up to the end of the ninth week. For the development during the third month we possess as yet no satisfactory information, hut emhryos three months old are quite frequently obtained, and my own collection gives a good series of specimens up to the end of the fifth month.


Twenty-three Days

The first figure I give is that of His' embryo «, Fig. 31G, described by him in his "Anat. menschl. Enibryonen," Heft I., 100-115. The specimen was from a chorionic vesicle meaeui-ing 2.5 by i.O cm. ; the greatest length of the embryo was 4 mm., measured from the end of the hind brain iv, to the four teenth segment of the rump. It lay with its left side against the chorion, with which it was connected by a short allantoic stalk the yolk-sac measured 2.7 by 3.0 mm and had a short pedicle His stat«B that the probable age of the specimen was twenty three da^s and apparently bases the determination upon comparison with slightly younger and older specimens of known age. The shape of the embryo is very different from that of Fig. 180, p. 307, owing to the whole body having become rolled up, so that tho dorsal outline describes more than a complete circle ; the body has a marked spiral twist, the head being bent to the right, the tail to the left; the bending of the body is specially marked at the region of the mitl-brain (head-bend) and at the posterior limit of the hind-brain {neck- fio, hb — ma' Embrjo -. ak? p'yiend, Nackenkrihiuamig). the thn*i>ay». x.iK«.t.o5i primitive segments show externally; the anlages of both pairs of limbs have appeared as oulgro^vtha of the so-called Wolffian ridge, hut the leg is less developed than the arm. In the region of the head the divisions of the cerebral vesicles can be recomized. The optic vesicles are indicated by small protuberances. The oval otocyst fies about at the level of the second gill-cleft. The cephalic Itorder of the mouth lias become ridge-like; the dorsal end of the ridge joins the dorsal end of first visceral arch, which is known a.s the mandibular arch; the ri<lgo on the cephalic side is known as the maxillary process. The second, third, and fourth gill-arches Jire distinct and I>ehind each the imiierforate gill-cleft can be distinguished, but the fifth arch is indistinct. The heart forms a marked Iin itubt'rance, the bulbus aortie showing most on the left side. Fig. 'Wi, and the vyntiicles on the right.

An embryo of C. Rabl's. vorj' similar to His' «, just descril>ed, is figured by O. Hertwig, "Entwickelungsges.," 3te Aufl., Fig. 137.

His points out that the embryos numbered by him XXVI.. (D 2), LVI., (\V), and LA'II., (R), are very near the one just described. though a little older. In the same group belongs the embryo of Cost*', 47.1, PI. 11., Fig. 5, of which the age was determined at twenty to twenty-five days ; also Thompson's fourth embryo, figured and dencribed by Kulliker, "EiitwickelungH^os.." p. 311, Fifj. "i'M; alao that described by Hoiisen, 77.1, mid finiilly Ecker's specimen, 80.1. Of all these Conte's most desorvea attention on jicoyunt of ttie superb manner in which it has iH-eii figured. Concerning His' embryo R, Bome data alwnt thf cfflom have been given by His, 81.1, 311.


Twenty-Five Days

Embryos of thin age are extremely rare. Fnl has given a fiill but not wholly «atiafact<iry dewription, 84.2, of an embryo presumably of this age, though no datail were obtained in regard to it. The embryo, Fig. 'ill, as coini)are<l with that at twenty-three days, has grown rapidly; its greatest length is hSi mm.; itH form ha» clianged by tlio body having iNirtially unrolled, but tne head-bend and neck-ljendreniiiiniindai-e more prominent than bt> fore, <iwing to the embryo as a whole being less curved. The region of the foif-br.iiii is brought elo^e to the heart, the hejwl being still bout to the right; the liml)s are a little larger and thei-e is a well develnjH-d, distinct tail. The other prin(.■i|iid change is that oiily tlin"*' gill -aii'hes show externally, i^itl 1. :.'. the third and fnurth being already iiivaginat<'d in (■onne<-tinn wSlh the furiniition of the eirM(alsmu*< It iiiu'»t l)e added that this embryo WIS not (|Uit< nonnal is i-* shown ("JiH-eially by the cmdition of its vein« Tht n pnsent ition of tin (\t<nud Honn nf thu hend in the figure IS pruliabh not entiixh eorrttt

