2o6 PHYLUM CHORDATA 



Exercise 7, Draw a sketch of the urinary system within an outline of 

 the body and the body cavity. 



The nervous system consists of (i) the central nervous system, 

 which includes the brain and the spinal cord ; (2) the peripheral 

 nervous system, which includes the paired cranial and spinal 

 nerves and the sympathetic nervous system ; and (3) the special 

 sense organs. 



We shall study first the special sense organs and then the 

 brain. The peripheral nerves will not be studied in this dissec- 

 tion. The special senses are located in the integumentary sense 

 organs, the nasal capsules, the eyes, and the ears. 



The integumentary sense organs consist of (i) minute, scattered 

 sense buds which occur principally on the head but also on the 

 body, and (2) of the lateral line. This line is a straight canal in 

 the integument which extends along the side of the body from 

 the head to the caudal fin, with branches also upon the head, in 

 which are groups of sensory cells. 



The nasal capsules are a pair of sacs situated in front of the 

 eyes and communicating with the outside by two nostrils on each 

 side ; no communication with the mouth is present. Cut off the 

 outer wall of one of the capsules and observe the delicate folds 

 of the sensory epithelium radiating from a central point. 



Exercise 8, Make a drawing of the capsule on a large scale. 



The Eyes. Observe the central pupil, through which light is 

 admitted to the interior of the eye ; the iris, which surrounds the 

 pupil ; and the transparent cornea, which lies in front of both and 

 forms the outer coating of the eye. Observe carefully the circular 

 fold of the skin which surrounds the front of the eyeball. 



With strong scissors cut away the circular ridge of the skull 

 which surrounds the eye, and remove the muscles of the head 

 just beneath and back of it. Remove also the slimy fold of the 

 skin just mentioned, which surrounds the front of the eye. Note 

 that a transparent layer of the skin passes over the cornea and 

 may be peeled off ; this is the conjunctiva. 



Observe the position of the eye in the orbit ; it is held in place 



