OCR Text |
Show 6 MR. A. H. GARROD ON THE [Jail. 2, be a row of papillae indicating the rudiments of laminae of a fifth power- for, when disappearing, laminae always end as rows of papillae. In the case of a transverse section of a quadruplicate psalterium (in other words, of one in which there are laminae of four powers) the quaternary folds being rudimentary, imagine it to be cut through longitudinally along the middle of its groove, and opened out in such a way that the outer wall forms a straight line, whilst the laminae depend from it; then the appearance will be that ot tig. J. Diagram of transverse sections of psalterium. This being from an actual specimen, there is a slight want of uniformity at b and c, which is usually found to be the case. The laminae of each cycle, or power, gradually diminish in size laterally ; and it will be noticed that, though the organ is quadruplicate where the folds are relatively largest, the smallest laminae disappear at the sides. This is nearly always the case, as it is also that near the orifice of communication with the reticulum they are stronger than they are further on. In different genera the relative depths of the laminae which constitute the separate cycles is not always the same. The arrangement depicted above is the most usual, in which the secondary folds are about two thirds the size of the primary, a similar difference existing between them and the tertiary, and so on. Fig. 4 is from the psalterium of Gazella arabica, in which, though the disposition is triplicate, it is seen that the secondary laminae are very little larger than the papillary rows which form the tertiary cycle, the primary laminae being of considerable depth. The structure in Cephalophus is the same, only that, the psalterium being much smaller, all the parts are much reduced in size, the lateral laminae especially so. In Nannotragus nigricaudatus the equally small psalterium is even more simple, there being but six primary laminae of any depth; and these are covered with peculiarly large and pointed papillae, three more being evidently their lateral homo-logues, although reduced to papillary rows. The conditions are represented in figs. 2 (Cephalophus) and 3 (Nannotragus). |