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THE ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS (SUS SCROFA)[edit] J. A. BADERTSCHER

From the Department of Anatomij, Indiana University, Bloomington, Indiana

FOUR FIGURES

In a recent study ('18) of the ultimobranchial bodies in a wide range of successively older developmental stages of pig embryos (before their fusion with the median thyroid anlage to full term), the writer w^as convinced that these bodies contribute to the structural elements of the thyroid gland. The time at which they are completely transformed into typical thyroid structures, that is, when they can no longer be recognized structurally from the median thyroid anlage, varies greatly. Even in a full-term embryo a portion of the ultimobranchial bodies may be free from colloid. It thus became evident that in order to follow out a more complete developmental history of these structures, the thyroid gland of postnatal pigs must be examined.

The material used for this investigation was obtained from a litter of pigs and from three young adult hogs (age unknown) . The pigs were killed at the following ages: one a few hours after birth, one 7.5 days old, one 15 days old, one 28 days old, one 42 days old, and one 56 days old. The thyroid and a portion of the trachea were removed from the pigs, while only the thyroid was removed from the adults. All the material was fixed in Zenker's fluid and imbedded in paraffin. The thyroid glands of the pigs were cut transversely into sections 15/x in thickness, all the sectiotis were mounted in serial order, and stained with eosin and Unna's alkaline methylene-blue solution. The thyroid gland of the adults were cut transversely into sections 20m thick, only every fifth section was mounted, and stained with hematoxylin and eosin.

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14 J. A. BADERTSCHER

In the description of the following stages special attention will be given: 1) to the sti-ucture of the ultimobranchial bodies and to their location in the thyroid gland, and 2) to the location and extent of areas of unusually large (cystoid) follicles. Since in the embryonic material it was found that cystoid follicles may develop in the ultimobranchial bodies, the latter consideration is of importance.^

Pig at birth. The thyroid gland is 9.3 mm. long and its greatest width is 4.8 mm. Caudally it terminates in a rather blunt point, while the anterior portion is drawn out into a slender streamer. The greater portion of the bulk of the gland is thus located in its posterior half. The more bulky part of the gland is crescent in shape in transverse sections. In the middle third of the left lateral half of the thyroid gland the ultimobranchial body is represented by three small areas which are composed of tortuous syncytial cords and masses quite closely packed together. These areas are embedded beneath the dorsal surface of the gland lateral to its medial plane, a position usually occupied by the ultimobranchial bodies in the later embryonic stages. Anterocaudally, they extend through eight, six, and twelve consecutive sections, respectively. The most anteriorly located of these areas is free from colloid and lies in a field of folhcles that are on an average smaller than the average size of the majority of follicles present in the thyroid gland. In the central and caudal areas the colloid is just beginning to form. On account of the absence of colloid in one and its scanty amount in the other two of these areas, they stand out sharply from the thyroid follicles immediately surrounding them. No difference could be observed between the structure of the nuclei in these areas and the nuclei in the cells composing the follicles. In the right lateral half of the thyroid gland the ultimobranchial body is absent.

1 As this work is practically a continuation of a previous investigation ('18) by the author of the ultimobranchial bodies in pig embryos, it was deemed unnecessary to repeat an historical sketch of this subject in this article. Also the bibliography includes only those references to articles in which may be" found more or less definite statements concerning the fate of the ultimobranchial bodies. If an extensive bibliography on this subject is desired, reference should be made to the. works of Verdun ('98) and Grosser ('12).


ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 15

Unusually large follicles are present in both lateral halves of the caudal fourth of the thyroid gland. These are located mainly near the dorsal and dorsolateral surface of the gland. A few very large follicles are located near the most caudally located area of the ultimobranchial body. Also an area of very large follicles (extending through a series of thirty-four sections) is present in the caudal portion of the middle third of the right lateral half of the thyroid gland just below its dorsal surface.

