Paper - Testes descent 1909 - 3

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Hart DB. The nature and cause of the physiological descent of the testes. (1909) Trans Edinb Obstet Soc. 1909;34:101-151. PMID 29612220

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This historic 1909 paper by Hart described the descent of the male testes.

See also by this author:

Hart DB. The nature and cause of the physiological descent of the testes. (1909) J Anat Physiol. 43(3): 244-65. PMID 17232805

Hart DB. The nature and cause of the physiological descent of the testes. (1909) J Anat Physiol. 44(1): 4-26. PMID 17232824

Hart DB. The nature and cause of the physiological descent of the testes. (1909) Trans Edinb Obstet Soc. 1909;34:101-151. PMID 29612220

Hart DB. The physiological descent of the ovaries in the human foetus. (1909) J Anat Physiol. 44(1): 27-34. PMID 17232822

Modern Notes testis

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General: 1901 Urinogenital Tract | 1902 The Uro-Genital System | 1904 Ovary and Testis | 1912 Urinogenital Organ Development | 1914 External Genitalia | 1921 Urogenital Development | 1921 External Genital | 1942 Sex Cords | 1953 Germ Cells | Historic Embryology Papers | Historic Disclaimer
Female: 1904 Ovary and Testis | 1904 Hymen | 1912 Urinogenital Organ Development | 1914 External Genitalia | 1914 Female | 1921 External Genital | 1927 Female Foetus 15 cm | 1927 Vagina | 1932 Postnatal Ovary
Male: 1887-88 Testis | 1904 Ovary and Testis | 1904 Leydig Cells | 1906 Testis vascular | 1909 Prostate | 1912 Prostate | 1914 External Genitalia | 1915 Cowper’s and Bartholin’s Glands | 1920 Wolffian tubules | 1935 Prepuce | 1935 Wolffian Duct | 1942 Sex Cords | 1943 Testes Descent | Historic Embryology Papers | Historic Disclaimer
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David Berry Hart
David Berry Hart (1851-1920)

The Physiological Descent of the Testes=

V. Descent in Marsupials

By D. BERRY Hart, M.D., etc., Lecturer on Midwifery, Surgeons’ Hall, Edinburgh ; Hon. Fellow, American Gynecological Society ; Carnegie Research Fellow.

At this time of life the testis is connected in a very particular manner with the parietes of the abdomen, at that place where in adult bodies the spermatic vessels pass out, and likewise with the scrotum. This connection is by means of a substance which runs down fromthe lower end of the testis to the scrotum, and which at present I shall call the ligament, or gubernaculum testis, because it connects the testis with the scrotum and directs its course in its descent” (p. 6).

  • It is plain from this description, that the cavity of the bag or of the elongation of the peritoneum which contains the testis in the scrotum, must at first communicate with the general cavity of the abdomen by an aperture at the inside of the groin” (p. 11).

“When the testis is descending, and when it has even passed into the scrotum, it is still covered by the peritoneum exactly in the same manner as when it was in the abdomen”: (p. 10).—JoHN Huntrr, “A Description of the Situation of the Testis in the Foetus, with its Descent into the Scrotum,” in Observations on Certain Parts of the Animal (iconomy, London, 1786.

“The parts in the female appropriated for the purpose of supplying the young are variously placed in different animals. In the horse, black cattle, sheep, and other graminivorous animals, their situation is between the hind legs, which is also the place allotted for the testicles of the male of this tribe ; (and probably of all those in which they come out of the cavity of the belly) therefore in the hermaphrodite which has both these parts, the testicles are in some degree obliged to come down into the udder, which does not receive them so readily as the scrotum.”

—Joun Hunter, “Account of the Free Martin,” in p. 55, op. cit.

IN a previous communication I described a central canal in the ovary of the rat-kangaroo, apparently derived from the Miillerian duct. The question arose as to whether this was exceptional or normal in marsupials, and therefore, at Dr James Ritchie’s suggestion, and through his kind services, I obtained from Professor Wilson of Sydney the pelvic ends of five kangaroo embryos in good preservation. Four of these were Macropus ruficollis; the fifth and largest, Dasyuwrus vwerrinus. After suitable preparation, they were cut in transverse serial sections and stained with logwood and eosin. In this way about three thousand sections were obtained. I now found that two were female and three male. This seemed at first a disappointment; but, on examination, the male embryos were found to be of great interest and novelty in many points, so that the results of their examination and of an extended investigation into the whole question form the subject of the present paper.

  • This inquiry was carried out at the Laboratory of the Royal College of Physicians, Edinburgh.

The results of the examination of the female specimens, so far as the development of the mammary pouch and round ligaments is concerned, will be found in another paper; but the conditions in the two sexes are intimately connected with one another, and must be read together to get a complete view of the subject. I found no central canal in the ovary.

In two of the male specimens (MJacropus ruficollis) the Wolffian bodies were present with the developing testes on their inner and upper surfaces; the inguinal canal, gubernaculum, and cremaster had developed, and the scrotum was developing; in a third, more advanced, the Wolffian bodies had disappeared, the scrotum had developed and separated, and the testes were in the inguinal canal. One special point of value in the last specimen was that, although the testes were in the inguinal canal, its size was such that serial sections could be conveniently made. In the human male foetus at this stage the specimens are too large for this being done.

I shall therefore take up —

I. The development of the scrotum, inguinal canal, and gubernaculum prior to the descent of the testes. ; em bo Oo

Fig. 1. — T.S. embryo, Macropus rujicollis ; Wolffian bodies and testes in abdomen. ({.)

1, epidermal ridges ; 2, lymph-sinuses; 8, pyramidalis muscle,

II. The condition of the scrotum and inguinal canal after the testes were in the inguinal canal.

1II. The mechanism: of descent of the testes as shown in the marsupial specimens.

IV. The descent of the testes in the human feetus.

V. The phylogeny of descent of the testes and of the parts involved in it.

I. The Development of the Scrotum, Inguinal Canal, and Gubernaculum Prior to the Descent of the Testes

This was well shown in two specimens, but I describe the conditions in one only: the other corroborated these. The sections are first considered from above down, and begin a little above the suprapubic region.

Development of the Scrotum. Structure of the Abdominal Wall on Transverse Section—The epidermis of the anterior abdominal wall in the suprapubic region has two ridges, one on each side of the middle line, the depression between the two | lying opposite the linea alba. The deep epidermal cells are well marked. Behind it lies a layer of fibrous connective tissue, and then comes a layer of denser connective tissue continuous on each side with lymph-sinuses to be presently described. This special layer has a homogeneous ground-substance interspersed with connective-tissue corpuscles and unstriped muscle. Next comes a layer of mesenchymatous tissue, and finally the peritoneum. Lower down on the abdominal surface the epidermic ridges are larger in section, and each has in it a circular space filled with connective tissue of a myxomatous nature surrounded by deep epidermal cells. These are evidently sections of double solid cones in the epidermis. The sections of the cones below this lose their intermediate epidermal septum, and we get a larger hour-glass space. Then they lose their posterior epidermal wall, and the core has in it a double fan-shaped expansion of unstriped muscle derived from the inguinal fold, and broader in front (gubernacular fibres). There are thus formed in the suprapubic epidermic ridges double cones, complete above, but with the internal and posterior boundary walls incomplete lower down. They are formed by the deep epidermal layer passing backwards and snaring in the connective tissue completely above, but less -completely below, where the epidermal horns do not meet. These cones—best termed the scrotal cones—form the scrotum, into which the testicles. ultimately pass. The fully formed scrotum is solid at first, but ultimately develops a cavity as the gubernaculum grows into it, as Klaatsch and Frankl and Katz figure in their specimens (Figs. 1, 2, 3, and 4).

The marsupial scrotum has long been known to be prepenial, but the reason has never been fully explained. All writers, except Klaatsch, consider it homologous and analogous to the ordinary scrotum in higher mammals. If so, however, it has not only appeared prematurely in phylogeny, but should not be prepenial and suprapubic. The account I have given of its development explains its nature. It is the analogue of the female mammary pouch, and, although this may seem paradoxical, its homologue too. It develops like the mammary pouch, but the deep epidermic layer passes backwards in crescentic form, the double fold containing little more than the deep epidermic cells, as the cavity of the pouch is to be formed, not by the desquamating epidermis as in the mamma, but from the enclosed connective tissue. This development of the scrotum in the suprapubic region necessarily makes it prepenial, and the desquamation of the cells enclosed by the deep epidermic horns, at a later stage render the scrotum free and pendulous.

After making out the above developmental points in regard to the scrotum, I was glad to find it confirmed by Klaatsch’s opinion, given in his paper. He there suggests that, from its position and relation to the gubernaculum — the analogue of the round ligaments — the scrotum must be the analogue of the mammary pouch. This question will be discussed, however, later on. I may mention here that it occurred to me that the adult scrotum might show a furrow in its mesial aspect as evidence of the development. The specimen Klaatsch figures does not show this, but it is well seen in the scrotum of Acrobata pygmea figured by Katz. He describes this scrotum as heartshaped, and states that he has seen it in young male specimens from Brazil, and in an adult specimen of the opossum (Fig. 5).

Fig. 2.—T.S. Macropus ruficollis embryo. (2°.) 1, phallus; 2, scrotal cone; 3, lymph-sinus. Note median partition disappearing.

Fig. 3. — T.S. Macropus ruficollis. (52). 1, gubernacular fibres in scrotum ; 2, inter-sinus band displaced up and back; 8, horn of deep epidermis passing back; 4, solid scrotum formed from scrotal cones.

Fig. 4,— Gubernacular fibres in scrotum. (2{°.) 1, epidermal ridge (3 in Fig. 8).

Fig. 5. — Scrotum in Acrobata pygmaa. (3.) a, anus; p, phallus; s, scrotum; r, groove between original cones. (Katz.)

In the male embryo where the testes were in the inguinal canal, the scrotum was separated from its epidermal bed and projected at right angles from the abdominal surface. It was still solid (Fig. 15).

I may sum up this point here, then, by saying that the scrotum in marsupials is the analogue and homologue of the mammary pouch of the female in every respect, but the full proof of the latter is only given in the section on Phylogeny (V.). |

The Development of the Inguinal Canal and Gubernaculum.— The development of the inguinal canal and its contents, excluding the testes and epididymis in the male, is intimately bound up with that of the lymph-sinuses in the groin, and of the gubernaculum, acting in association with the muscular and fascial structures in the abdominal wall on which the inguinal fold, to be presently described, abuts. In both the specimens we are now considering, the testes were abdominal and developing on the Wolffian bodies, 7.e. were abdominal and high up. This fact must be emphasised, as we shall see just now that the inguinal canal had developed while the testes were in the abdomen, so that, broadly speaking, the inguinal canal, contents and lining, tunica vaginalis, the gubernaculum (at this special stage), and cremaster owe their presence to a penetrating growth of gubernacular fibres, peritoneum, and cremaster along a definite lymphatic tract while the testes are abdominal, and thus not to any mechanical dilating process connected with the descent of the testicles. To understand this we must consider the structure of the abdominal wall. The anterior abdominal wall of the embryos, viewed on transverse section, has the following structure. First, on the surface, on each side of the middle line, is the epidermal layer with the two ridges already described, in which the scrotal cones are developed. Behind this comes a thin layer of unstriped muscle, and then a thicker layer of connective tissue of a mesenchymatous nature, but with fibrous cells condensing it. Next this, lies a deeply stained band of connective tissue joining the inner ends of the lymph-sinuses; then more mesenchymatous tissue; and lastly, the pyramidales, recti, and transversales muscles, the external oblique and peritoneum, the last closely bound up with a fascia into which in the flanks the transversalis radiates. This fascia forms the transversalis fascia;. the cord-covering known as the cremasteric fascia is derived from the tendon of the internal oblique. The fascial structures implicated in descent are well seen (Figs. 1, 9, and 10). :

I must now describe the lymph-sinuses as seen in the male.

