178 



VETERINARY PHYSIOLOGY 



btk. Developmental Methods. — Flechsig has found that 

 bands of fibres going to certain parts of the cortex get their 

 medullary sheaths earlier than others, and that the fibres to 

 each part of the cortex become medullated at a definite date. 

 The areas, the fibres of which get their sheaths first, he calls 

 the primary projection areas, and they correspond very 

 closely with the receiving areas determined by other methods 

 (figs. 51 and 52). 



Qth. Comparative Anatomy. — The complexity of different 



BODY SENSE: 



AUDITORY 



OLFACTORY 



Wffi SENSES 

 AUDITORY 

 ■OLFACTORY ^ 



*j|KVISUAL 



Fig. 89. — A purely Schematic Diagram to show the relations of receiving, 

 associating, and discharging parts of the cortex cerebri, and to illus- 

 trate that each of these is in itself receiving, associating, and dis- 

 charging. The mechanism of reaction to visual impressions is given, 

 and the modifying influence of other incoming stimuli is indicated. 



parts of the cortex is very different in different animals, and 

 this affords some indication of the probable function of the 

 various parts. Thus, the sub-granular layers are first 

 developed and are best marked in the lowest mammals, and 

 it may be concluded that they have specially to do with 

 simple instinctive activities. The granular layer is best 

 developed in what other evidence indicates to be receiving 

 areas. The supra-granular layers are the last to develop and 

 attain their greatest thickness in the higher mammals, 

 especially in the frontal part of the brain, the development 



