ORGANS OP VOICE AND RESPIRATION. 117 



tubercular surface, and an irregular triangular form. Upon the left 

 the labyrinth has the form of a somewhat irregular tetrahedron, from 

 the basal surface of which the left bronchus arises, its three sides 

 being occupied by oval membranous fenestrae. The membranes are 

 stretched within arched bony frames, so that the whole resembles a 

 lantern. In the female the inferior larynx forms only the usual bony 

 tympanum, but is still somewhat asymmetrical in form. This laby- 

 rinth obviously acts in modulating and strengthening the voice, and 

 reminds us of that bony dilatation of the os hyoides constituting an 

 apparatus of resonance in the Howling-apes, as has been already 

 described under the head of the Respiratory Organs in Mammalia. 

 The male Ducks have, as is well known, a stronger voice than the 

 females, and can even produce a considerable variety of tones. 

 Among the more remarkable diversities of the inferior larnyx, one in 

 particular deserves to be here indicated. In Sula-alba (at least in 

 the male) the trachea is formed as usual, and the bronchi are com- 

 posed of half-rings, but there invariably projects in the direction out- 

 ward from between the first and second bronchial demi-ring a 

 yellowish body, tolerably hard and solid, of the size of a pea, and 

 which contains fibres and a great quantity of adipose-cells ; with its 

 basis is connected the strong inferior larynx, and by means of this 

 arrangement the bronchi admit of being drawn much apart from each 

 other. This body does not appear to be a gland, for no excretory 

 duct can be detected. 



As regards the immediate organs of respiration, the Lungs, they 

 are in Birds, as in Mammalia, invariably two in number, but propor- 

 tionally of very small extent to what they are in the latter class. 

 They are flattened, irregularly triangular, and attached posteriorly 

 to the vertebrae and ribs (from the heads of which last they receive 

 deep permanent impressions) by cellular tissue. They are of a bright 

 florid red color, invested in front only by the pleura, and made up 

 of a loose parenchymatous tissue. They are of largest proportional 

 size in the Singing-birds, but are destitute of lobes throughout the 

 whole class, and exhibit great uniformity of character. The bronchi 

 as soon as they have entered the lungs form always a wide vesicular 

 cavity, perforated by a number of apertures. It is only anteriorly 

 and posteriorly that there are some imperfect cartilaginous arches, 

 and there are here found between the fifth to the sixth most anterior 

 cartilaginous demi-rings, four or five oval apertures, which are kept 

 open by the cartilages already named, and their mutual lateral 

 connexions ; they lead into larger superficial membranous tubes, 



