54 



GENERAL ANATOMY. 



elastic fibres, branching and anastomosing in all directions (Fig. 25). The fibres 

 resemble those of yellow elastic tissue, both in appearance and in being unaffected 

 by acetic acid ; and according to Rollett their continuity with the elastic fibres 

 of the neighboring tissue admits of being demonstrated. 



The distinguishing feature 

 of cartilage as to its chemical 

 composition is that it yields 

 on boiling a substance called 

 chondrin, very similar to 

 gelatin, but differing from it 

 in not being precipitated by 

 tannin. According to Kiihne 

 there is a small amount of 

 gelatin in hyaline cartilage. 

 Virchow believes that the 

 semilunar disks in the knee- 

 joint are wrongly denomi- 

 nated cartilages, since they 

 yield no chondrin on boil- 

 ing; and he appears to re- 

 gard them as a modification 

 with the cartilages in the 



FIG. 25. Yellow cartilage, ear of horse. High power. 



agrees 



of a tendinous structure, which, however, 

 important particular of being non-vascular. 



Temporary cartilage and the process of its ossification will be described with 

 Bone. 



/ BONE. 



Structure and Physical Properties of Bone. Bone is one of the hardest struc- 

 tures of the animal body ; it possesses also a certain degree of toughness and 

 elasticity. Its color, in a fresh state, is of a pinkish white externally, and deep 

 red within. On examining a section of any bone, it is seen to be composed of two 

 kinds of tissue, one of which is dense and compact in texture, like ivory ; the 

 other consists of slender fibres and lamellae, which join to form a reticular struc- 

 ture ; this, from its resemblance to lattice- work, is called cancellous. The com- 

 pact tissue is always placed on the exterior of the bone ; the cancellous is always 

 internal. The relative quantity of these two kinds of tissue varies in different 

 bones, and in different parts of the same bone, as strength or lightness is requisite. 

 Close examination of the compact tissue shows it to be extremely porous, so that 

 the difference in structure between it and the cancellous tissue depends merely 

 upon the different amount of solid matter, and the size and number of spaces in 

 each ; the cavities being small in the compact tissue and the solid matter between 

 them abundant, whilst in the cancellous tissue the spaces are large and the solid 

 matter in smaller quantity. 



Bone during life is permeated by vessels and is enclosed in a fibrous membrane, 

 the periosteum, by means of which many of these vessels reach the hard tissue. 

 If the periosteum is stripped from the surface of the living bone, small bleeding 

 points are seen, which mark the entrance of the periosteal vessels ; and on section 

 during life every part of the bone will be seen to exude blood from the minute 

 vessels which ramify in it. The interior of the bones of the limbs presents a 

 cylindrical cavity filled with marrow and lined by a highly vascular areolar 

 structure, called the medullary membrane or internal periosteum, which, how- 

 ever, is rather the areolar envelope of the cells of the marrow than a definite 

 membrane. 



The periosteum adheres to the surface of the bones in nearly every part, 

 excepting at their cartilaginous extremities. Where strong tendons or ligaments 



