ON THE ANATOMY OF PASSERINE BIRDS. 363 
In Menura superba the last sixteen rings of the trachea are 
peculiarly narrow from above downwards. These are carinate in 
- front; in other words, instead of being flattened from without inwards 
(as is usually the case, and is so in the rings above the sixteenth in 
this bird), they are compressed from above downwards, by which 
means a sharp-edged ridge is developed, which projects outwards a 
short way beyond the level of the interannular membrane. The 
lowest of these rings, the last tracheal, whilst participating in this 
peculiarity, is modified to form the three-way piece, whence start the 
bronchi, an antero-posterior bar joining the downward-directed angles 
which are developed on the middle of the front and back of the ring, 
and supporting the syringeal semilunar membrane. 
As in the typical Oscines, the first three bronchial semirings par- 
ticipate in the formation of the syrinx, and are modified accordingly, 
being stronger, deeper, more flattened, and more approximate than 
those which follow. The first of these is simple; the second is 
peculiar in being hollow and thin-walled, broader in front than behind, 
and broadest a short distance (about equal to its depth at the spot) Page 515. 
posterior to its anterior extremity; the third is narrower, and termi- 
nates behind by a short descending hook. 
The syringeal muscles are three in number on each side at their 
insertion, although at their origin only two can be distinguished. 
___These are an anterior and posterior longitudinal, which, from a lateral 
point situated opposite the tracheal ring 19 above the last one, diverge 
forwards and backwards to the tips of the bronchial semirings. In 
Plate [25] LII. figs. 1, 2, and 3 the front, back, and side views of 
the syrinx of Menura are figured. 
The anterior longitudinal muscle, whose diameter is about four 
times that of the depressor trachee, is of uniform size throughout, 
being constituted of parallel fibres. It is inserted into the lower 
margin of the expansion at the anterior extremity of the second 
bronchial semiring, at a short distance behind its apex. 
The posterior longitudinal muscle, from being single above, divides 
into two below. 
P Before proceeding further it will be necessary to explain the way 
in which these muscles arise. There is a large air-cell, the anterior 
thoracic,* in which the syrinx and base of the heart are situated. The 
visceral walls of this cell are so thin that the trachea may, to all 
intents and purposes, be said to perforate it. Where it does so, the 
membrane blends with its fascial sheath most intimately ; and it is 
from the thus formed ring of junction that the long fibres of the 
syringeal muscles spring. This ring is not a simple horizontal circle 
* Vide Owen’s “‘ Anatomy of Vertebrates,” vol. ii., p. 211. 