Pig 7.5 days old (fig. 1). The thyroid gland is 15 mm. long and its greatest width is 6.8 mm. The greater portion of the anterior half of the thyroid gland is in form a slender band, so that by far the greater portion of its bulk hes in the posterior half of the gland. The more bulky portion of the gland is crescent in shape in transverse section. Traces of both ultimobranchial bodies are present in the caudal fourth of the thyroid gland. The left one is represented by three oblong areas composed of closely packed syncytial cords and masses which are almost free from colloid. The nuclei in the syncytium have a structure identical to the structure of the nuclei in the cells composing the follicles. Anterocaudally, these areas extend through nineteen, seven, and thirty consecutive sections, respectively. The most anteriorly (fig. 1, U.) and caudally located of these areas are partially exposed to the free surface on the dorsal border of the thyroid gland, while the centrally located one is embedded only a short distance below the dorsal surface of the gland. The ultimobranchial body on the right side has a structure similar to the left one. It extends through a series of ten sections and is entirely embedded below the dorsal surface of the thyroid gland.

In the left lateral half of the thyroid gland and just anterior to the ultimobranchial body represented in figure 1 is the caudal termination of an elongated area containing many large (cystoid) follicles. This area of large follicles is located just below the dorsal border of the thyroid 'gland and extends through seventy consecutive sections. Very large follicles are also found in the immediate neighborhood of the centrally located area of the ultimobranchial body. Two rather large follicles lie near

THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, NO. 1


16 J. A. BADERTSCHER

the right ultunobranchial body. A few large folHcles are found near the caudal end of the thyroid gland.

Pig 15 days old (fig. 2). The thyroid gland is 10.5 mm. long and its greatest width is 6.3 mm. It tapers to a blunt point at each end. Only the right ultimobranchial body is present. It is embedded deeply below the dorsal surface in the posterior half of the thyroid gland. It is represented by two areas which are composed of syncytial cords and masses in which follicles containing colloid are quite numerous, but on an average much smaller than the majority of follicles in the immediate neighborhood of these areas. The more anteriorly located and larger of these areas (fig. 2, U.) extends through a series of eighty-five sections, while the more caudally located one extends through sixteen consecutive sections. Thirty-six sections intervene between the two areas. The structure of the nuclei in these areas is identical to that of the nuclei in the cells composing the follicles. In the caudal fourth of the thyroid gland there are many very large follicles which are located chiefly in the dorsolateral margin of the gland.

Pig 28 days old. The thyroid gland is 11.1 mm. long and its greatest width is 7.7 mm. It tapers to a blunt point at each end and its more bulky portion is crescent in shape in crosssection. Both ultimobranchial bodies are present. They are located just below the dorsal surface in the caudal portion of the middle third of the thyroid gland, lateral to its medial plane. The right one is similar in structure to the ultimobranchial body in the thyroid gland of the 15-day-old pig. It extends through a series of sixteen sections. The left ultimobranchial body is composed largely of an attenuated syncytial mass in which are found a few small follicles. It extends through a series of thirty-eight sections.

In the immediate neighborhood of the left ultimobranchial body are found a few very large follicles. Many very large folhcles are present in the taudal fourth of the thyroid gland. These are located chiefly near the dorsal and dorsolateral border of the gland, excepting near its caudal end where they are scattered throughout the entire thickness of the gland.


ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 17

Pig 42 days old (fig. 3). The thyroid gland is 14.6 mm. long and its greatest width is 7.3 mm. It tapers to a point at each end and, excepting near its ends, is crescent in shape in transverse section. The ultimobranchial body on the right side is located midway between the two ends of the thyroid gland and is embedded just below the dorsal surface of the gland lateral to its medial plane. It extends through a series of twenty-six sections and is composed of syncytial cords and masses. In both ends and in the peripheral portion of this structure the follicles are quite numerous but comparatively small, while in places its center is free from colloid. The ultimobranchial body on the left side is located in the anterior portion of the caudal fourth of the thyroid gland and is embedded just below the dorsal surface of the gland lateral to its medial plane. It extends through fifty-four consecutive sections and has a structure (fig. 3, U.) similar to the right one. In place it is almost separated from the rest of the thyroid gland by connective tissue.

