When the cranial part of the neural tube is closed to the brain there are three pairs of ganglions; that is trigeminal, acousticofacial and vago-glossopharyngeal. The trigeminal ganglion is the largest, the vago-glossopharyngeal the smallest.
In the earliest author's embryos which belong to the Streeter's horizon XIV, the three nerves of the trigeminus are protruding thick and straight from the ganglion toward respective regions. The portio minor of the mandibular nerve is becoming eminent in this period. Asregarding the facial nerve the chorda tympani is earlier developing than the stem in the same horizon, the N. petrosus superficialis major a little later in the next horizon XV, when the stem is almost the same as in the earlier stage.
In the horizon XIV the vagus is also already well developed, its root and trunk ganglions are completely separated by nerve fiber bundle, from the trunk ganglion the upper laryngeal nerve is protruding while the stem is not yet elongating, as in the case of the chorda tympani to the facial nerve stem. The glossopharyneal nerve is a little later developing than the vagus, its root and trunk ganglions are not completely separated in the early stage, the tympanic nerve from the trunk ganglion is only in the horizon XVI to be observed.
The peripheral nerve bundles which come from the epithelium of the otic vesicle and reach the statoacoustic ganglion are developing from the horizon XV to XVI and in the horizon XVII all nerves already discernible.
Among the motor nerves the hypoglossal is the first developing, it reaches to the level of the trunk ganglion of the vagus in the early horizon XIV, while the others for the optic bulb muscles : the oculomotorius, trochlearis and abducens are not yet protruding from the brain wall. Among these three nerves the oculomotor is the earliest developing, the trochleal the latest. The former is in the horizon XV, the latter in the next horizon XVI protruding from the brain wall.

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The nasal pit of the early human embryo appears in the Streeter's horizon XV, in the next horizon XVI it becomes a nasal fossa which is surrounded by mesenchymal tissue of the socalled medial, lateral nasal and maxillary processes. This nasal fossa deepens in the next horizon XVII and in the horizon XVIII the thin bucco-nasal membrane at the bottom of the fossa gives way and disappears. Thus the primitive choana is open in this stage.
This structure of the primitive nasal cavity is visible in the author's 10 to 20 mm long embryos, by which the absolute thickness of the nasal septum does not change, while the dimensions of the cavity increase twice in this period. During this period of the primitive nasal cavity the palate process on the pharyngeal surface of the maxillary process is becoming prominent and at the end of this period the anterior end of this swelling visible on the maxillary process lateral to the primitive palate, which structure is missed in the succeeding more developed embryos.
Among three elder embryos a 35 mm long have a distinct secondary palate, by which the palate processes of both sides are above the tongue, the incisive canal at the anterior third is surrounded by osseous tissue of the maxillary and premaxillary processes. By the other two 22 and 27 mm long embryos the palate processes of both sides are lateral and under the tongue, their anterior parts protruding not vertically, but horizontally under and before the tongue and continued to the palate. By these two embryos the Jacobson's organ comes more foreward on the hinder third (22 mm) or middle (27 mm) of the palate, which condition is not by the primitive palate, by which the organ comes above the posterior margin of the palate.
The olfactory fibers are from the beginning of the nasal pit discernible, the terminal nerve later before the perforation of the primitive choana. The nasopalatine nerve comes from the maxillary on the surface of the nasal septum under the epithelium and reaches the anterior naris early in the horizon XV, the palatine nerves a little later in the horizon XVII, when the palatine processes are becoming eminent. The anterior ethmoidal and infratrochlear nerves are also in the latter stage observed.
During the primitive nasal cavity is the maxilloturbinale alone visible on the lateral surface, the ethmoturbinale later in the 22 mm long embryos, also the maxillary sinus.
The precartilage of the wall of the nasal cavity appears first in the nasal septum in the horizon XVIII, then in the lateral wall a little later. The precartilageous septum becomes cartilageous first in the 27 mm, then the laterawall in the 35 mm long embryo.

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