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O Slabý

Publications and source records attributed to O Slabý.

At least 19 recordsLinked to original sources
PubMed1991

The nasal apparatus of the red squirrel (Sciurus vulgaris L.) embryo at the stage of the fully formed chondrocranium.

The nasal apparatus of the squirrel embryo at the optimum stage of the chondrocranium displays simple (though not always primitive) features and individual structures developed largely as in other rodents and even in insectivores. Primitive features include the presence of a cartilago paraseptalis communis and probably the simplicity of the olfactory labyrinth, whose main support in the region as a whole is ethmoturbinale I, whose dorsal and ventral lamella divide off the basic recesses; anterior (frontalis), maxillaris and frontoturbinalis. Completely caudally we find ethmoturbinale I, the frontoturbinalia and the relevant secondary (greatly reduced) recesses. The zona annularis is interrupted by failure of the rostral processes of the lamina transversalis anterior (corresponding to the processes laterales ventrales) to fuse with the capsula nasi ant. or with the anlage of the septum nasi. We did find a fenestra nasi superior (lateralis). The atrioturbinale is well developed, the maxilloturbinale only as a trace, but we have a very striking nasoturbinale. In the rostral region of the olfactory segment, the cartilaginous capsule has a very conspicuous thickening, which in this part is formed of paranasal cartilage. The thickening presents outwardly as the prominentia anterior; cavity of the recessus anterior (frontalis) is formed inside it. The rest of the dorsal and caudal wall of this cavity forms the crista semicircularis, which further caudally circumscribes the foramen olfactorium. A foramen epiphaniale is present. The vestibular region of the epithelial nasal tube is interestingly formed. In cross section it is crescent-shaped; the nasal tube itself opens into the convexity, but the lamina transversalis ant. sends a turbinale into the concavity. A cartilago alaris superior, which develops independently in situ, is present; in our stage it is associated with the wall of the capsule, but ventrolaterally it terminates freely and is not joined to any other element. The morphological interpretation of particular elements is discussed.

Animals↗
PubMed1990

Contribution to knowledge of the morphogenesis of the nasal apparatus of the fallow deer (Dama dama L.).

As in the red deer, in the fallow deer embryo we found a number of ancestral structures reminiscent of relationships in other mammals, such as paraseptal cartilages, a septum nasi with trabecular widening, a lamina transversalis ant., a cart. ectochoanalis, a capsule wall with a roof and a lateral wall formed of a clearly distinguishable cart. parietotectalis and cart. paranasalis, an ethmoturbinale I projecting a long way rostrally and additionally, in the fallow deer, cart. paraseptales posteriores. I regard the relationship of the cart. alaris inf. to the parietotectal cartilage (or "marginoturbinale") as relatively "primitive"; this may mean that the term "atrioturbinale" is also justified in mammals and that the relevant structure is homologous with the one known by the same name in birds. The specializations found during study of the morphogenesis of the nasal apparatus in the red deer (Slabý 1990b) are accentuated in the fallow deer. The chief ones are the specific rostral processes of the anlage of the nasal septum, which are a significant part of reinforcement of the nostril, the marked widening of the nasal capsule in a lateral direction (so that even the paranasal cartilages have a largely horizontal course), the striking ventrolateral bulge in the nasal capsule at the beginning of the olfactory region and the final resultant decrease in the height (i. e. flattening) of the capsule. This leads to reduction of the frontoturbinalia and their corresponding recesses, which - where they are developed - are oriented more horizontally. The structure of ethmoturbinale I, together with its insertion, is also simplified. As in the corresponding red deer embryo, the paranasal cartilage zone in the anterior part of the olfactory region is strikingly thickened; the frontoturbinalia do not, however, originate (in our stage) by the formation of cavities in the cartilage, but develop as simple processes. A crista semicircularis and foramen epiphaniale and also, as distinct from the red deer embryo, cart. paraseptales posteriores, are clearly discernible. In conclusion, it can therefore be claimed that the morphogenesis of specialized cervid features is accentuated in Dama more than in Cervus and that relationships in the fallow deer represent a further step in specialization, or - if we are speaking of the development of radiations - specialization here has progressed further.

