352

322

backward from the cerebral divisions of the entocarotids (g). The basilar artery
transmits or receives the branches from the vertebral arteries (h). A division of the
macromyelum, defining a "pons," is not more definitely marked than in most other birds.

The cerebellum (Pl. XCI. figs 1 & 2,c) is of a subcompressed, subconical shape ; it
gives 6 1/2 lines in vertical, 5 lines in transverse diameter, and 6 lines in antero-posterior
extent at the base. A rudimentary appendage or prominence represents the side lobes :
the superficies is multiplied by about fifteen transverse folds, averaging 1 1/2 line in depth ;
their grey and white matters are shown in the section (ib. fig. 6,c). About seven of
these folds are visible on the exposed surface of the cerebellum (figs. 1, 2, c). a short
fissural trace of the primitive cavity (ib. fig. 6,c') communicates with the macromyelonal
one, called "fourth ventricle."

The distinctive peculiarity in the base view of the brain in Apteryx is the small
relative size of the optic lobes (figs. 3 & 4, b). M. Dareste was struck with the pecu-
liarity in the specimen of the brain of an Apteryx in the Museum of Comparative
Anatomy in the Garden of Plants. He speaks of the optic lobes as "a peine visible a
L'exterieur" 1, and justly notices this confirmation by comparative anatomy of the
relation of the optic lobes to vision, which relation MM. Flourens and Mayer had
inferred from physiological experiment.

The optic lobes, reduced as they are in Apteryx, adhere, however, to the ornithic type
by the degree in which they have diverged laterally from each other in the course of
the brain's acquisition of its mature characters 2 ; they are ovate and subdepressed.
The optic thalami (ib. fig. 4,i) form a larger and more definite tract than in other
birds, and contribute in a greater degree to the "radix optica," or chiasma.

The cavity or ventricle of the small optic lobe is shown in the section (fig. 6, b'), and
in the base view (fig.4, b'), in which the macromyelon, removed by a transverse section
through the back parts of the optic lobes (b b') and the "crura cerebri" (k), exposes
the rudimental hippocampal enlargements (l) and the fissures (m) by which the artery
of the "choroid plexus" penetrates the lateral ventricle.

The cerebral hemispheres (a, a', figs. 1 & 2 ) are smooth : a feeble indent at the side
of the base indicates the "Sylvian fissure," which received a branch of the cerebral
entocarotid (fig. 3, g) ; there is a more feeble indication of a mid longitudinal tract at
the upper and hinder part of the hemisphere (fig. 2, a), and still more feeble indication
of a transverse frontal depression marking off, as it were, an anterior lobe (ib. a'). The
structure of the hemisphere adheres closely to the avian type. Each "crus" expands
and commingles its white fibres with grey matter to form a large ganglion or "corpus
striatum" (fig. 5, n), from the outer side of which the neurine, chiefly of the white

1 Annales des Sciences Naturelles, Zoologie, 1856. His notice of this specimen is as follows :- "Le
cerveau de l"Apteryx, tel que je l'ai entrevu au travers de ses membranes, m'a paru presenter des particu-
larities interessantes. Malheureusement je n'ai pu obtenir l'autorisation de le dissequer, or meme seulement
de le depouiller de ses membranes." - Tom. cit. p.50. 2 Anat. of Vertebrates, vol. ii.p. 119.