172 



THE ARTICVLATIONS. 



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 classification. 

 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, condijles, cotyles, glenes, pulleys, etc. There is no need to revert to their 

 general description, as they have already been suihciently studied in the osteo- 

 logy ; 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 

 depressions named synovial fossce, or hollows for the insertion of ligaments. The 

 first are a sort of natural reservoirs which receive the unctuous fluid secreted by 

 the interarticular serous membranes ; the second give attachment to interosseous 

 ligaments. 



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 carti- 

 lages 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 perpen- 

 dicular to the bony surfaces, and im- 

 planted in these by one of their ex- 

 tremities ; the opposite extremity corre- 

 sponding to the free surface of the 

 cartilage. Viewed by the microscope, 

 they are found to present the characters 

 of true or hyaline cartilage. 

 The fundamental matter is amorphous and homogeneous ; but under the 

 influence of slight dessication, there appears in the hyaline substance a partition- 

 ing formation, which may be regarded as an agent in the distribution of the 

 nutritive juices in the substance of the cartilaginous tissue (Renaut). 



The cavities (cartilage capsules) are irregular, and more or less wide. They 

 contain from one to five cells without walls, and their contents — slightly granular 

 — have in the centre of each cell one or two nuclei with nucleoH (Fig. 1 IG). These 

 cavities are elongated, and are directed almost perpendicularly towards the osseous 

 articular surface in the deep layer ; in the middle layer they are round ; and 

 they are lenticular, and parallel to the surface of friction, in the superficial layer. 

 (It has been stated that a membrane lines these spaces. In addition to the 



SECTION OF BRANCHIAL CARTILAGE OF 

 TADPOLE. 



, Group of four cells separating from each 

 other ; b. pair of cells in apposition ; c, c, 

 nuclei of cartilage-cells ; d, cavity contain- 

 ing tiiree cells. These cells are embedded 

 in the finely granular matrix, or funda- 

 mental substance. 



