ixix 
Meckel, in the tenth volume of his Comparative Anatomy, 
alluded to the discovery of this air sac by Fremery, in the 
year 1819, but states that he has noticed it in a vague and 
imperfect manner. I have not had an opportunity of consult- 
ing this work of Fremery. Meckel does not describe this air 
sac with that clearness and precision so characteristic of this 
writer. His account rather consists of quotations from Knox, 
and of the varying statements of other writers, than of any 
observations of his own. Carus, in his System of Compara- 
tive Anatomy, makes no mention of it. It does not appear 
to have been known to Cuvier, as there is no. notice of it 
either in his Anatomie Comparée, or in his Regne Animale, 
neither is it alluded to inthe new edition of that invaluable 
work, now in course of publication. In the elaborate and 
excellent article ‘* Aves,” in the Encyclopedia of Anatomy 
and Physiology, edited by Dr. Todd, of London, and which 
article is from the pen of Mr. Owen, who is justly regarded 
as the first comparative anatomist and zoologist of the present 
day, this peculiar appendage is alluded to; but, strange to 
say, the brief and imperfect account which is there given of it 
is wholly incorrect, a circumstance I can only attribute to 
some accidental inadvertence. Mr. Owen says, ‘that the 
trachea of the emu is remarkable for a sudden dilatation; 
but, in this instance, the cartilaginous rings do not preserve 
their integrity at the dilated part, but are wanting posteriorly, 
where the tube is completed by membranes only.” I have 
made some researches into the writings of other authors also, 
but have not met with any accurate description of this appa- 
ratus, 
As I have lately had an opportunity of examining this 
_ appendix in the living bird, as well as in one recently dead, 
I shall state such facts as I have observed in the former con- 
dition, as well as the appearances I have remarked in the 
latter. I may first observe, that this exists both in the male 
and female; for some time since I dissected a male emu, and 
2 
