closing muscles. Compared with other birds, the jaw muscles of both fringillids and estrildids scale strongly positively allometric with body size. Muscle fibre length scales negatively allometric with body size, which results in relatively high muscle and bite forces. Comparison with the scarce data available for other trophic groups suggests that the scaling of jaw muscle size depends on diet and that jaw muscle size in finches is an adaptation to their feeding behaviour.

Cranial kinesis is an important feature in avian feeding behaviour and involves the transmission of quadrate movement to the upper bill by the Pterygoid-Palatinum Complex (PPC). The PPC in Palaeognathae is remarkably different from that found in Neognathae. In this study we analyse whether the special morphology of the PPC is an adaptation to the feeding behaviour of the Palaeognathae. Behavioural analyses of the rhea Rhea americana showed that the feeding behaviour of the rhea is typical 'Catch and Throw' behaviour, independent of the size of the food item. Drinking is achieved by a scooping movement followed by a low-amplitude tip-up phase. During feeding rhynchokinetic movements of the upper bill were observed. However, cranial kinesis was limited and may differ from rhynchokinesis in neognathes as a clear bending zone seemed absent. Since the movement patterns are considered very similar to the basic feeding behaviour in neognathous birds it is concluded that the specific morphology of the PPC is not the result of specific functional demands from palaeognathous feeding behaviour.

No abstract

The intratelencephalic and descending connections of the archistriatum of the mallard were studied using anterograde and retrograde tracers. Autoradiography after injections of [ 3 H]-leucine served to visualize the intratelencephalic and extratelencephalic efferent connections of the archistriatum. Horseradish peroxidase (HRP), HRP-wheatgerm agglutinin, and fluorescent tracers were used to identify the precise origin of the projections to the various terminal fields found in the anterograde experiments. Four main regions can be recognized in the archistriatum of the mallard: (1) the rostral or anterior part that is a source of contralateral intratelencephalic projections, in particular to the contralateral archistriatum; (2) the dorsal intermediate archistriatum that is the origin of a large descending fiber system, the occipitomesencephalic tract, with projections to dorsal thalamic nuclei, the medial spiriform nucleus, the intercollicular nucleus, the deep tectum, parts of the mesencephalic and bulbar reticular formation, and the subnuclei of the descending trigeminal tract. There are no direct projections to motor nuclei. This part corresponds to the somatic sensorimotor part as defined by Zeier and Karten (1971, Brain Res. 31:313-326); it also contributes to the ipsilateral intratelencephalic connections and, to a lesser degree, to contralateral intratelencephalic connections. (3) The ventral intermediate archistriatum is another region that is also a source of intratelencephalic projections, in particular of those to the lobus parolfactorius. The most lateral zone sends fibers to the septal area. (4) The caudoventral intermediate and posterior archistriatum is another region that is a source of the projections to the hypothalamus and thus corresponds to the amygdaloid part of the archistriatum as defined by Zeier and Karten; it also contributes a modest component to the occipitomesencephalic tract. The different cell populations are not spatially separated, which makes it impossible to recognize distinct subnuclei within the four main regions of the archistriatum of the mallard.

Muscle forces are more than sufficient to overcome bending forces and to elevate the upper bill. The resistance against bending by the bony elements alone is very low, which might indicate that bending of bony elements can occur during food handling when muscles are not used to stabilise the upper bill. Model calculations suggest that the large processi basipterygoidei play a role in stabilizing the skull elements, when birds have to resist external opening forces on the upper bill as might occur during tearing leafs from plants. We conclude that the specific morphology of the palaeognathous upper bill and PPC are not designed for active cranial kinesis, but are adapted to resist external forces that might cause unwanted elevation of the upper bill during feeding.