1881.] Origin and Déscent of the Human Brain. 517 
which shows at once the folly of attaching psychological impor- 
tance to the number and intricacy of folds in animal brains. With 
phrenology, which finds bibativeness in the mastoid process of the 
temporal bone and amativeness in the occipital ridge, the convolu- 
tional controversies must die out, as has the old.so-called science 
of palmistry, which read one’s fate and fortune in the skin-folds 
of the hand. 
The most noticeable change in form, as we pass up the scale of 
mammalian life, occurs in the production of the fissure of Sylvius. 
In most quadrupeds the olfactory lobe fills up largely the anterior 
part of the cranium. As the smelling sense diminishes this lobe 
degenerates to a mere tract and the frontal lobe of the brain in- 
creases in size, lifting the forehead into a vertical plane. The 
medulla is pushed forward to a less oblique angle with the front 
of the brain, from Lemuridz to chimpanzee and man, and the frontal 
lobe pressure covers the cerebellum with the backward progress of 
occipital, till finally the occipital forms the temporal by curling 
under and forwards, forming the Sylvian fissure. These stages of 
Progress are evident in the horse, elephant and human embryo. 
Often, in idiots, we find through want of development of this 
frontal lobe, that ossification takes place in a plane inclined at an 
angle corresponding with that of lower animals, and the cerebel- 
lum is uncovered. This is an adaptation of the skull to its con- 
tents, which, however, does not always take place. There are 
other elements at work to cause the skull to develop normally or 
€ven enlarge it abnormally, as for example, an accumulation of 
water in the ventricles will change the relative positions of the 
cranial bones to such an extent as to give to the hydrocephalic 
idiot the “ front of Jove.” 
_ While the ontogenetic stages of development resemble strik- 
ingly the forms mentioned by Haeckel, the nervous system is not 
apparent in the embryo until we reach the ninth stage or Acranial, 
after this the cerebral vesicles rapidly develop and resemble in 
eneral the Cyclostome stage, and just as the sharks and mud 
fishes possess the intervertebral ganglia, which the hags and lam- 
Preys have not, the human fcetus, subsequent to the shaping of the 
cerebral vesicles, develops the posterior spinal nerve root swellings. 
From this point upward, it is easy enough to observe, that like the 
brains of ‘Marsupial adults, the cerebellum is at first uncovered, 
then by frontal lobe growth the temporal lobe is formed as in 
Simiadz, | 
