The discovery of the premaxillary bone (os incisivum, os intermaxillare or premaxilla) in humans has been attributed to Goethe, and it has also been named os Goethei. However, Broussonet (1779) and Vicq d'Azyr (1780) came to the same result with different methods. The first anatomists described this medial part of the upper jaw as a separate bone in the vertebrate skull, and, as we know, Coiter (1573) was the first to present an illustration of the sutura incisiva in the human. This fact, and furthermore its development from three parts:-(1) the alveolar part with the facial process, (2) the palatine process, and (3) the processus Stenonianus-can no longer be found in modern textbooks of developmental biology. At the end of the nineteenth and in the early twentieth century a vehement discussion focused on the number and position of its ossification centers and its sutures. Therefore, it is hard to believe that the elaborate work of the old embryologists is ignored and that the existence of a premaxillary bone in humans is even denied by many authors. Therefore this re-evaluation was done to demonstrate the early development of the premaxillary bone using the reconstructions of Felber (1919), Jarmer (1922) and data from our own observations on SEM micrographs and serial sections from 16 mm embryo to 68 mm fetus. Ossification of a separate premaxilla was first observed in a 16 mm embryo. We agree with Jarmer (1922), Peter (1924), and Shepherd and McCarthy (1955) that it develops from three anlagen, which are, however, not fully separated. The predominant sutura incisiva (rudimentarily seen on the facial side in a prematurely born child) and a shorter sutura intraincisiva argue in this sense. The later growth of this bone and its processes establish an important structure in the middle of the facial skull. Its architecture fits well with the functional test of others. We also focused on the relation of the developing premaxilla to the forming nasal septum moving from ventral to dorsal and the intercalation of the vomer. Thus the premaxilla acts as a stabilizing element within the facial skeleton comparable with the keystone of a Roman arch. Furthermore, the significance of the premaxillary anlage for the closure of the palatine was documented by a synopsis made from a stage 16, 10.2 mm GL embryo to a 49 mm GL fetus. Finally the growth of the premaxilla is closely related to the development of the human face. Abnormal growth may be correlated to characteristic malformations such as protrusion, closed bite and prognathism. Concerning the relation of the premaxillary bone to cleft lip and palate we agree with others that the position of the clefts is not always identical with the incisive suture. This is proved by the double anlagen of an upper-outer incisor in a 55 mm fetus and an adult.

Hydatids, as appendices of testis or epididymis, were discovered by Morgagni in 1703 and 1705 and published by him in 1761. Hydatids are considered to be remnants of the cranial part of the Mullerian duct (MD), Wolffian duct (WD), or mesonephric tubules. They are localized as sessile or pedunculated appendices at the cranial pole of testis and at the head of epididymis, or at analogous organs in women. The clinical relevance is known: acute scrotum with torsion of appendices, or metaplasia. However, little is known about the embryological development of hydatids. Therefore, we studied the origin and development of appendix testis (AT) and appendix epididymidis (AE) in human embryos from stage 14 (Carnegie Collection), 6.5 mm GL, 32 days, to fetuses of 170 mm, 17th week. Light and scanning-electron microscopy as well as plastic reconstructions from serial sections of the cranial parts of MD and WD reveal that hydatids already form during regression or transformation of the ducts. At stage 18, 15-16 mm GL, 44 days, the cranial parts of MD and WD exhibit morphological features that give a preview on the definite form and position of later appendices. In fetuses from 45 mm GL, ninth week onward, we found anlagen of pedunculated hydatids (AE) deriving from the ampullated cranial end of the WD, which in many cases opened into the coelomic cavity. The unpedunculated AT derived from the persisting funnel region of the MD. The development of duct-independent, accessory appendices was observed. We paid special attention to a pedunculated hydatid in a fetus of 120 mm, 14th week, and the cranial regressing WD. A classification of hydatids is presented. Photographs and histological sections of (sessile) appendices testis (AT), and (pedunculated) appendices epididymidis (AE) with torsion of stalks exhibit the final forms and positions of hydatids in adult.

The rostral part of the notochord reveals many peculiarities compared with the trunk mesoderm. Furthermore, its role in head formation and inductive processes in the head is not as well understood as the interaction of the trunk notochord with the spinal cord and somites. To interpret experimental and molecular biological examinations in the developing head region, exact knowledge about morphological features of the rostral notochord is fundamental. Here we show that the rostral notochord reveals variations that depend on species and individual. We describe morphological characteristics of the rostral (head) notochord in human embryos (Carnegie stages X-XIV), which are shown in semithin sections and three-dimensional graphic reconstructions. Special attention is paid to the relationship of the notochord with the prechordal mesoderm and the adenohypophysis. We propose that in the human the rostral notochordal tip terminates at Rathke's pouch, whereas in the chick prechordal mesoderm is found in between the notochordal tip and the anlage of the adenohypophysis. The behaviour of the notochord at the end of the embryonic period proper and early fetal time is shown in sagittal histological sections of 16 to 49 mm CRL human embryos. Position and disintegration of the rostral notochord is also described in embryos of cat (8-25 mm), mouse (stage 21-24 according to Theiler) and chicken (stage 22-26 HH). A synopsis reveals the different course of the notochord within, at the inner or outer side of the basioccipital cartilage. The course of rostral notochord is determined by its attachment points at the hypophysis, the pharynx or the footplate of the brain. In all species, it has an undulating course. Its rostral tip is highly coiled, and fragments or splinters are found within the anlage of the dorsum sellae. Thus, we have reasons to believe that the adenohypophysis is a hindrance for the rostral elongation of the notochord. Variable adhesions between notochord and pharyngeal epithelium are considered to be responsible for invaginations of the pharyngeal wall forming bursae pharyngeae. In contrast to other authors, we observed in the mouse that rostrally the notochord bends ventral and penetrates the chondrocranium at the level of the later synchondrosis basisphenoidale to build a bursa pharyngea. Finally, partial duplications of two human notochords are described.

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The rostral notochord plays an important role in the head development of vertebrates. Yet, in contrast to trunk notochord, the course and behavior of the head notochord shows species-specific variations. To analyze normal and abnormal development in the head region, knowledge of the normal behavior of the rostral notochord is a prerequisite. Therefore, we studied the rostral notochord of Ichthyophis kohtaoensis, not only in anatomical view a relatively unknown order of Gymnophiona, in embryos of the stages B, C, D, E according to Himstedt (1996) or stages 21, 22, 26, 31 according to Dünker et al. (2000). We described the course, form, and structure of this part of the notochord and compared it with morphological features and variations of the notochord in existing studies of higher vertebrates (Barteczko and Jacob 1999). We found that the rostral notochord of this oviparous Gymnophiona from Thailand is quite similar to that of higher vertebrates: its tendency to elongate directly in a rostral direction is prevented by the adenohypophysis as a barrier; at stage B the neurohypophysis/infundibulum takes the role of a hindrance. Light microscopic results, laser scanning micrographs, and plastic reconstructions based on serial sections showed unequivocally in stages B-E the effects resulting from this hindrance: buckling, variations in volume, screw-like torsions, undulations, deviations, and splintering. The notochord was found to lie dorsal to the developing cartilaginous basicranium. The tendency to press the dura towards the brain was conspicuous. The formation of a bursa pharyngea was likewise observed; the predisposition of several such structures exist. We suggest that the vertebrate phenotype with the appearance of preaxial structures, in contrast to the chordata phenotype, correlate with the formation of a hypophysis. Experiments have yet to prove this hypothesis.