848 COMPARATIVE ANATOMY 



Figure 474 shows the five ways in which impulses are and may be 

 distributed. 



Ganglia are those centers similar to brain nuclei which lie outside 

 the brain, although some books still use this term interchangeably with 

 brain nuclei. 



Brain stem (also called segmental apparatus, because it is supposed 

 that the primitive type of brain consisted of a mere tube of nerve-cells 

 with which the peripheral nerves were connected, a pair from each seg- 

 ment, similar to the spinal cord of the higher forms now), is that portion 

 of the cephalic end of the central nervous system upon which the enor- 

 mous cerebral and cerebellar hemispheres develop in all higher forms. 

 These latter are then called the suprasegmental apparatus. 



Cerebrum consists of fore-brain and mid-brain, the most cephalic 

 part of which develops into the cerebral hemispheres which are again 

 divided as seen in the table. 



The pallium in the highest animal forms is the cerebral cortex or 

 mantle (Fig. 472), but in the lower forms such as the fish, in which the 

 entire hemispheres are a part of its olfactory apparatus, the pallium con- 

 sists of this olfactory apparatus and the two tracts of nervous matter 

 connecting the olfactory lobe with the hinder portion of the cerebrum. 

 One of these tracts, the hippocampus, passes dorsal, and the other, the 

 olfactory tract, passes ventral to the foramen of Monro. They lie on the 

 medial side of each hemisphere. 



Archipallium is the word now used to a considerable extent for the 

 pallium in the lower vertebrates where this mantle is concerned prac- 

 tically only with the olfactory apparatus. 



Neopallium has therefore come into existence as a term to designate 

 the pallium of the vertebrates whose brain is not governed entirely by 

 its olfactory apparatus, but where impulses from the general somatic 

 senses may be adjusted and be redistributed in a great correlation region 

 the cerebral cortex. In the table the pallium corresponds to this neo- 

 pallium which has grown out lateral to the hippocampus. 



Rhmencephalon (nose-brain), the entire olfactory apparatus divides 

 into peripheral and central regions as in the table. 



Corpus Striatum (Figs. 472, 473). This is the name given to the 

 entire mass of large nerve cells which connect the brain-stem with the 

 cerebral hemispheres. It is also called the basal ganglion. It will be 

 noted that the corpus striatum thus forms the main portion of the stem 

 of the end brain. It is called striated because it consists of masses of 

 gray matter separated by sheets of white matter, thus making it appear 

 striated. 



In the lower forms of vertebrates (Fig. 473) some have this body 

 fairly well developed even though there be no cortex, while in reptiles 

 and birds in which there is a small amount of cortex it is quite highly 



