280 SCIENCE OF AGRICULTURE. Taut II. 



Si i-siii. l. Osseous Structure of Animals* 



1881. The organs of external anatomy are generally considered as destined for pro- 

 tcction ; \\ bile those of i be interior of the animal, or the hones, give stability to the power, 

 support the muscles, and afford Levers for the performance of locomotion. Bones may be 

 consid sred with regard to their composition, articulations, and arrangement. All bones 

 are composed of the periosteum, cartilaginous basis, earthy matter, and fat. 



'. The periosteum bears the same relation to the bone as the skin to the body, 

 serving a a covering for its surface, and a sheath for the different cavities which enter it. 

 It varies in thickness according to the nature of the bone. Its texture is obviously 

 fibrous; and it possesses blood vessels. Its sensibility indicates the existence of nerves. 



1883. The cartilaginous basis consists of gelatine and coagulated albumen, the earthy 

 matter IS chiefly phosphate of lime, and the fat resembles that of the fixed oils. 



1884. Bones increase in sisse, not as in shells, scales, or horns, by the addition of layers 

 to the interna] surface, but by the expansion of the cartilaginous basis; which, when it 

 becomes saturated with earthy matter, is incapable of farther enlargement. This is the 

 reason why the bones of young animals are soft and flexible, while those of old animals 

 are hard and brittle. 



1SS.1. 'Hie proportion between the cartilaginous basis and the earthy matter differs, 

 not only in every animal according to age, the earthy matter being smallest in youth, 

 but, likewise, according to the nature of the bone itself, and the purposes which it is 

 destined to serve. The teeth contain the largest portion of earthy matter. Remarkable 

 differences are likewise observable, according to the class or species. 



1886. Bone is readily reproduced, in small quantities, especially in youth. In the case of fracture, the 

 periosteum inflames and swells, the crevice is filled up by a cartilaginous basis, abounding in vessels, and 

 the earthy matter is at length deposited, giving to the fractured part, in many cases, a greater degree of 

 strength than it originally possessed. In animals of the deer kind, the horns, which are true bone, 

 are annually cast off; a natural joint forming at their base, between them and the bones of the cranium, 

 With which they are connected. They are afterwards reproduced under a skin or periosteum, which the 

 animal rubs off when the new horns have attained their proper size. In some cases of disease, the earthy 

 matter is again absorbed into the system, the cartilaginous basis predominates, and the bones become soft 

 and tender. This takes place in the disease of youth termed rickets, and in a similar complaint of 

 advanced life, known under the name of ?>wlli/ies ussium. In other instances, bone is formed as a 

 monstrous production, in organs which do not produce it in a state of health, as the brain, the heart, and 

 the placenta. {Monro's Outlines of Anatomy, p. (13.) 



1887. Curtilage can scarcely be said to differ in its nature, from the cartilaginous 

 basis of the bone. It is of a fine fibrous structure, smooth on the surface, and re- 

 markably elastic. It covers those parts of bones which are exposed to friction, as the 

 joints, and is thickest at the point of greatest pressure. By its smoothness, it facilitates 

 the motion of the joints, and its elasticity prevents the bad effects of any violent con- 

 cussion. It is intimately united with the bone, and can scarcely be regarded as different 

 from an elongation of the cartilaginous basis. Where it occurs at a joint with consider- 

 able motion, it is termed articular or obducent cartilage. In other cases, it occurs as a 

 connecting medium between bones which have no articular surfaces, but where a variable 

 degree of motion is requisite. The ribs are united to the breast-bone in this manner. 

 Between the different vertebra', there are interposed layers of cartilage, by which the 

 motions of the spine are greatly facilitated. As these connecting cartilages are com- 

 pressible and elastic, the spine is shortened when the body remains long in a vertical 

 position, owing to the superincumbent pressure. Hence it is that the height of man is 

 always less in the evening than in the morning. All these cartilages are more or less 

 prone to ossification, in consequence of the deposition of earthy matter in the interstices. 

 To this circumstance may be referred, in a great measure, the stiffness of age, the 

 elasticity of the cartilages decreasing with the progress of ossification. 



1888. The articulations of bones exhibit such remarkable differences, in respect to 

 surface, connection, and motion, that anatomists have found it difficult to give to each 

 manner of union an appropriate name and character. We shall only notice the most 

 obvious kinds and motions, and these admit of two divisions, the true joints and the 

 motionless ju?ictions. 



1889. In the motionless junctions, the connecting surfaces come into close and per- 

 manent contact, as in the serrated edges of the bones of the human skull, or the even 

 edges of the bones of the heads of quadrupeds and birds. Sometimes a pit in one bone 

 receives the extremity of another like a wedge, as in the case of the human teeth; in other 

 cases, the one bone has a cavity with a protuberance at its centre, which receives another 

 bone, as in the claws of cats, seals, &c. The human ribs are united with the breast- 

 bone by the intervention of cartilage, as are the two sides of the lower jaw with each 

 other in vertebral animals. 



1890. In true joints the articular surfaces are enveloped with cartilage, remarkable 

 for the smoothness of its free surface, and its intimate union with the bone, of which 

 it form'; a protecting covering. The periosteum is not. continued over the surface of 

 the cartilage, but is prolonged like a sheath over the joint, until it joins that of the 



