THE SKELETON OF THE DOG. THE VERTEBRAE. 383 



also look more inwards, and the postzygapophyses more out- 

 wards than in the more typical thoracic vertebrae. 



THE LUMBAR VERTEBRAE. 



The lumbar vertebrae are seven in number, and their 

 general characteristics have been already described. As a 

 group they are characterised by their large size, and the great 

 development of the transverse processes, inetapophyses and 

 neural spines. 



THE SACRAL VERTEBRAE. 



Three vertebrae are commonly found fused together, forming 

 the sacrum ; the divisions between the three being indicated 

 by the foramina for the exit of the spinal nerves. 



Of these three vertebrae, the first is much the largest, 

 and is firmly united to the ilium on each side by a structure 

 formed by the transverse processes and expanded ribs. In the 

 adult this structure forms one continuous mass, but in the 

 young animal a ventral portion formed by the rib is clearly 

 distinguishable from a dorsal portion formed by the transverse 

 process. All three have low neural spines. The anterior 

 sacral vertebra bears a large pair of prezygapophyses, while 

 the posterior one bears a small pair of postzygapophyses. 



THE CAUDAL VERTEBRAE. 



The caudal vertebrae are about nineteen in number. 

 The earlier ones have well-developed neural arches, transverse 

 processes, and zygapophyses, but as the vertebrae are followed 

 back they gradually lose all their processes, and the neural arch 

 as well, becoming at about the thirteenth from the end reduced 

 to simple cylindrical centra. 



B. THE SKULL. 



The skull consists of the following three parts : (a) the 

 cranium, with which are included the skeletal sfpports of the 

 various special sense organs, and the bones of the face and 

 upper jaw ; (6) the lower jaw or mandible, which is movably 

 articulated to the cranium, and (c) the hyoid. 



