A quantitative study of the torus semicircularis of Barbus meridionalis Risso.

In the quantitative study of the torus semicircularis of the teleost Barbus meridionalis Risso determination was made of the total volume of the torus and of each of the nuclei comprising it: the nucleus centralis and the nucleus lateralis; also studied were the volume of the two regions that can be differentiated in the nucleus lateralis: the pars lateralis and the pars medialis. The number of neurons and neuronal density were also determined throughout the whole of the torus and in each of its components; the torus can be considered as a structure rich in cells since both global and partial neuronal densities are high. Of the three neuronal types observed in the torus: fusiform, rounded-ovoid and triangular-stellate, the highest percentage corresponds to the neurons with rounded-ovoid somata, followed by the triangular-stellate and then the fusiform neurons. Considering cell size, in layer two of the nucleus lateralis all the neurons are small whereas in layer four of this nucleus and in the cellular region of the nucleus centralis, the highest percentage corresponds to medium-sized neurons; the small and large neurons are present in similar proportions.