HOW THE ANIMAL BODY IS FORMED I5 



vertebrae and the sacrum. The number is five in the 

 horse, six in the hog, ox and goat, and seven in the 

 sheep. The sacrum is made up of a certain num- 

 ber of vertebrae, which are rigidly united and 

 serve as an articulation for the pelvic arch. The 

 number of sacral vertebrae is five in the ox and 

 horse, four in sheep and hogs, and 12 to 17 in birds. 

 The caudal or tail vertebras naturally vary in num- 

 ber according to the length of the tail (7 to 10 in 

 sheep, 21 in the ox, 23 in hogs, 17 in the horse, 22 

 in the cat, 16 to 23 in the dog). 



In ungulates the anterior ribs are scar'cely curved, 

 the chest being very narrow in front. The number 

 of pairs of ribs is the same as the number of dorsal 

 vertebras with which they articulate. 



The Skull. — This part of the skeleton is really 

 composed of a number of modified vertebrae, just 

 how many is not determined. The diflference in the 

 shape of the skulls of dffiferenl animals is deter- 

 mined by the relative size of the various bones of 

 the skull. In hogs, for example, the head has been 

 much shortened as a result of breeding, thus giving 

 the skull of the improved breeds a very different 

 appearance from that of the razorback. 



The shoulder girdle consists of a shoulder blade, 

 collar bone and coracoid on either side. The fore 

 leg (or wing, in case of birds) articulates with the 

 socket formed by the junction of these three bones. 

 In all the ungulates the shoulder blade is high and 

 narrow, the coracoid is never much developed, and 

 the collar bone is absent. In fowls all three bones 

 of the shoulder girdle are well developed, the collar 

 bone being represented by the " wish bone." 



The Pelvic Girdle. — This consists of three bones 

 on either side, viz., ilium, ischium, and pubis. The 

 first two are directly articulated to the spinal 