An area of large follicles in the right lateral half of the thyroid gland extends anteriorly from the ultimobranchial body. This area of large follicles is located chiefly just below the dorsal border of the gland, but in places it extends to its dorsalateral margin. In the dorsolateral portion of the middle third of the left lateral half of the thyroid gland is an area, variable in width, of very large (cystoid) follicles. Near the caudal portion of the anterior third of the thyroid gland these areas of large follicles become continuous just below its dorsal surface and gradually extend more deeply into the gland so that large follicles are found throughout its extreme anterior portion. No follicles of an unusually large size are found in the extreme caudal portion of the thyroid gland.

Pig 56 days old. The thyroid gland is 13.5 mm. long and its greatest width is 10.2 mm. It tapers to a blunt point at both ends. The left lateral half of the gland is considerably more bulky than the right lateral half. The only traces of an ultimobranchial body is an area of very small follicles near the dorsolateral margin in the right lateral half of the thyroid gland.


18 J. A. BADERTSCHER

This area extends through a series of ten consecutive sections and is located nearly midway between the two ends of the gland. A feature very noticeable in the thyroid of this pig is the presence of only a small number of large follicles. These are located chiefly near the dorsal border in the caudal fourth of the gland.

Young adult hog no. 1 (fig. 4). The thyroid gland is 26 mm. long and its greatest width is 18.5 mm. Its anterior end terminates in a single blunt point, while its posterior end terminates in two blunt processes each about 3.5 mm. long. The only structural feature representing a possible derivative of an ultimobranchial body is an elongated area of small follicles (fig. 4, U.) which extends through 125 consecutive sections. This area is located along the dorsal border in the posterior fourth of the right lateral half of the thyroid gland and extends for a short distance into its right terminal process. More interfollicular connective tissue is present in this area than in other parts of the gland. The anterior two-thirds of the thyroid is free from unusually large follicles. Many are found in the posterior third of the gland. Two large follicles (C.F.) are represented in figure 4.

Young adult hog no. 2. The thyroid gland is 29 mm. long and its greatest width is 20 mm. The anterior end terminates in two blunt processes each 6.5 mm. long, while the posterior end terminates in a single blunt point. The only structural feature representing a possible remnant of an ultimobranchial body is an area of small follicles in the posterior fourth of the left lateral half of the thyroid gland. This area extends through a series of forty sections and has a structure similar to that of the ultimobranchial body represented in figure 4.

Two areas of large follicles are present. In the interior and middle thirds of the thyroid gland these areas extend from the tip end of the two anterior processes along the dorsolateral margin of the thyroid. In the caudal third of the gland these areas gradually become larger, so that at the extreme caudal end they are found throughout the entire thickness of the gland.

Young adult hog no. 3. The thyroid gland is 26.5 mm. long and its greatest width is 20 mm. At each end it tapers to a blunt


ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 19

point. No remnants of the ultimobranchial bodies are present. Only a few follicles of an unusually large size are present in the extreme anterior and posterior ends of the gland.

SUMMARY

In pig embryos^ it was found that the peripheral portion of the ultimobranchial bodies generally develops into typical thyroid structures before its more central portion. It thus becomes evident that the ultimobranchial bodies which can be recognized structurally as such in the thyroid gland of postnatal pigs are mere remnants of these structures that have not fully developed into typical thyroid structures. Also, the structure of the ultimobranchial bodies in the late developmental stages of pig embryos and in the postnatal pigs are similar, namely, areas composed of nucleated syncytial cords and masses the central portion of which may be free frum colloids. Areas of small follicles (developmentally young) are not so marked in th^ immediate neighborhood of the ultimobranchial bodies in postnata pigs as in the immediate vicinity of these structures in most of the late embryonic developmental stages.

One of the ultimobranchial bodies in the thyroid gland of three pigs is not a continuous structure, but is broken up into segments. For example, the one on the left side in the 7.5-dayold pig is composed of three oblong areas which vary in length. It seems that a satisfactory explanation for this condition is a more rapid transformation into typical thyroid structures of some parts of the more central portion or core than of other parts, thus dividing it into segments which are separated from each other by follicles. The length of the portion of an ultimobranchial body broken up into segments is obtained by measuring the distance between the anterior and posterior parts of the most anteriorly and most posteriorly located segments, respectively. Thus the left ultimobranchial body in the 7.5-dayold pig extends through a series of seventy-five sections. The

- In the summary it will be necessary to refer quite frequently to the writer's previous work on the ultimobranchial bodies in pig embryos. This will be done without calling attention to the bibliographic reference of that article.


