Resumen por la autora, Evelyn Holt.

Ausencia de la parte bucal de la hip6fisis en un embri6n de cerdo de 40 mm.

El objeto del presente trabajo es la descripci6n de un embri6n de cerdo de 40 nm., el cual aunque parecia normal en todos 10s demhs rasgos, no poseia la parte bucal de la hipofisis. Mientras que dicha parte bucal falta, la parte neural estk bien desa- rrollada, estando reunida con el cerebro, y presentando posicih, tamaiio y estructura normales. Esth rodeada por una con- densaci6n de mesenquima que es continua con la pia y se parece a una membrana basal, except0 cerca del Bpice del proceso, donde la diferencia entre 10s tejidos epitelial y neural se pierde por completo. La tiroides, suprarrenales y gonadas aparecen normales cuando se las compara con embriones de cerdo de 38 y 42 mm., respectivamente. Como no se ha descrito ning6n caso semejante, esta anormalidad debe considerarse como rara. Tiende a rechazar la teoria que atribuye el desarrollo del proceso infundibular a la presi6n ejercida por la bolsa de Rathke sobre la vesicula cerebral anterior.

Translation by J d F. Nonidez Cornell Medical College, New York

AWFHOR’S ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPRIC SERVICE, OCTOBER 17

ABSENCE OF THE PARS BUCCALIS OF THE HYPOPHYSIS IN A 40-MM. PIG

EVELYN HOLT Cornell Universitil, Ithaca, New York

TWO FIGURES

Belonging to the Department of Histology and Embryology at the Cornell University Medical College in Ithaca is a 40-mm. pig embryo, remarkable for the fact that, while the infundibulum is well developed, the oral portion of the hypophysis is wholly absent; in other respects the embryo appears normal. Because no similar case has been recorded and because this abnormality may help to make clear the normal development of the hypophy- sis, a brief description of the specimen is here given.

The embryo (series 148) is well preserved, cut transversely in sections 10 /i thick, and stained with hematoxylin andeosin. For purposes of comparison, there were used two pig embryos of 38 and 42 mm., respectively. These were also cut in the transverse plane. Photographs at a magnification of twenty- two diameters were made of the hypophyseal region of the 40 and 42-mm. pigs, and are here reproduced, side by side, as figures 1 and la, 2 and Za, because it is believed that the untouched photographs present the true condition more accu- rately than line drawings or verbal descriptions. Owing to the inevitable slight difference in the plane of section, the levels do not correspond exactly.

In the 40-mm. pig the pars buccalis of the hypophysis is wholly absent, there being no trace of it in the usual position about the pars nervosa-where at this stage it should be a conspicuous feature-or in the roof of the pharynx, or along the route of development, where a craniopharyngeal canal sometimes exists. The pars neuralis, on the other hand, is well developed, connected with the brain, and normal in position, extent, and

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PARS BUCCALIS OF HYPOPHYSIS IN 40-MM. PIG 209

structure. It is tubular, extends downwards and backwards from the diencephalic floor, and is made up of two zones, a medulla consisting of several layers of closely packed cells, and a cortex made up of fibers and cells in looser arrangement. This point, the normal appearance of the pars nervosa, is of special interest in connection with the work of Smith (’20)’ who re- moved the anlage of the epithelial hypophysis (pars buccalis) from frog larvae of 3.5 to 4 mm. in length.’ On the basis of his work, Smith says (p. 78) : “It thus seems clear that in the absence of a nearly normal epithelial component, the neural hypophysis can not undergo its normal development nor attain its typical size or shape.” He found the pars nervosa in the operated tadpoles to be smaller than normal, asymmetrical in

Fig. 1 Section of the hypophyscal rcgion of a 40-mm. pig embryo, showing

Fig. 1-a Comparable section of a (normal) 42-mm. pig embryo. In the mesenchyme of the sella turcica appears the pars nervosa, alone in

figure 1: nearly surrounded by pars buccalis in figure 1-a. On either side of the hypophysis is the corresponding internal carotid artery. Anteriorly (above) the optic chiasma may be seen, while posteriorly (below) is a par t of the cartilage of the sella turcica.

