OF THE NEUVUS OCTAVUS. 



2. The operations through the bulla ossea. 



If the bulla ossea is to be laid bare, a rather large area of 

 operation must be prepared, having the shape of a rectangular 

 trapezium, whose upright rectangle-side is in the cervical part of 

 the mid-ventral line of the animal. 



Cranial wards the boundary of this area is a line, starting from 

 the lateral canthus of the eye and crossing the cheek, standing 

 vertically on the mid-ventral line. It is the basis of the trapezium. 



The dorsal boundary, is a line, drawn from the lateral canthus 

 of the eye along the auricular root towards the mid-dorsal line. 



The caudal boundary , the oblique side of the rectangular trape- 

 zium , is indicated by a line, starting from the mid-dorsal line a 

 little way behind the ear and reaching the mid-ventral line at the 

 manubrium sterni. 



Nearly in the centre of this trapezium is found the angulus 

 maxillae inferioris, serving as ,, point de repere". 



Especial care is given to the disinfection of the roots of the ear 

 and of the external auditory rneatus, that after having been cleansed, 

 are filled with Bruns's wadding. 



Thus prepared, the animal is stretched with its back turned 

 upward; and the head, retained in Czermak's trap, is placed in 

 such a manner that the area of operation is turned upward. 



After care fal re-disinfection of the area of operation, the stret- 

 ched animal with its surroundings is wrapped up in sterile gauze, 

 only the area of operation remaining visible and accessible to the 

 operator. 



The operator finds his way by the aid of the angulus maxillae 

 inferioris, that may be felt through the skin. 



The incision of the skin commences somewhat laterally from the 

 lateral eye-canthus, passes midway between underjaw and ear, des- 

 cending at first parallel to the ascending branch of the underjaw , 

 till it has reached the angulus maxillae inferioris and until then 

 it continues standing nearly vertically on the mid-ventral line. 



It then commences to deviate slowly caudalward, forms a right 

 angle with its original direction, courses parallel to the mid-ventral 

 line, and terminates about 2 cM. from its bend. In this manner 

 the skin-incision describes part of a circular line around the bony 

 and the membranous auditory meatus, or, if one likes, above and 

 over the bulla ossea lying in the depth. 



This incision having been made, we meet in the caudal part of 



