42 ANIMAL PHYSIOLOGY. 



Plates of matted fasciculi of fibrous tissue, with elements 

 of cartilage sometimes interspersed, occur in various positions, 

 but particularly as movable discs between the articular sur- 

 faces of certain joints, such as the knee, and combine the 

 elastic resistance of cartilage with toughness which endures 

 the action of rubbing, and are named jibro-cartilages. 



22. Bone is a more complex tissue than cartilage; its 

 complexity depending 011 the impermeability of its matrix to 

 fluids, and the consequent necessity of canals for nutrition. 

 The matrix consists two-thirds of mineral matter, principally 

 phosphate of lime with some carbonate of lime, and the 

 remaining third of animal matter; the two being so intimately 

 blended that they form a homogeneous mass, translucent in 

 thin sections. When the animal matter is removed by cal- 

 cination the form of the bone still remains ; and when the 

 mineral matter has been gradually dissolved by dilute hydro- 

 chloric acid, the animal matter retains the same bulk and 

 microscopic structure as before, presenting the consist- 

 ence and flexibility of cartilage, but yielding gelatin by 

 boiling. 



The only microscopic structures common to all bone are the 

 bone-corpuscles, which are nucleated corpuscles characterized 

 by a multitude of fine processes, and are imbedded in hollows 

 of corresponding shape and size, called lacunce; while their 

 processes occupy exceedingly fine canaliculi, which radiate 

 from the lacunae, those of one lacuna inosculating with those 

 of others, so that fluids may be conveyed from one lacuna to 

 another. 



Bony tissue is found, however, in two different forms, the 

 cancellated and the compact. Cancellated or spongy tissue, 

 such as one finds in the bodies of the vertebrae, the tarsal 

 bones, and the ends of long bones, consists of minute spicules 

 and occasional laminae of bone with the spaces or meshes 

 between them filled with fine connective tissue, copiously 

 supplied with blood-vessels, and loaded more or less with 

 adipose matter. Compact or solid bony tissue, such as is 

 found in the shafts of the long bones, is traversed by blood- 

 vessels, and presents a remarkable microscopic arrangement 

 connected therewith. The passages for the blood-vessels, 

 named Haversian canals, after Havers, who first mentioned 