These, when examined in transverse section from above down, appear as an oblique chain of lymph-sinuses lined with nucleated endothelium, the connective tissue between the sinuses consisting of deeply staining round cells with a large nucleus; it thus stands out more markedly than the connective tissue behind and in front of it. A very important landmark is, as we shall see, the band of connective tissue joining the inner ends of the sinuses. At the outer end of the lymph-sinuses lie an artery and vein. We have thus in the mesenchymatous tissue of the anterior abdominal wall a ladder, as it were, of lymph-sinuses, of which we get transverse sections as we pass from below at the base of the scrotal cones obliquely up and out, showing on section the oblique inguinal chain I have just described. They spread up to form the superficial abdominal lymphatics, and in the specimens could be traced as far as the ribs. I traced them also in the sections down to a central group of sinuses lying behind the phallus, and this apparently poured by a deep channel into the Wolffian mesentery. The distribution of these lymph-sinuses is best understood by reference to papers by Gulland and Lewis, and especially to those of Dr Florence Sabin (Figs. 1, 2, 3, 6, and 11).

Fig. 6. — Lymphatic system at lower end of abdominal wall in 3 cm. long pig embryo (F. R. Sabin). P.L.H., posterior lymph hearts ; R.C., receptaculum chyli; K., kidney; W.B.,

Wolffian body; D., diaphragm; 8.V., sciatic vein; F.V., femoral vein; | M.P., ducts to mesenteric plexus.

In this valuable research Dr Sabin has shown that in the skin “the lymphatic system in the embryo pig begins as two blind ducts which bud off from the veins in the neck. At the very start the openings of these ducts into the veins are guarded by valves formed by the direction the epithelial bud takes as it buds off from the veins. In the ducts themselves there are no valves at first. . From these two buds, and, later, from the two similar buds in the inguinal region, ducts grow towards the skin and widen out to form four sacs or lymph hearts, and from these sacs the lymphatics grow to the skin and cover its surface. At the same time there is a growth of ducts along the dorsal line, following the aorta to make a thoracic duct from which the lymphatics grow to the various organs” (p. 387, op. cit.).

In some of the illustrations Dr Sabin figures a chain of lymph-sinuses running in the line of the inguinal canal and also pouring deeply to the Wolffian mesentery. The nature of the lymph-sinuses in the groin which I have described in the kangaroo embryo is quite evident. They correspond tothe lymph-sinuses in the pig, and are the posterior starting-points of lymphatic development for the skin of the anterior abdominal wall. Below, in my specimens, they unite in the tissue behind the phallus to form there a deeper single system of sinuses; these thus communicate with the superficial system Dr Sabin describes, and the latter can be traced in this specimen up as far as the ribs. Between the pubes and the deep system of sinuses lies connective tissue of a mesenchymatous nature (Fig. 12). :

Lewis has confirmed Dr Sabin’s views as to the origin of the lymphatics, but found in the rabbit more than four centres of origin.

The outer edge of this sinus system, and the lymphatic [Face page 108.

Fig. 7.— Lymph-sinuses (1) in front of pyramidalis.

tissue connected with it, corresponds with the outer edge of the pyramidalis on each side at this stage of the development of the inguinal canal; its upper limits are, at this stage, in the rib region, but may be higher; while, beneath, it ceases at the level where the inguinal fold passes in, and the muscles run from the front of the pubes to the hip bone; above this level the mesenchymatous tissue begins to be well developed. This tissue and the superficial abdominal lymphatic sinuses form the path along which the gubernaculum develops to form the inguinal canal and its contents (Figs. 7 and 9).

The primitive inguinal canal, as I call it at this stage, runs from below up to reach the suprapubic scrotum, and thus transverse sections do not cut it in its full course. It will therefore be best now to describe the sections from below up, beginning at the point where the peritoneal dimple receives the inguinal fold, and passing up to the region of the scrotal cones. Before doing so, however, the nomenclature must be considered, as it is not in a satisfactory condition. The wellknown term of Hunter, the gubernaculum testis, 1s used in different senses, and embryologists have introduced new terms which human anatomists have not yet adopted. I use the terms “plica” or “fold” when the peritoneum is the nakedeye structure described; “gubernaculum” and “ligament” when the contained muscle or connective tissue is meant. In the stage at which the testes are still in the abdomen and attached to the Wolffian bodies, we have the following terms :—

(1) The Wolffian mesentery attaches the Wolffian body to the posterior abdominal wall, and its upper end is the diaphragmatic fold of the Wolffian body; its lower, the inguinal fold. |

(2) The testis has an upper, cephalic, and a lower, caudal, fold or ligament. The former passes up to the diaphragmatic fold; the latter down to the inner and upper aspect of the genital ducts. 110 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

(3) The inguinal fold (plica inguinalis; gubernaculum before it penetrates the abdominal wall) is an important one. It is the caudal fold of the Wolffian-body mesentery, with an upper origin opposite the lower end of the caudal ligament of the testis, the width of the genital ducts thus separating them. Below, it ends at the inner abdominal ring. It is the peritoneal portion of the gubernaculum testis, and corresponds to the abdominal portion of the round ligament (Figs. 8 and 9).

(4) Gubernaculum testis—This is John Hunter’s term, and is a valuable one. In using this term gubernaculum testis, or “rudder” of the testis, Hunter evidently did not mean to attach more than a “guiding influence” to it. It is often held to involve the idea of traction, but this is unfortunate. Hunter defines it as being the connection between the testis and bottom of the scrotum, and figures it in a six-months fcetus as extending down to that point. His line really, in the figure given by him, marks out the primitive inguinal canal. I shall use the term “developing gubernaculum” as meaning the structure extending from the genital ducts to that point in the inguinal canal or scrotum it has developed to. This makes the caudal ligament a separate structure. It is thus the “ developing gubernaculum” testis while the testis is in its original or early position. Its peritoneal portion is the inguinal fold. The term “developed gubernaculum” I shall use when the testis is in the inguinal canal or scrotum. Its upper end is in line with the caudal ligament of the testis and attaches it indirectly to the epididymis where the epididymis joins the vas deferens. The exact upper attachment of the gubernaculum is always really to the epididymis, and at the point where the globus minor and vas deferens meet (Bramann, Frankl) (Fig. 8).

When the testis is passing into the scrotum, the gubernaculum begins to shrink, the involution of the gubernaculum. We should therefore speak of it at this time as the involuting gubernaculum. Its traces pass from epididymis to scrotal base. Fic. 8.—Pig embyro, 128 mm., injected and cleared (E. C. Hill) to show testis relations.

1, epididymis; 2, origin of caudal ligament; 3, caudal ligament; 4, ductus epididymis; 5, inguinal fold at origin; 6, inguinal fold.

[Face page 110. Fic. 9.—T.S. embryo, Macropus ruficollis. (5,°.)

1, Wolffian body; 2, inguinal fold; 3, Miiller’s duct; 4, external oblique tendon ; 5, inguinal wedge. Wedge beginning to penetrate into lymphatic tissue.

[Face page 111. Fic. 10.—To show inguinal wedge. (2{°.

1, tendon of external oblique; 2, wedge of transversalis and internal oblique muscles; 3, lymphatic tissue.

The gubernaculum, when it begins to penetrate the abdominal wall, is made up of a peritoneal roof like an inverted V, has unstriped muscle as its important constituent, and also connective tissue. It has at its lower end cremasteric striped muscle passing into it from below up, but this is a phylogenetic relic of the “conus inguinalis” of rodents and insectivora, At the caudal end of the developing and penetrating gubernaculum there grows with it, through the abdominal wall, the internal oblique and transversalis muscles, with the tendon of the external oblique in front of these. Thus the peritoneum of the inguinal fold, the unstriped muscle between its folds, and the internal oblique and transversalis muscles form a penetrating wedge which, as we shall see more clearly soon, invades a definite tract of lymphatic tissue. Ata point in the anterior abdominal wall to the one side of the top of the pubes, and immediately above where the muscles in front of the pelvic wall pass out to the hip bone, the inguinal fold meets the abdominal wall, without, however, penetrating it. It is then merely two lateral folds of peritoneum with connective tissue and unstriped muscle between them. A little above this we see the developing subernaculum making its way through the wall. Here~ the peritoneum, fascia, the transversalis and internal oblique muscles, with the tendon of the external oblique in front, form a growing wedge which passes abruptly up and forward through the abdominal wall, towards the base of the scrotal cones. This penetrating wedge makes its way at first in the mesenchymatous tissue. Soon, in the succeeding sections, the internal peritoneal opening is lost, and we now get what Klaatsch terms the inguinal bursa—the inguinal canal with its coverings and main contents. We see the developing gubernaculum on section, with its partial peritoneal covering, and the part free from it and continuous with the connective tissue. Outside, comes the tunica vaginalis and the striped muscular and fascial coverings forming the walls of the bursa. These striped muscular cover112 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

ings will ultimately form the cremaster. The inguinal wedge now passes on near the deep central lymphatic sinuses without invading them much, if at all, and next passes across the chain of superficial sinuses I have described and identified with those Dr Sabin has injected in the pig embryo. That the developing gubernaculum invades these sinuses, there is indubitable evidence. It has been already pointed out that these superficial abdominal sinuses, higher up than this level, have their inner ends joined by a deeply stained band of connective tissue and unstriped muscle, the lymph-sinus band, thus forming with the sinuses a continuous crescent. on transverse section. At this lower level, where the developing gubernaculum is penetrating . the superficial sinuses, some of these lie to the outer side, while the joining band lies distinctly to its inner and posterior aspects. The developing gubernaculum thus actually traverses the sinuses. The gubernacular wedge now curves up to the open base of the scrotal cones, the unstriped fibres alone radiating into the cones as already described (p. 104, and Fig. 4). The tunica vaginalis and the cremasteric fibres are now absent (Figs. 10, 11, 12, and 13).

The developing gubernaculum with the peritoneum and cremasteric fibres thus forms the inguinal canal with its tunica and cremaster by a growth of its wedge-shaped end in the line of lymphatic tissue and lymph-sinuses. The development of the sinuses at this stage is inside the outer edge of the pyramidalis, and it is then the gubernaculum, with the associated peritoneum and muscle, begins its growth, and its course seems to be influenced by this local lymphatic area. Dr Sabin states: “In the posterior part of the body there are two centres for the radiation of the ducts—first, over the crest of the ilium for the ducts of the back and of the hip; and secondly, in the inguinal region, for the ducts that grow into the abdominal wall and down the leg. The ducts of the anterior and posterior system anastomose freely over the body.” Fic. 11.—T.S., to show gubernaculum and cremaster. (5,2.)