hnntifiii Ihui'i —\ln\\ 91 3 gnes a suiK-rb figure and nmiitkte an itomu al destriptinn of m i nibryo, the |)i->>babl<- jtge uf which ht h\es at t\vint\ si\di\ IiUHti/ tfien lit Tiiiiih/ 1 i<fht D'ti/i. — Enibn-cis of this ag<' are cliarai ti I i/A (1 b^ the i\ti(.ini diM.1 pineiit of the neck-Uinl. Fig. ■JIh thi ain\ of tthuh f inis a^ it wue, the suinniit uf the cuduyi); tilt gnah-vt lingtli In ni thisHi>i\ is *-s mm. Tu the ;igc of ;ilii>ut tvnnt\ light dn -tare ti>l« i-.-.ignHi the embrvo des.-ribed hv.Inlumnes Mulki 30 2 one hgimd U ( .«te. 47. 1, PI. lll..'.>ir.- deBcnlx-d In "\\ dili>ei 62 1, md fom embi-yos in His' eolleitiiai, numbered by him ("Anat. menschl. Ehnbryonen," Heft II., 8), I. (B), LXI. (Eck. I.), II., (A), and XL. {3tt.); concerning XL. seeHiB, I.e., pp. 24, 93. Of A and B His nas published a detailed anatomical account { " Anat. menschl. Embryonen," Heft I., 1499).

I choose for my illustration Fig. 318, His' embryo A, because it shows the neck-beud most perfectly; how entirely the prominence of the neck-bend alters the shape of the embryo will appear immediately if Fig. 218 be compared with Fig. 175. As changes since the twenty-fifth day we note especially the distinctness of the olfactory pit (Riech(jruhe) and of the still open invagination to form the lens of the eye, the deepening of the cerviciil sinus (sinus pr^cervioalis of His) , and the piirtial closure of the allantois-stalk {Bauchstiel) around the proximal part of the now narrow pedicle of the yolk-sac ; the closure of the Bauchstiel forms the umbilical cord, but the cord itself is very short and in ])roportion to the embryo very thick. In all parts there haa lieen an obvious development since the twenty-fifth day. Fig. 317, but further details may be omitted. Comparison of this embr^'o with others of the same stage show that ther^ is a considerable variation as to the nature and degree of curvature of the back, in consequence of which the specimens <iiffer somewhat in general form, though agreeing citB«;ly in structure.

Twenty-nine to Thirty Days

Embryos 8-10 mm. A number of specimens, which probably belong to the middle of the fifth week are known. For my illustration I give u drawing. Fig. 210, of an embryo sent to me by Dr. H. J. Garigues of New York; the datasufBce only to determine the age as the fifth week ; the specimen appeared normal imd vr-ell-preserved, but upon microtoming it, it was found to 1m! in poor condition histologically; it has interest because it shows with psijeoial clearness the relations of the foetal appendages. The embryo proj^Kir has begun to straighten its body, and as the outline over till' region of the medulla oblongata, comjiare Fig, 217, Fr, has iH-come leas curve<l, the head begin ato appear to form a right angle with the body ; the olfactory pit, ol, has deepened ; the lens of the evf, Dj), is well marketl, as is also the lachrymal groove descending from the eye; the cervical sinus, c.s, has deepened but is still open; the limbs have lengthened and in other specimens begin to show the differentiation of the hand and foot. About two-thirds of the allantois-stalk has closed to form the umbilical cord, C7m, from the end of which extends the anmion, Am. The long yolkstalk, Vi.Sj ends in the pear-shaped yolksac, Vi; the allantois-stalk or Bauchstiel, V^ / Bs, which runs to the chorion, Cho.


In this group belong the embryo of Rabl (O. Hertwig, "Entwickelungsges.," 3te Aufl., Fig. 158), the embryo of 10 mm. of which Phisalix gives a detailed anatomical description, 88. 1, — also seven embroys, enumerated by His, " Anat. menschl. Embryonen," Heft II., 8, and described there p. 45-7, and His' embryo Pr., /. f., p. 10, 238, Taf. X., Fig. 8, Taf. XIII., Fig. 47 — this last by far the most perfect drawing of this stage which we possess.