Fig. 2 Section of 40-mm. pig showing infundibular stalk connected with the brain.

Fig. 2-a Comparable section of 42-mni. pig. From before backward the following parts of the brain appear, optic chiasma,

postchiasmatic eminence (medial eminence of tuber cinereum) , pars nervosa of hypophysis, and, behind the sella turrica, pons. The fact that in figure 2 the chiasma and postchiasmatic eminence appear continuous, while in figure 2-a they are separated by mesenchyme, is due t o a slight difference in the plane of section. I n figure 2 the pars buccalis is lacking and the pars nervosa is directly related to the mesenchyme, while in figure 2-a the pars buccalis is present appear- ing on either side of the infundibular process and extending forward (pars tu- beralis) over the surface of the tuber cinereum. The internal carotid arteries appear as before.

complete absence of the pars buccalis.

* Smith classified the results of the operation as, 1) disturbances of pigmenta- tion; 2) changes in the rate of growth, and, 3) endocrine disturbances. The first of these does not apply to the pig and will not be considered here. The second is difficult to determine from one specimen, especially as we have not the litter mates to use as a basis of comparison. I n point of differentiation, however, the embryo is comparable t o other pigs of the same length. The third point, endocrine disturbances apart from the pars nervosa of the hypophysis, will be considered a little later.

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form, and atypical in position. As the oral component was removed before the formation of the primitive infundibulum and without injury to the neural tube, these changes were not considered traumatic, due to the operation. They might be explained as due to one of two factors or to these two acting conjointly. They might be an expression of a general endocrine disturbance due to hormone deficiency, atrophic or non-develop- mental changes comparable with the marked peculiarities noted by Smith (pp. 83 to 97) in the thyroid and adrenals; or they might be due to the lack of a mechanical stimulus normally derived from the pars buccalis. While he does not deny the possibility of the former factor, Smith states quite plainly (p. 83) that “the neural lobe and pituitary floor are dependent upon the association with the epithelial hypophysis for their full development.” The pars nervosa of this pig embryo, being normal in position, size, and shape, does not support the theory that the association of a normal pars buccalis is necessary for the development of the infundibulum. It is probable, however, that the presence of the whole gland would be necessary for the complete development and normal functioning of the pars nervosa. Here we encounter a difficulty, as the exact functional processes of the gland and the relation of the two parts are little understood. That the relation is a close one seems evident on histological grounds. Atwell (’18, pp. 303, 304, fig. 21) states that in sixteen-day rabbit embryos there are definite contacts between the two portions of the hypophysis, these contacts indicating outgrowth of one or the other part. These may also be observed in pig and calf embryos. Herring (’08 a, p. 149) says that in adult cats epithelial cells may be demonstrated in the infundibular process, these cells having migrated from the pars buccalis. In that these contacts and ingrowths obviously cannot exist in the absence of the pars buccalis, the pars nervosa cannot reach full development alone; but that in the absence of the pars buccalis the infundibular stalk and process not only may appear, but may appear normal, in the mammal at least, is demonstrated by this embryo.

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The infundibular process is surrounded by a mesenchymal condensation which is continuous with the pia and resembles a basement membrane except near the tip of the process where the line of demarcation between the two tissues becomes lost and there seems to be a confluence of neural and mesenchymal tissue. Here the nervous tissue appears to end in an irregular scalloped manner, while the mesenchyme filling in the irregulari- ties (fig. 2) has the appearance of actually invading the nervous process. This is probably normal, as the same thing was ob- served in sagittal sections of 35- and 54-mm. pigs. Atwell ('18) states that in the rabbit portions of the original basement mem- brane may be seen between the cortical and medullary zones of the infundibulum. It was perhaps this appearance which led Miiller and Mihalkovics ('75) to believe that mesenchymal cells replace the proper nervous tissue of the infundibulum, converting it into a connective-tissue appendage of the brain. Herring ('08) showed that connective tissue is never present in the infundibulum to a considerable extent, the fibers which were described as connective tissue being ependymal or neurog- lial in character. The condensation which represents the arachnoid and inner layer of the dura appears to surround the neck of the infundibulum as it would were the whoIe gland present.

