PROFESSOR OWEN ON THE AYE-AYE. 69 
the part of the hemisphere, viz. the ‘sylvian’ or ‘temporal’ convolution (c), which it 
defines, is indented by a short vertical fissure (6). A shallow vascular impression goes 
from the summit of the suprasylvian fissure towards the longitudinal one. A shallow 
indentation (5) divides the suprasylvian convolution (6, 6) from the anterior lobe. These 
fissures or anfractuosities, which are very symmetrical in the two hemispheres, mark 
out the folds or convolutions called the longitudinal (a, a), the suprasylvian (0, b), and 
sylvian (c, f) convolutions, the latter terminating below in the ‘ natiform protuberance,’ n. 
The continuation of a@ with b forms the hinder protuberance of the cerebrum: its 
inferior and internal surface is smooth and unfissured. The bifurcation of the fissure (2 ) 
marks out the anterior lobe, which is also divided by a shallow vascular groove, con- 
tinued from the lower branch of fissure (2) from the fore part of the suprasylvian 
convolution (b). The anterior lobes are marked by a few feeble indentations, not 
symmetrically repeated, but of which one (1) seems to answer to the one so marked in 
the brain of the Cat. There is sufficient resemblance in the pattern of the markings of 
the cerebral surface of the Chiromys and Cat, to determine the homologous fissures and 
folds, and I use the same figures and letters to indicate these as in the ‘ Memoir on 
the Cheetah,’ in the first volume of the ‘ Zoological Transactions’'. But, in the 
number and disposition of the primary convolutions and fissures, the brain of Chiromys 
most closely resembles that of Lemur proper’. 
The cerebellum has a large and prominent superior ‘ vermiform’ lobe (Pl. XXIV. 
figs. 3 & 4, m), a pair of small lateral lobes (2b. n), and the ‘ flocculus’ (ib. 0). The inferior 
vermiform lobe (2b. 1) extends beyond the superior, where it rests upon the back part of 
the fourth ventricle. Behind the flocculus (0) is the tract (s) where the white matter 
appears, and to which can be traced the ‘ crus cerebelli ad pontem.’ The breadth of the 
cerebellum, including the ‘ flocculi,’ exceeds, by about a line, that of the cerebrum: 
the length of the cerebellum is 9 lines; the uncovered extent is 6 lines, from the posterior 
border of the cerebrum. 
The pons Varolii (Pl. XXIV. fig. 2, v) is but slightly prominent, defined anteriorly 
from the cerebral crura (u) by a feeble transverse interrupted linear groove and by the 
third pair of nerves (s), and posteriorly chiefly by the sixth pair («). The basilar artery 
feebly impresses the middle line of the pons. The pyramidal bodies, p, are feebly 
defined, and slightly expand to their insertion into the pons, where they received the 
nerves of the sixth pair(*). The cerebral crura (uw), short and thick, are divided by the 
infundibular fissure, in front of which is the single median mammillary body. The 
optic nerves (fig. 2, 2) form a chiasma of which the breadth is twice that of the length. 
* « Anatomy of the Cheetah,”’ Zool. Trans. vol.i.p. 129, pl. 20. fig. 4. In this memoir, read September 1833, 
I published my first attempt at determining the homologous convolutions of the cerebrum, a subject which was 
extended in a subsequent Course of Hunterian Lectures at the Royal College of Surgeons, and illustrated by the 
preparations and coloured diagrams now in that Institution. 
* See Prep. No. 9, Physiol. Series, Hunterian Museum, determined by dissection ef the Lemur mongoz to 
belong to that species, in 1832, ‘ Physiological Catalogue,’ vol. i. 4to, p. 3. 
