ABSTRACT
This is specimen number 609 in the Carnegie Collection, designated here as C609. A normal female fetus with a crown-rump length (CR) of 32 mm was collected in 1916, and is estimated to be in gestational week (GW) 8. The entire fetus was embedded in paraffin, cut transversely in 50 µm thick sections, and stained with aluminum cochineal. Since there is no photograph of this brain before it was embedded and cut, a specimen from Hochstetter (1919) that is only partially comparable to C609 has been modified to show the approximate section plane and external features of the brain at GW8 (Figure 8). Like most of the specimens in this Volume, the sections are not cut exactly in one plane; C609’s cortex is cut midway between coronal and horizontal planes, and is presented as a “horizontal” brain. The C609 section planes through the cortex and brainstem are not at the same angle when transferred to Hochstetter’s CR27 mm specimen. Instead, brainstem planes of section appear to fan upward and downward from sections in the cortex apparently around a fulcrum centering in the invagination of the medullary velum overlying the rhombencephalic superventricle. We interpret this to indicate that the brain flexures are more loosely folded in the Hochstetter specimen than in C609. But it is difficult to determine how the brainstem is folded in C609 to make the section planes line up with those in the cortex. Photographs of 23 sections (Levels 1-10) are illustrated at low magnification in Plates 170-179. High-magnification views of different areas of the brain are shown in Plates 180-185. To maximize image size within page space, all of C609’s sections are rotated 90˚ (landscape orientation). The anterior part of each section is on the left (page bottom), and the posterior part of each section is on the right (page top).