20 J. A. BADEETSCHER

right ultimobranchial body in the same pig is represented by a single area which extends through a series of ten sections. Judging from the so variable developmental behavior of these structures in pig embryos, this single area (and similar single areas in the thyroid gland of other pigs) undoubtedly does not represent the greatest length of the central core of this ultimobranchial body, but only what is left of it at the time the pig was killed. It underwent a more rapid transformation than the left one.

A considerable lapse of time intervenes between the age of the pigs and the young adult hogs, thus producing an undesirable break in the continuity of the postnatal developmental history of the ultimobranchial bodies. Although the conclusion in regard to these structures in the young adult hogs is thus rendered somewhat uncertain, I have a strong feeling that the areas of small follicles in the thyroid of the young adult hogs nos. 1 and 2 represent the ultimobranchial bodies in an advanced stage of development. Their structure, location in the thyroid gland, and their proximity to unusually large follicles strengthen this - interpretation.

In some of the later developmental stages of pig embryos it was found that unusually large (cystoid) follicles develop in connect' on with the ultimobranchial bodies. The extent and location of areas of this type of follicles in the thyroid gland of postnatal pigs need therefore to be considered.

The existence of a possible interrelationship between the large follicles and the ultimobranchial bodies is exemplified in a single thyroid gland in some of the postnatal pigs. Thus, in the pig at birth the ultimobranchial body that is present is located in the middle third of the left lateral half of the thyroid gland, while an area of large follicles occupies an almost corresponding position in the right lateral half of the gland. Also a few very large follicles are found near the most caudally located segment of the ultimobranchial body. In the thyroid gland in pig 7.5 days old large follicles are found in the immediate neighborhood of the right ultimobranchial body and near the central segment of the left one. Also cephalad to the most anteriorly located


ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 21

area of the left ultimobranchial body is an elongated area^ of large follicles that extends into the middle third of the thyroid gland. A few very large follicles are found in the immediate neighborhood of the left ultimobranchial body in the thyroid gland in pig 28 days old. Large follicles are present in the immediate neighborhood of the ultimobranchial bodies (?) in the young adult hogs nos. 1 and 2.

In a general way, it can be stated that the unusually large follicles are most numerous in the majority of postnatal stages in the portion of the thyroid gland in which the ultimobranchial bodies are generally found, that is, in the posterior half of the gland. This feature is in accord with the fact that in embryos from about 50 mm. in length to full term the ultimobranchial bodies are also usually located in the posterior half of the thyroid gland, although in some they are located in the middle third or in the middle two-fourths of the gland. Exceptions to the usual location of the majority of large follicles in a single gland are not wanting. The most striking example of this exception is found in pig 42 days old, in which the great majority of large follicles are found in the anterior half of the thyroid gland. In consideration of the variable developmental behavior of the ultimobranchial bodies^ in pig embryos, it is therefore, not surprising (granting an interrelationship between the large follicles and the ultimobranchial bodies) to occasionally find large follicles out of their usual place (pig 42 days old) or the almost entire absence of large follicles, as is the case in the thyroid gland in pig 56 days old and in the young adult hog no. 3.

Another significant feature of the location of the very large follicles is the depth at which they are embedded in the thyroid gland. In the more bulky portion of the gland they are located near the dorsal or dorsolateral border of the gland, that is, in the region in which the ultimobranchial bodies may be found, and not in the ventral or ventrolateral region which is derived

^ Variations as to their size, the time of their complete transformation into typical thyroid structures, their location in the thyroid gland, and the presence or absence of large (cystoid) follicles in connection with them.


22 J. A. BADERTSCHER

from the median thyroid anlage. The caudal end of the thyroid gland in some of the postnatal pigs (pig at birth, pig 15 days old, and young adult hogs no. 1 and 2) contains many large follicles. This feature apparently bears with it a significance when it is correlated with the fact that in some of the comparatively early embryonic stages the caudal portion of the tripartite complex is largely composed of ultimobranchial bodeis.

