500 WILLIAM H. F. ADDISON 
connection. (3) The taenia semicircularis, also, arises somewhere 
in the neighborhood of the base of the corpus striatum, probably 
mainly from the lobus parolfactorius, follows the boundary be- 
tween the thalamus and the nucleus caudatus and ends, curving 
downwards and forwards, in the nucleus amygdalae. (4) The stria 
medullaris thalami (taenia thalami) too, ending in the median 
side of the thalamus in the ganglion habenulae, is usually thought 
to be part of the olfactory structures. Edinger’s work, however, 
has made it very probable that it belongs not, or at least not 
only, to the olfactory apparatus, but to what he calls the parol- 
factory apparatus, whose center lies in the lobus parolfactorius. 
The anterior commissure (commissura ventralis) is generally 
considered as the most important commissure of the olfactory 
apparatus. In its frontal bundle it contains fibers uniting the 
two olfactory bulbs, while its more caudal and dorsal bundle 
connects cortical parts which stand in some way related to the 
olfactory apparatus, viz., lobus pyriformis and _ subiculum. 
Also in many lower mammals where the hippocampus lies dor- 
sad of the brain stem, and is not yet pushed back by the corpus 
callosum, there is a third bundle in the anterior commissure. 
Since Owen’s work, and, more recently, by that of Elliot Smith 
and Symington, we know that this third part consists of a thick 
strand of fibers which runs to the dorsally placed hippocampus. 
Thus while in most mammals the commissura anterior has 
the form of a double horse-shoe lying in a horizontal plane, as is 
well shown in figure 290, page 386, of Edinger’s Vorlesungen (’11), 
in monotremes and marsupials there is a third horse-shoe stand- 
ing upright upon the connection of the other two, uniting the 
aforementioned dorsal cortical parts. 
The other commissure of the olfactory apparatus is the psalter- 
ium (commissura dorsalis), which is made up of crossing fibers 
between the two hippocampi themselves. 
Other structures which may be partly connected with this 
system are the claustrum, lying outside of the nucleus lenti- 
formis and under the cortex; and (with more certainty in the 
lower vertebrates) the corpus striatum. Whether these should 
be included in mammals is quite doubtful. 
