ON THE ANATOMY OF PASSERINE BIRDS. 375 
some light upon the method of development of the ienclsicighons 
syrinx. This consists in the way in which the characteristic very 
slender rings of the specialized voice-organ, instead of ceasing 
abruptly at its upper end, continue upwards on the anterior surface of 
the trachea for a considerable distance, whilst posteriorly they 
suddenly change their breadth superiorly where the syrinx ceases. 
Figures 4 and 5 of Plate [27] LIII represent the anterior and 
posterior views of the organ. 
The processus vocales, which rest on the first and second modified 
and ossified bronchial semi-rings, extend up as far as the tracheal 
true ring, twelfth from the bottom. These twelve lowermost tracheal 
rings are incomplete opposite the processus vocales (in other words, at Page 524. 
their sides), as they are in all the Tracheophone; and the lowest is 
also broken, as it were, in the middle line behind. 
Posteriorly the lower nine are extremely slender; the tenth 
(counting upwards) is somewhat thicker, the eleventh still more 
evidently so, whilst the twelfth is as thick as any of the superior 
mings. 
Anteriorly there are twenty-three of the lower tracheal rings, 
which are quite slender in the middle line, especially the lowest three ; 
and of these the twelve lowest (those split laterally) are slender from 
one side to the other, whilst the upper eleven appear thick at their 
_ extreme ends on account of the intrusion, for a short distance round 
the sides of the tracheal tube, of the thickening above recorded of 
their hinder parts, which diminishes rapidly in a spindle-pointed 
manner. 
The lowest tracheal ring is as slender as those just above it; and 
it is worthy of note that the processus vocales rest upon the thickened 
second bronchial semi-ring as well as on the first. These vocal pro- 
cesses cannot be detached from the sides of the trachea withont in- 
juring it; and the sterno-tracheal muscles arise from their apices, to 
which are also attached thin muscular sheets which extend up the 
. windpipe laterally and a little posteriorly. 
| Grallaria guatemalensis.—In this species also the specialized syrinx 
t does not cease abruptly at its upper end, the superior rings of the 
trachea, which help to constitute it, gradually losing their individual 
character. Figs. 1 and 2 (Plate [27] LIII.) represent the front and 
back view of the organ, which is peculiarly shallow for its width, and 
involves but six of the lowermost tracheal rings. These six are in- 
complete at their sides where they are in contact with the processus 
vocales, which latter are small, flat, fusiform ossifications, pointed both 
at their upper and lower ends, and just touch the upper of the two 
superior enlarged and ossified bronchial semi-rings, the remainder of 
each bronchus being of the normal character. The lowermost 
