o 



8 



CESTRUS OVIS, Linn. 



Plate III. 



Fig. 1. Section of head of sleep made a little to the right of mesial plane : a, a, 

 a, a, a, section of bone surrounding J>, the brain, and c, the nasial cavity; 

 d, the lower jaw bone : e, nostril ; /, opening of tear duct ; g, g, g, turbi- 

 nated bones; h, the posterior opening of the nasal cavity, and near the 

 opening of Eustachian tube ; t, placed on the turbinated bone over a grub 

 in the groove leading to the frontal sinus; fc, the frontal sinus ; I, the nasal 

 sinus ; m, the thin perforated plate of bone called the cribriform plate ; «, 

 n, n, larvae of (Estrus ascending the uares and wanderiug about its surface; 

 i, one ascending to the sinus; fc, opposite three, nearly mature larv£e in the 

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



Fig. 2. Outline drawing of the skull surrounding the frontal sinus after removal of 

 part of the turbinated bone, lettered as in Fig. 1; o, o, straws passed 

 through the channels connecting the nares with the sinuses, marliing 

 the path by which the larva reaches the sinus ; p, cut ends of the removed 

 bones. 