Upon careful examination, the development of other parts appeared normal, and that the embryo was alive and growing is proved by the presence of mitotic figures. The mesenchyme of the sella turcica shows evidences of erythrocyte formation and does not differ appreciably from the mesenchyme of this region in a normal embryo. The notochord ends, as in the case of the 38- and 42-mm. pigs, in the cartilaginous sphenoid. How it ended in an earlier stage when, in the pig, it would nor- mally be attached to the wall of Rathke's pocket, we have, unfortunately, no means of determining.

-Because of the emphasis placed by various workers on the relation between the hypophysis and the other ductless glands, the thyroid, gonads, and suprarenals of the three pigs were compared. The results of this comparison were negative. In

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the 40-mm. pig the thyroid was slightly larger than in either of the others, but this difference did not seem sufficient to be connected in any way with the non-development of the hypophysis, especially as the gland was a trifle larger in the 38- than in the 42-mm. pig. The structure of the gland was similar in all cases, a well-vascularized cord- or platework of cuboidal cells with deeply staining nuclei. Colloid was not yet present. The ovaries of the 40- and 42-mm. pigs were similar in state of development. The suprarenals seemed to be entirely normal. These observations differ from the findings of Smith ('20), but the difference may well be due to the fact that the pig develops in utero and receives pituitary secretion from the maternal organism. At any rate, this embryo offers no evidence of a primary relation between the endocrine organs.

While there are numerous descriptions of hypophyseal tumors and accessory glands, such as the pharyngeal hypophysis situ- ated in the roof of the pharynx (Cushing, '12, and Schwalbe, '09), it has been impossible to find the record of a single case of absence of either lobe. As the pars buccalis is considered essen- tial to life, an animal presumably could not live after birth with this portion of the gland congenitally absent. In this connection perhaps it should be noted that Smith's hypophysectomized tadpoles were never able to complete metamorphosis. As the literature contains no account of such an abnormality, whether in a fetus or in an animal after birth, it must be assumed that the defect is rare. Because neither part of the gland has been described as existing without the other, most workers have assumed the relation between neural and buccal parts to be fundament a1 .

Although there are several theories to account for the develop- ment and relations of the two parts of the gland, no one affords adequate explanation of this anomaly. His, Dursy and Muller, believed that the notochord exercised a mechanical influence in drawing out the infundibulum. Mihalkovics ('75), however, disproved this theory, and again WoerdemaIin ('14) pointed out that what the earlier workers had described as contacts

The 38-mm. pig was a male.

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were not true contacts-that is, while the two parts may be close together they are always separated by a slight amount of connec- tive tissue. Others, notably Reichert and His, noting the con- tact between the notochord and Rathke’s pocket, held that the notochord served to draw out the oral portion of the hypophysis. Mihalkovics (’75), Woerdemann (’14), and Atwell (’18) disproved this theory, basing their conclusions on the following observations : The contact does not exist until after Rathke’s pocket is formed; that is, the ‘cause’ follows the ‘effect.’ The contact is by no means constant; in some forms it appears at the superior pole of the pocket, in others at the inferior, while in the rabbit it is variable, present in some but not in all specimens.

Mihalkovics, observing that the oral evagination is the first to form and that it is closely related to the neural tube, attributed the formation of the infundibulum to the pressure exerted by Rathke’s pocket. Or, as Herring (’08 a, p. 163), who adopted this theory, said, “The wall of the sac presses upon the base of the anterior brain vesicle, giving rise at its upper extremity to a fold which becomes the primitive infundibulum. ” This theory fails to explain the presence of the infundibulum in the absence of the pars buccalis, unless we assume that Rathke’s pocket appeared, pressed upon the base of the brain to start an evagination, and then involuted quickly and completely. We have no basis for this assumption, and it would leave us - with three problems instead of o n e w h a t caused the develop- ing pocket to disappear? Why did not this factor cause some other abnormality? Why is there no trace of an oral evagination?

