The last nerve which contributes to the ischiadic plexus leaves the spinal column in most birds either between the two primary sacral vertebrae, or just below the hindmost of them, and sends a branch to the pubic portion which is composed of post-ischiadic nerves, partly imbedded in the kidneys, and innervates the ventral muscles between the tail and pubis, together with those of the cloaca and copulatory organs.
Both present the appearance of diminutive clusters of grapes, at the anterior end of the kidneys, close to the suprarenal bodies, separated from each other by the descending aorta and by the vena cava where this is formed by the right and left vena iliaca communis.
The action of colchicum or colchicine upon the kidneys has been minutely studied, and it is asserted on the one hand that the urinary solids are much diminished and, on the other hand, that they are markedly increased, the specific gravity of the secretion being much raised.
It is not quite certain whether these are to be regarded as the remnant of an earlier excretory system, replaced among the Oligochaeta by the subsequently developed paired structures, or whether these "head kidneys" are the first pair of nephridia precociously developed.
F, Gill lamellae (not ctenidia, but organs of the pallial complex, having two kidneys, in some cases two branchiae, and two auricles.
How would you define kidneys? Add your definition here.