36 



CESTRUS ovis, Linn. 

 Plate II. 



Dissection of the head of a sheep to show the cavities into which the gad-fly grubs 

 penetrate. The straws indicate the passages from the cavities into the iuside of 

 the nose : a, the superior maxillary sinus in which there is imprisoued the calci- 

 fied remains of a fully developed larva ; b, the ridge made by the infra-orbital 

 division of the fifth pair of nerves; c, the infra-orbital foramen; d, an opening 

 into the nares; e, e, the frontal sinuses with young larvaiin them. The dotted 

 line /,/, indicates the level at which trephining, if it is done, should be per- 

 formed. Figure reduced to three-fourths of natural size. 



