1886. ] MAMMALS IN T'1E SOCIETY’S GARDENS. 212 
curious deformity, for at the junction of the upper and middle third 
the shaft was bent almost at a right angle. The corresponding 
bones of the opposite side presented precisely similar lesions. 
The sebaceous glands of the skin very frqeuently in the human 
subject suffer obstruction of their excretory duct. The result is 
that the gland continues to secrete, but the outlet being closed, the 
sebaceous matter accumulates until at last a definite swelling results, 
which may remain of insignificant proportions, or attain a diameter 
of two or three inches in exceptional cases. Technically such 
swellings form one of a group known as “ retention cysts.” 
The museum of the Royal College of Surgeons possesses some 
specimens of symmetrical sebaceous cysts growing from the wings of 
Wood-Pigeons. The specimens were presented by Mr. Tegetmeier. 
It appears that in certain seasons a large number of birds are found 
with swellings such as these on the wings, legs, and feet. 
A Cockateel, Culopsitta nove-holiandie, with symmetrical sebaceous cysts 
on its wings, 
An excellent example of this affection has recently come under 
my notice in a Cockateel, Calopsitta nove-hollandie. In this pretty 
bird there has developed on the inner surface of each wing a seba- 
ceous cyst. The position, size, and shape of the ‘‘ swelling’ in the 
two cases exactly correspond, as may be seen on reference to the 
drawing (fig. 4). The specimen serves as an excellent illustration 
of symmetrical disease. 
Malformations are frequently as symmetrical as tumours and skin 
eruptions. Mr. Forbes has recorded in the ‘ Proceedings’ of this 
Society (1882, p. 442) an example of webbed fingers in a Pitheci« 
satanas. ‘*The third and fourth digits of the manus on each side 
were completely connected down to their tips by a fold of nude skin, 
with their nails closely apposed, though not connected, along their 