1, gubernaculum; 2, cremaster with future inguinal canal between 1 and 2; 3, inter-sinus band displaced by gubernacular wedge; 4, lymphatic sinus.

[Face page 112. SIL 26nd 007]

Fic. 12 as in Fig. 11.—To show deep central lymphatic system. (*°.)

Fig. 13. — Gubernaculum in preformed inguinal canal.

Note its basal attachment preventing its acting as a tractor.

It is thus at a certain stage of the development of the inguinal lymphatic system that the gubernaculum has its way shown, and this seems to me a new and valuable fact in embryology, viz., that of lymphatic distribution influencing the line of growth of other structures. So far, then, we see that in these embryos the growth of the developing gubernaculum has not influenced the position of the testes, as these are still high up in the abdominal cavity. It has formed the inguinal canal, the tunica vaginalis, and the cremasteric coverings with its fasci only; the cavities of the tunica and cremaster are merely potential, not as yet actual. The next point to consider is as to how these potential cavities are influenced by the change in position of the testes.

I have spoken of the inguinal wedge at the caudal end of the developing gubernaculum as growing in a lymphatic tissue and sinus track, and thus forming the inguinal canal. It is made up of peritoneum, striped muscle (cremaster), and with unstriped muscle in the peritoneal fold. Which of these is the active one? The peritoneum is usually considered to lead the way, and to push the others before it, as it were. I think this wrong, and my reasons are as follows :—The round ligament has only a little peritoneal invagination ; the rest is penetrating upstriped muscular fibre. Then again one sees in the developing gubernaculum, in the appropriate sections, the unstriped muscle radiating into the scrotum ahead of both peritoneum and striped muscle. I consider the unstriped muscle the active penetrating tissue. Its occasional abnormal course in the human wall seems to show this. We thus get the perineal testicle in the male; and in the female its perineal penetration gives an anomalous and very rare perineal hernia in women, as in a case described by Smyly and one in my own practice. Here the hernia comes down below the lower end of the labium majus, and is best explained by supposing we have here an abnormal burrowing of the unstriped muscle of the round ligament analogous to the abnorma! burrowing wide would. be followed by the testicle in the male.

Lockwood, in his valuable memoir, describes the gubernaculum in man as having insertions in the groin, scrotum, pubes, and root of penis. In the marsupials, the pubic fibres of man are represented specially; in the rodents and insectivora the inguinal ones; and in man the scrotal ones.

The question arises here as to the penetrating power of the gubernacular fibres. We know that the early division cells of the fertilised ovum in the mole have a phagocytic action, considered now to be of a biochemical nature. The action of the gubernaculum at any rate seems to me to be of the same nature ; but this is a difficult point, and one that I suggest more as probable than demonstrate as actual.


One embryo in perfect preservation was available for this stage. The scrotum had developed and separated so that it projected from the anterior wall, to which its base was attached ; but it was still solid, with the gubernacular fibres radiating into each half. The inguinal canal on each side had undergone remarkable changes. It was markedly dilated, and contained the testis, gubernaculum, and epididymis. The inguinal wedge - had thus differentiated and formed a large and roomy sac, the cremasteric sac, lined with peritoneum, for the testis. The cubernaculum and testis are thus caudal in the canal, with the epididymis cephalic in the sac and on a level with the testis. To understand these remarkable changes, we must now study the serial sections, at first, from above down. No lymph-sinuses can be seen in the abdominal wall, as were noted in the earlier embryos. In the site of the inguinal canal, high up, and really caudal in its topography, there is first to be noted to the outer ‘etl abnd ang}

Fic. 14.—Inguinal canal with testis in left canal.

1, lymphatic gland; 2, inguinal canal; 3, scrotum ; 4, testes. Dasyurus viverrinus embryo.

50 a


Fig. 15.—Inguinal canals with testes. (4°.)

1, testes; 2, Miiller’s duct ; 8, Wolffian duct ; 4, gubernaculum $ 5, scrotum with gubernacular fibres radiating in.

side a large lymphatic gland with some fat. Then appears, to the inner side, the inguinal canal, circular on section at. this level, with a well-marked striped and unstriped muscular wall and a granular epithelial lining. . As we pass down, the canal soon has its transverse diameter wider, and its lining of a flattened endothelial type. The testis next can be seen lying apparently free in the canal,! but at a lower level in the sections. it has the gubernaculum plus the caudal ligament attached to its caudal end, while at the caudal end of the canal there is special thickening of the cremaster, of its longitudinal fibres, below it. This is an important section and merits full description, The inguinal canals here lie side by side and are triangular in shape, the long base to the lower and outer side. The gubernaculum is continuous with the epididymis, attached at one part near the lower end of the testis, with the Millerian and Wolffian ducts each at one level and in a bulging thickening, The cephalic part of the epididymis is not shown, but appears in the lower sections. The gubernaculum testis, at its lower insertion in the canal here, runs up a little on its walls, so that its caudal attachment between peritoneum and cremaster is really a concave, disc-like one, on section like an anchor (Figs. 14, 15, and 16).

The septum between the two inguinal canals is well developed, with unstriped muscle in the lower half, fatty tissue in the upper (Figs. 15 and 16).

Lower down in the sections a unique point is to be nore viz., aN Opening in the upper and outer wall of the canal where the testis must have passed into the canal, or the canal developed up over the testis. Here a fold, the diaphragmatic fold, is continuous with the outer boundary of the peritoneal cavity. The edges of the aperture are thinned and pointed and not in any way ragged, and give the impression of a gradual thinning and not of an artefact (Fig. 17).

1 Most probably the testes and sac walls were in contact originally, and floated out as the result of the necessary manipulation in mounting.

The cremuaster is well developed. In the earlier embryos, where the primitive inguinal canal is being formed, it was noted that the developing gubernaculum had in front of it the internal oblique and transversales muscles, with the tendon of the external oblique in advance. In the present specimen the cremaster surrounds the dilated canal in its whole periphery, with special thickenings at the cephalic and caudal ends. It arises as follows. A little to the outside of the top of the marsupial bone, the combined internal oblique and transversales muscles split into two lamelle, the inner passing along _ the upper wall of the canal, the outer round the outer wall © to meet its fellow and thus line the canal. The fibres pass up above their origin, as the pouch end of the inguinal canal is up in the abdominal wall considerably above the internal ring. Outside, the cremaster has a fibrous covering derived in its lower aspect from the fibrous tissue outside the transversales. If now we compare the primitive inguinal canal with the developed one containing the testis, the following points are worthy of notice. When the primitive canal is being formed, the testes are high up in the abdomen, on the inner side of the Wolffian body, which is still large. From the caudal end of the epididymis the caudal ligament passes down to a point on the inner aspect of the genital ducts; and from a point in the genital duct wall opposite this the inguinal — fold of the gubernaculum arises, passes to the internal abdominal ring, sends its growing fibres along the inguinal lymphatic track, to end in the scrotum and thus complete the gubernaculum (Fig. 8).

When the testis is in the developed inguinal canal, the apparent gubernaculum (developed gubernaculum) reaches from near the caudal pole of the testis to the base of the scrotum, but really represents, from above down, the caudal ligament Fie. 16 as in Fig. 15.—Shows union of cremaster and gubernaculum. of the testis and the gubernaculum. The testis has the mesepididymis with which the primary mesorchium has blended attaching it to the scrotal wall.

1, cremaster; 2, gubernaculum.

Fig. 17. — Inguinal canal with opening above communicating with peritoneal cavity. Note thickening of cremaster at lower end. (5°.

Fig. 18. — Shows caudal end of cremaster thickening. (#{°.)

A very important point is that the inguinal canal has increased markedly in size, that the testis lies in it loosely with room to spare. In the primitive inguinal canal and in the peritoneal cavity the developing gubernaculum was an attached structure with only part of its periphery covered by peritoneum, and therefore unfitted to act as a tractor. The same holds good of the testis and gubernaculum when the testis is in the inguinal canal or scrotum. The testis has its secondary mesorchium, and the gubernaculum also has its attached aspect; the latter can thus not act as an actual tractor.

III. Tot Mechanism Of The Descent Of The Testes As Shown In The Present Specimens

I wish now to explain how the descent of the testes has taken place in the marsupial embryos examined. Two of the specimens showed the testes in the abdomen and the primitive inguinal canal formed. In the third the testes were lying, each in the much-expanded inguinal canal. The scrotum was present but solid.

We have to consider the descent in three stages :—

(a) Lhe change in position of the testes so that they lie at the — mternal abdominal ring.—I have no marsupial specimen to show this, but it has been described in the human and other foetuses, and is not a difficult one to clear up, nor one on which much difference of opinion exists. When the Wolffian body in great part disappears, the testis naturally occupies its position, and thus sinks. The testis in the first two specimens lies to the inner and upper side of the Wolffian body, and thus guided by the inguinal fold comes necessarily to lie at or near the internal opening of the inguinal canal. No traction by the inguinal fold or by the rudimentary inguinal conus (v. V.) is necessary to explain this movement. Probably when actual intermediate stages are examined it may be found not to be a mere descent all the time; there may be a temporary stage of ascent, indeed, as in the human fcetus; but practically we may consider what I have described as probably correct.

1 There is thus a primitive mesorchium while the Wolffian bodies are still present; but when these atrophy, their peritoneal folds or mesentery—mesepididymis—blend with the mesorchium and thus form what we may call the “secondary or ordinary mesorchium” of the surgeon. Lockwood terms it the mesorchium, but the term secondary mesorchium recalls its strict origin.

(b) Passage of the testis into the inguinal canal.—This is a much more difficult stage to explain, but I hope to make it fairly clear. First I must notice that the third specimen shows an unusual condition of the developed inguinal canal, viz., that there is an opening in its upper wall to the inner side of the diaphragmatic fold. I have already stated that I do not think this opening has been artificially made in cutting the sections, as its edges taper; but until it is confirmed I do not insist on it as normal in the specimen. It makes no difference in the explanation of the change in position of the testes whether they pass by this opening or wid the processus vaginalis. The important point is the enlarged condition of inguinal canal. It is relatively much larger than the testis in it. At its highest and caudal point, and outside it, as I have shown, a lymphatic gland lies, and this and the fat round it is the natural result of its development in a lymphatic tract; the increase in size has been due to growth.

Now, the reason the testis lies in the inguinal canal is not that it has been drawn into it, but that the inguinal canal has grown so large as to surround it; that is, the inguinal canal has, as it were, ascended to the testis and thus become its temporary home. It is thus not so much an actual descent of the testis into the inguinal canal at this stage, as an ascent of the inguinal canal. All the specimens of marsupials at this stage figured by Katz and Klaatsch show, as my one does, the relatively great enlargement of the canal. to the testis. In my specimen the testis now lies in the canal uncovered by peritoneum, but with germ epithelium in single layer as its outer envelope. Above, it is suspended by the representative of the diaphragmatic ligament; below, it has the developing gubernaculum attaching it to the lower end of the inguinal canal; and it has a mesentery, the blended mesorchium and mesepididymis, 7.e. the secondary mesorchium. We have an analogous process in the stages of the relations of the female ' pelvic organs to the brim of the true pelvis. In the foetus the uterus and bladder lie above the level of the pelvic brim; afterwards, in the adult female, they lie below its level. They have not descended or been drawn down, but in the development of the bony pelvis the brim of the true pelvis grows above them.

