160 MARION HINES 
transversely directed portion by a deep sulcus” (p. 66). This 
fissure is considered by His to be the same as the ‘vordere Bogen- 
furche.’ ‘The first embryo to have such a fissure is Se (16 mm. 
G. L.) thought by His to be six weeks of age. There is little 
doubt that this measurement in no way compares with those in 
this series. Here there is no well-developed olfactory bulb until 
the 27.8-mm. is examined, although there is a slight olfactory 
evagination in the 19.1-mm. Then the fissure in all of the series 
after 27.8 mm. is the same as that of His’ description. It is 
quite possible that the bulb in His’ embryos was delimited ar- 
tificially. His also models a small bulb in C. R. (13.6 mm.), 
in which case the writer believes that some of the olfactory fila 
may have been included in the drawings of the projection of the 
brain. In the later stages the anatomy of the fissure is the same 
in all cases. Further, he thinks it divides the olfactory system 
into two parts. ‘‘Atno time does it extend posterior to the lamina 
terminalis. Its remnant is the fissura parolfactoria posterior of 
the B. N. A.” (His, ’04, p. 76). This fissure is not, then, the an- 
terior portion of the fissura arcuata; rather it is continuous with 
the mesorhinic fissure. 
Besides this fissure in embryos of the second month, His 
finds a sickle-like fissure extending posteriorly beginning in the 
region of the terminal plate. He finds also that in many cases 
the mesenchyme fills the fissure and that there are no evident 
postmortem artefacts. He finds the same kind of thickening in 
the medial wall in the cat embryos of 14 mm. G. L., as Zucker- 
kandl (01) showed in his paper on the development of the corpus 
callosum. The hintere Bogenfurche lies dorsal to the fissure of 
the choroid plexus, its anterior limit does not pass beyond the 
terminal plate. This fissure is undoubtedly the one the writer 
has identified as the fissura hippocampi. However, besides these, 
His described another, the ‘accessoriche Bogenfurche,’ in his draw- 
ings of three- and four-month embryos. ‘This lies on the anterior 
part of the medial wall, arching over the terminal plate. The 
writer finds nothing to correspond with this fissure and considers 
it an artefact. 
