128 THE ARTICULATIONS. 



a cavity of appropriate form. This articulation may be the seat of the most 

 extensive and varied movements : flexion, extension, abduction, adduction, 

 circumduction, and rotation. Example : the toxo-femoral articulation. 



2. The trochlean, angular ginglymoid, or perfect hinge articulation, 

 when the articular surfaces are formed into trochlea, reciprocally fitting 

 into each other, and whose movements — flexion and extension only — are 

 executed with the precision of a hinge. Example : the tibio-tarsal ar- 

 ticulation. 



3. The condyloid, or imperfect hinge articulation, which permits, like the 

 preceding, the two principal movements of extension and flexion, and. the 

 accessory movements of rotation or lateral inclination. The articular 

 surfaces, fhough very diversely shaped, nevertheless exhibit in all the 

 articulations one or more condyles opposed to an equal number of oval 

 excavations. Example : the femoro-tibial articulation. 



4. The pivot, trochoid, or lateral ginglymoid articulation, is a diarthrosis 

 formed by a pivot which turns in a semi-cylindrical cavity. Eotation 

 is the only movement. Example ; the atlo-axoid articulation. 



5. Arthrodia, or planiform diarthrosis, is constituted by plane, or nearly 

 plane facets. Gliding is the only possible movement. Example : the carpo- 

 metacarpal articulation. 



NoMENOLATUKE. — The namcs of the articulations are usually those of 

 the bones which form them. Eor instance, the scapulo-humeral articulation 

 is the joint between the scapula and humerus ; the intervertebral articulations 

 join to each other the various pieces constituting the spine. When the 

 qualifying name of an articulation is composed of two elements, as in the 

 first instance, it is well to place first the word which indicates the bone 

 usually most fixed. 



GENERAL CHARACTERS OF THE SYNARTHROSES. 



Sutures are the temporary articulations which exist only at an early 

 period of life. They nearly all disappear in the adult animal, in con- 

 sequence of the. bones forming them becoming consolidated. They belong 

 almost exclusively to the bones of the head. 



Articdlar Surfaces. — The bones forming these come in contact by their 

 borders or angles, which, for this purpose, generally present very anfractuous 

 surfaces. 



Sometimes they are cut perpendicularly and simply roughened; at 

 other times they are bevelled and joined by means of fine laminse or trifling 

 inequalities ; again, they are notched into deep and sinuous dentations ; 

 and lastly, one bone is fixed into a groove cut in the other. It will be 

 understood that such conformations of the articular surfaces ought to limit 

 their movements and assure the solidity of their union. 



Modes of Union. — Cartilage interposed between these synarthrodia! 

 surfaces directly unites them to each other. It absolutely possesses the 

 same texture as the primary cartilage of the bones, and like it, has the 

 property of becoming ossified after having been vascularised. This ossi- 

 fication, which causes the disappearance of the sutures, occurs earlier 

 inwards than outwards. The periosteum, in passing from one bone to 

 another, adheres intimately to the sutural cartilage, and also aids in bringing 

 about a more complete synarthroses. It should, therefore, be included in 

 their means of union. 



Movements.— These are very obscure, and only noticeable in young 