Although the evidence of an interrelationship between the large follicles and the ultimobranchial bodies in postnatal pigs is circumstantial, yet when this evidence is correlated with their development in connection with the ultimobranchial bodies in some of the later embryonic developmental stages, it appears that the ultimobranchial bodies are largely responsible for the large (cystoid) follicles.

In conclusion, it can be said that since the ultimobranchial bodies fuse with the thyroid gland and also form colloid the boundary between these structures and the gland becomes obhterated, so that it is impossible to determine the exact relative proportion that is contributed to the thyroid gland by the ultimobranchial bodies and the median thyroid anlage. Owing to the variable developmental behavior of the ultimobranchial bodies, the relative proportion they contribute to the thyroid gland undoubtedly varies in different pigs. It is, however, quite evident that only a relatively small portion of the gland is derived from the ultimobranchial bodies.


ULTIMOBRANCHIAL BODIES IN POSTNATAL PIGS 23

BIBLIOGRAPHY

Badertscher, J. A. 1918 The fate of the ultimobranchial bodies "n the pig (8iis scrofa). Amer. Joiirn. Anat. vol. 23.

lioRN, G. 1883 ttber die Derivate der embryonalen Schlundbogen und Schlundspalten bei Siiugetieren. Arch. f. mikr. Anat., Bd. 22.

Grosser, O. 1910 Zur Kenntnis des ultimobranchialen Korpers beim Menschen, Anat. Anz., Bd. 37.

1912 The development of the i)hai-ynx and of the organs of respiration. Manual of Humaik Embryology, edited by F. Keibel and F. P. Mall, vol. 2.

Herrmann, G., and Verdun. 1899 Persistance des corps post-branchiaux chez riiomme. Remarques sur 1' anatomic comparce des corps postbranchiaux. Comptes Rend. Soc. Biol. Paris.

1900 Note sur les corps post-branchiaux des Cameliens. — Les corps post-branchiaux et la thyroide; vestiges kystiques. Comptes Rend. Soc. Biol. Paris.

Kingsbury, B. F. 1914 On the so-called ultimobranchial body of the mammalian embryo Man. Anat. Anz., Bd. 47.

Maurer, F. 1899 Die Schilddriise, Thymus und andere Schlundspaltenderivate bei der Eidechse. Morph. Jahrb., Bd. 27.

1899 Die Schlundspalten — Derivate von Echidna. Anat. Anz. Ergiinzinigsheft. Bd. 16.

Moody, R. M. 1912 Some features of the histogenesis of the thyroid gland in the pig. Reprints of papers from the Dept. of Anat. of the Univ. of Cal., vol. 4.

Prenant, a. 1894. Contribution a I'etude organique et histologique du thymus, de la glande thyroide et de la glande carotidienne. La Cellule, T. 10.

Rabl, H. 1913 Die Entwicklung der Derivate des Kiemendarms beim Meerschweinchen. Arch. f. mikr. Anat., Bd. 82.

Simon, Ch. 1896 Thyroide laterale et glandule thyroidienne chez les mammiferes. These de Nancy.

Verdun, P. 1898. Contribution a I'etude des derives Branchiaux chez les vertobres superieurs. These, Toulouse.


PLATE 1

EXPLANATION OF FIGURES

1 From a photograph of a portion of a transverse section of the caudal fourth of the thyroid gland showing the left ultimobranchial body (U.). The colloid in the thyroid gland is represented by black dots. From a pig 7.5 days old. X 60.

2 From a photograph of a portion of a transverse section of the caudal half of the thyroid gland showing the more anteriorly located segment of the right ultimobranchial body {U.). The white spots in the thyroid gland represent follicles out of which the colloid has dropped. From a pig 15 days old. X 60.

3 From a photograph of a portion of a transverse section through the caudal fourth of the thyroid gland showing the left ultimobranchial body (U.). From pig 42 days old. X 60.

4 From a photograph of a portion of a transverse section of the posterior fourth of the thyroid gland showing the right ultimobranchial body (U.?) and two very large (cystoid) follicles {C.F.) which are filled with colloid. From young adult hog no. 1. X 45.

ABBREVIATIONS

C.F., cystoid follicle; T., thyroid; f^, ultimobranchial body


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