254 
40. TrinGoipEs MACULARIvs (Linn.). 
41. RuyacopuHiLus soLirarivs (Wils.). 
42. ErisMaTuRA DoMINIcA (Linn.). 
43. QUERQUEDULA CAROLINENSIS (Gm.). 
44, QueRQUEDULA Discors (Linn.). 
6. On THE SrructurRE, ReLativeE Size, AND UsE oF THE TAIL- 
Guanps 1n Birps. By Epwarps Crisp, M.D., F.Z.S., erc. 
It is strange that all (as far as I know) who have written upon 
these glands speak of one gland only ; but, as I shall show hereafter, 
there are two distinct glands, from each of which proceeds a duct or 
canal for the conveyance of the matter secreted ; and it would not 
be more incorrect to speak of the lungs or of the kidneys of a bird 
in the singular number than to describe the oil-glands as one gland. 
As the heading of my paper states, my first endeavour will be to 
describe the structure of these glands, and then I shall pass on to 
consider their use. 
The only English writers that I am acquainted with who have 
written generally upon the anatomy of birds are Professor Owen 
(article “ Aves”’ in the ‘ Cyclopzedia of Anatomy and Physiology ’) 
and Mr. Macgillivray in his ‘ History of British Birds, their Organi- 
zation, Habits, &e.’ 
The first-named writer speaks of these glands, or rather of the 
gland, as follows :— : 
“The unctuous fluid with which birds lubricate their feathers is 
secreted by a gland, which is situated above the coccyx or uropygium. 
This gland consists of two lateral moieties conjoined; as might be 
expected, it is largest in the birds which frequent the water. In the 
Swan it is 1} inch in length, and has a central cavity which serves 
as a receptacle for the accumulated secretion; but this cavity has 
not been observed in other species. Each lateral portion is of a py- 
riform shape, and they are conjoined at the apices, which are directed 
backwards, and are perforated by numerous orifices. The longitu- 
dinal central cavities also present internally numerous angular open- 
ings in which there are still smaller orifices. The surrounding glan- 
dular substance consists of close-set, almost parallel, straight tubes, 
and is not irregularly cellular. The tubercles extend to the super- 
ficies of the gland without ramifying or intercommunicating, and 
preserve an equable diameter to their blind extremities. The tu- 
bercles are longest at the thickest part of the gland, and become 
shorter and shorter towards the apex.” 
It will be seen presently that my description of these glands differs 
materially from that given by Professor Owen. 
Mr. Macgillivray, in the work alluded to (vol. i. p. 44), says,— 
«These feathers have their basis supported by the last coccygeal 
