282 ' SPECIAL HISTOLOGY. 



found to present, almost universally, excepting where muscles arise 

 directly from it, two layers, which, although closely connected, differ, 

 more or less distinctly, in their structure. The outer layer is composed 

 chiefly of connective tissue, with occasional fat-cells, and is the principal 

 seat of the true periosteal vessels and nerves, whilst in the inner layer, 

 elastic fibres, commonly of the finer sort, constitute continuous, and often, 

 very thick networks — true elastic membranes — superimposed one upon 

 another, the connective tissue forming the less important element. Nerves 

 and vessels occur in this layer also, but they do little more than merely 

 pass through it, being destined for the bone itself. 



The parts of the surface of bones unprovided with periosteum are : 

 1. The articular extremities covered with cartilage, and all other places 

 where the bone is covered with cartilage or fibro-cartilage. 2. Where 

 ligaments and tendons are attached to the borders and surfaces of bones 

 at a certain angle, as, for instance, at the insertions of the ligamenta 

 jiava, intervertebralia, iliosacra, interossea, teres ossis femoris, patellse 

 &c., of the tendons of the deltoid, coracobraehialis, popliteus, iliopsoas 

 triceps, surce, quadriceps femoris, glutcei, &c. In all these situations 

 the tendons, ligaments, and cartilages, are attached directly to the bone, 

 as has been already in part described, and not a trace of periosteum can 

 be detected. 



§ 93. Marrotv of tJie Bones. — Almost all the larger cavities in the 

 bones are occupied by a soft, trasparent, yellowish or reddish, highly 

 vascular substance, the 3Iarroio (medulla ossiuyn). In the cylindrical 

 bones, this substance is found in the medullary canal, and in the cancelli 

 of the apophyses, whilst it is wanting in the compact substance, unless it 

 be in the larger canals; the same is the case in ihe fiat and short bones, 

 the cancelli of which are filled with marrow ; but the diploe of the flat 

 cranial bones, besides the marrow, also contains large veins, of which 

 more will be said afterwards. In accordance with what has been re- 

 marked, these venous spaces, the canales nutritii, Haversian canals, and 

 the above described nerve-canals and air-cavities of the bones, contain 

 no marrow. 



The marrow appears in two forms, one yellow, the other red. The 

 former, as a semifluid substance, occurs principally in the long bones; 

 and according to Berzelius, consists, in the humerus of the Ox, of 96*0 

 fat, 1"0 connective tissue and vessels, and 3*0 fluid with extractive matter, 

 such as is found in muscle ; whilst the latter occurs in the apophyses, 

 flat and short bones, above all in the bodies of the vertebrae, the basis 

 cranii, the sternum, &c., and is distinguished not only by its reddish or 

 red colour and less consistence, but also by its chemical composition ; 

 for, according to Berzelius, this substance, in the diploe, contains 75*0 



