OCR Text |
Show 1882.] PTERYLOSIS OF MESITES. 269 being of a furcate form, with the united part about 1 inch long, and inclosing a fairly broad median space. The limbs of this posterior fork are strongly dilated in the middle part of their extent, being there 6 to 7 feathers broad, and united externally by scattered feathers with the very broad and long lumbar tracts, which are arranged in about six rows of not closely-placed feathers, the posterior row of these being considerably the stronger. The humeral tracts are not very broad or strong, and are quite distinct, anteriorly, from the inferior tract. This last, which (as already described) commences on each side about halfway down the neck, springing at once independently from the continuous feathering of the anterior cervical region, ceases altogether at the commencement of the pectoral region (extending as far as the most anterior of the ventral powder-down patches to be presently described). It recommences, however, a little lower down as a very narrow tract, composed at first of only single feathers, but subsequently becoming stronger and broader (though even here only two feathers broad), in which condition it runs on, as the main inferior tract, to terminate near the vent. Strange to say, what must be considered the equivalent of the outer pectoral branch of ordinary birds is here quite free throughout from the main stem, with which it is not even united anteriorly, where it is separated by the already-mentioned powder-down patch, whilst posteriorly it runs parallel to, but quite free from, the main stem. The powder-down patches of Mesites resemble those of the Ardeida, of Leptosoma, and Podargus in their compactness, as well as in the definiteness of their areas, as opposed to the more scattered and diffused forms they present in Rhinochetus, Eurypyga, Crypturus, and other birds. But in their exact distribution they differ materially from any of these. As already described by M r . E . Bartlett, there are five pairs*• of powder-patches in Mesites. Of these two pairs are dorsal, two ventral, and one lateral in position. All have the form of well-defined more or less oval areas, covered by a dense mat of closely aggregated long powder-down plumes. The most anterior pair is placed close to the median line, the patches being only slightly separated from each other, at the commencement (apparently) of the interscapular region and inclosed between the two dorsal tracts, a little before these pass into their weaker posterior fork. The second dorsal patch is situated on the rump, close to and just outside the terminal part of the dorsal tract, between that and the posterior termination of the lumbar tracts of each side. 1 In the Ardeidce the number varies from one pair (Balceniceps) to four pairs (Cancroma). Three is the most ordinary number. The presence of a single caecum in Balceniceps (as fortunately demonstrated by a preparation mounted in the Museum of the Eoyal College of Surgeons), together with these powder-down patches, renders its Ardeine nature nearly certain, as already suggested by Mr. A. D. Bartlett (P. Z. S. 1861, p. 131). |