The locomotor apparatus and the bones
 The locomotor apparatus defines in the body the spaces used to contain organs and viscera and, at the same time, it gives a characteristic aspect to the organism.
It is made up of bones, joints and muscles. It is extremely vascularized, therefore it requires a great deal of metabolic energy.
The bones
The bones have various shapes and volumes and they are all equipped with a solid mechanical resistance. Their structure is suitable to host the muscular insertions designated for the transmission of movement, therefore each bone is shaped according to the mechanical needs it must meet.
The bones are a deposit for mineral salts (mainly calcium), and can be divided, by virtue of their shape and location, into:
Long bones, found in the arms and legs, are longer than they are wide and have a central body, basically a cylindrical shape (diaphysis) and two ends that are shorter, thicker and more robust (epiphyses);
Flat bones include the skull bones and the ribs, they consist of thin plates of compact bone containing a central spongy body;
Short bones, a typical example of which are the bones in the carpal and tarsal structures, are made up of a spongy matrix covered by a sheet of compact bone;
Irregular bones may have any number of shapes and therefore do not belong to any of the aforementioned groups. An example is the vertebral column (the vertebrae) and the numerous skull bones. Their constitution is similar to that of short bones.
Bones have a series of characterizing elements, in particular defined projections or prominent bumps, according to their size: processes, tuberosities, tubercles and spines; but also impressions and concavities more or less emphasized, which are called: sulcum and fossa.
The functional role of projections is to provide points of attachment for skeletal muscles, the role of bone impressions is almost always to receive the muscular bulge (the fleshy part of the muscle) or the vascular-nervous branches that nourish and control.
All the bones appear to be covered by a fibrous membrane called periosteum with the function of adding bone during growth or repair phases. The periosteum is extremely vascularized, with vessels reaching deep into the bone below.
On a diasphyseal level we can find the medullary canal inside the bone covered by endosteum.
Bone growth is initially regulated by genetic factors and is then modulated by hormonal elements. Apart from parathormone and calcitonin, sexual hormones and SHT stimulate activity and ossification of the connective cartilage. Naturally the role of vitamin D is essential, a lack of which can cause episodes of rachitism, and vitamins C and E and minerals such as phosphorous and calcium are also important.
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