. The cat; an introduction to the study of backboned animals, especially mammals. Cats; Anatomy, Comparative. 20 THE CAT. [chap. II. adjacent lacunfe unite, and thus fluid can traverse every part of the bone. The Haversian canals grow larger as they proceed inwards (in such a hone as that of the thigh,) and open into still larger channels and yet wider interspaces which are called cancelli, ultimately merging into a hollow central part called the mechillari/ cnritij of the hone because it contains that deHcate fibrous tissue and fat which constitutes marrow, as already mentioned. Some bones ha
. The cat; an introduction to the study of backboned animals, especially mammals. Cats; Anatomy, Comparative. 20 THE CAT. [chap. II. adjacent lacunfe unite, and thus fluid can traverse every part of the bone. The Haversian canals grow larger as they proceed inwards (in such a hone as that of the thigh,) and open into still larger channels and yet wider interspaces which are called cancelli, ultimately merging into a hollow central part called the mechillari/ cnritij of the hone because it contains that deHcate fibrous tissue and fat which constitutes marrow, as already mentioned. Some bones have their entire substance replete with cavities or cancelli, and such are called cancclMed or spongy. § 6. Ossification may take place either through pre-existing carti- lage or through membrane, and in either case blood-vessels advance into the pre-existing ma- te ^^-^ he terial, and therewith that material is absorbed and disappears around them and is replaced by calcareous substance. The lacunoe are inter- spaces which have been left uncalcified owing to the presence there of certain cells. These cells have sent out radiating processes (like some of the connective-tissue colls, as already noticed,) which have also escaped the general calcification of the intercellular substance, and thus the canaliculi have been produced. Thus contents of the lacunae are truly bone-cells or corpuscles. Bone tissue therefore is, except as to its calcareous nature, very like connec- tive tissue and cartilage. The bony substance answers to the matrix of these other tissues, and the "bone cells" to their corpuscles. When the earthy matter of bone is dissolved their original cellular contents may often be detected. When a bone ossifies from cartilage, as all thick bones do, the deposit begins in the form of opaque granules of calcareous matter, which Fig. 6.—Vertical Section of surround and somctimes iuvade the cartilage Cat's Thigh-bone (Femur), capsulcs and form a dcuso and irrcgul
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