1886.] 



MAMMALS IN T^!E SOCIETY S GARDENS. 



211 



curious deformity, for at the junction of the upper and middle third 

 the shaft was bent ahuost 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 lloyal 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. 



Fig. 4. 



A Cockateel, Lalopitifta iiuia holiOhdid, with bjumietjic.il sebatpous cysts 

 on its wings. 



An excellent example of this affection has recently come under 

 my notice in a Cockateel, C'alopsitta novce-holhmdicB. 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 (18S2. p. 4-42) an example of webbed fingers in a Pitheciu. 

 satanas. " The third and fourth digits of the manus on each side 

 were conipletely connected down to their tips by a fold of nude skin, 

 with their nails closely apposed, though not connected, along their 



