1886.] GEOCOCCYX CALIFORNIANUS. 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 Geococcyx, 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 supplied. Viewing 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, 
a. 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- 466, 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 Gallinz, 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. 1879, p. 354). As the paper I 
refer to is profusely illustrated by drawings of the g!linaceous 
trachea, I have been enabled to compare them with the corresponding 
parts as I found them to exist in Geocoecyx. 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 
