ANATOMICAL STRUCTURE OP THE SHEEP. 107 



so long; it corresponds to the lower ann bone or radius of the 

 fore extremities, and its inferior part forms with the bones im- 

 mediately underneath the hock joint. 



The hock joint is composed of six bones arranged in layers, 

 forming three distinct joints, the motion being confined to the 

 upper layer the bones below, serving as buffers to minimize con- 

 cussion, with the exception of the bone projecting upwards from 

 the back of the joint, which is called the calcis, and acts as a 

 lever for the powerfvil extensor muscles of the hind leg. 



The bones below the hock correspond with those below the 

 knee joint in the fore extremity, and the description of them 

 also applies to these. 



■Cbc Nervous and Muscular System. 



The brain is a softish grey body, situated in the cranial 

 cavity. It is the seat of the mind and sensation. Its size in the 

 sheep as compared with man is small. The outer surface is 

 covered 'with ridges, called convolutions, with a dividing furrow 

 from before backwards, separating it into two halves called the 

 right and left hemispheres. The anterior larger part of the 

 hrain is called the cerebrum, the middle and small part the cere- 

 bellum, while the underlying posterior portion is called the 

 medulla oblongata. Between the brain substance proper and 

 the bones forming the cranial cavity we find a strong dense 

 membrane closely attached to the bony structure, called the 

 dura mater, immediately underlying which and attached to the 

 brain substance, is another called the pia-mater, the space be- 

 tween these two membranes being called the arachnoid space. 

 The spinal cord is virtually a continuation of the brain extend- 

 ing from the medulla oblongata through the vertebrae and 

 terminating in the sacrum at the root of the tail. It is envel- 

 oped by the same membranes disposed in the same manner as 



