THE NERVOUS SYSTEM 127 



cord at that region, I am inclined to think that some connection 

 exists between the latter and tne 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. 



BKAIN 



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 eininentia collateralis Meckelii. Conspicuous among variable 

 cerebral furrows we note the parieto-occipital fissure (f.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. 1 



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. H. 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 througli the press, 

 Beuham, in a very careful study of the Chimpanzee's brain, has shown (Qu. Jour. 

 Micr. Sci., vol. xxxvii. 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. ] 



