Explanation of Plates 
Reference Planes 
The horizontal zero plane (HO) for this atlas is defined as the plane passing 
along the inferior flat surfaces of the eyepieces through the center of the ear 
bars (see Methods). All brain structures anterior to the medulla oblongata lie 
above this plane. The frontal zero plane (AP 0) is defined as the plane which 
passes through the center of the ear bars and is perpendicular to the horizontal 
zero plane. The lateral zero plane is defined as perpendicular to the horizontal 
and frontal zero planes and passing midway between the two ear bars in their 
final position. The sagittal suture usually lies within 1 mm. of the lateral zero 
plane; best reliability is obtained by exposing and utilizing the superior sagittal 
sinus. 
Frontal Series 
In the plates for the frontal sections (SM12), AP designations represent 
the plane for which the section is considered representative. Positive AP numbers 
refer to distances in millimeters anterior to AP 0. Deviations between the de- 
sired and actual positions of any section are no more than 0.2 mm.; the calcu- 
lated position of each section is given in smaller type. The grid overlying one-half 
of the frontal section is scored in millimeter intervals. Numbers along the 
sides of each plate represent 5 mm. intervals in the lateral and horizontal planes. 
Sagittal Series 
Following the frontal series are plates showing representative sagittal sec- 
tions stained by the Weil-Weigert method. These are presented to indicate the 
relative position of brain structures anterior and posterior to those in the frontal 
series and to facilitate visualization of spatial relationships. These plates are 
alphabetically identified. The approximate distance of the section from the 
midline appears beneath the letter. The abbreviations are listed in tables III 
and IV. 
Nomenclature 
The terminology of this atlas is based on that compiled by Riley in his re- 
markable and recently republished “An Atlas of the Basal Ganglia, Brain Stem 
and Spinal Cord” (9). In 15 instances terms have been taken from other refer- 
ences; these are indicated by an asterisk in tables III and IV. 
Labeling and Abbreviations 
Structures which are comprised largely of white matter are labeled in 
italics on the plates showing sections stained by the Weil-Weigert method; 
principal cellular groups are identified by Roman letters on the plates showing 
the Nissl-stained sections. The corresponding abbreviations are given in tables 
III and IV. Initials for generic terms (e.g., nucleus) are not used except for the 
following: brachium, capsula, commissura, lemniscus, pedunculus, radiatio, stria 
and stratum. In these instances cross-references are given. 
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