22 THE FRAMEWORK OF THE BODY 



(lakes). In each lacuna is a living cell, called a bone-corpuscle. 

 These bone-corpuscles feed on nourishment brought to them 

 through the canaliculi ; and deposit about themselves layers of 

 gelatin and phosphate of lime. These layers are called lamel- 

 lae, and make the matrix of the bone. These lamellae are well 

 shown in Fig. 3. 



7. Another element of power is found in the curved out- 

 line of the bones. The curved line is said to be "the line 

 of beauty/ 7 as it certainly is the line of strength. It is uni- 

 formly present in the bones whose position exposes them to 

 accident. The surface of all bones, except the articulating 

 surfaces at the ends, is covered by a tough membrane, called 

 periosteum. This is pierced by numerous openings through 

 which pass the blood-vessels which carry the blood to and into 

 the bones. 



8. The Skeleton. The bones in the human body number 

 two hundred and six, and when joined together in their proper 

 places, form what is termed the skeleton (Fig. 2). The 

 skeleton embraces three important cavities. The first of 

 these, surmounting the frame, is a box of bones, called the 

 skull; below this is a bony case, or "chest" ; and again below 

 this, separated only by a thin muscular membrane, called the 

 diaphragm, is the abdominal cavity, which ends at the lower 

 portion of the trunk in a bony basin called the pelvis. The 

 two latter cavities compose the trunk. The trunk and skull 

 are maintained in their proper relations by the " spinal 



The transverse section shows the compact, hard outer layer, enclosing 

 the soft pulp or marrow. 



The longitudinal section shows, at its upper end, the layer of cartilage, 

 its thickness and intimate connection with the bone ; the outer layer of 

 bone here is thinnest and gradually increases toward the middle of the 

 shaft, where it is thickest ; the central canal, containing the marrow, 

 becomes smaller as it approaches the head of the bone, where it is lost in 

 the dense network of bony structure. The latter is best demonstrated by 

 holding the cut surface for a while under a faucet, so as to wash away the 

 blood, etc., contained in the meshes. It will now be seen that these 

 meshes are composed of delicate, but strong, bony partitions, and 

 arranged in such angles to the outer wall and to themselves as will sup- 

 port the greatest weight. 



7. Bones, why curved ? 8. What constitutes the skeleton ? 



