342 THE TISSUES. 



more or less in structure, though closely connected. The external 

 layer is composed chiefly of white fibrous tissue, with occasional 

 fat-cells, and in this are the true vessels and nerves of the peri- 

 osteum. The inner layer contains elastic fibres, usually of the finer 

 sort, constituting very thick networks true elastic membranes 

 superimposed one upon another. The white fibrous tissue consti- 

 tutes the least important element. Nerves and vessels occur in this 

 layer, also; but they merely pass through it, preparatory to entering 

 the bone itself. 



The following surfaces of the bones are not covered by peri- 

 osteum : 



1. All surfaces where the bone is covered by the articular (or 

 other) cartilage, or fibro-cartilage. 



2. Where ligaments and tendons are attached to bones at a cer- 

 tain angle ; e. g. the ligamenta subflava, ligamentum teres, liga- 

 mentum patellae, and the inter vertebral, ilio-sacral, and interosseous 

 ligaments; and the tendons of the deltoid, the coraco-brachialis, 

 popliteus, triceps, psoas-iliac, gastrocnemii, quadriceps femoris, glu- 

 taei, &c. On all these surfaces the structures just mentioned are 

 attached directly to the bone, and not a trace of periosteum is found. 



Articular Cartilages. 



The articular cartilages cover the bones at their articular extre- 

 mities. They are closely applied to the bone with a rough, hol- 

 lowed, or raised surface, but are not united to it by any intermediate 

 substance. On its free surface, it is in most joints quite bare in the 

 adult; but covered in the foetus by a delicate epithelium like that 

 lining the vessels, as has been already asserted (p. 318). TliQfibro- 

 cartilages of circumference, so called (glenoid and cotyloid ligaments, 

 &c.), are firm, yellowish-white rings of white fibrous tissue, con- 

 taining a few isolated cartilage-cells, attached at the border of the 

 articular cartilage, by a wider base, immediately to the bone, or 

 partly also to the cartilage. They are generally free, and not co- 

 vered by the sy no vial membrane or any epithelium. Reichert 

 found fine desquamated flakes of cartilage in the synovia, which 

 fell readily into folds, and thus resembled a fibre-cartilaginous tissue. 



In its intimate structure, articular cartilage is peculiar only in the 

 fact that the cartilage-cavities near the free surface are small, nu- 

 merous, flattened, and parallel to it; while those in the deeper por- 

 tions next to the bone are elongated, and arranged perpendicularly 





