THE BRAIN OF.A F@TAL ORNITHORHYNCHUS. 203 
The following anatomical facts concerning the brain of 
Platypus appear to be associated with one another :—an enor- 
mous trigeminal nerve; a huge development of substantia gela- 
tinosa Rolandi in pons and medulla, and fillet in the mesence- 
phalon; a large and precocious development of the optic 
thalamus (where in the adult the great bulk of the fillet ter- 
minates), and an exceptionally abundant supply of fibres con- 
necting the latter with the corpus striatum and cortex cerebri. 
The important bearing of this upon the vexed question of the 
termination of the fillet (lemniscus) will be discussed later on 
when dealing with the adult. It may bestated here, however, 
that an examination of the Ornithorhynchus brain clearly 
shows that the great majority of the fillet fibres terminate by 
terminal arborisations around the large multipolar cells of the 
optic thalamus, which, in turn, are connected with the cortex 
cerebri and corpus striatum. 
The huge stria terminalis, which arises from the neuroblasts 
in the nucleus amygdalz, extends vertically upwards behind 
the “‘radiatio strio-thalamica,” and then takes a sudden bend 
into the horizontal plane (fig. 12, ¢.s.). The picric stain does 
not permit one to accurately trace its anterior connections. 
The account of the optic nerve and its central connections 
will be deferred until the rest of the brain is under considera- 
tion. Before then I hope to examine a series of foetal Echidne, 
and to be able to supplement these fragmentary and imperfect 
notes. 
Literature. 
The last few years have yielded an unusually rich and abun- 
dant contribution to the knowledge of the difficult subject of 
cerebral morphology; and in spite of the different interpreta- 
tions of the vast mass of data collected, there is, beneath all 
the conflicting statements, a remarkable degree of uniformity 
in the essential facts of cerebral development and phylogeny. 
No purpose would be served in a descriptive paper such as 
this in quoting all this bulky literature. In a paper entitled 
“ Die Homologien des Zwischenhirndaches und ihre Bedeutung 
