THE NERVOUS SYSTEM 127 
cord at that region, I am inclined to think that some connection 
exists between the latter and the coccygeal gland. This gland 
is undeniably a vestigial organ, but we have as yet no certain 
knowledge of either its significance or its primitive history. 
BRAIN 
The human brain, in the course of its development, passes 
in regular order through conditions characteristic of certain of 
the lower Vertebrata (ex. disposition of the cerebral vesicles, 
smooth surface of the hemispheres), and these lower con- 
ditions are in rare cases retained, as in many microcephalous 
individuals, as the probable result of arrested development. 
There are not infrequent deviations from the normal arrangement 
of the cerebral furrows and convolutions, which are closely con- 
nected with the development of the gray matter. These 
deviations can be best studied by the aid of Comparative 
Anatomy and Ontogeny, and the same may be said of the 
posterior cornu of the lateral ventricle, the calcar avis, and 
the eminentia collateralis Meckelii. Conspicuous among variable 
cerebral furrows we note the parieto-occipital fissure (/po., Fig. 78), 
which is occasionally very pronounced. This fissure runs out 
laterally, and may probably be a reversion to the pithecoid type 
(it is called in German the “ Affenspalte”). In its normal 
condition it seems almost to be vanishing, as compared with its 
supposed homologue in the brain of the Ape.’ 
In spite of difference in detail, there is a closer general 
resemblance between the human and the Anthropoid brains than 
between the brains of any other two Vertebrate groups. 
With regard to the weight of the brain in Anthropoids 
generally, the material as yet examined is not sufficient for the 
determination of averages and formulation of general conclusions. 
With the Chimpanzee, however, this is not the case, as a rela- 
1 [The term parieto-occipital fissure insufficiently defines this supposed homologue 
of the ‘‘ Affenspalte.”” Cunningham in a recent elaborate treatise (Cunningham 
Memoirs, vii. Rk. Irish Acad., 1892) has devoted much attention to this topic. He 
and other leading authorities are agreed that, whether the ‘‘ Affenspalte” of the Ape 
is present in the human adult or not, the ‘‘fissura perpendicularis externa” of the 
foetus is its homologue. During the passage of these pages through the press, 
Benham, in a very careful study of the Chimpanzee’s brain, has shown (Qu. Jour. 
Mier. Sci., vol. xxxvil. p. 47) that the transverse occipital fissure which replaces this 
external perpendicular may be genetically related to it, and that therefore Ecker’s 
original view that the ‘‘ Affenspalte” of the Ape is represented in the adult human 
brain by that which he termed the ‘‘ sulcus occipitalis transversus”’ may be correct. } 