Thirty-one to Thirty-two Day

Embryos of 10-12 mm. (see His, Z.c, Heft II., 47-51 and, for a list of ten specimens, p. 8-0, Taf. X., Figs. 13, 14, and 15, Taf. XIII., Fig. 6). The age of the embryo at this stage can as yet only be estimated, as in no case have we data sufficient for a reliable determination. For a typical illustration of this stage we may take His' Br. 1, Z.c, Taf. XIII., Fig. G, which measured 11 mm. The back has straightened out, though the lower end of the body is still rolled over; the head has risen somewliat and enlarged both absolutely and in proportion to the rest of the Ixxl}'. Between the end of the region of the hind-brain and the level of the arm the outline has become slightly concave; this concavity His designates as the Nackengrube, The cervical sinus is so deep that the second, third, and fourth gill-clefts have disappeared from the external surface ; the first gill-cleft remains and can already be recognized as the anlage of the external auditory meatus ; it is separated from the mouth by the prominent mandibular arch. On the cephalic side of the mouth the maxillary pnx^ss has IxH^omc^ more prominent, but the two processes do not yet met*t in the median line. The primitive segments are still marked externally. The limbs show the tripartite division ; the fore limb is more advanced than the hind limb; the division of the digits of the hand is {'ust indicated. The abdomen bulges out owing to the j>:r(>wtli of the iver. There is a true tail, which is now near its maximum development. The umbilical cord h&s lengthened and shows the conunencing spiral twisting; the amnion springs from the end of the cord, leaving only a short stretch cf the allantois- stalk between the cord proper and the chorion ; the amnion lies close to the embryo. In the fresh specimen something can be seen of the shape of the brain; especially noteworthy, among the points thus to be recog;nized, is the slmrp bend (Briickenkriiinntutig) at the deep-lying anterior end of the hind-brain or region of the sinus rhomboiclalis.


Fig. 219. Embryo of 9.8 mm. Minot Collection No. 145. Probable a^e thirty days, x 5 diams.


In embryo a little older than these the changes in form above mentioned have progressed further. The specimens measure 12-13 nun. the bo<ly ia straigliter ; the head is larger and has risen so as to be at alx>ut right angles to the bodv ; the concavity below the hindbrain in the outline of the neck {yacKenkriimmuTtg} is more marked; the limbs are longer, the lingers more distinctly marked; the tail is at its maximum development as a free appendage; where the mandibles meet iu the median line the separation of lip and chin has h^un; the second gill-cleft is invaginated into the cen-ical sinus and can no longer be seen on the outside.

Thirty-five Days

Embryos of 14 mm. The correlation of age and size of this stage cannot be regarded as absolute, though we can say (His, I.e., Heft III., iiO) that embryos of this length are about five weeks old. The body is now nearly straight the limbs project beyond the outline of the body iu profile views the abdomen owii^ to the large siae of the heart and uver bulges far out in side lews the ai-eiuif the head is about equal to that of the rest of the body; the outlint' of the head shows the head-bend and neck-bend most clearly marked ; the neck-bend is characterized by the prominence at that point; the prominence ia often less than in Fig. 220. The umhilical cord frequently contains one or several- coils of the intestine and makes one or two spiral turns. The stalk of the yolk-sac is long, and projects quite far from the end of the cord between the amnion and chorion. In a dorsal view we can see that the limbs are somewhat flattened and in a pliine nearly jiundlel with the longitudinal axis of the embryo, but the planes of the anus are inolineil so as to meet above the head, and the planes of the le^ are inclined to as to meet below the tail. Owiuf; to the flattening of the limits we can already distinguish the inner or pidmar surfaces from the outer.



Flu .Mil Luiln _t uhout 14 mn MInot t<lle«lo ^o IX Ab- dama CCom[«n) Fig



Noteworthy is the irregularly crenulated appearance of the walls of the medullary tube or spinal cord.

Fig. 222 is copied from Coste, and is valuable on accoimt of the very large number of anatomical facts which it records. Coste gives no data but states that the specimen was " about thirty-five days old."

Thirty-eight Days

Embryo of 15 mm., in a chorionic vesicle of 45 by 40 mm. The age of this specimen, Fig. 223, is known by estimate only. It has been superbly figured by His (" Anat. menschl. Embryonen," Taf. XIV., Fig. 5). This stage represents the transition from the embryo to the foetus, because after the fortieth day the form is distinctly human. The head has risen considerably, and the back has straightened still more, the rectangular neckbend thus becoming emphasized. The body has become still more protuberant on the ventral side, and in side views the arms no longer reach to the outline of the body.

