120 The American Naturalist, [February, 
sulcus, and even invisible in a part of its course, unless the sulcus 
be opened. In harmony with this the hippocampal lobule is 
relatively reduced, and remarkably flat. The auditory nerve is 
enormous, and with this the therewith connected trapezium, 
lemmiscus lateralis, posterior pair of the corpora quadrigemina 
and internal geniculate bodies are overgrown. There is a micro- 
scopically visible fluted tract on the caudal aspect of the thala- 
mus running ectad from the latter bodies to the auditory cortical 
field of the hemisphere. It is the enormous hypertrophy of this 
field which crowds the Sylvian into its unusual vertical, nay, 
actually anticlinal, position.” 
One of the most interesting proofs of the value of neuro-mor- 
phology in classification is offered by a comparison of the brains 
and spinal cords of the Cetacea,”? Sirenia,“ and Phocide. The 
phocidan brain is, as above stated, a physiologically aberrant, 
but morphologically genuine carnivore brain. The manatee has 
the brain of a hippopotamus. The Cetacea, in accordance with 
their to-day isolated position, have the most aberrant central 
nervous system of all, but to no other brain do they approach so 
nearly as to that of the Proboscidia, a group which, with the 
possible inclusion of other extinct and recent related forms, ap- 
proaches more nearly the common ancestral trunk from which so 
widely divergent branches have sprung.” Zoological characters 
12 In reality the position of this fissure is dependent on two factors: the lower, corre- 
sponding to the cephalic part of the human, has sunk ventr Aypa through the retro- 
gression of the sphenoidal lobe, and the upper (posterior part of the human) has been 
driven dorso-cephalal by the c ov iat ek auditory Sarion pne "The ERE pae sel 

g 
brain into a foreshortened skull model. ‘Thus the frontal lobe will sais to resemble the 
square and compact contour of the seal’s brain. That such a mechanical process 
been undergone by the latter is demonstrated by the evident violence to ree the 
olfactory tracts and lobes have been subjected. In no other carnivores are the bulbs so 
far cephalad and the tracts bodily driven into the cota of the sulcus rectus. 
13 A decayed Beluga’s brain, and a Phoczena Y. Aquarium, two beautifuy 
ones of Tursiops tursio and one of Delphinus eee as Mr. Eugene Blackford, 
of this city. To Professor Wm. F. True, of the Smithsonian, I am indebted for aid in 
determining the species. 
14 The brain axis and cord of Professor Wilder's specimen, loaned by him. 
15 In stating this I am not misled by the superficial characters, such as the richness in 
gyri, or in fact any quantitative features. I am determined by the ¢yfe of gyral develop- 
ment, the type of cerebellar foliation, and the character of the olive, which is of the 


