ARTICULATIONS OF MAMMALIA IN PARTICULAR. 129 



animals by the elasticity they communicate to the bony walls of the cranium, 

 or face. In the adult, they may be said to be null. 



CLASSIFICATION. There are four principal descriptions of sutures : 

 1. When two wide bones correspond by means of denticulations fitting 

 into each other, the suture is named true or dentated. Example : the 

 articulations uniting the three portions of the parietal bone. 2. If the 

 opposed borders of two bones in contact are widely bevelled, one inwards, 

 the other outwards, it forms a scaly or squamous suture. Example : the 

 parieto-temporal articulations. 3. When the union of bones takes place 

 by plane or roughened surfaces, cut perpendicularly on their borders or 

 angles, this constitutes the harmonia suture, or suture by juxtaposition (or appo- 

 sition). Example : the occipito-temporal articulations. 4. The scliindylesis, 

 or mortised suture, results from the reception of a bony plate into a groove 

 more or less deep in another bone. Example : the spheno-frontal and 

 supermaxillo-nasal articulations. 



GENERAL CHARACTERS OF THE AMPHIARTHROSES OR SYMPHYSES. 



ARTICULAR SURFACES. They are frequently smooth, and formed almost 

 on the same model as the diarthrodial surfaces. They are covered by a 

 thin layer of cartilage, but instead of being smooth and polished, they are 

 more or less rugged, without, however, presenting the anfractuous disposition 

 of the majority of synarthrodial surfaces. 



MODES OF UNION. The organs which perform this office are : 1, The 

 nbro-cartilage which establishes continuity between the articular surfaces ; 

 2, Kibbon-shaped or peripheral ligaments. These latter do not differ from 

 the analogous bands attaching the diarthrodial articulations. . With regard 

 to the nbro-cartilage, it is distinguished from the complementary discs of 

 these same articulations by a less intimate mixture of the cartilaginous and 

 fibrous elements entering into its composition. The last may be sometimes 

 absent, as well as the peripheral bands ; and then the articulation only differs 

 from the synarthroses by the extent of motion it permits Occasionally the 

 interarticular fibro-cartilages are excavated by one or two little narrow cavities ; 

 but these are never lined by a synovial membrane like the diarthrodial 

 cavities. 



MOVEMENTS. The amphiarthroses only permit of a see-saw or swinging 

 movement, the extent of which depends on the thickness of the intermediate 

 fibro-cartilage. 



CLASSIFICATION. Only one kind of amphiarthrosis is recognised, the 

 most remarkable example of which is found in the articulations between the 

 bodies of the vertebrae. 



CHAPTEK II. 



ARTICULATIONS OF MAMMALIA IN PARTICULAR. 



IN the special study of the articulations, the same order will be followed 

 as for the bones ; the articulations of the spine will be first noticed, then 

 those of the head, thorax, and anterior and posterior limbs. 



Preparation. The preparation of the bones which have been described 

 has not been made the subject of any particular recommendation, because 

 it suffices, in order to study them, to remove the soft parts by which they 



