THE ARTICULATIONS IN GENERAL. 123 



In the third, they are amphiarthroses, or mixed articulations ; so termed 

 because they participate in the movements of the other two classes ; synar- 

 throses, by the continuity established between the articular surfaces ; and 

 diarthroses, by the extensive motion they permit. 



The general characters that distinguish each of these three great classes 

 of articulations will be successively studied. 



(The study of the articulations, or rather of the ligaments, is termed 

 syndesmokgyfrom <rvv, together, and Seoyx,os, bond; or arthrology from 

 apOpov, a joint, and Aoyos, a description.^ 



GENERAL CHARACTERS OP DIARTHROSES. 



We ought to consider in the diarthrodial articulations : 1, The con- 

 tiguous bony surfaces which form them ; 2, The cartilaginous layer (cartilages 

 of incrustation) which cover these ; 3, The fibro-cartilaginous tissue (articular 

 fibro-cartilages) which complete them, when they are not shaped so as to be 

 reciprocally adapted to each other ; 4, The ligaments which maintain them 

 in contact ; 5. The serous membranes (synovial capsules) that cover the 

 internal face of the latter, and which secrete the synovia, a kind of animal 

 oil that facilitates the gliding of the articular surfaces ; 6, The movements 

 of which these articulations may be the seat ; 7, Their methodical classifica- 

 tion ; 8, Their nomenclature. 



ARTICULAR SURFACES. These surfaces have the common character of 

 being destitute of asperities, so that they can glide with the greatest facility 

 on each other. They are designated, according to their form, by the names 

 of facets, heads, condyles, cotyles, glenes, pulleys, etc. There is no need to 

 revert to their general description, as they have already been sufficiently 

 studied in the osteology; so we will confine ourselves to repeating that 

 they are found at the extremities of long bones, on the faces of short bones, 

 and on the angles of wide bones. We may mention also that they are often 

 excavated by one or several hollows named synovial fossae, a sort of natural 

 reservoirs which receive the unctuous fluid secreted by the interarticular 

 serous membranes : 



CARTILAGES OF INCRUSTATION. This designation is given to the layers of 

 cartilaginous matter which, as it were, varnish the articular surfaces they 

 adhere to by their inner face; their free surface is distinguished by a 

 remarkable polish and brilliancy Thicker towards the centre than at the 

 circumference when they cover bony eminences, these cartilages show an 

 inverse disposition when they line cavities. They are elastic, of a pearly 

 whiteness, and resisting, though they are soft enough to be cut by a sharp 

 instrument ; in a word, they possess all the physical characteristics of the 

 primary cartilage of bones They appear to be formed of parallel fibres 

 placed perpendicular to the bony surfaces, and implanted m these by one of 

 their extremities : the opposite extremity corresponding to the free surface 

 of the cartilage. Viewed by the microscope, they are found to consist of a 

 fundamental substance excavated by small cavities The cartilage of 

 incrustation therefore belongs to the group of true or hyaline cartilages. 



The fundamental matter is amorphous and homogeneous, and more or 

 less transparent, according to its thickness. It is transformed into chondrine 

 by boiling in water. 



The cavities are irregular, and more or less wide. They contain from 

 one to five cells whose walls are very thin, and their contents slightly gran- 

 ular; in the centre of each cell is a nucleus with a nucleolus. These 



