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Neurocranial growth during the first 40 days of postnatal development was biometrically investigated relative to the specific parameters of calvarium length and width; basioccipital length and width; basisphenoid length; biparietal width; frontal bone length and cranial vault length. Specimens were obtained from rat litters subject to moderate nutritional suppression by raising the litter numbers above the norm via the cross-fostering technique and causing the overtaxing of the lactational capacity. Alterations in growth rate occurred throughout the pre- and postweaning periods with clearly demarcated phases of growth. Male and female growth in the preweaning period was uniform within each litter type but the phasic growth changes in the experimental litters differed from the control litters with regression line breakage emerging at different points and altering the phasic lengths. The preweaning phasic spectrum in both control and experimental litters was evidently linked to the maternal lactation capacity--relative to quantity and duration. Weaning was insidious in both litter types but occurred earlier in the experimental litters although the continuity of growth was maintained up to the end of the definitive preweaning period (day 20). The definitive postweaning period (day 21-40) showed considerable heterogeneity--unsatisfactory scatter--with differing regression line breakage points and phasic lengths. Analysis based on the total period (day 1-40) brought compensatory adjustments and indicated more acceptable phasic patterns in the postweaning period with confirmation of catch-up growth in the experimental litters. Allometric analysis of the parameters revealed varying rates of growth, line breakage points and differing phasic lengths indicating that each neurocranial parameter and the skeletal unit forming it had an individual characteristic response spectrum mostly attributable to the functional matrix with emphasis on the capsular rather than the periosteal.

The skull morphology of the mink (Mustela vison Schreb) based on a sample of 97 (56 male and 41 female) mink, ranch bred and aged between 7 months to 2 years has been examined to provide the characteristic features of an inbred colony whose ingress into the natural environment by escapes of releases has led to a viable feral population. Behavioural adaptation including breeding of the feral group is confirmed and the need for a cranial morphological base line is therefore paramount if cranial morphological adaptations arising from the feral group are to be compared in the future. Morphological details have been recorded by various drawings, and the characteristics which form part of the species key were noted as: postorbital constriction marked, minimum width behind postorbital processes less than width of interorbital space, tympanic bullae are flattened and broad with anterior edges merging with adjacent bones, length of tympanic bullae greater than width, maxillary molar large with inner lobe expanded lingually until much greater than the outer buccal lobe. Sexual dimorphism was indicated from the skull measurements but was not significant due to the preponderance of immature adults present in the sample.

The pattern of skull growth of the rice rat (Oryzomys palustris natator) over the pre-weaning period of development reveals a characteristic triphasic outline which stems, in part, from the interplay of the external environment and the genetic endowment. Within the triphasic spectrum the neural skull growth exhibits an accelerated rate of growth during the early phases which eventually reverses to a rapid deceleration in the final phase. In contrast, the facial skull growth shows increased growth rate following the decline of the neural group, eventually reaching a slow linear deceleration. Thus the neural components appear to be synchronised to the brain growth while the facial elements gain a new and greater impetus following the neural decline. The general growth of the skull throughout these changes, i.e. triphasic and neural/facial, continues to show a basic slow linear increase.

A survey of skull development of the rice rat (Oryzomys palustris natator) covering a period of 21 days to 16 months involving equal numbers of males and females (108) was undertaken using various skull parameters. Sexual dimorphism in relation to body weight and length emerged before that of the skull which was only clearly marked by 2 months. A number of the skull parameters by virtue of their individual growth potential did not show sexual differences in size for a long time, whereas others were clearly marked. Once the differences between the sexes had been established they were maintained. One parameter - lenght of cranium - represents those parameters which show changes and it was found that the male rat continued to show a steady linear increase in length up to 16 months, whereas the female cranial length shows a deceleration with termination around 12 months. The skull differences are mirrored in the weight and length findings and it suggested that the earlier sexual maturity of the females is compensated by an earlier cessation of growth compared to the males which mature later and have a correspondingly later cessation.

Rat growth during the first 40 days of postnatal development was examined relative to cranial length, facial height and bizygomatic width of animals subject to nutritional suppression induced by increased litter size during the preweaning period. The postulate (Brody, 1927) that growth curves consist of phases of exponential activity delineated by alterations in the growth rate thus inducing breaks in the continuity was confirmed in the skull. The preweaning and postweaning periods showed three clearly demarcated phases of growth within each period. Breakage points of the phases--alteration in growth rate--differed between the control and experimental litters thus changing the length of the specific phases. Within the preweaning period of both types of litter the phasic characteristics appeared directly linked to the maternal capacity--quantitatively and in duration, while the latter part of the preweaning period and the postweaning period remained within the province of external or non-maternal food supplies. The postweaning of the experimental animals exhibited catch-up growth phenomena in all parameters with a slight variation relative to catch-up growth phenomena in all parameters with a slight variation relative to the sexes. In general terms, analysis of the total period of investigation indicated that growth within the preweaning period was more active although sexual dimorphism was not significant. In addition, relative growth (allometric) analysis of the three parameters showed varying growth rates, breakage points and hence phasic lengths indicating that irrespective of environmental factors that each parameter and the bone units incorporated in it manifested a response as a whole which was characteristic of the parameter.