Willey (’94, p. 287) believed the relation between neural and oral epithelia to be incidental, due perhaps to a tendency of contiguous embryonic tissues to fuse together. This seems improbable, because the relation between the two parts is close and constant, being marked from the earliest stages.

Minot (’92, pp. 573, 574) advanced another theory: “The ectoderm of the mouth over the hypophyseal area lies against and is apparently intimately soldered to the ectoderm of the brain, a point which has been generally overlooked, but which

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seems to me of great importance. . . . . It is probable that the cementing together over the hypophyseal area of the buccal and cerebral ectoderm is the mechanical condition causing the formation of the two diverticula.” On the basis of this theory, we might explain the absence of the pars buccalis in the following manner: the neural and oral epithelia came together as usual (before the formation of the hypophyseal angle), then the growth of the embryo was disturbed so that Rathke’s pocket failed to appear, the disturbance subsided, and the infundibu- lum, normally appearing somewhat later, developed as usual.

Perhaps it would be better to consider the development of the hypophysis in connection with the development of the rest of the head, paying particular attention to the mesoderm and the head bend. The cementing together of neural and oral epithelia without the intervention of mesenchyme is perhaps important as affording a fixed point. Then, Rathke’s pocket would be due not to a simple evagination of oral ectoderm, but to the fact that at one point two layers of epithelia are held together, while at all other points they are separated by mesen- chyme, the degree of separation increasing with the proliferation of the mesenchyme cells and the growth of the surface ectoderm. If at an early stage mesenchyme cells appeared between the oral epithelium and the wall of the brain, there would be no fixed point and consequently no Rathke’s pocket. If this were so, the presence of the infundibulum would be determined by the growth of the neural tube in its relation to the surrounding mesoderm. The anomaly here described, while it renders improbable Mihalkovics’ theory as to the mechanics of the development of the hypophysis, proves no other theory. It stands as an interesting and rare anomaly, an occurrence which must be explained by anyone who attempts to account for the development and relations of the two parts of the hypophysis cerebri.

To Doctor Kingsbury, who suggested this description and placed at my disposal the departmental material making it possible, I wish to express my thanks for his very generous help.

PARS BUCCALIS OF HYPOPHYSIS IN 40-MM. PIG 215

BIBLIOGRAPHY

ATWELL, W. J.

CUSHING, H. 1912 The pituitary body and its disorders. Philadelphia. HERRIN, P. T. 1908 Histological appearances of the mammalian pituitary

body. Quart. Jour. of Exp. Physiol., vol. 1, pp. 161-185. 1908 a The development of the mammalian pituitary body. Ibid., pp. 121-160.

v. MIHALKOVIC~~, V. 1875 Wirbelsaite und Hirnanhang. arch. f . mikr. Anat., Bd. 11, S. 379-441.

h!hoT, c. S. 1892 Human embryology. pp. 571-575. New York. SCHWALBE, E. 1909 Die Morphologie der Missbildungen des Menschen und

Thiere. 111 Teil, I1 Lieferung, Kapitel II., pp. 245 246. Jena. SMITIT, P. E. 1920 The pigmentary, growth, and endocrine disturbances in-

duced in anuran tadpoles by the early ablation of the pars buccalis of the hypophysis. Amer. Anat. Mem., No. 11.

1913 An analysis of the juxtaneural epithelial portion of the hypo- physis cerebri with an embryological and histological account of a hitherto undescribed part of the organ. Internat. Monatssch. f. Anat. u. Physiol., Bd. 30, S. 258-293.

WEED, L H. 1915 The formation of the cranial subarachnoid spaces. Anat. Rec., vol. 10, pp. 475-482.

WILLEY, A. 1894 Amphioxus and the ancestry of the vertebrates. New York. WOERDEMANN, M. W. 1914 Vergleichende Ontogenie der Hypophysk. Arch.

1918 The development of the hypophysis cerebri of the rabbit. Am. Jour. Anat., vol. 24, pp. 271-337.

TILNEY, F.

f. mikr. Anat., Bd. 86, S. 198-292.