Forty Days

Embryos of 19 mm. The hea^ has risen far toward its definite jxisition, with the result of a very rapid apparent increase in the length of the embryo. \ The change of position of the head results in bringing the mid-brain finally directly above the hind-brain, the embryo being conceived as having the body vertical. Durink the elevation of the head the concavity {Nackengnihe) at the bacg of the nock is gradujilly obliterated. In both head and rump the external modelling, which in earh'er stages indicated more or less the position of the internal organs, luis become blurred and in the next stage is found to have nearly or quite disappeared. The maxillary processes have met and united in the median line. The anlages of the eyelids have develoi)ed. The concha of the ear is indicated. The arm reaches beyond the heart; the fingers appear as separate outgrowths.

Fifty Days

Embryo of 21 mm. I have a fair specimen which came into my possession with no history whatever, but it agrees verj' closely with Fig. 23, Taf. X., in His' "Anat. menschl. Embryonen," of His' embryo Ltz, of which he fixes the probable age as just over seven weeks. The head is nearer its final position than in Fig. 223, and relatively larger in proportion to the body. In the eye, cornea and conjunctiva are clearly separated ; the face has the foetal form, the nose, mouth, and chin being fully marked off. The arms are clearly divided into upper and lower segments ; the five digits are well developed ; the hands rest over the heart and nearly touch one another. In the specimen figured the outline of the abdomen is abnormal. The leg shows the tripartite division ; the toes are just beginning to be free, but the hind limb is much less advanced than the fore limb. The tail is still a freely projecting appendage.



Fig. 888— His Embryo XXXIV. (Dr.), 15 mm. long from the Neck-bend to the Coccygeal Bend. Age estimated at thirty-seven to thirty-eight days. X 5 diams.


Fifty-three Days

Embryo of 22 mm. The specimen, Fig. 224, is probably not quite normal, but except for the extreme and unusual cun'atiu-e of the back it agrees closely with His' embryo Zw, which is figured by him, Z.c, Fig. 24, Taf. X., as a normal embryo of presumably about seven and one-half weeks. My specimen I received in 1884 with the following history: " Menstruation began January 20th. February and March slight show every few days. Abortion March 3()th," which is insufficient to determine the age. As compared with the last stage there are comparatively few changes of external form ; the most noteworthy are perhaps the increased development of the legs and feet and th(» commencing disappearance of the free tail. At this time the protrusion of the coils of the intestine into the coelom of the umbilical cord is about at its maximum.



Fig. 223. — Embryo of '.H mm. Miuot rullt*c'tioD. No. 54. lYobable a^. flfty -three days. X 3 diamn


Minot1897 224.jpg

Fig. 224. — Embryo of 22 mm. No. 144 of Minot Collection. Assumed a^^, sixty days. X 3 diam.


Minot1897 225.jpg

Fig. 225. — Embryo of 28 mm.

Sixty Days

Embryo of 28 mm. The specimen figured resembles closely in form, though larger than, His' embryo Wt (Fig. 25, Taf. X., Z.C.), which he has determined as a normal embryo of about eight and one-half weeks. My specimen. Fig. 225, came to me with no data. The head is still larger in proportion to the body than in Fig. 223. The face shows the two lines, which, as seen in profile, mark the two ridges which run over the chtH?k, one alongside the nose to the corner of the mouth, the other from the eye , these ridges are highly characteristic of the ninth week, and traces of them not rarely persist in the adult physiognomy. The limbs have grown considerably, the hands being lifted toward the face; at the elbow there is a considerable bend; the toes are all free and the soles of the feet are turned toward one another. The tail has disappeared as a free appendage. The external genitalia are considerably developed; the clitoris-penis projects some distance.

