THE FROG 45 



out under water in a small dissecting tray, examine it with 

 a lens and sketch a small portion of its inner surface. For 

 this purpose a lung that has been preserved while slightly 

 inflated is desirable. 



Of what importance in the respiration of the frog is the 

 hyoid apparatus? 



IX. THE THYROID GLANDS. 



On each side of the hyoid apparatus, lateral to the base of 

 the thyrohyoid process, is a small body known as the thyroid 

 gland. Under a dissecting lens, examine a preparation of 

 the hyoid apparatus with these glands attached, and observe 

 that each gland is mainly composed of a mass of thin-walled 

 vesicles. Find the glands in your own preparation of the 

 hyoid apparatus. Sketch the glands, together with an out- 

 line of the hyoid apparatus, under the dissecting lens; the 

 object of this sketch is mainly to show the location of the 



glands. 



Under the low power of the compound microscope, study 

 a prepared section of a thyroid gland. Observe that each 

 vesicle is formed of a single layer of epithelial cells, enclos- 

 ing a central cavity which in life is filled with fluid; the 

 space between the vesicles is filled with connective tissue 

 and blood vessels. Under high power, study and sketch a 

 portion of the section. 



X. THE INTEGUMENT. 



A. Obtain a small piece of the outer or horny layer 

 (stratum corneum) that has been shed from the skin of 

 the frog; mount it in water on a slide and cover it with a 

 cover glass. Examine it with the microscope and select for 



