1886.] GEOCOCCYX CALIFORNIANXJS. 487 



The interval thus formed, which is not very great, is occupied by 

 a thin membrane which is continuous with the internal tympaniform 

 membrane of the lower larynx. As to shape, the trachea diminishes 

 in calibre gradually from above downwards, and nowhere in its con- 

 tinuity does it present any enlargements or dilatations. 



This does not apply exactly to the bronchial bifurcations, for each 

 one of them shows a disposition to swell just before arriving at the 

 contracted parts of these tubes, where they impinge upon the lung, 

 tissue. 



We may reckon either of these bifurcations as being partially sur- 

 rounded by 13 semirings. Of course in this bird, as I say, the 

 entire trachea may be regarded as having only semirings, but had 

 the usual number of these united behind, there would still have 

 remained the 13 semirings to each bronchial tube. An osseous 

 pessulus is not present in Geoeoecyx, and the internal tympaniform 

 membrane is quite extensive. There does not even seem to be any 

 thickening of this membrane in our subject where this bony little 

 bridge is located in those birds where it exists. 



As to its myology, the lower larynx is exceedingly simple in 

 arrangement and meagrely supphed. Vievring the inferior part of the 

 trachea and the bronchial tubes from in front, we can see but one 

 pair of muscles, and these are the delicate sterno-tracheales. They 

 are attached on either side to the last five tracheal rings (fig. 3, 

 Plate XLIII.) ; the insertion seemingly consisting of two slips, the 

 inferior one being attached to the lowermost of the five rings. 

 These muscular slips soon merge with each other ; and the muscle 

 itself stretches across in the usual manner, for attachment to the 

 inner surface of the costal process of the sternum . 



From a near view we discover another pair of muscles ; these are 

 the tracheo-laterales (fig. 4, Plate XLIII.). They here extend the 

 whole length of the tracheal tube, on its postero-lateral aspect, rather 

 than fairly on its sides, as in the majority of birds. On either side they 

 are carried down clear to the last bronchial semiring for attachment, 

 i. e. not reckoning the aforesaid few semideveloped rings which we 

 find at the terminal extremities of these bronchial bifurcations. 



This position of the tracheo-lateralis muscle is just the reverse of 

 what Garrod found in such a bird as Opisthocomus (Scientif. Mem., 

 p. 46G, fig. 1) ; for, according to this authority, these muscles may be 

 seen in the Hoatzin on an anterior view, and, moreover, in it they 

 pass down in front of the sterno-trachealis. 



Garrod made many excellent examinations of the thoracic extremity 

 of the trachea in the Gallinae, and among the representatives of this 

 group an extraordinary variety of forms of this part of the bird's 

 economy was discovered (P. Z. S. 18/9, p. 354). As the paper I 

 refer to is profusely illustrated by drawings of the gallinaceous 

 trachea, I have been enabled to compare them -with the corresponding 

 parts as I found them to exist in Geoeoecyx. But of all the types 

 given, I fail to find a single one that in any way resembles the 

 subject before us. 



This is the less to be looked for, however, when we come to 



