358 MANUAL OF HISTOLOGY. 



diverticulum (the lagena), the membranous labyrinth is fully 

 developed, and, as it is large and easy of access, has always 

 been a favorite object for demonstration. Its method of prep- 

 aration will be given here, while that for the cochlea will be 

 described farther on. 



The membranous labyrinth. Our knowledge of this part 

 has been chiefly derived from studies upon the pike (esox lu- 

 cius), perch (perca fluviatilis), or cod (gadus morrhua). The 

 head is divided longitudinally in the median line, and the brain 

 carefully removed by means of the handle of a scalpel, when 

 there is seen directly behind the eye a second cavity filled with 

 a grayish translucent mass, composed principally of fat and a 

 sort of mucous tissue. This can be removed with the aid of 

 fine forceps, and there is usually drawn out at the same time 

 more or less of the semicircular canals with their ampullae and 

 the remains of the utricle and saccule. With a little practice, 

 and by carefully freeing the canals from the short, bony chan- 

 nels by which they are held in place, the membranous laby- 

 rinth, with a portion of the acoustic nerve, can be removed 

 entire. 



Within the utricle and saccule are found the otoliths, con- 

 cretions of lime. After the lime has been removed by means 

 of a weak acid, they show a coarse, fibrillated structure on 

 section. These serve as a ready means of distinguishing be- 

 tween the saccule and utricle, as the largest otolith (called 

 sagitta) and the smallest (asterix) occupy the saccule, the 

 former lying on the expansion of the acoustic nerve in the sac- 

 cule proper, while the latter lies on the expansion of the nerve 

 in that part of the saccule called the lagena, and which corre- 

 sponds to the cochlea of the higher animals. The medium-sized 

 stone (lapillus) lies upon the expansion of the nerve in the utri- 

 cle. The otoliths are embedded in a mucilaginous mass lying 

 directly upon the termination of the nerve. In the higher ani- 

 mals they are represented by cretaceous particles in the macula 

 acustica. 



The labyrinth thus removed is to be placed, during twenty- 

 four hours, in a 1 per cent, solution of osmic acid, and then 

 carefully washed in distilled water. In order to obtain the 

 separate cells, the point where the nerve enters (known by its 

 darker color) is to be carefully teased with fine needles and 

 examined in glycerine. To obtain good sections, the por- 



