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Show 368 PROF. A. H. GARROD ON THE [Apr. 1, teriorly they are not expanded and scarcely touch; anteriorly they expand a little and articulate freely. The interannular intervals in essential points are not different from the preceding genus. The bronchial semirings below the second are peculiarly lengthy ; their extremities turn inwards toward one another, and so slightly intrude into the membranous inner wall of each bronchus. One or more of the semirings may be bifid at their anterior ends. The bronehidesmus is particularly powerful in the Tetraonidae, including Lagopus, and, as it were, pulls the two tubes into nearer relationship than would otherwise appear to be their tendency. Lagopus mutus agrees with L. scoticus in every respect. Tetrao urogallus and T. tetrix conform to a type which has several important differences from Lagopus scoticus, although in common they have the yielding cartilaginous (and never ossified) rings throughout the organ under consideration, as well as the great development in length of the bronchial semirings beyond the second. In the female of Tetrao tetrix the first feature that strikes the observer is the consolidation of all the intrathoracic tracheal rings along the mid-posterior surface into a vertical bar, rendered more than it would be otherwise conspicuous by the considerable thinning of the lateral third or more of each ring on each side, and the consequent formation of lateral interannular spaces slightly deeper than the rings enclosing them. In the adult bird no trace of the transverse lines of junction between the constituent transverse annular elements of this vertical posterior bar can be seen ; in the young bird, however, they are conspicuous. Anteriorly the rings above the antepenultimate are separated by an interval which sligbtly reduces the lowest of them, and that only, towards the middle line. There is a median semifusion in front, of considerable breadth, between the antepenultimate and penultimate rings, below which a broad cordiform cartilage represents the fused mid-anterior elements of the penultimate and last rings, with which the anterior extremity of the first bronchial ring is blended, and the second articulates, in such a way as to form lateral extensions of its apex. The line constituting the actual angle between the contiguous sides of the bronchi -produced, as just indicated, by the apex of the cordiform cartilage, together with the inferior margins of the lateral expansions, composed of the anterior ends of the first and second bronchial semirings -is less concave downwards than in Lagopus (in fact almost straight), and much less so than in the other Gallinae. It has, in Tetrao, a very slight descending protrusion in the actual centre-the apex of the cordiform cartilage. Posteriorly each free end of the last tracheal ring expands and sends downwards and outwards a small process for the articulation and fusion with the similarly enlarged extremity of the first bronchial semiring. Upwards it blends with the base of the vertical posterior cartilage, which is considerably broader opposite the lowermost three tracheal rings than higher up. Into the middle of its base the narrow pessulus is seen to run. There is a great similarity between the depth and shape of all the interannular intervals in the bifurcating portion of the tube, the compara- |