2,2 2 VERTEBRATE ZOOLOGY 



The sacral vertebrae in the adult form a single bone called the sa- 

 crum ; the two innominate bones which form the pelvis are closely 

 joined with it. Note the intervertebral foramina in each side of it. 



The caudal vertebrae gradually become smaller toward the 

 hinder end of the tail, the terminal ones consisting of centra only. 

 Note the loss of parts of the vertebrae toward the hinder end. 



Exercise 43. Draw the following views of the cervical vertebrae : the 

 anterior end of the atlas, the lateral aspect of the axis, and the an- 

 terior end of the sixth vertebra, all on a scale of 2. 



Exercise 44. Draw the anterior end of the fourth thoracic vertebra ; 

 also the lateral aspect. 



Exercise 45. Draw the anterior end and also the lateral aspect of the 

 fourth lumbar vertebra. 



Exercise 46. Draw the ventral surface of the sacrum. 



Exercise 47. Draw a ventral view of the second caudal vertebra ; also 

 one of the last caudal vertebrae. 



The Skull. The skull is made up of two portions, the cranium 

 and the visceral portion. The former protects the brain and the 

 organs of special sense; the latter forms the framework of the 

 greater part of the face, the jaws, and the tongue. 



Observe the general character of the skull. Note the sutures by 

 which the bones are joined with one another ; they are growing- 

 surfaces, and in an old animal tend to become obliterated by the 

 fusion of the bones. The teeth, although they are integumentary 

 structures, are sunk into deep depressions in the bones of the jaws 

 and are so firmly joined with them that a very solid biting-surface 

 is formed. 



On the side of the skull is the large orbit, in which the eyeball 

 and its muscles, glands, and other accessory organs are contained ; 

 the prominent ridge over it is the supra-orbital ridge. The orbit 

 is not complete, as in man, but is open behind. The lower boundary 

 of the orbit is formed by a prominent bony arch, the zygomatic 

 arch. Just back of the orbit and the hinder end of the zygomatic 

 arch is a narrow groove, the temporal fossa, which is very small in 

 the rabbit ; it is the surface of attachment of the temporal muscle, 

 which helps to close the mouth. 



