THE TURTLE. 203 



the pulmonary vein back to the heart. Trace branches 

 of the aortie anteriorly to the head. Trace the aortae 

 themselves posteriorly, to see their union and subsequent 

 division, and distribution to the various parts. Now 

 make a diagram showing the general arrangement of the 

 circulatory system. 



V. Retractor and Protractor Muscles. Study the action 

 of the long retractor muscles which extend from the middle 

 of the spinal column to the base of the skull, and of the 

 protractor muscles, which extend from carapace and pec- 

 toral arch to the neck. Pull first on one and then on the 

 other, and note the effect on the head and neck. 



VI. Trachea and Lungs. Extend the neck, and fasten 

 it so. Dissect out the trachea and the lungs. Inflate the 

 lungs, and keep them inflated by tying the trachea with a 

 thread. Hang them up, and let them dry, and preserve 

 them for comparison with the lungs of other vertebrates. 



The narrow slit by which the trachea opens on the 

 floor of the mouth is the glottis. Why does not food 

 which is being swallowed get into the trachea? 



VII. Spinal and Cranial Nerves and Brain. Remove 

 the viscera, and find spinal nerves. Compare in number 

 and arrangement with those of the frog. Remove the roof 

 of the cranium, and find cranial nerves and brain. In the 

 brain find in order from the front, (1) olfactory lobes, 

 (2) cerebral hemispheres, (3) midbrain, (4) optic lobes, 

 (5) cerebellum, and (6) medulla. 



Study of the Skeleton. Study the shell of the turtle, 

 especially in its relation to the bony skeleton. In a 

 prepared skeleton of an adult turtle, note : 



1. That the pectoral and pelvic arches, and the bases 

 of the legs, are contained within the shell. 



2. That both arches are attached more or less closely 

 at several points to both carapace and plastron. 



