174 VERTEBRATES. 



5. That portion of the brain below and behind the 

 cerebellum is the medulla. It tapers posteriorly into the 

 spinal cord. 



Preserve this brain for comparison with that of other 

 animals yet to be studied. 



Muscles of Body Wall. Make a longitudinal cut close 

 beside the dorsal fins, and down to the spinal column. 

 Extend this incision backward to the caudal fin, and for- 

 ward to the pectoral arch. Remove the great flap of flesh 

 thus partly freed from one side, dissecting it away from 

 the ribs and from the inferior projections of the vertebrae 

 posterior to the ribs. Observe the arrangement of the 

 white bands of muscles, of which it is principally com- 

 posed. 



Separate two of the vertebrse, and find the spinal cord 

 extending longitudinally through them. 



Plan of Structure. Consider well the arrangement of 

 parts as you have found them in the fish. Here i" a new 

 plan of structure. The hard parts (bones) are inside, 

 and the muscles are attached to prominences on their 

 exterior. What general arrangement of skeleton and 

 muscles have you found in the other animals studied? 



The central parts of the nervous system are inclosed 

 within a bony canal which extends along the dorsal side 

 of the body. The anterior end of this canal is expanded 

 into the wide cranium; the remainder of this tube is the 

 neural canal, which extends backward through the verte- 

 brse. The part of the nerve center occupying the cranium 

 is called the brain ; the part occupying the neural canal 

 is called the spinal cord. There are apertures throughout 

 the length of this bony tube for the passage of nerves 

 outward through its walls to all parts of the body. 



Ventral to this tube of bone, which holds and protects 