Fig. 19. — Testis (2) and primary mesorchium (8) with Wolffian body (4). The secondary mesorchium is formed by union of 3 and 4 when latter shrinks; 1, kidney. Macropus ruficollis. (*2.)

The same is seen in regard to the spinal cord. In the early embyro the spinal cord is seen in the lower end of the spinal canal; afterwards its lower end is much higher, a change due _ to disproportionate growth.

It will be seen that I have not given prominence to traction of the gubernaculum as an important cause of descent. I do not because it is unnecessary and unlikely. The gubernaculum in these specimens has only unstriped muscle: it has an attachment to the wall of the canal nearly in all its length, is not attached directly to the testis, and is not a cord, free at its periphery. It is thus not likely to be muscularly active in a dynamic or change-of-position sense. One cannot, of course, deny that it 1s not active to a certain extent, but its activity has not been proved and has been exaggerated.

(c) Passage of the testis into the scrotum.—In my specimen the testis was in the inguinal canal and the scrotum was solid. The scrotum was in course of being canalised, however, as 120 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

the unstriped muscle of the gubernaculum was radiating into it, and peritoneum and cremaster were acting with it. The solid scrotum would thus soon have its cavity lined with peritoneum, and the testis in it.

How would the testis get into the scrotum? No doubt, as the scrotum became invaded by the growing gubernaculum, the testis would necessarily lie lower and enter it, a change permitted by its slack mesentery—would be carried into it with the involuting gubernaculum. Here again muscular action of the unstriped muscle of the gubernaculum may be invoked as the gubernaculum is shrinking. But it does not seem to me to be an important factor. The whole descent seems to me to take place by a series of growth processes. The second stage is best explained as an unequal growth phenomenon ; the third as due to gubernacular shrinking; but here those who believe in muscular gubernacular action may dissent. The disappearance of the Wolffian bodies, the directing action of the gubernaculum—the rudder more than the tractor—the disproportionate and marked growth of the inguinal canal, and the final involution of the gubernaculum: the play to the testis afforded by the diaphragmatic fold and the secondary mesorchium, its mesentery,—all these acting in series or in conjunction seem to me to account for the altered position of the testes.

In the marsupial it is, at its last stage, an ascent into the scrotal pouch, although on the whole it is a descent from its primitive position.

IV. The Descent Of The Testes In The Human Foetus

We are not yet in a position to explain descent thoroughly, but with a distinct approach to this. The first naked eye and comparative work was done after Haller by John Hunter in his well-known paper, published in 1786. Since that time, BY DR D. BERRY HART. 121

papers on the subject have been sparse in Great Britain, with the exception of those by Cooper (1830), Cleland (1856), Owen (1868), and Lockwood (1888). Thus in the literature summarized by Frankl in his paper in 1900, 121 references are given, but of these only three are British (Cooper, Owen, Cleland); and Lockwood, the most recent, is not quoted.

On the other hand, research has been abundant in Germany, less so in France, and important papers have been written by Bramann (1884), Frankl (1895-1900), Katz (1882), Klaatsch (1890), Nagel (1891), Weil (1884), Weber (1886), and by others.

While one recognises in Hunter’s paper, /eonem ex ungue, a large amount of comparative and microscopic work has been done abroad since his work, and very little if any has crept into our text-books and teaching. The reasons for this are that in the first place the idea that the abdominal wall was unbroken until at the earliest, the 3rd month, and that at or about the 7th month the testes were drawn into the inguinal canal and scrotum by the gubernaculum, deriving their coverings during this progress, was held by many as a sufficiently exact account of the matter, although in several of our text-books the description of a preformed canal is mentioned so far as its peritoneal and even its muscular elements are concerned.

‘Then, again, an evident inaccuracy is present in all British and American text-books and most foreign ones, viz. the description of the testes as lying at first extraperitoneally in the abdomen and passing down into the scrotum extraperitoneally, either by muscular traction purely, or by the aid of mutual unequal growth of inguinal canal and gubernaculum, so that after the obliteration of the processus vaginalis, we find a peritoneal covering to the testes (tunica serosa) and a peritoneal lining to the scrotum (tunica vaginalis). This mechanism is described in order to give a peritoneal covering to the testis. I need not criticise these statements in detail, but may shortly say that: 1. The testes in the abdomen of the fcetus are not covered by peritoneum, but by germ-epithelium. 2. The testes are not extraperitoneal in the abdomen after the Wolffian bodies have involuted, but have a distinct mesentery, in the main developed from the diminished Wolffian structures. 3. In the scrotum the testes are not covered by peritoneum. If they were, the peritoneum would strip off as it does from a tumour such as the epoophoritic (parovarian) developing in the broad ligament. 4. The testes in the scrotum are really covered with involuting germ epithelium as the ovary is (Frankl, Hoffmann). 5. However the human testes get into the scrotum, their route is vid the processus vaginalis, into the tunica vaginalis, and then the processus becomes obliterated. John Hunter says this distinctly. I came to this conclusion during the study of my specimens, and was beginning to verify some points, but found it unnecessary to do so, on noting in the course of reading that Frankl in 1895 showed clearly that “the testis has a peritoneal envelop (the tunica vaginalis), but not a peritoneal covering.”

Fig. 20. — To show usual View of Fig. 21. — To show more exact View Descent and its Errors. (Frankl. ) of Descent. (Frankl.) _t, testes; P, peritoneum; 0b, proc. vag. v.d., vas def.; ¢, testes covered with germopen; S, scrotum. The lower b shows epithelium ; Z, epididymis; P, peritoneum; obliterated proc. vag. s, scrotum.

He points out, too, that Hoffmann (in the Quain-Hoffmann Anatomie, Erlangen, 1870) drew attention to this fact and showed the similarity of the testicular outer covering to the ovarian one.

Frankl’s paper is of great interest. He shows that the testis, like the ovary, is not extraperitoneal, but covered by germ epithelium. The foetal testis in the scrotum is covered by low columnar epithelium—a contrast to the squamous endothelium of the adjacent parietal layer. He shows that the descent of the testes must occur through the processus vaginalis, and that then, only the epididymis and inner wall of the scrotum are covered by peritoneum ; the testes’ outer covering is, as already said, involuting germ epithelium. There is, indeed, an evident naked-eye boundary between testes and epididymis, corresponding to the well-known white line of Farre in the ovary. This makes the explanation of the descent very much easier.

We may now consider the question of how the testes descend in the human embryo. I base this account on my own specimens and on the facts given by Bramann, Weil, Eberth, Lockwood, Klaatsch, and Frankl. The papers of these observers are of the greatest value. In Wiedersheim’s work the description so far as it goes is excellent and suggestive.

We may consider descent of the testes in man under the following heads :—

(a.) The development of the testes in relation to the Wolffian bodies in the early embryo (about 4th week).

(b.) The development of the preformed Inguinal Canal.

(c.) The abdominal changes in position, of the testes.

(d.) The passage of the testes into the Inguinal Canal and Scrotum.

(a.) The Development of the testes in relation to the Wolffian bodies

I need not go into detail on this point, but only mention facts relevant to the inquiry. Details of this early development are well given by Lockwood and in all text-books of embryology. The testes develop on the inner aspect, and the Wolffian bodies have a short mesorchium and are recognisable as such by the 5th week. When the Wolffian bodies atrophy, usually about the 2nd month, this primary mesorchium of the testes is amplified by the Wolffian mesentery, and we thus get a secondary mesorchium. At this time (2nd to 3rd month) the testes lie in the abdominal cavity.

(b.) The Development of the Preformed Inguinal Canal.

The material for determining this point is not great in the human male foetus, but we have microscopic (serial sections in the main, by Weil, Klaatsch, and Frankl), as well as serial sections of two human female embryos (5th and 6th to 7th week) in my possession. If we summarise these as to sex and age, they are as follows :—

Male. — In a 14.5 mm. embryo (Frankl, measurement from head to breech) approximately 25 to 28 days, “the caudal end of the Wolffian body and that of the Wolffian duct are placed at the abdominal wall: no inguinal fold, ze. gubernaculum, is present.

In a 16 mm. embryo (28 days), the same conditions are present. : , In a 285 mm. embryo (5th to 6th week) we have a marked change (Fig. 22). There is not only an inguinal fold but a beginning processus vaginalis. The inguinal fold has begun to penetrate, and a peritoneal dimple has formed. The transverse and internal oblique muscles are distinctly seen,. but are, as yet, not beginning to penetrate, with the peritoneum and gubernaculum, as a wedge, through the abdominal wall. Into the base of the inguinal fold a few striated muscle fibres have radiated. The aponeurosis of the external oblique is also shown unbroken.

In a 4cm. and 4 to 8 cm. embryo (3rd month) the peritoneal dimple was no deeper.

In an 8 cm. embryo (3rd month), Frankl figures the gubernaculum passing through the abdominal wall and _ presenting in the main the appearance I found in the Macropus ruficollis specimens (Figs. 11 to 18). He divides the developing gubernaculum into three portions: an abdominal portion, a vaginal portion (in the peritoneal dimple), and an infravaginal portion below the level of the peritoneal dimple. It is into the last only that striated muscle radiates from below, the analogue of the Conus inguinalis (v. V., section on Phylogeny), and forms really what has been described as the ascending fibres of the cremaster.

Klaatsch, in an 8 cm. embryo, figures these ascending fibres as well-marked, and indeed as forming by an inversion of the gubernaculum into the peritoneal cavity a structure quite comparable with the Conus inguinalis of rodents; and in fact in the 17 cm. embryo he figures the processus vaginalis as obliterated (shown in 8 cm., 11 cm., 15 cm., and 17 cm. (4th month) foetuses). He would thus make the processus vaginalis be present as an eversion of this conus in the 17 cm. embryo. Frankl criticises this, and indeed it is evident that the peritoneal dimple or fossette is formed in 25 mm. embryos by, or along with, the passage of the gubernaculum through the abdominal wall.

As the sections of the Frankl 8 cm. embryo are followed down, we see how the processus is formed by the penetration of the double crescentic peritoneal folds, and finally at the lowest sections we come on the end of the developing gubernaculum, uncovered by peritoneum, and with the cremaster on all its aspects but the lowest. At or about this time (10 cm. embryo) the gubernaculum increases in size, mainly by growth of its connective tissue elements, and at this period, too, the external abdominal ring has formed.

In the 12 cm. embryo (4th month) the gubernaculum is deeper and the testis is at the internal abdominal ring.

In the 19 cm. embryo (5th month) the gubernaculum thickens and lengthens, and the testis rises a little from the internal ring—a real ascensus.

  • 1 This division of the gubernaculum comes up specially under the changes at the 7th month.

