EXCRESCENCE ON A LAPWING. 15 



muscle-tissue, the latter doubtless being brought into 

 play in voiding the secretion. If the capsule were torn 

 and the tubules damaged the secretion would involuntarily 

 make its escape through the rent, and, if circumstances 

 allowed it to accumulate, it would harden ; the hardened 

 part would be pushed on by the ever-oozing fresh secretion, 



LAPWING WITH A LARGE SEBACEOUS "HORN. 



which in turn would be hardened and pushed on. In 

 this manner these curious sebaceous " horns " are formed. 

 Sebaceous " horns " are, perhaps, best known from 

 their occasional occurrence in the human subject, and 

 may be formed on any part of the skin where sebaceous 

 glands occur, but are commonest on the scalp. These 

 glands also occur in other mammals, and there is in the 



