312 



RESPIRATORY APPARATUS. 



but can be examined by passing the hand, palm upwards, into the 

 pharyngeal cavity, when the fingers may be slipped behind the soft 

 palate and thus introduced into the posterior nasal chamber. The 

 animals should first be very carefully secured and a strong gag intro- 

 duced into the mouth. 



Sinuses. Frontal sinus. — The frontal sinus occupies the greater 

 part of the anterior cranial region and the summit of the head, ex- 

 tending from the highest point of the poll as far forward as a line 

 drawn between the two orbits. Above, it directly communicates with 

 the sinus of the horn core. In this upper region, where it abuts on 

 the sinus of the opposite side along the median line, it is of greatest 



Fig. 163. — Median section through an ox's head. Sf, Frontal sinus; N.Ph. naso- 

 pharnyx; Vp., hard palate ; C, turbinated bones ; V., vomer ; L., tongue; V. pa., 

 soft palate ; E., epiglottis ; La., larynx ; (E., oesophagus. 



size. Below, on the other hand, it is very narrow, much broken up 

 and incompletely divided into a series of cells, by thin,, bony plates 

 running in all directions. 



It is in direct communication with the nasal cavity. 



The frontal sinus, then, occupies all the supero-lateral portion of 

 the cranial box, which is thus provided with a double wall. At one 

 point, however, over a lozenge-shaped area, the cranial cavity is only 

 protected by a single wall. It is in this region that the slaughter- 

 man strikes the animal when killing it. 



The frontal sinus may be examined by inspection and palpation. 