In the 23 cm. embryo (5th month) the processus vaginalis is deeper, and in the neighbourhood of the pars vaginalis of the gubernaculum, there is striated muscle, and more of it in the infravaginal portion. This thickening of the gubernaculum may dilate the processus vaginalis, but probably there is a combined growth of the two.

At the end of the dth month and beginning of the 6th, the aponeurosis of the external oblique and the cremaster fascia are everted along with the gubernaculum, which is now at the entrance to the scrotum. The gubernaculum is shorter, and striated muscle fibres (vertical and circular) are present in the infravaginal portion.

It must be noted that the ages of the embryos given are based on measurements, are difficult to give exactly, and are therefore only approximate.

There is thus complete evidence that in the human embryo, prior to the passage of the testes through the abdominal wall, there ws a preformed inguinal canal, due to a passage of the peritoneum, gubernaculum, and transverse and oblique muscles, to the outer side of the rectus, forwards and inwards towards the scrotum.—lt happens as in the marsupial embryo, with the difference that the gubernaculum contains scrotal, not abdominal unstriped fibres, and that the marsupial scrotum is suprapubic and not perineal as in man. None of Frankl’s or Klaatsch’s drawings show lymphatics, but this is probably merely an omission. I found them in relation to the developing round ligament, as I shall explain in a subsequent paper.

(c.) The Abdominal Changes in Position of the Testes

These have been given with great accuracy and clearness, so far as dissection can go, by Bramann, who examined forty specimens, and his results may be briefly summarised as follows :—

In a specimen at the end of the 2nd or beginning of the 3rd month, the testes 3 mm.x1°3 mm. were about 1 mm. from the internal abdominal ring. Behind them lay the epididymis: the vas deferens ran in a horizontal direction to the bladder. From the point where the Vas deferens issues from the epididymis, or, as Frankl puts it, at the junction of the globus minor and Vas, the gubernaculum, 1 mm. long and ‘5 mm. broad, passed to the internal ring, where there was a shallow peritoneal depression—the beginning of the processus vaginalis.

At the end of the 3rd month or beginning of the 4th, the testes lay lower and at the region of the internal abdominal ring. The testes were 4 mm.x2 mm. in a 14 to 15 weeks embryo, and close on the internal ring, with an inguinal fold 1 mm. long. The mesorchium was longer, and allowed mobility to the testis. 3

After this, the testes ascend somewhat, owing to the increase in length and thickness of the developing gubernaculum —its length and breadth at this period (13th to 16th week) being about 1 to 3 mm. by 4 to 1 mm. (average in seven specimens). } |

At the end of the 4th or beginning of the 5th month, the testes are larger (54 mm.x34 mm.), the mesorchium is longer and the upper portion of the epididymis has a mesepididymis (Mesorchiagogos of Seiler). The gubernaculum measures 3 to 2mm.inlength. By dissection, from without, in the region of the external abdominal ring, and removal of skin, superficial fascia and aponeurosis of external oblique, one can see white fibres issuing from the external ring, and these pass to the external oblique aponeurosis.

Up to the end of the 6th month the gubernaculum seems to have attained its highest development, its length being from | 3 to 8 mm., and its breadth, a little below the testes, 2 to 4 mm. The processus vaginalis is about 3 to 34 mm. deep and its entrance admits a fine sound.

At the beginning of the 7th month the real descensus begins. The testes, which were 5 to 8 mm. from the internal ring, now approach it, and the inguinal fold is shorter, the processus vaginalis deeper, so that a sound can be passed to the aponeurosis of the external oblique. The testes, as the age of the foetus increases, still descend, and now pass to near the internal ring, and the processus vaginalis now projects from the external ring, covered by the external SLOG a hollow. cylindrical structure 6 mm. xX 4 mm.

If the aponeurosis and peritoneum be incised we now come on the peritoneal sac, and can see, on the posterior wall, the gubernaculum about 12 mm. long, projecting into the sac-lumen for about 14 mm. without a mesentery, and reaching from the epididymis (where the globus minor meets the vas deferens, according to Bramann and Frankl) to the base of the - inguinal canal.

In the 74 month the testes are now in the inguinal canal, the gubernaculum shorter; and when they pass the external ring, the peritoneal sac is covered by the unpenetrated aponeurosis of the external oblique, and the fibres of the internal oblique and transversalis. The lower end of the peritoneal sac is attached to the fascia superficialis, and not united to it by a rudiment of the gubernaculum. The fibres of the gubernaculum blend with the tissue of the processus. This is also what I have found in the marsupial embryo when the testis is in the inguinal canal. In fact the gubernaculum then spreads out as a thin layer between peritoneum and cremaster (Fig. 16). The testes at last pass into the scrotum.

The changes beginning about this last stage have been well worked out by Frankl and Eberth. I have already spoken of the division of the gubernaculum into three parts by Frankl, and must now consider it according to his description in the - 7th month foetus. He gives three useful diagrams on this point.

In the first (Fig. 23) the right testis is at the internal ring, and we see the abdominal part, vaginal part, and infravaginal part of the gubernaculum. The testis and gubernaculum show marks of contact with the small intestine. On the left side the testis was much deeper, the lowest third of the gubernaculum being in the processus vaginalis.

In a third specimen at the 7th month, the testis has passed the inguinal canal, is partly in the scrotum, the processus vaginalis has begun to involute, and both the vaginal and infravaginal portions of the gubernaculum are shorter (Figs. 24 and 25). Frankl’s diagrams give the descent somewhat earlier than other observers.

Fic. 22.—Trans. section through the body-wall, proc. vaginalis, inguinal fold, and sexual gland of a male embryo. .28°5 mm. _head-breech diameter. The mass of cells at 11 is traversed by muscular fibres.

1, Wolffian body; 2, testis; 3, duct of Miiller; 4, Wolffian duct ; 5, inguinal fold; 6, p.v. peritonei ; 7,m.r. abdominis; 8, m. trans. abd. ; 9, m. obl. uterus ; 10, aponeurosis m. obl. extern. ; 11, mass of cells. (Frankl and-Eberth.)

Fic. 24.—Deepening of proc. vag. and approach to base of scrotum: 8th month foetus.

1, peritoneum ; 2, muscles; 8, external oblique; 4, testis; 6,'gubernacnlum; 6, cremaster; 7, scrotum ; 8, vaginal portion of G. (Frankl and Eberth.)

Fic. 23.—Position of testes to ligt. inguinal and proc. vaginalis in a 7th month fcetus.

1, testis; 2, peritoneum; 3, muscles; 4, ligt. ing. (gubernaculum) ; 5, ext. obliq. ; 6, cremaster ; 7, vaginal part of G.; 8, infravaginal part of G. (Frankl and Eberth.)

Fig. 25. — Shortening of vaginal part of gubernaculum in 8th month foetus. 1, peritoneum; 2, muscles; 38, abd. ext.; 4, testis; 5, cremaster; 6, gubernaculum; 7, scrotum ; 8, vaginal portion of G. (Frankl and Eberth.)

Fig. 26. — Male foetus (11 cm. h.-b.), sagittal mesial section. (14.) 1, peritoneum ; 2, epididymis; 3, mesepididymis; 4, blood-vessels in mesepididymis; 5, ductus deferens; 6, inguinal fold; 7, entrance to proc. vaginalis; 8, inguinal ligament ; 9, os coccygis ; 10, symphysis; 11, testis; 12, body-wall. (Eberth.)

Fig. 27. — Male foetus before birth. (1.) 1, ureter; 2, mesorchium; 8, epididymis; 4, d. deferens; 5, testis; 6, p. V- peritonei ; 7, pars vaginalis, lig.-genito-ing. ; 8, pars infravag. lig.-genito-ing. (Hberth.)

Eberth gives an excellent figure of the relations at this time. Similar conditions may be found at the eighth month and in the newly born (Fig. 27). Increased growth of the processus vaginalis and shortening of the involuting gubernaculum, are the conspicuous features in the 7th to 8th month.

(d.) The Passage of the Testes into the Inguinal Canal and Scrotum.

It may now be asked what are the causes of descent of the human testicle, and the approximate explanation is as follows :—

The disappearance in great part of the Wolffian body, and the guidance as a rudder, but not as a tractor, of the inguinal fold (gubernaculum at this stage) determines the position of the testes near the internal abdominal ring, at or about the 3rd month (Fig. 26).

The subsequent hypertrophy of the developing gubernaculum and its appearance in the peritoneal cavity as a thickened projection analogus to the Conus inguinalis, if we follow Klaatsch’s specimens of this period, cause a temporary ascent of the testicle. The hypertrophy with increased projection into the peritoneal cavity is a fact, whatever view as to its analogy to the Conus in rodents we adopt, and has the result of causing the testis to lie higher. It may also have a dilating effect on the processus vaginalis; but as I have already said, there is more probably a combined growth of cubernaculum and processus.

The next stage (6th month to 8th month) is probably an increase in the capacity and length of the processus vaginalis, so that it expands and grows up, as it were, over the testis, enclosing it, in the inguinal canal (Fig. 28). In the meantime the unstriped muscle gubernacular fibres with the striped muscle at its apex, and the peritoneum are developing into the solid scrotum, thus forming a cavity in it, lined with peritoneum. At this stage a shrinking of the gubernacular fibres takes place, and this is one factor (with probably some play allowed to the testis by the secondary mesorchium or mesepididymis of Frankl) in determining its ultimate position in the scrotum.

It will be seen therefore that in explaining the passage of the testis into the inguinal canal, a growth and development of the canal and of the gubernaculum, and not an actual descent of the testis, is considered the great factor. This is well demonstrated in the marsupial specimens, as well as in those of Klaatsch and Frankl.

I have said little of gubernacular traction. The penetrating power of the unstriped muscle of the gubernaculum is of importance, but it develops in the canal, beneath the peritoneal ridge derived from the inguinal fold, .e., is in the main sessile and not effective for exerting downward traction. It is not attached directly or even indirectly to the testis, as the upper attachment of the caudal ligament is to the epididymis and not to the testis. Bramann, however, says it is, at the 4th month.

The striped muscle in connection with the gubernaculum ultimately forms the external cremaster. It does not favour descent by any means: indeed any action, if it really occurred in foetal life, would cause ascent of the testicle, as it does in adult life. ‘The external cremasteric fibres passing into the lower part of the gubernaculum form the ascending cremasteric fibres, and are analogous to the Conus inguinalis of rodents.!

1 Lockwood in his work rightly says that “the ascending cremaster of the human embyro is so trivial that perhaps it ought to be looked on as a mere survival of a muscle which in some of the lower animals is more active and better developed ” (op. cit., p. 108). Klaatsch’s work on the Conus inguinalis confirms this. Fic. 28.—A transparent section of the right testis of an embryo pig, 210 mm. in length x 6.

Left testis nearly in inguinal canal; right testis, T, just entered; K, right kidney; A dorsal aorta; E, epididymis; U, ureter; R, rectum; M.D., W.D., Miillerian and Wolffian ducts; U.A., umbilical artery. (Eben. C. Hill.)

The internal cremaster is unstriped muscle round the Vas and vessels, and in the tunica vaginalis propria.

Thus while the cremaster fibres advance at first at the apex of the penetrating gubernaculum, their function is in relation to the adult cord and testis.

