A cytoarchitectonic and myeloarchitectonic study of the insular cortex of the bull, Bos taurus.

The mammalian Insula is characterised by considerable morphologic variability, however, it shows a cytoarchitectonic homogeneity within the species so far studied. Three cytoarchitectonic areas are generally recognisable in the Insula: an "agranular", a "dysgranular" and a "granular" area. The numerous functions attributed to the Insula (visceral sensory, visceral motor, somatosensorial, supplementary motor area, area speech and/or language related, etc.) have recently attracted renewed interest. Considering the involvement of the Insula in the control of gastroenteric motility and the structural and functional complexity of this region in ruminants, it seemed interesting to analyse the cyto- and myelo-architectonic arrangement of the Insula of the bull, Bos taurus. Unlike that of the other species described, all the insular Neocortex of the bull, is of the "agranular" type. The latter includes at least four variants that differ according to the organisation of the cortical layer pattern. Considering the available evidence in laboratory animals and primates of a role played by the agranular insular cortex in gastroenteric motility control, the trademark presence of a very much extended insular agranular cortex in the Insula of the bull may be related to the necessity of motor activity control of a gastroenteric complex that is extensively more developed than in the monogastric species.