[Morphogenesis of the cranium of Cavia porcellus L. I: Introduction, classification and descriptive part].

The craniogenesis of Cavia porcellus has been investigated in 7 embryos of different ages. From the developmental stage of 36 mm CRL, a reconstruction of the chondrocranium is described. As there is still a gap in the tectum posterius, the foramen magnum is not closed posteriorly. The course of the notochord is retrobasilar at the beginning, more rostrally it runs intrabasilar. After ossification, the place where the notochord enters the basioccipital is marked by a cavity. This cavity is not identical with the posterior basicranial fenestra. The laminae alares build up strong paracondylar processes. The auditory capsule is connected with the occipital region only by the exoccipitocapsular commissure, but there is no supraoccipitocapsular commissure. The fossa subarcuata is pierced by a subarcuate foramen. The very short lamina parietalis is not in contact with the orbital wing as there is no orbitoparietal commissure. The processus recessus divides the perilymphatic foramen into fenestra rotunda and aquaeductus cochleae. The suprafacial commissure arises from the upper margin of the canalicular part of the auditory capsule, but it does not reach the superior surface of the cochlear part at this stage. The tegmen tympani is well developed. The foramen singulare is not yet separated from the inferior acoustic foramen. At the stage of 36 mm CRL there is no septum spirale cartilagineum. Mm. tensor tympani et stapedius are developed in the typical way. The auditory capsule is connected with the basal plate by the anterior basicochlear and the alicochlear commissures. The floor of the orbitotemporal region is incomplete, the temporal wings are small. The alicochlear commissure, the alar process, the anterior basicochlear commissure, and the basal plate surround the carotid foramen, but there is no blood vessel passing through it. The temporal wing is at the beginning of ossification and shows a fissura ovalis for the mandibular nerve. Although the hypophysial canal is still present, there are no structures passing through it. There is no foramen rotundum. The orbital wing is still cartilagineous. The basal plate and the pre- and postoptic roots border the optical foramen. The straight muscles of the eyeball are attached to the ala hypochiasmatica which projects from the postoptic root. The interorbital septum is absent. The ophthalmic artery, which instead of the obliterated internal carotid artery, contributes to the circulus arteriosus cerebri is well developed. There is no orbitonasal commissure . The epiphanial foramina are present.(ABSTRACT TRUNCATED AT 400 WORDS)