Minor factors may help descensus. Thus Eberth mentions intestinal pressure, and Bramann considers the distended sigmoid had some influence in depressing the left testis. Increased inclination of the pelvis has been considered to — have an influence by altering the direction of the inguinal fold favourably for traction. The lengthening of the cremaster has been supposed to exert traction, but all these, if not wrong, | are insignificant, so that Eberth is right in his contention, “Vielmehr scheinen aktive und complizierte Wachstumsvorgiinge bei der Verlagerung des Hodens die Hauptrolle zu spielen.”

I agree with this, and would minimise even the ultimate shrinking traction urged by Frankl, were it not for its apparent action in Ectopia testis.


The phylogeny of an organ or developing process in a plant or animal, is the history of its occurrence and development in some division of the animal kingdom, usually in the phylum or class of the animal or vegetable world to which it belongs. We are specially concerned just now with the phylogeny of the anatomical structures or organs involved in testicular descent In mammals, and with the phylogeny of the process itself. Up to this point we have been considering their ontogeny, 7.¢. their development in special animals or species. From the fact that we have, in this question of descent of the testes, to consider the organs and descent in the various species of the mammalia so far as known, as well as the 132 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

embryology in many of them, the problem is a most fascinating one, and will repay careful consideration.

I purpose therefore to state the main facts bearing on the phylogeny of our subject. Some repetition is unfortunately . unavoidable, especially as some of the structures, for instance the gubernaculum and cremaster, are joined with one another anatomically and functionally.

The organs concerned are the scrotum, gubernaculum, eremaster, and inguinal canal, and we shall consider these first, and then the process of descent itself.

The scrotwm is a temporary or permanent pouch or sac for the testes.. In the former instance, in certain mammals, at the rutting period, the testes pass back into the abdominal cavity, to re-enter the scrotum after the rutting period is over; in the latter case in other mammals they remain permanently in the scrotum when once they have passed in. In some of the latter, the processus vaginalis may be closed or open.

In the monotremata we start from “ bed-rock,” inasmuch as in these, the lowest of known mammals, there are none of the structures present whose phylogeny we are considering ; they appear at first sight to come into the existing mammalian species per saltwm, first in the marsupials, but the significance and accuracy of this requires to be carefully scrutinised. In the marsupials the scrotum is, in its position and development, the analogue and also the homologue of the female mammary pouch. In some males, apparent rudimentary mammary skin folds remain, but these are merely the folds after the scrotum has separated from its epidermic bed. The development of the mammary pouch in the female is by a passage backwards and outwards of the deep and superficial layers of the epidermis into the subjacent connective tissue; the connective tissue beneath the epidermis is not snared in. In the development of the marsupial scrotum the deep layer of the epidermis passes back and in and snares in the connective tissue which forms the site of the BY DR D. BERRY HART. 133

future interior of the scrotal sac. The amount of superficial epidermis passing in is slight, but its ultimate desquamation frees the scrotum, superficially embedded at first as it is in the epidermis, and allows of its pendulous character. In most marsupials the mammary pouch has its opening above for obvious reasons, but in one at least, Katz figures the aperture as opening below with a sphincteric muscular arrangement of evident utility. This position of the aperture is of importance as showing an intermediate stage relative to the openings of the mammary pouch and its analogue. In regard to the muscular arrangement of the mammary pouch, the round ligaments act, according to Cunningham, as a compressor mamme, while the sphincter is developed from the subcutaneous unstriped muscle.

The mammary pouch, then, may have a caudal or cephalic aperture, but the scrotum, its analogue and homologue, has its aperture cephalic and communicates up to its later stages with the peritoneal cavity (open processus vaginalis), has the testis ultimately in it, and then usually becomes shut off from the peritoneal cavity by the closure of its processus vaginalis. In rodents and insectivora the scrotum is a shallow pouch in the abdominal wall in the region of the inguinal teats, the cremaster sac or pouch. When the testes are in the abdomen in the adult, the transversales and internal oblique muscles project into the inguinal fold, thus forming a conical projecting eminence in the peritoneal cavity—the inguinal cone (Conus inguinalis) of Klaatsch, who first drew attention to it. The nature and functions of this “Conus” will be considered presently.

In rats the scrotum is lower down, towards the perineum, and finally in higher mammals it becomes the pendulous, saclike scrotum. |

The following summary gives the scrotal conditions known to us in the chief species of the mammalia. For convenience, I add in this summary the main facts as to position of testes, the cubernaculum and the cremaster. The conditions, however, vary 134 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

very much; there is no gradual gradation but an undulating one, and we must therefore conclude that variation is still going on in regard to these organs and to their descent.

Scrotal conditions and those as to Gubernaculum and Cremaster wm the chief orders of Mammalia (mainly from Frankl).

Monotremata.—Testes abdominal ; no scrotum; no inguinal fold; no cremaster. Echidna shows ligamentum testis joined to Vas deferens,

Marsupialia—Suprapubic scrotum with processus vaginalis closed ; mesorchium broad and four-angled ; inguinal fold well developed.

Edentata.—Testes abdominal ; position of testes really varies ; may be primary abdominal, subintegumental, or secondary abdominal ; no scrotum; no inguinal fold; cremaster has transverse and internal oblique fibres; no conus; Jn Dasypus sexcinctus, inguinal fold marked and runs to equivalent of processus vaginalis, ending in its fundus; Jn Dasypus novemcinctus, short conical cremaster sac from internal and transverse below aponeurosis of external oblique. |

Cetacea.—Testes primary abdominal and no inguinal fold.

Proboscidea.—Testes abdominal.

Kodentia.—Testes in scrotal pouch but return to abdomen at “rutting” ; cremaster from transverse and internal oblique, and forms “ Conus inguinalis.”

Insectivora.—Much as in rodentia; have conus inguinalis, but not

| always ; testes in some, abdominal, and no descent; in others, abdominal, and return to scrotum after rutting.

Cliroptera.—Testes return ; Conus present ; cremaster from transverse and internal oblique.

Pinmipedia.—Testes extra-abdominal, subintegumental in inguinal canal; shallow cremaster sac from transverse and internal oblique ; no scrotum ; no return of testes ; In Phoca Vitulina.

Carmvora.—Show beginning involution of processus ; cremaster from transversus.

Artiodactyla.—Processus vaginalis narrow; cremaster from internal oblique.

Perissodactyla.—More primitive conditions; processus vaginalis wide open; traces of inguinal ligament even in adults; cremaster from internal oblique and well marked.

Prosimie.—(Lemurs) Processus vaginalis narrow; cremaster from internal oblique and transversus (mainly).

Primates.—Conditions very varied (v. Frankl, p. 186-187) from simple to complex.

| BY DR D. BERRY HART. * 135

The facts are too varied to give any definite results, but some points are interesting.

The monotremes show the most rudimentary conditions. The marsupials, however, approach man in having definite scrotum, usually closed processus vaginalis, well - marked gubernaculum, very definite descent of testes in embryo, with a preformed inguinal canal.

Their scrotum shows clearly the most primitive type of scrotum, being evidently mammary in its nature and suprapubic in position. Its cremaster is derived from the transverse and internal oblique muscles as in man, and its fasciee are much the same. Its gubernaculum, however, is not the specialised scrotal fibres of man, but consist of wellmarked abdominal fibres which are normally rudimentary in man. The transition from Monotreme conditions to Marsupial ones is thus extraordinary.

We may put down, abdominal testes; absence of, or rudimentary scrotum; open processus vaginalis; return of testes to abdomen at “rutting,” all as characteristic of a low position in mammalia; while permanent scrotum, especially if perineal ; closed processus vaginalis, are all evidence of a high position. Exceptions, however, are plentiful, and in the Hdentates and Primates we find almost all forms.

Primitive or comparatively primitive conditions are found in Monotremes, Edentata, Proboscidea, Cetacea, Rodents, Insectivora, Chiroptera, Pinnipedia, Carnivora; while in the Artiodactyla, Perissodactyla, Carnivora, Prosimie, Marsupialia, and Primates the arrangements are more advanced and finally culminate in the most advanced type as found in man.

Klaatsch has shown that in many mammals the site of the future scrotum is marked out by a certain area of skin, the area scroti, evident both by its naked-eye and microscopic character. The hairy covering is less marked, the small hairs arise from projections due to elevations of the cutis which 136 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

possess a thin epidermic covering. Its most characteristic microscopic structure is a layer of unstriped muscle, ceasing abruptly at the edge of the “area.” In the middle line the “arez scroti” coalesce. The full phylogeny and nature of the scrotum will be best taken up after the gubernaculum and cremaster and conus have been considered.

The Gubernaculum, Cremaster, and Conus Inguinalis—I need not recapitulate the facts as to the gubernaculum, but merely point out the constancy of its type in all mammals above monotremes. Thus its lower end is always in a mammary area, its upper at the Wolffian duct. It is not connected directly or indirectly with the testes. Its origin and insertion, in constant relation to primitive structures, viz., the mammary area and Wolffian body, explain its almost uniform structure and relations in all species. In all, it acts as the active agent, with peritoneum and cremaster, in preforming the inguinal canal.

The cremaster is quite constant in all mammals above monotremes, and is derived, in almost all mammals, from the internal oblique and transversalis muscles. In front of it, as it passes in with the peritoneum and gubernaculum, lies the aponeurosis of the external oblique. Occasionally only one muscle forms the cremaster. In the marsupials the pyramidalis is well developed, but takes no part in the cremaster, as the gubernaculum skirts its outer edge, as it does that of the rectus. The great function of the cremaster is in the adult, as I have already stated, and it takes no part in causing the descent of the testes. It grows down with the inguinal fold, but how far, actively or passively, is difficult to say.

Conus inguinalis.—This is an important modification of the cremaster and gubernaculum found in rodents and insectivora, and first described by Klaatsch. I have found what appear to be 1ts representative in marsupials, but in them it plays no part in changing the position of the testes. In rodents it can be BY DR D. BERRY HART. 137

seen as a cone projecting into the abdomen from the scrotal site, and it consists of fibres from the internal oblique and transversal muscles, passing into the inguinal. fold. When the testes are in the scrotal inguinal pouch, the “conus” runs from the inguinal fold to the base of the scrotum. The muscular fibres must have grown into the fold (Wiedersheimer). They do not draw the testes into the scrotal pouch, as the direction of their fibres prevents this; nor can they draw it out. It would be absurd to consider them as drawing the testes at one time into the abdomen and at another time into the scrotum. Probably the best idea is to consider the cremaster fibres of the Conus as first growing up into the inguinal fold to form the Conus. Then they grow into the scrotum after rutting. Thus, at rutting, the Conus develops or grows into the incuinal fold and by its shrinkage or involution after rutting, and by accommodation, the testes resume their scrotal position. This is the most probable and consistent explanation in the present state of our knowledge, but serial sections at the various stages would be needed to confirm or reject it.

Klaatsch figures a Conus in the human embryo, and Eberth does so too. |

Thus the Cremaster has its share in the function of developing the inguinal canal and the cavity of scrotum, and ultimately, in men for instance, forms a muscular incomplete covering to the cord and testes. It is a valuable supporting constituent in a pendulous organ, and has a probable function in preventing dilatation of vessels in the cord and testes. Its action under voluntary impulses in man is known and is well figured by Wiedersheimer, but in the descent of the testes into the preformed inguinal canal it has not as yet been shown to play any direct part.

