EXTENSION OF THE CHORIOID PLEXUS INTO THE OLFACTORY VENTRICLES

FRED A. METTLER Department of Anatomy, Cornell University Medical School

The olfactory bulb of the armadillo is of great relative size, as might be expected in a lowly macrosmatic mammal. In this connection we have observed that the olfactory canal of the fetal armadillo is persistent and contains a rostra1 extension of the chorioid plexus of the lateral ventricle on both sides.

One of a quadrad of nine-banded armadillo embryos was stained ‘in toto’ with silver nitrate and embedded in paraffin. The length (CR) of this animal was 80 mm.

I n this particular specimen the central canal measured 0.5 mm. in diameter. Sections which were taken through the snout region disclosed that they contained chorioid plexus. These could be traced caudally, where they were found to be continuous with the plexuses of the lateral ventricles. I n cross-section the olfactory extension presented the appear- ance of a number of irregular folds arranged so that they formed a disc within, but not quite filling, the central canal. The arrangement of these folds was an entirely natural one, the cellular constituents having plenty of room and being not at all distorted. Most rostrally, the plexus was separated from the inside wall of the bulb by about a tenth of a milli- meter. Within the central canal the plexus did not touch the inner wall of the olfactory bulbs at any point. The remainder of the plexus of the lateral ventricle occupied an apparently normal position.

Neither in the mother of this animal nor in any other adult armadillo have we noticed any such extension of the plexus

251

TI%% ANATOM.IIC.4L RECORD, TWL. 51, NO. 3

252 FRED A. METTLER

into the olfactory canals. Attention should be directed to the improbability of herniation by manipulation during prepa- ration, f o r at no time was the brain case opened, nor did the disposition of the plexus seem to be influenced by any ab- normal factors. The chorioid tissue can be seen extending rostra1 to the region of the accessory olfactory bulb, in which terminates the accessory olfactory nerve. The morphology of these structures can be clearly made out, since in this form the whole olfactory apparatus lends itself to study. It may be noted that these accessory bulbs are small in the specimen, but are situated in the dorsal medial side of the major olfactory bulb near the caudal end, as in other mammals.

Two fetuses of the tetrad have been deposited with the Department of Histology.

BI3LIOGRAPHY

NEWMAN, H. H. 1917 Biology of twins. University of Chicago Press.

NEWMAN, H. H., AND J. T. PATTERSON 1910 Development of nine-banded 1923 Physiology of twinning. University of Chicago Press.

armadillo. Jour. Morph., vol. 21, p. 359.