44 



STRUCTURE OF BONE. 



Fig. 11.' 



of vessels and nerves. They articulate with long bones by means of smooth 

 surfaces plated with cartilage, and with each other either by fibrous tissue, 

 as at the symphysis pubis ; or by suture, as in the bones of the skull. The 

 two condensed layers of the bones of the skull are named tables ; and the 

 intermediate cellular structure, diploe. The flat bones are the occipital, 

 parietal, frontal, nasal, lachrymal, vomer, sternum, scapula, and ossa 

 mnominata. 



The Irregular bones include all that remain after the long and the flat 

 bones have been selected. They are essentially irregular in their form, in 

 some parts flat, in others short and thick. In preceding editions of this 

 work the short and thick bones were made a separate class, under the 

 name of short bones. This subdivision has been found to be disadvan- 

 tageous, besides being arbitrary, and is, therefore, now omitted. Irregular 

 bones are constructed on the same general principles with other bones ; 

 they have an exterior dense, and an interior more or less cellular. The 

 bones of this class are, the temporal, sphenoid, ethmoid, superior maxil- 

 lary, inferior maxillary, palate, inferior turbinated, hyoid, vertebra, sacrum, 

 coccyx, carpal and tarsal bones, and sesamoid bones, including the patellae. 

 Structure of Bone. Bone is a dense, compact, and homogeneous sub- 

 stance (basis substance) filled with minute cells (corpuscles of Purkinje), 

 which are scattered numerously through its structure. The basis substance 

 of bone is subfibrous and obscurely lamellated, the lamellae being concentric 

 in long and parallel in flat bones; it is traversed in all directions, but es- 

 pecially in the longitudinal axis, by branching and inosculating canals 



(Haversian canals), which give 

 passage to vessels and nerves, 

 and in certain situations the la- 

 mellae separate from each other, 

 and leave between them areolar 

 spaces (cancelli) of various mag- 

 nitude. The lamellae have an 

 average diameter of g^oo f an 

 inch, and, besides constituting the 

 general structure of the basis sub- 

 stance, are collected concentrically 

 around the Haversian canals, and 

 form boundaries to those canals of 

 about 2 J(j of an inch in thickness. 

 The number of lamellae surround- 

 ing each Haversian canal is com- 

 monly ten or fifteen, and the di- 

 ameters of the canals have a me- 

 dia u average of g j-^ of an inch. The cancelli of bone, like its compact 

 substcjice, have walls which are composed of lamella? ; and, such is the 



* M : nute structure of bone, drawn with the microscope from nature, by Bagg. Mag- 

 rnfied 300 diameters. 1. One of the Haversian canals surrounded by its concentric 

 lamellfB. The corpuscles are seen between the lamellae; but the calcigerous tubuli are 

 omitted. 2. An Haversian canal with its concentric lamellae, Purkinjean corpuscle, 

 and tubuli. 3. The area of one of the canals. 4, 4. Direction of the lamella! of the 

 great medullary canal. Between the lamellae at the upper part of the figure, seveml 

 very long corpuscles with their tubuli are seen. In the lower part of the figure, the out- 

 lines of three other canals are given, in order to show their form and mode of arrange- 

 ment in the entire lone. 