Statement as to Nature of Relations of Scrotum, Gubernaculum, and Cremaster.—In man the scrotum develops partly in the perineal region and partly above this, and the question now 138 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

arises: Is this region and that of the labia majora in the female related phylogenetically to the suprapubic region of the marsupial or to the inguinal in rodents where the scrota respectively develop? If so, it would enable us to make the consistent statement that the gubernaculum and round ligament, and with them for a certain distance the peritoneum and cremaster, are developed in relation to a mammary region in all mammals, thus extending the striking generalisation first made by Klaatsch in his suggestive paper. Developmentally the labia majora and scrotum are due to an extension downwards and backwards from an area contiguous to and blending with the inguinal region. We have seen that the developing gubernaculum abuts on the abdominal wall at this point before it begins to penetrate, and thus the scrotal or labial skin is practically a pendulous extension of the inguinal.

The nerve and vascular supply to the scrotum bear this out. The upper part of the scrotum is supplied by nerves and bloodvessels common to the inguinal region. Cooper states that: (1) a branch of a lumbar scrotal nerve . . . divides into numerous branches which supply the skin of the groin, scrotum, and skin of the root of the penis; (2) the external spermatic

nerve... 1s distributed to the cremaster and the cellular tissue of the scrotum ... sends a branch to the skin of the groin. ... The perineal nerve supplies the lower part of the scrotum.

A striking confirmation of this generalisation would be an abnormal teat or mamma on the scrotum or labium majus. I ventured to predict to a scientific friend that this would be found, and finally came on a reference to a mamma on the labium majus in Bateson’s invaluable work on Materials for the Study of Variation (page 187), where he quotes Harting, “Ueber einen Fall von Mamma accessoria,” the mammary structure of the gland being verified microscopically. I have said that Klaatsch has drawn attention to the fact that the BY DR D. BERRY HART. 139

gubernaculum and round ligament end in a mammary area, and I have confirmed and extended this. This would lead one to the conclusion by Klaatsch that the changes in the mamma induced by pregnancy are analogous to the changes in the conus inguinalis of the resting and rutting male. One might indeed look back, as Klaatsch suggests, to a primitive period when the young were suckled by both parents, and that then the differentiation took place which ended in the predominance of the mammary function in the female, with a round ligament equivalent to the developing gubernaculum only, and a rudimentary inguinal canal; while in the male the mammary function became rudimentary, and the gubernaculum initiated the changes in the abdominal wall, which not only gave the inguinal canal, but also the descent of the testes. This, however, is very speculative. JI agree with Klaatsch in his views as to the mammary area insertion of the gubernaculum, but he has not pushed his most interesting theory far enough.

Let us apply it to the marsupials. In the male we have a scrotum, topographically and developmentally equivalent to the mammary pouch; it contains the testes. In the female we have a mammary pouch with the round ligament, the analogue _ of the gubernaculum, ending in it, in relation to the mammary gland. One usually looks on the mammary pouch as only a pouch for the mamma, and for the young marsupial. To make it exactly equivalent to the male scrotal arrangement, it should, however, contain the ovary. It does not; but if we go back to the monotreme echidna, we find, as Haacke has shown, that it carries its egg—the product of the ovary—in a pouch developed for it at the time, a pouch large enough to hold almost completely a gold watch. Zhe mammary pouch therefore is primitively the egg or ovarian-product pouch just as the scrotum is the testicular pouch. Thus in all mammals above monotremes the developing gubernaculum joins the lower end of the primitive Wolffian body to an area of skin 140 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

which is primitively an ovarian-product or testicular pouch —a mammary area; and when it loses the fcoetus-carrying functions (as it does in all above marsupials) retains in the female the mammary function, and in the male the testicular pouch function. The development of the inguinal fold and cremaster thus begins primitively in rodents in Klaatsch’s inguinal cone, and develops to the more perfect gubernaculum of higher mammals. The active agent in the gubernaculum is the unstriped muscle; thus the peritoneum only forms a shallow processus in the female processus; it is the unstriped muscle that mainly forms the round ligament and preforms the inguinal canal. |

The Inguinal Canal.—On this one can be brief, as much of its phylogeny is involved in the previous sections. There is no inguinal canal in the monotremes. It may be a shallow pouch (rodents, insectivora); a deeper canal, with its processus narrow or closed; a well-formed canal in the embryo, with closed processus (marsupials, carnivora, primates, man). Its line of evolution is thus, increase of depth in abdominal wall (its direction varying according to the position of the scrotum), and closure of processus. Its highest development is thus in man, but it is high, as already noted, in marsupials. The position of the inguinal fossa or canal, as the case may be, is , determined by two factors: the direction of radiation of the gubernaculum fibres and the area of spread of a developing lymphatic centre. This is best seen in the marsupial embryo, but probably holds good for others.

Descent of the Testes—There is no descent in monotremes, edentates, cetacea, or proboscidea. The first beginning is in rodents and insectivora, and there the descent is temporary and periodic after rutting. As we pass up the mammalian scale the descent becomes more marked, penetrating the abdominal wall and into a scrotum either inguinal, suprapubic or perineal. While we use the term “descent” it must be noted that this is BY DR D. BERRY HART. - 141

most marked in the abdominal phases; afterwards when the testes are in the inguinal canal, the testes are relatively stationary, and growth of the inguinal canal is the active factor ; descent again asserts itself if the testes reach the perineal scrotum; but if the scrotum is suprapubic, this last stage is really an ascent. We thus must always use the inevitable term “descent” with these reservations.

The relation of Descent of the Testes to Heckel’s Law and to Mammalian Classification.—Heeckel’s law (or rather the MiillerHeckel law) is briefly stated as follows':— Ontogeny repeats and condenses phylogeny in whole or in part—the development of the organs and their functions in man repeats and condenses in time and stages the parts of various organ-ontogenies and their functions necessary to complete the ontogeny of the whole organism. In some stages, indeed, it gives what may appear an irrelevant reminiscence of its lower mammalian origin, as in the ascending cremaster fibres and temporary ascent of the testes.

This is a great generalisation and is. completely vindicated when we consider testicular descent in man. We cannot but accept this law, which points most probably to the continuity of the germ plasma as being at the root of the phylogenetic repetition in ontogeny. Let us consider the phylogeny of testicular descent. There is no descent in monotremes, in some edentates, in cetacea, and in proboscidea. The testes lie in ashallow inguinal pouch in rodents, and during rutting are abdominal from change in the “Conus inguinalis,” their cremaster; they are suprapubic in marsupials; perineal and usually in a pendulous scrotum in higher mammals.

The “ontogeny” of the process in man repeats in a few months of foetal life (2nd to 8th) all these stages in the

1 See Weismann’s Theory of Lvolution, ii., p. 160 ; and also Darwin’s Life, where Darwin claims this law. 142 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

long phylogeny of the lower mammals. The testes are in the human male foetus abdominal in the 2nd month (as in monotremes) at the peritoneal fossette, and afterwards a little higher in the 38rd to 4th month (as in the rutting of rodents); in the inguinal canal, ie. subintegumental at the oth to 6th month, as in the rodents after rutting; and finally, perineal and scrotal at the 8th to 9th month.

In man the gubernacular fibres are scrotal, but in the pubic and perineal and inguinal rudimentary fibres, we see a phylogenetic reminiscence of these conditions in marsupials and rodents. Those who believe in active gubernacular fibres in man, as causing descent, regard these rudimentary fibres as aiding mechanically, like guy-ropes, the scrotal ones; but that the sessile or attached unstriped muscle of the gubernaculum can act “dynamically,” 2.e. cause transition, is erroneous; the true interpretation of the rudimentary fibres in man is seen in this, that they are an illustration of Heckel’s law.

In the development of our knowledge of testicular descent; indeed, it was really by a reversal of Heckel’s law that progress was made, ze. the conditions in the lower mammals, a long-spun-out history, as it were, of what occurs in man, explained in the hands of the great early investigators— Hunter, Owen, Seiler—the more rapid and condensed stages in man—Heckel’s law was worked backwards by them.

But Heckel’s law can be used to bring back lost history, and supply stages in phylogeny we have lost; just as in his great periodic law as to the chemical elements, Mendeleef rightly predicted that chemical elements would be discovered with certain definite atomic weights, and in approximate places in his scale, to complete the series.

Let us apply Heckel’s law to its logical extent. The monotremes and marsupials are lowest in the mammalian scale, and yet the marsupial has a development of inguinal canal, and a condition after descent in many respects reBY DR D. BERRY HART. 143

sembling the human male, and higher than that in rodentia, for example. So far, therefore, as the conditions we are discussing go, we cannot adopt a linear mammalian classification. Mammals must be classified in several lines radiating from an ancestor more primitively developed than the monotreme. If then we wish to speculate as to this ancestor, we must consider early ontogenetic stages of the region in which the descent process takes place, ze. the rump end of human embryos. Such stages are to be found in the human embryo as shown by Keibel, when the entodermal cloaca * is formed, the urogenital ducts opening into a common closed chamber. Here the cloaca is closed in front by the cloacal membrane, devoid of the mesoblast which afterwards develops. The yielding of this membrane gives the distressing “ectopia vesice” of the human adult, but this yielding and patency of the cloacal membrane may have been normal in some predecessor of the monotremes. The egg may have been incubated in the upper part of the entodermal cloaca, which lay beneath the region in which the abdominal egg-pouch afterwards developed. From such an hypothetical ancestor the mammals may have developed, and the subsequent grouping may be arranged as follows :—

After the hypothetical mammalian ancestor, the first group would include the monotremes and marsupials. Between these, however, there is, in their testes arrangement, a tremendous gap, one being testiconda, the other having a well-formed scrotum, a closed-off processus vaginalis, and a descensus only differing from that of man in having a suprapubic scrotum, (the analogue and homologue of the mammary pouch), and a gubernaculum, the fully developed abdominal fibres of which are rudimentary inman. This gap must have either been gradually filled with slowly evolved and now extinct members of the marsupials, or we may hold that the inguinal fold came into mammals per saltwm, in a way analogous to the “ Mutation” theory of de Vries. The existence of intermediate forms of testicular position and descent as in the higher mammals, as in rodents, however, negatives this.

1 This is better termed “penultimate gut,” pars penultima of the primitive gut: the “tail gut” is then pars ultima.

The next diverging group would hold the edentata, sirenia, cetacea, proboscidea, and hyracoidea; then would come a parallel group of rodents, insectivora, and chiroptera; next the ungulata and carnivore, and finally the lemurs, anthropoids, and primates. Intermediate forms exist in the edentata, lemurs, and anthropoids, so that the groups are not sharply differentiated.

I merely throw out the arrangement of classification according to the position of testes and the evolution of their descensus, as a suggestion, and one that must be modified greatly, as our knowledge increases.

My final conclusion is that the testis, appendix testis, and prostatic utricle, Wolffian body and its duct, the gubernaculum, the mamma, the external genitals, form an associated anatomical unit, the male urogenital and mammary unit—for shortness, the male genital unit; and in the same way, the ovary, epoophoron, Wolffian body and its duct, the round ligament, the mamma, the external genitals, are the female urogenital unit—for shortness, the female genital unit.

