262 Microscopie Structure of Cortical Areas 
5. Internal or deep layer of giant pyramids. 
6. Layer of polymorphic cells (fusiform and medium-sized pyramids of 
some writers). 
Von Monakow seems to share the view formerly expressed by Ramon 
y Cajal. Golgi describes three layers, and even the cortex of the occipital 
lobe, according to this author, contains only three layers. 
Koelliker divides the cortex into four and six-layer types, as follows: 
1. The white cortical layer of the stratum zonale, poor in cells. 
2. Layer of small pyramidal cells. 
3. Layer of medium-sized and large pyramidal cells. 
4. Layer of polymorphous cells. 
In many convolutions, he found,,as did Hammaberg, six layers, thus: 
1. Stratum zonale. 
2. First layer of small pyramidal cells. 
3. First layer of medium-sized and large pyramidal cells. 
4. Second layer of small pyramidal cells. 
5. Second layer of medium-sized and large pyramidal cells. 
6. Layer of polymorphous cells. 
Obersteiner assumes a type of five layers: 
1. Layer of neuroglia cells, or stratum moleculare. 
2. Layer of small pyramidal cells of outer nerve-cell layer. 
3. Layer of large pyramids, formation of the corun ammonis or middle 
nerve cell layer. 
4. Layer of the small irregular cells, granule formation, or mixed nerve- 
cell layer. 
5. Layer of spindle cells, claustral formation. 
According to Obersteiner, a few slight variations occur which are, how- 
ever, not so important as to prevent their inclusion in the five-layer 
structure. He is unable to find the eight layers of Meynert, and believes 
that nowhere, and especially in higher animals, do sharp differences appear 
in the structure of the cortex. 
Bevan Lewis described, in the cortex, a structure of five and six layers. 
The five-layer structure is found in man and monkeys in front of the 
central sulcus, corresponding to the anterior central gyrus. In the lower 
animals which he examined, he found it surrounding the fissura cruciata. 
This five-layer type is, according to him, characteristic of the motor area. 
The six-layer type is found behind the central suleus and is believed to be 
characteristic of the sensory cortex. 
Hammaberg, who made a great number of accurate investigations of the 
human cerebral cortex, seems to incline towards the opinion of Lewis. 
COMPARATIVE ANATOMY OF CORTICAL REGIONS. 
I shall now endeavor to describe the cortex of various animals, com- 
paring the functional] centers according to structure and localization. 
I have examined sections of six different animals, which are phylo- 
genetically fairly well separated from one another. 
