LESSON XXXVIII 



THE SENSE ORGANS (Continued) 

 THE STATIC AND DYNAMIC SENSES 



1. Dissection of the Ear of the Dog-fish. Remove the cartilage be- 

 tween the eyes. Identify the different parts of the brain. Proceed 

 toward its hinder part, carefully removing the cartilage from within 

 outward. Having reached one of the semicircular canals, remove its 

 upper wall as far as possible. Identify its membranous canal with its 

 ampulla. Follow this canal until it joins a membranous sac, the utricle. 

 Carefully expose the other semicircular canals. Open one of the am- 

 pulla and identify the crista acustica, a transverse ridge carrying the 

 sensory epithelium. 



FIG. 105. POSITION OF THE THREE SEMICIRCULAR CANALS IN THE SKULL OF THE PIGEON. 



(Ewald.) 



2. The Position of the Semicircular Canals. Procure a human skull 

 in which the semicircular canals have been exposed, i. e., the bone has 

 been removed, leaving only the bony walls of the canals behind. In- 

 side this shell lies the membranous canal containing endolymph and 

 invested by perilymph. 



Hold the skull in its proper position and indicate by a diagram the 

 position of these canals. How many are there and what position do 

 they occupy toward one another? What planes in space do they cor- 

 respond to? 



Diagrammatically represent the canals on the other side of the head, 

 and compare their positions with those just sketched. Note that the 

 canals are paired, comprising the following groups: the two horizontal 



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