392 THE ANATOMY OF THE HORSE 



bone in a peculiar manner, to be presently described. Lastly, an elastic 

 fibrous tissue (yellow) is met with in certain situations, the most remarkable 

 being the great ligament of the neck. Each of these different structures 

 will require a separate description ; for as the diseases of the joints are of 

 great importance, a knowledge of the structure of their component parts 

 must be carefully obtained before entering upon the treatment with any 

 hope of success. 



CARTILAGE 



True cartilage (which is familiarly known to all when it shows the 

 large white masses in a breast of veal, as dressed for the table) is a homo- 

 geneous, white, semi-transparent substance, possessing a certain amount of 

 elasticity, and easily cut with a knife. In the early embryo it exists as the 

 sole foundation of the skeleton, bone being afterwards deposited in its 

 meshes and finally substituted for it. This is called the temporary cartilage. 

 In after life it invests those parts of the bones which enter into the com- 

 position of the joints (articular cartilage, which is what we are considering 

 just now), and also forms the costal cartilages, the ensiform and cariniform 

 cartilages, and those of the larynx, trachea, and nose. Reticular or 

 memhraniform cartilage, diffei'ing slightly from true cartilage, is met with in 

 the Eustachean tube, the external ear, and the epiglottis. 



Structure. — On putting a slice of true cartilage under the microscope, it 

 is seen to consist of a number of minute cells disseminated through a 

 vitreous substance. The cells are oval, oblong, or polyhedral in shape, and 

 more or less flattened by packing. The membrane forming the cell- wall is • 

 usually blended with the matrix, but sometimes consists of concentric layers. 

 White fibres usually enclose the mass of cells, and even dip sometimes into 

 those cells more superficially placed. The cells or corpuscles are contained 

 in hollow cavities, called lacunae. Sometimes they do not entirely fill up the 

 lacunte, so that a vacant space is left. The corpuscles are usually dispersed 

 in groups, A^arjdng in size and form, through the matrix ; the groups towards 

 the surface of the cartilage are generally flattened conformably with the 

 surface. In articular cartilage, the matrix in a thin section appears dim 

 and presents a granular aspect, the cells and nuclei of which are small. 

 The parent-cells enclose two or three younger cells. The groups they form 

 are flattened near the surface and lie parallel with it. In the internal part 

 of this cartilage the cells assume a linear direction, and point towards the 

 surface. Near its attached surface cartilage blends with the bone, the cells 

 and nuclei of which become surrounded by little granular bodies, which 

 seem to be the rudimentary deposit of bone. In costal cartilage the cells 

 are very large ; they contain two or more nuclei, which arc clear and 

 transparent, and some contain a few oil globules. The cells, internally 

 situated, form oblong groups, disposed in lines radiating to the cii'- 

 cumference. We observe a great quantity of intercellular tissue, in the 

 form of white fibrous structure, the fibres of which are parallel and 

 straight. 



Perichondrium ("Trept, around, and xovhpos, cartilage}) is a white fibrous 

 Bubstance, which covers the external surface of all cartilages, except those 