This is an important and convenient condensation of the relation of these organs, and in a future paper on Mendelism in the differentiation of the human genital tract and of sex I go on to analyse the nature and significance of these units as to these questions.

I may, however, sum up descensus testiculorum in terms of the male unit. The essence of the process is this:—The testis is united to a mammary area, at first by the testicular caudal ligament and the inguinal fold or gubernaculum, afterwards by the involuting caudal ligament and developing gubernaculum. The developing gubernaculum, with the aid of the cremaster and peritoneum, forms a pit or fossa for the testes in the rodentia; a more complete canal and more or less pendulous scrotum in higher mammals. By subsequent disproportionate growth of canal and testes, and finally (according to Frankl) by the involution and shrinkage of the gubernaculum, the testes in man become lodged permanently in the scrotum. I need not bring in intermediate stages in this Summary. The progression in mammals is thus primary testiconda, secondary testiconda; finally, more or less of a descent of testes into a closed sac. The gubernaculum site of origin is primarily a Wolffian duct area and only indirectly, by means of the caudal ligament, testicular; the insertion, always mammary.

What the reason of testicular descent is I do not know, but the gubernaculum always penetrates to a mammary area, and this area, in the human male, is finally a scrotal or labial one, and the formula of the progressive change in the relations of the testes, commonly called “descent” in all mammals is this: the gubernaculum always develops towards, and ends in a mammary area, suprapubic, inguinal, perineal, scrotal. The testis appears to follow its guide—its canal-former —the gubernaculum, and the gubernaculum in marsupials certainly passes through the substance and skirts the edge o a developing lymphatic area.

As the heading of this paper I have given three quotations from John Hunter’s works,

The second one shows plainly that Hunter held that the testis came through the processus vaginalis.

In the first quotation we see Hunter laying the foundation of the subject of testicular position and descent. The gubernaculum, the term which has rightly become permanent in anatomy, he never uses in the sense of a “tractor,” but always of a “rudder,”—its true meaning. Here again, Hunter’s teaching hhas been for long discarded with disaster to accuracy and clear comprehension, and the gubernaculum has been credited with powers that the examination of serial sections shows to be illusory.

Hunter held the only possible view at that time as to the testis-covering, viz., that it was a peritoneal one in the abdomen and scrotum.

The last quotation is a remarkable one, and shows Hunter’s unique powers as an unprejudiced observer. We see in the record of this fact, shadowed forth the modern view that the scrotum is equivalent to a mammary area, towards which the gubernaculum develops and the testis passes: and so we may fitly and finally say that in the investigation of this great anatomical and physiological question there is one observer who was at the beginning and is still in the van—John Hunter.


BatEson.—WMaterials for the Study of Variation, Macmillan & Co., London, 1894.

BRAMANN.—“ Beitriige zur Lehre vom Descensus testiculorum und dem Gubernaculum Hunter’s des Menschen,” Arch. fiir Anat., 1884. The best account in any language of the descent in man.

CHAMPNEYS.—Med. Chir. Jour., 1886, p. 419, as to axillary mamme. |

CLELAND.—TZhe Mechanism of the Gubernaculum Testis, Maclachlan & Stewart, Edinburgh, 1856.

Cooper, Str A.—Obdservation on the Structure and Diseases of the Testes, London, 1830. A magnificent atlas.

CunnincHam, D. J.—TZeatbook of Anatomy, Y. J. Pentland, Edinburgh and London, 1902, v. also Manual of Practical Anatomy. |

EBERTH.— Die Mannlichen Geschlechtsorgane, Fischer, J ena, 1904.

FRANKL.—“Einiges iiber die Involution des Scheidenfortsatzes BY DR D. BERRY HART. 147

und die Hiillen des Hodens,” Arch. fiir Anat. und Entwick, 1895, S. 339.

Not only did Frankl clearly show the points as to the testicular covering detailed in my paper, but he quotes Hoffmann in the Hoffmann-Quain Anatomy, Erlangen, 1870, as saying, “Allein auch an der vordere Abtheilung des Hodens fehlt der Peritonealuberzug, indem dieser nur mit einem schmalen Saum auf die hintere Abtheilung der Hodens in der Umgebung des Nebenhodens sich erstreckt, fast genan so wie Waldeyer das Verhalten des Peritoneums zum Kierstock beschrieben hat. Der grossere theil des Hodens ist frei vom Bauchfell.” This was written thirty-nine years ago.

Beitriige zur lehre vom Descensus testiculorum. Sutzbericht der K. akademie der Wissenchaften, Wien, Bd. 109, Hft. L, 1900. A most valuable monograph in comparative anatomy.

GuLLAND.— “The development of lymphatic glands,” Jour. of Path. and Bacteriology, I1., 1894. Gulland notes the abundance of the lymphatics in the groin of early human embryos. |

HaAackr, W.—“On the Marsupial ovum, the mammary pouch and the male milk glands of Echidna Hystrix,” Proc. Roy. Soc. of London, vol. 38, p. 72, 1885. The Echidna

ege found in the pouch was 15 mm. x13 mm., and thus nearly exactly round.

HARTUNG, ERNST.—* Ueber einen Fall von Mamma accessoria,” Inaugural Abhandlung der Mediz. Facultét zu Erlangen.

Erlangen, 1875, Druck der Universitiits-Buchdruckerei von E. Th. Jacob.

As this rare case is in a somewhat inaccessible form, I give a short résumé of it. The patient was under the care of Drs Dietz and Heydenrich, at Nirnberg. She was 30 years of age, and had observed this labial tumour for several years. During the suckling of her infant a milky fluid oozed from an ulcerated surface.

The whole tumour was about the size of a large gooseegg, and had a special isolated palpable part the size of a walnut. The mass was pediculated, the pedicle being about 1 cm. long. It was easily removed. Macroscopic examination showed mammary structure, and a flattened-out teat with small openings was found. The fluid had fat globules. Without giving further detail, it may be said that the evidence of its mammary nature was absolutely complete.

His statistics are interesting. In 63 cases of accessory mamma he found 55 in women, 11 in men. In the women, 29 had one accessory mamma, 25 had two, and 3 had one. Of the 29, one was mammary, three in the groin, one on the back, one on the thigh, two above the navel, one in the axillary line, two in the axilla, eighteen on the breast.

Such cases are not uncommon. I[ have in my museum, drawings of two specimens of double nipple and a cast of the axillary mammary or milk secretory condition to which Champneys has drawn attention.

HI, Espen. C.—<On the gross development and vascularisa tion of the testis,” Jowr. of Anat., vol. vi, p. 489. Hill gives very fine reproductions of descent in pigs, and the best figure of the relation of the Gubernaculum and caudal ligament to the testis yet published.

HUNTER, JOHN.—Observations on certain parts of the Human


Giconomy, London, 1786.

It must not be forgotten that Haller’s work in 1755 set the Hunters investigating.

—“Zuy Kenntnis der Bauchdecke und der mit ihr ver knupften Organe bei den Beutelthieren,” Zs. ftir Wissenschaft. Zoologie, Bd. 36,8. 644. Katz gives very valuable dissections and drawings of marsupial anatomy.

Keitu, ArtHUR—Human Embryology, 2nd edition, London, 1904.

Kuaatscu.— Uber den Descensus Testiculorum,” Morph. Jahrbuch, 16, 1890. Klaatsch, of all authors, gives the most penetrating account of descent. His points as to the area scroti, Conus inguinalis, and the relations of the mamma to descent are of the greatest value.

KOLLMANN.—Lehrbuch des Entwickelungsgeschichte des Menschen, Jena, 1898. See also his Handatlas.

LEwis, J. T.—“The development of the lymphatic system in rabbits,” Amer. Jour. of Anat., v., 95. Lewis states that “the study of rabbit embryos confirms the chief conclusions established by Prof. Florence Sabin, that the lymphatic system is a derivative of the venous system,” op. ctt., p. 12.

Locxwoop, C. B.—Hunterian lectures on the Development and Transition of the Testes.

NaceEL, W.—“Uber die Entwickelung des Urogenital System des Menschen,” Arch. fiir Mik. v. Anat., 1889.

OWEN, RicHarp.—‘“ On the Anatomy of Vertebrates,” Mammalia, vol. iu1., London, 1868.

PELLACANI.—“ Bau des Menschlichen Samenstranges,” Waldeyers Arch., Bd. xxiii.

QUAIN. —Anatomy, “Embryology,” by Dr T. H. Se: 1ith edition, London, 1908.

SABIN, Pror. Frorency.—“On the origin of the lymphatic system from the veins and the development of the lymph hearts and thoracic duct in the pig,” Amer. Jour. of Anat., I., No. 3; “On the development of the superficial lymphatics in the pig,” Amer. Jour. of Anat., IIL, p. 183; “The development of the lymphatic nodes in the pig, and their relation to the lymph hearts,” Amer. Jour. of Anat., vol. TY.

WALDEYER.—Lierstock und Hi, Leipzig, 1870.

Werser, Max.—sStudien tiber Saugethiere, Fischer, Jena, 1898. In addition to valuable facts from comparative anatomy, 150 THE PHYSIOLOGICAL DESCENT OF THE TESTES,

Weber gives two excellent diagrams, showing at a glance the various views held as to what constitutes the gubernaculum of Hunter.

WeIL.—“ Ueber den Descensus testiculorum, u.s.w.,” Zeitschrift fiir Heilkunde, Bd. v., S. 225. Very valuable in its sections of human embryos.

WEISMANN.—The Evolution Theory, E. Arnold, 1904.

WIEDERSHEIM. — Vergleichende anatomie der Warbelthiere. Sechste Auflage, Jena, 1906. “Der Bau des Menschen, vierte Auflage,” Lauppschen Buchhandlung, Tubingen, 1908 (v. also Bernard’s Translation). For a curious explanation of the prepenial scrotum, v. p. 624, note in former.

This represents the chief literature consulted. It is, however, fully given by Frankl and Klaatsch.

Paper Discussion

The President, after remarking on the importance of the paper, invited discussion.

Sir Halliday Croom said that this was an exceedingly clever paper. It was impossible to discuss it after merely hearing it read, but he looked forward to its publication. In the meantime he congratulated Dr Berry Hart on a magnificent piece of work.

Dr Ballantyne thanked Dr Berry Hart for his clear and convincing paper. He discussed the question of “mammary areas,” and also the descent of the testicle, pointing out that its embryological descent was quite different in mechanism from the descent which occurs at puberty in cases of “undescended testicle.”

Mr E. Scott Carmichael was much interested in the paper, especially in its relation to hernia associated with undescended testicle in young children. He found that in cases of unBY DR D. BERRY HART. 151

descended testicle in young children the testicle had, in many instances, quite a distinct mesentery, and this supported Dr Berry Hart’s statement that the testes descended in the funicular process.

Dr Berry Hart in reply stated that he could see no difficulty with regard to his theory of “mammary areas.” That disproportionate growth caused apparent change of position, was one of the most important things in embryology. He was much interested in Dr Carmichael’s remarks.

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