SECTION OF INTERNAL ANATOMY OF HEAD 167 



b. The frontal bone, under which are cavities called the 

 frontal sinuses, marked 16, 16. 



These frontal sinuses are cavities intervening 

 between the frontal bone and a transverse plate of 

 bone which grows within it. They communicate 

 with the cavities of the nose, as also with those of 

 the sphenoid, ethmoid, and upper jaw-bones. In 

 consequence of this conformation, they increase the 

 loudness and clearness of neighing. It sometimes 

 happens that the larvae of certain flies crawl up 

 the nostrils and locate themselves In the frontal 

 sinuses, occasioning great pain to the animal. 

 Happily, this is not of very frequent occurrence 

 with the horse, although sheep and horned cattle 

 are more liable to such intrusion. 



These sinuses are occasionally opened by tre- 

 phining the bone, in order that the pus cells, which 

 they frequently contain in large quantity, may be 

 removed by direct Injection of water and as- 

 tringents. 



In performing the operation we suppose a line 

 to be drawn across the forehead from 2 and 3, 

 one foramen to the other, Plate viii, fig. g, g, g. 

 On that line, and about half an inch from the 

 suture, or line which separates the frontal bones, 

 the sinuses or cavities are situated, and extend to 

 an inch in depth, as represented In Plate in, ^g. 

 3, immediately under b, and marked 16, 16. If the 

 position of g, g in fig. 3, Plate viii and b in fig. 3, 

 Plate III, are compared, a perfect idea of their seat 

 in the forehead will be formed. At this part a small 

 circular portion of bone Is drilled out with a 

 trephine, and into this warm water Is injected by 

 means of a comm.on syringe, which will run out at 

 the nostrils. 