Sixty-four Days

Embryo of 32 mm. The specimen, Fig. 226, came to me with the following history : ** January 4th, 1886, last flow began; March 13th, 1886,

abortion ; " between these two dates are sixty-eight days ; but as the flow took place conception probably occurred after menstruation ) therefore if we deduct four days, making the age sixty-four days, we shall probably not be far wrong. It will be noticed that the head has not yet assumed its final angle with the

Collection Probable age sixty-four days. X8,,

diauw body. On the other hand the protuberance of the abdomen is much reduced, so that the body as a whole has begun to have a more slender form than in earlier stages. In this specimen the eyelids have not even begun to meet; in another I have they have met, Fig. 227, except just in the centre where is still a loophole.

This specimen was brought to me with the statement that it was just sixty days. I endeavored, unsuccessfully, to get data. The large size, 43 mm., and advanced development of the embryo led me to consider the age given as erroneous, and to believe the true age to be perhaps sixty-seven days.

Sixty-five Days

Embryo of 55 mm. I figure next, Fig. 228, a foetus concerning which I possess no data. Comparison with embryos of two and three months leads me to place it a little under half-way between them. The specimen has essentially the configuration of the young child; but the head is very large, and the body slender ; the position of the limbs is typical ; the upper arm is bent down, thb forearm extends toward the chin ; the knee is bent so as to throw the foot toward the median line; the soles of the feet are placed obliquely facing one another; the anlages of the nails can be recognized on both the fingers and toes.



Fig. 227.— Enibr>'o of 34 mm. Collection. l-Yont View of Face.


Minot


mm. A88iimed


Fig. 228. — Embryo of 36

No. 97 Minot Collection.

ai?e, seventy - five


X 3 diams. tne exaCt days. Natural size.





Fm. 280. - Front View of the Head and Face of the Embryo, Fig. 229.



Fig. 289.— Euibrvo of 78 mm. No. 74 Minot Collection. Age three mouths.


embryos of the eleventh and twelfth weeks are very rarely obtained. I have never had a normal one of this period with data to determine the age.

Three Months

Embryos of 78-80 mm. In my experience there is no other age at which abortion of normal embrj^os occurs so frequently as at three months, and I possess a number of specimens of this age, which agi'ee very closely with another in size and form. The foetiis drawn in Fig. 229 may be taken to represent very accurately the form and size of the human embrj^o at three months. The position of the limbs is typical for this age, but there are slight variations in that the hands, one or both, may project more or be higher or lower; usually the right foot lies in front of the left, but not always. Fig. 230 gives the front view of face of the same embrv'o to show the closed evelids, the broad triangular nose, the thick lips and pointed chin.


Fig. 290.— Embryo of about lO) mm. No. lection. Assumed, a^, one hundred and ten days ural fdze.



Three and One-half Months

Embryos of 108-110 mm. I have several specimens which represent this age. I figure two of them, one to show the natural attitude, Fig. 231, in utero, the other to show the natural attitude assumed by the embryo when released from its membranes. The first specimen wune to me with no history, but as it is certainly a little larger than several other foetus of about one hundred and six days it is probably a little older. The head is bent forward. Fig. 231; the back is curved ; the arms and legs are toth raised toward the face ; the right leg is nearly straight so that the toes are brought against the forehead, while the left leg is bent at the knee, bringing the left foot against the right thigh. In this attitude the embryo fills out as ^^ 282. -Embryo of ii8 perfectly as possible an oval space, and fits mm. No. is Minot coiiectherefore the cavity of the uterus. The second slx^dayr*' nSuuSS size.*" specimen, Fig. 232, shows the attitude assumed by the embryo when free, and proves that the position in utero. Fig. 231, is a constrained one. This fcetus was received November 30th, 1883. The delivery took place on the morning of that day, and the last menstruation *had ceased one hundred and six days previously ; the remarkably fresh condition of the foetus indicated that it had been dead only a very short time, so that we cannot be far wrong in putting its exact ago at one hundred and six days.

Four Months

Embryo 155 mm. The foetus, shown in Fig. 233, came to me in a very fresh condition, January 2d, 1887, with the statement : " Conception said to have taken place September 1st, 188G; foetus came away January 2d, about noon." The embryo is typical in size and development for four months, except that the crown is higher than usual, and the antero-posterior diameter of the head somewhat below the average.

The natural attitude in utero is similar to that of Fig. 231, the attitude shown is that assumed bv the foetus, when released from the membranes.


Fig. 2Sa. Embryo of 155 mm. No. IHO KlBOt Collection : A^. one hundred and twenty-three days, natural alxe.




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