Splanchnocranium

Abstract: The inception, and development of the cephalic skeleton of Barbus barbus from hatching to 24 days passes through periods of fast and slow growth; these rates are not the same in different parts of the skull. Trabeculae, parachordal plates, Meckelian cartilages and hyposymplectics are present at hatching. Then the cartilaginous floor of the neurocranium develops, the pars quadrata, the hyoid bars and branchial arches elements appear shortly before the first movable dermal bones, the dentaries, maxillae and opercles. The first bone of the braincase to appear is the parasphenoid; other bones develop subsequently and at the same time: the angular, quadrate, interopercle and fifth ceratobranchial. Later the splanchnocranium continues to develop at a relatively fast rate while the neurocranium shows little growth. The braincase does not begin to close before the 24th day, nor do the first bones of the skull roof appear, while the bucco-pharyngeal apparatus is complete, having the adult shape. The early constitution of the latter structures seems to be linked with the mechanical demands of biological functions such as breathing and feeding.

Abstract: Twenty weanling 6-month-old male squirrel monkeys were allotted to the following treatments: 1) first control animals were killed at weaning; 2) second control animals were killed when 24 months old; and 3) malnourished animals were fed on a low-protein diet and killed at age 24 months. Lateral and vertical teleradiographies were taken. Growth of the neurocranial and splanchnocranial components were measured by volumetric (size estimators) and morphometric (shape estimators) indices. All facial components grew. The neurocranial components showed a heterogeneous behavior: The anteroneural component remained stable, and the increase of the midneural component was compensated by a decrease in the posteroneural component. Malnutrition affected the growths of 1) the craniofacial complex, 2) the splanchnocranium, and 3) the respiratory and midneural components. Growth influenced skull shape through 1) increases of the splanchnocranium and the midneural component relative to the neurocranium; 2) decreases of the masticatory and optic components relative to the splanchnocranium, and 3) decreases of the anteroneural and posteroneural components relative to the neurocranium. Malnutrition influenced skull shape through the relationship between the anteroneural component and the neurocranium. These results confirmed the existence of functional interrelationships among the cranial components. A new approach to craniological studies is suggested.

Abstract: At hatching, Heterobranchus longifilis does not display any primordia of the cephalic skeleton The latter appears 12 h post–hatching and develops in three stages up to day 16 The first stage (12 h to 2 days) involves almost exclusively the development of the chondrocranium During the second period (days 3–8), dermal elements of the splanchnocranium appear The final stage is marked by resorption of the cartilages, progressively replaced by ossifications (days 10–16) At their appearance the elements of the splanchnocranium are fused together, as are the first neurocranial elements Later, the splanchnocranium splits up By the time the yolk sac is completely resorbed, the buccal and pharyngeal jaws are present, the suspensoria and hyoid bars are partially developed, and the parasphenoid partially closes the hypophyseal fenestra These structures delimit a buccal cavity that is probably functional, ie capable of participating in the intake of exogenous food Next to continue its development is principally the splanchnocranium, completing the walls of the buccal cavity Cartilage resorption parallels the appearance of endochondral ossifications (except for the trabecular bars) Braincase closure begins to accelerate once the buccal system is complete

Abstract: Summary ‐ The skull of the howler monkeys (Alouatta spp., Atelidae) is characterised by a generalised rotation of the splanchnocranium with respect to the neurocranial antero-posterior axis. This process, referred to as airorhynchy, is the result of a derived structural relationship between basicranium, vault, and facial districts. A number of variables ‐ such as diet and social behaviour ‐ probably co-evolved with the remodelling of the cranial functional matrix. We used a landmark-based analysis to explore the geometrical model of the skull in the genus Alouatta. Shape comparisons were performed by using superimposition procedures and the Euclidean distance matrix. In the latter analysis, a method is proposed in order to visualise variations of form through chromatic maps and interpolant functions. The comparison with other genera of Atelidae shows a marked neurocranial flattening in Alouatta as well as muzzle projection and enlargement, nuchal flattening, relative basicranial lengthening, and tilting of the occipital foramen. Only minor differences were visible in relation to facial shape, suggesting that significant changes depend on the relationship between splanchnocranium and neurocranium, rather than on localised anatomical variations. The limited vault development constrained by the basicranial structures probably involved the extreme retroflexion of the basal angle. Airorhynchy can be interpreted as an additional adjustment to fit this structural network beyond the biomechanical range of the cranial base hypoflexion. This cranial functional matrix is directly related to feeding and social changes, representing an interesting evolutionary “package”. In Pongo pygmaeus a similar process is associated with a different structural pattern, mostly related to the flattening of the upper facial structures, maxillary midsagittal enlargement, and palatal tilting.