130 ARTICULATIONS. 



surface, and they are firmly held together by means of short bands of 

 glistening fibres, which are called ligaments (ligare, to bind). The study 

 of the ligaments is named syndesmology (rfuv together, <5so>o bond), which, 

 with the anatomy of the articulations, forms the subject of the present 

 chapter. 



The forms of articulation met with in the human frame may be consi- 

 dered under three classes : Synarthrosis, Amphi-arthrosis, and Diarthrosis. 



SYNARTHROSIS ( rfuv, ^W<TIJ articulation) is expressive of the fixed form 

 of joint in which the bones are immovably connected with each other. 

 The kinds of synarthrosis are four in number. 1. Sidura. 2. Harmonia. 

 3. Schindylesis. 4. Gomphosis. The characters of the three first have 

 been sufficiently explained in the preceding chapter, p. 83. It is here 

 only necessary to state that, in the construction of sutures, the substance 

 of the bones is not in immediate contact, but is separated by a layer of 

 membrane which is continuous externally with the pericranium and inter- 

 nally with the dura mater. It is the latter connexion which gives rise to 

 the great difficulty sometimes experienced in tearing the calvarium from 

 the dura mater. Cruveilhier describes this interposed membrane as the 

 sutural cartilage ; I never saw any structure in the sutures which could 

 be regarded as cartilage, and the history of the formation of the cranial 

 bones would seem to point to a different explanation. The fourth, Gom- 

 phosis (/ofApog, a nail), is expressive of the insertion of one bone into 

 another, in the same manner that a nail is fixed into a board ; this is il- 

 lustrated in the articulation of the teeth with the alveoli of the maxillary 

 bones. 



AMPHI-ARTHROSIS (apupj both, ag&gutfis) is a joint intermediate in aptitude 

 for motion between the immovable synarthrosis and the movable diarthro- 

 sis. It is constituted by the approximation of surfaces partly coated with 

 cartilage lined by synovial membrane, and partly connected by interosse- 

 ous ligaments, or by the intervention of an elastic fibro-cartilage which 

 adheres to the ends of both bones. Examples of this articulation are seen 

 in the union between the bodies of the vertebra, of the sacrum with the 

 coccyx, of the pieces of the sternum, the sacro-iliac and pubic symphyses 

 (ffvv, <pusv, to grow together), and according to some, of the necks of the 

 ribs with the transverse processes. 



DIARTHROSIS (&a through, a^wrfic;) is a movable articulation, which 

 constitutes by far the greater number of the joints of the body. The de- 

 gree of motion in this class has given rise to a subdivision into three genera, 

 Arthrodia, Ginglymus, and Enarthrosis. 



Arthrodia is the movable joint in which the extent of motion is slight 

 and limited, as in the articulation of the clavicle, of the ribs, articular pro- 

 cesses of the vertebrae, axi* with the atlas, radius with the ulna, fibula 

 with the tibia, carpal and metacarpal, tarsal and metatarsal bones. 



Ginglymus (yty/Xu/juXc, a hinge), or hinge-joint, is the movement of 

 bones upon each other in two directions only, viz. forwards and back- 

 wards ; but the degree of motion may be very considerable. The instances 

 of this form of joint are numerous ; they comprehend the elbow, wrist, 

 inetacarpo-phalangeal and phalangeal joints in the upper extremity; ;md 

 the knee, ankle, metatarso-phalangeal and phalangeal joints in the lower 

 extremity. The lower jaw may also be admitted into this category, as 

 partaking more of the character of the hinge-joint than the less movable 

 arthrodi? 



