236 ON THE TEACHEA IN THE " EATITE " BIRDS. 



bifurcating trachea not existing in the other " BatitaB." In Casuarius 

 galeatus (figs. 5, 6, p. 237) the trachea is somewhat dilated for the ter- 

 minal inch or so of its extent, transversely and also posteriorly. The last 

 tracheal rings (for a number varying in different specimens, in the 

 specimen in question 12, in another 23) are incomplete in the middle 

 line behind, though the posterior ends are closely approximated 

 together *. 



These rings are tolerably uniform in breadth posteriorly, tapering only 

 somewhat at their extremities; the interannular intervals are mere 

 chinks. Anteriorly, however, the rings being dilated in the median 

 line and attenuated laterally, the intervals are better developed. The 

 last 5 or 6 rings are more and more curved downwards anteriorly, whilst 

 their posterior moieties are somewhat dila.ted, their ends gradually rece- 

 ding more and more from each other in the middle line. There is no 

 trace of a pessulus. 



The first bronchial semirings much resemble the last tracheal rings, 

 their anterior extremities being closely approximated together, and their 

 posterior ones dilated, and somewhat pointed, terminally. The second, 

 third, and fourth bronchial semirings are simple cartilaginous hoops, 

 tolerably deep, separated only by narrow intervals, and, as usual, com- 

 pleted internally by a membrana tympaniformis. The fifth, sixth, and 

 seventh are similar but longer semirings, the sixth and seventh being 

 dilated anteriorly. The succeeding rings are similar but quite simple 

 hoops, never forming anywhere complete circles. 



There is no trace of any intrinsic muscles. The sterno-tracheales are 

 inserted on the trachea at about the twelfth ring from the last. Ante- 

 riorly they expand on the tracheal wall, and are in contact with each 

 other over the middle line, as is also the case in Dromceus, though not in 

 the other three genera. A small part of each muscle runs to be inserted 

 into the posterior wall of the trachea near the margin. The lateral 

 muscle of the trachea passes between these two portions of the sterno- 

 trachealis of its side, but does not pass down further than the com- 

 mencement of the tracheal tympanum. 



* Between the extremities of each imperfect tracheal ring runs a short band of 

 connective and elastic tissue, with the fibres running transversely. These extend the 

 whole length of the trachea, and when well developed have the appearance of a longi- 

 tudinal band running along the middle line of the tube posteriorly. By the contraction 

 of these fibres, the ends of the tracheal rings, where these are incomplete, or their 

 more slender middle portions where perfect, are drawn together, and pressed into the 

 interior of the tube, so forming what at first sight looks very much like a longitudinal, 

 though incomplete, tracheal septum, such as is found in some Procellariidas and other 

 birds. In consequence of this structure, a transverse section of the tracheal tympanum 

 posteriorly presents two strong convexities separated by a median concavity. 