Animals↗
PubMed1990

Contribution to knowledge of the morphogenesis of the nasal apparatus of the domestic sheep (Ovis aries L.).

The author studied the morphogenesis of the nasal apparatus in a sheep (Ovis aries L.) embryo with a length of 57 mm, at the optimum stage of development of the chondrocranium, as a part of his studies of development of the nasal apparatus in ungulates. The nasal apparatus is in general constructed according to the general scheme for mammals. Attention is drawn to the development of the superior alar cartilage, which is reminiscent of the situation in reptiles, to the strikingly developed atriturbinale auctorum (the author does not agree with this morphological designation, which is reserved for the vestibular turbinale in birds), to the well developed anterior paraseptal complex, to the extremely large maxilloturbinale and to the massive trunk of the ethmoturbinale I, which suppresses the corresponding recesses. The olfactory labyrinth is developed at three levels, the upper (rostral) level corresponding to the frontoturbinalia region, the middle to the ethmoturbinale I and the third (caudal) level to the region of the ethmoturbinalia II, III and IV (the recessus ethmoturbinalis). There is no foramen epiphaniale, no crista semicircularis and no crista Galli. A posterior paraseptal cartilage is present; in the author's opinion it is joined to the lamina orbitonasalis and not to the lamina transversalis post., since the latter is absent.

Animals↗
PubMed1990

Morphogenesis of the nasal apparatus of the red deer (Cervus elaphus L.).

Three stages of morphogenesis of the nasal apparatus of the red deer (Cervus elaphus L.) were studied. Many ancestral traits reminiscent of relationships in other mammals and even in reptiles were found, including a cart, ectochoanalis, paraseptal cartilages, the septum nasi and its ventral trabecular enlargement, a lamina transversalis ant., clear separation of the cart, parietotectalis and cart, paranasalis from each other and a crista semicircularis. A maxilloturbinale, was present, but not a nasoturbinale. The main specific features were a completely rostrally localized, peculiar cartilaginous structure in the preseptal space, for which there is as yet no morphological explanation, and pronounced bulging of the cartilaginous wall of the nasal capsule in a ventrolateral direction, level with the rostral region of the olfactory labyrinth (caudally to the aboral end of the maxilloturbinale). In the early stages of morphogenesis, it was found that the ethmoturbinalia might be formed by fusion of the edges of the anlagen of the paranasal cartilage and the lamina orbitonasalis. The structure of the olfactory labyrinth was reminiscent of its organization in the sheep embryo; the recessus frontalis was completed by a series of frontoturbinal recesses and frontoturbinalia, which are poorly developed in the red deer, however. The floor of the caudal part of the nasal capsule was very little developed and there was no cart, paraseptalis post.

Animals↗
PubMed1990

The action of stabilizing selection on the perfection of new characters in evolution.

In birds, fusion of the carpal elements to a carpometacarpus during morphogenesis takes place during the evolutionary process at different rates, i.e. heterochronically, in different groups (developmental radiations), like the elements of the nasal apparatus in Sauropsida. This is because new characters spread and are pushed back at different rates from the terminal to the initial levels of morphogenesis. The shift is most likely automatic, in that it does not require further mutation, but it is set in motion by selection. Selection does not take effect only when an adequate character (which at first is very imperfect) is accepted; it also causes the character to grow, pushes it back towards the threshold of morphogenesis and thereby increases its perfection and its fitness. The path along which the shift takes place is determined by the morphogenetic route of recapitulation of the ancestral structure and since this movement is caused by protracted stabilizing selection, we can describe it as orthoselective movement. This means that recapitulation is flexible. At the same time, cellular and epigenetic interactions with surrounding structures are reciprocally influenced. The shift continues until adequate adaptation and perfection have been achieved. Stabilizing selection then ceases to act. The shift shows the evolutionary trend or further developmental possibilities. Its chief role is probably in the development of specializations.

Animals↗