HISTOLOGY 29 



and also encloses a cavity in the joint, the synovial cavity. In the 

 living animal this cavity contains a small amount of fluid, the synovial 

 fluid, which serves to lubricate the joint. Cut through this ligament 

 and expose the head of the femur. Notice how it fits into its socket. 

 In what directions can such a joint move? The hip joint is known as a 

 ball-and-socket joint. Study the knee joint in like manner. How does 

 it differ from the hip joint? The knee joint is known as a hinge joint. 



II. RELATED FORMS 



Exercise 25. — The Frog's Relatives. 



(a) It will be recalled from your reading that the Subphylum 

 Vertebrata to which the Class Amphibia belongs is a division of the 

 Phylum Chordata. Examine specimens of Dolichoglossus {Balano- 

 glossus), representing the Subphylum Hemichorda; various tunicates 

 or sea-squirts, representing the Subphylum Urochorda; and Branchio- 

 stoma {Amphioxus), representing the Subphylum Cephalochorda. 

 Understand why these animals and the vertebrates are classified to- 

 gether as chordates. 



(b) What are the distinguishing characteristics of the Subphylum 

 Vertebrataf It is divided into seven classes. Understand the basis of 

 this division, and examine specimens from the several classes. Recall 

 any information concerning the internal structure of these vertebrates 

 as compared with the frog. 



III. HISTOLOGY 

 A. The Microscope 

 Exercise 26. — The Parts of a Microscope and Their Use. 



(a) Before beginning the study of histology, or microscopic 

 anatomy, you must learn how to use the microscope. In this exercise 

 it is important that you become familiar with the names of the parts 

 of your instrument and the correct procedure for microscopic study. 

 Since the microscope is an expensive instrument of precise construc- 

 tion it must be handled carefully and kept clean. The metal parts 

 and the mirror can be cleaned with soft cloth, but the lenses must be 

 cleaned only with lens paper or they may be scratched and perma- 

 nently damaged. Do not unscrew any part of or attempt to repair 

 your instrument; report any unusual condition immediately. 



(b) The microscope is an instrument w^iich magnifies objects. 

 The compound microscope with which you are working consists essen- 

 tially of two sets of lenses fixed in a tube by means of which they can 

 be moved with reference to, or focused on, the object to be magnified, 



