422 PRACTICAL ANATOMY. 



to side. Observe the free movement of the fingers on the metacarpals forward 

 and backward, and the limited movement from side to side. The movement of 

 lower jaw is the same. We can see plainly that this variety of joint is a com- 

 promise between ball-and-socket and the hinge -joint. (3) Ginglymus, or hinge- 

 joint, in which there is free movement in two directions, as in the elbow, knee, 

 ankle, and interphalangeals of all the digits of both feet and hands. In these 

 articulations note the impossibility of lateral movement without violence ; note 

 the intermediate position between this variety and the ball-and-socket variety, 

 occupied by the preceding condylarthrosis subdivision. (4) Lateral ginglyinits 

 is a term used to express a subdivision of movable joint which differs from the 

 hinge movement in no essential, except in the direction of motion. The supe- 

 rior and inferior radio-ulnar articulations and the atlanto-odontoid belong to 

 this subdivision. (5) Arthrodia includes the simplest subdivisions of all the 

 movable articulations. In this kind the surfaces are plane, or nearly so. The 

 movements are limited, by virtue of the strong and unyielding nature of the liga- 

 ments, which represent the lowest organized variety of capsular ligament. Ex- 

 amples of this subdivision are in the carpal and tarsal articulations ; between 

 the metacarpals and metatarsals ; in the articular processes of the vertebrae ; in 

 the costo-transverse and interchonclral articulations. 



I desire you to dissect and study the movable articulations the diarthroses 

 according to the following outline : 



1. Give the name of the class diarthrosis, for example. 



2. Give the name of the subdivisions of the class. 



3. Give the technical name of the locality. 



4. Give the osteological units in the joint. 



5. Give subdivisional parts of osteological units. 



6. Name the articular surfaces according to the rule. 



7. Give the basis of a movable joint a capsule. 



8. Give the local subdivisions of the capsule. 



9. Name the strengthening bands of the capsule, if any. 



10. Name the incorporated tendons of obsolete muscles, if any. 



1 1. Name the bony limitations of movements of the joint. 



12. Name the nerve-supply apd blood-supply of the joint. 



13. Name the ligamentous muscles of the joint. 



Let us review now the above outline, and understand its specific scope. 



1. There are five subdivisions of the class diarthrosis. (Page 424.) By 

 examining the articulation, you find movement in two directions. Your entry 

 should read : Class, diarthrosis ; Subdivision, ginglymus. 



2. Let us assume the particular joint is the elbow : then the technical name 

 is humero-radio-ulnar articulation ; the common name, elbow-joint. 



3. The osteological units in this joint are the humerus, radius, and ulna. 



4. The subdivisional parts of the osteological units are the outer and inner 

 humeral condyles, radial head of humerus, head of radius, olecranon process 

 of ulna, coronoid process of ulna, greater sigmoid cavity of ulna. 



5. Articular surfaces should take the name of the occupant. Then in this 

 joint we find the radial and ulnar surfaces of the humerus ; the humeral surfaces 

 of the radius and ulna. The ulnar surface of the humerus is called technically the 

 trochlear or pulley surface ; the radial surface of the humerus is called the 

 capitellum, or little head. 



6. The basic principle in every movable joint is a capsule derived from peri- 

 osteum, lined by a more or less extensive synovial membrane. 



7. The subdivisions of the capsule are anterior, posterior, internal lateral, and 

 external ligaments. A complete capsule is equal to the sum of its subdivisional 

 parts. The usage by which capsules are thus subdivided is a useless (except 



