462 GENERAL AXATOMY. 



The pituitary gland exists in all animals. It is very larirc 

 compared with the encephalon in all the inferior classes. The 

 pineal gland appears to he wanting in the class of fishes. 



The olfactory lobes terminate the encephalon anteriorly. 

 According to M. Desmoulins they form what is called the 

 brain in the cartilaginous fishes. They equal the brain in size 

 in many osseous fishes and reptiles. They are very small in 

 birds, greatly developed and hollow in many mammifera, and 

 rudimentary in the human species. 



The principal differences which the nervous centre presents 

 in man, are, therefore, the volume of the cerebellum and ce- 

 rebrum, compared with the spinal marrow, the tubercles and 

 the olfactory lobes; the size of the lateral lobes of the cere- 

 bellum compared with the middle lobe; that of the cerebial 

 hemispheres, and their posterior prolongation; the existence 

 of its posterior lobe and its appendages; the thickness of the 

 nervous membrane which forms the hemispheres, the size of 

 its central medullary mass, the number and depth of its sulci, 

 the number and thickness of its convolution, whence results a 

 greater extent of its surface; and, lastly, the extent of the cor- 

 pus callosum. 



740. The ancients, commencing with Galen, and many 

 moderns, have regarded the nervous system as having a single 

 centre in the encephalon, and prolongations (the spinal mar- 

 row and nerves.) It has already been seen that G. Bartholin 

 transferred the nervous centre to the spinal marrow, which he 

 did from the consideration that fishes have a very large spinal 

 marrow, and a very small encephalon, and yet that these ani- 

 mals possess a great power of motion. Bichat, developing 

 some ideas that had been vaguely advanced before him, re- 

 specting the action of the ganglia, proposed two distinct nerv- 

 ous centres, the one (the cerebral, or encephalic and spinal) 

 subservient to the sensations accompanied with consciousness, 

 intellect, and voluntary motion; the other (the ganglionary) 

 subservient to the functions which are performed without con- 

 sciousness and volition. In this latter he at the same time 

 placed the seat of the passions. M. Cuvier considers the 

 nervous system as a vast net-work embracing the whole ani- 



