THE SKELETAL SYSTEM 209 



should include the entire thickness of bone with the attached scalp and dura 

 mater. Treat as in technic i, p. 202, except that the sections which are cut per- 

 pendicular to the surface of the bone should be stained with ha;matoxylin-picro- 

 acid-fuchsin (technic 3, p. 21) and mounted in balsam. 



(2) Developing Bone — Intracartilaginous and Subperiosteal. — Remove the 

 forearms and legs of a human or animal embryo by cutting through the elbow, 

 and knee-joints. (Foetal pigs from five to six inches long are very satisfactory.) 

 Treat as in technic (i). Block so that the two long bones will lie in such a plane 

 that both will be cut at the same time. Cut thin longitudinal sections through 

 the ossification centres, stain with haematoxyhn-picro-acid-fuchsin, and mount 

 in balsam. Cut away the ends of one or two of the embedded bones, leaving 

 only the ossification centres. Block so as to cut transverse sections through the 

 ossification centre. Stain and mount as the preceding. 



In the picro-acid-fuchsin stained sections of developing bone the cartilage is 

 stained blue; cells, including red blood cells, yellow; connective tissue from pale 

 pink to red, according to density; bone a deep red. 



The Cartilages 



The costal cartilages are hyaline. They are covered by a closely 

 adherent connective- tissue membrane, the perichondrium. Where 

 cartilage joins bone there is a firm union between the two tissues 

 and the perichondrium becomes continuous with the periosteum. 



The articular cartilages are described below under articulations. 



The other skeletal cartilages, such as those of the larynx, trachea, 

 bronchi, and of the organs of special sense, are more conveniently 

 considered with the organs in which they occur. 



Articulations 



Joints are immovable (synarthrosis) or movable (diarthrosis) . In 

 synarthrosis union may be cartilaginous (synchondrosis), or by means 

 of fibrous connective tissue (syndesmosis) . 



Synchondrosis. — The cartilage j.s usually of the fibrous form 

 except near the edge of the bone, where it is hyaline. The interver- 

 tebral discs consist of a ring of fibro-cartilage surrounding a central 

 gelatinous substance, the nucleus pulposus, the latter representing 

 the remains of the notochord. 



Syndesmosis. — Union is by means of ligaments. These may 

 consist wholly of fibrous tissue, the fibres and cells being arranged 

 much as in tendon, or mainly of coarse elastic fibres separated by 

 loose fibrous tissue. In such syndesmoses as the sutures of the cranial 

 bones, the union is by means of short fibrous ligaments between the 

 adjacent serrated edges. 



