THE SKELETON. 9 



The skeleton is divided into trunk and limbs. 



1. The trunk offers for consideration, in the middle line, the spine or 

 vertebral column — a flexible stalk measuring the entire length of the animal, and 

 composed of a series of distinct pieces articulated one behind the other. An- 

 teriorly, this stalk supports the head — a pyramidal mass which results from the 

 assemblage of a large number of bones. On each side of the middle portion of 



Fig. 3. 



SKELETON OF THE PIG. 



I 



the spine, there are detached bony arches which have received the name of ribs, 

 and which rest, directly or indirectly, by their inferior extremities, on a single 

 bone called the sternum. These bony arches in this way circumscribe the thorax — 

 a spacious cavity destined for the reception of the principal organs of respiration 

 and circulation. 



2. The limbs, four in number — two anterior and two posterior — are the ap- 



Fig. 4. 



SKELETON OF THE RABBIT. 



pendages which support the trunk of the domestic Mammals. They are usually 

 distinguished as anterior and posterior (or fore and hind), but it will be more 

 convenient to name them according to their relations, as thoracic (or pectoral) and 

 abdominal limbs. Each represents a column divided into several rays resting upon 

 one another, and generally forming more or less open angles. The anterior limbs 



