THE CAT 265 



ber of caudal vertebrae near the forward end of the tail bear 

 each a pair of short ventral processes called the haemal proc- 

 esses ; the space between the two members of each pair is closed 

 by a small median chevron bone and contains the caudal artery 

 and vein. 



Exercise 52. Draw the following views: the anterior end of the atlas, 



the lateral aspect of the axis, and the anterior end of the sixth 



cervical vertebra, on a scale of 2 or 3. 

 Exercise 53. Draw the anterior end of the fourth thoracic vertebra ; 



also the lateral aspect. 

 Exercise 54. Draw the anterior end and also the lateral aspect of 



the fourth lumbar vertebra. 



Exercise 55. Draw the ventral surface of the sacrum. 



Exercise 56. Draw a ventral view of the fourth caudal vertebra ; also 

 one of the last caudal vertebra. 



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

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

 organs of special sense, and 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 the 

 growing-surfaces, and in an old animal tend to become obliterated 

 by the fusion of the bones. Of the animals studied in this course, 

 only the turtle has such a compact and strongly built skull. 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 each side of the skull is the large orbit, in which the eye- 

 ball and its muscles, glands, and other accessory organs are con- 

 tained ; the prominent ridge over it is the supra-orbital ridge. The 

 orbit is not complete, as in man, but is open behind. Just behind 

 it and communicating with it is a depressed area called the tem- 

 poral fossa. The prominent arch on the side of the skull, forming 

 the lateral boundary of the orbit and the temporal fossa, is the 

 zygomatic arch. The large temporal muscle, which helps to close 

 the mouth, arises on the surface of the temporal fossa. 



