primary convolutions may be traced. The Proboscidia, fig. 108, and Cetacea, fig. 85, show excess of convolution of the cerebral surface.

Erasistratus affirmed the convolutions to be most numerous in the brain of Man, and associated them with his superior intelligence. Willis pointed out that the convolutions, though present, were fewer in brutes than in Man; that the Ape had more of them than the Fox or Dog, &c.; that paucity was associated with regularity and symmetry of folding and with more definite and limited instincts, while the want of symmetry of the more richly convoluted brains was associated with greater diversity and

freedom of mental operations. By these remarks Willis initiated the comparative anatomy and physiology of this part of the brain. Vicq d'Azyr noted the symmetry of the convolutions in the brain of the Monkey, and contrasted it with the want of such symmetry in Man. Malacarne first defined a particular convolution, that, viz., which overlies and follows the contour of the corpus callosum. Tiedemann does not enter upon the comparison of the convolutions; but he first showed the order and periods of their successive appearance in the human brain. Serres stated them to be too inconstant to characterise species or families of Mammalia. I early made observations to test this question, and in 1833 I communicated the results in ed to the convolutions

of the cerebrum in the Felida," d

6

homologues could be traced from species to species in that family, I distinguished most of them by names. I further entered upon their classification, and defined the primary' and secondary' fissures and folds, showing that the secondary fissures were in general less symmetrical than the primary ones' (XLVII". p. 134), and that the differences observable in the brains of the Felida were due chiefly to the absence of more or less of the secondary convolutions in the smaller species; in the common Cat the principal fissures, or anfractuosities, are less obscured by fissures of the second degree than in the larger Felines' (ib. p. 133).' M.. Leuret, in citing this attempt to bring the convolutions within the domain of comparative anatomy,2 has extended, in association with his colleague, M. Gratiolet, the like comparison to other species and families of Mammalia. Foville3 arranges the cerebral convolutions into those of the first,' second,' third,' and fourth orders,' characterised partly by position, partly by direction; and, in each order, they are subdivided into groups.' This system, based mainly on the study of the parts in the human brain, has its utility limited to Anthropotomy; the comparisons not having been carried to the extent requisite for defining the cerebral fissures according to their order of appearance or constancy in the Mammalian series. Prior to the appearance of both these works I had continued my observations as opportunities presented themselves; and gave the result of such extended comparisons in the Course of Lectures delivered at the Royal College of Surgeons of England in 1842: my diagrams there, in which homologous convolutions are indicated by colours, may still testify in part to the extent to which the comparisons had been carried; the main aim which I had in view being the determination of the homologous and superadded convolutions in the more complex prosencephalon of Man."

15.

86

6

In the Carnivora, to the rhinal, figs. 90, 92, 2, hippocampal, fig. 86, 4, callosal, ib. 7, and sylvian, fig. 90, 5, fissures, are added, in the smallest species (Putorius), the fissures 8 and 14, fig. 87. The first, commencing near the posterior part of the hemisphere, at 11, extends forward, equally bisecting that part of the surface Inner surface of hemisphere, between the interhemispheral and sylvian (5) fissures, then bends outward parallel with and in front of the sylvian fissure. That marked 14 extends

Felis.

The preliminary sketch of the history of this part of cerebral anatomy is from the 13th Lecture of the Hunterian course for 1842. 2 XII. vol. i. p. 380. 4Medical Times,' Nov. 12, 1842, vol. vii. p. 101.

3

XXV. (1844).

On the surface

121

19'

13

On the occipital surface are several but irregular fissures, which, from their position, may be termed mid-, super-, ent-, and post-occipital; they define, more plainly in Quadrumana than in Man, the lambdoidal, fig. 119, p, suroccipital, q", midoccipital, q', suboccipital, q'", and postoccipital, q*, folds. On the tentorial surface they affect a longitudinal wavy course, and are commonly three in number; of these, the middle one is the 'tentorial' fissure, fig. 120, 18, the inner one the entotentorial,' ib. 18', the outer one the ectotentorial,' 18". next the falx, or septum dividing the hemispheres, fig. 121, the fissures have a radiating tendency from the anterior angle outward the most constant and important of these, in Man, has already received the name of posthippocampal,' being a continuation of that deep fissure the corresponding fold of which partly protrudes into the posterior horn of the ventricle, as the hippocampus minor;' the rest I called septal' fissures, reserving the term falcial' to those on the corre- Inner or septal surface of posterior sponding surface of the anterior cerebral lobe, human cerebrum. lobe. The fissure above the posthippocampal' is the septal fissure, 19; that beneath the posthippocampal is the 'subseptal,' 19"; the fissure between the septal and entolambdoidal, 13', fissures is the superseptal, 19'; their outer ends are frequently lost in a fissure following more or less extensively or interruptedly the posterior contour of the posterior lobe; this is the postseptal fissure, 19"; it is peculiar to Man. The folds so defined on the septal surface are: the entolambdoidal, p', superseptal, s', septal, s, posthippocampal, a', subseptal, s", and postseptal, s'".

6

6

The human brain, in its development, passes through stages in some degree like those which are permanent in and characteristic of the Quadrumana, in respect to its cerebral folds and fissures; bearly manifests its distinctive archencephalous proportions, fig. 109, Foetus. About the twentieth week the fissures begin to appear upon the upper surface of the hemispheres, fig. 116, three months' Fœtus. After the hippocampal' and 'callosal' have cleft the inner surface, and the ectorhinal' and sylvian' the under surface, the entolambdoidal ascends upon the mesial side of the upper surface (fig. 116, 13); the postsylvian, 9, appears; then a faint trace of the longitudinal fissure, fig. 116, 14', indicative of the midfrontal and ectofrontal tracts. The coronal,' fig. 113, 12, is

speedily followed by the 'postsylvian' 9. A more or less interrupted fissure divides lengthwise the sylvian or supersylvian fold, ib. g, from the median, , and medilateral, m, tracts. The lambdoidal fissure, 13, extends toward the outer part of the hemisphere: the pre-coronal tract of brain is fissured into subdivisions, chiefly longitudinal: the foetal brain, at seven months, figs. 113,116, resembles, in superficial cerebral marking, that of the latisternal apes, ib., Chimpanzee, but is broader anteriorly, deeper and longer behind.

In the foregoing summary we have seen that the fissures which break the surface of the mammalian brain are of different kinds, degrees, and values. Some, in the course of development and elevation of the primary masses, divide one from the other; as the cerebrum from the optic and olfactory lobes, the cerebrum from the cerebellum, and this from the macromyelon. Some subdivide primary masses into symmetrical halves, as e.g., the inter-hemispheral fissure, the inter-olfactory fissure, and the shallower indent between the mammalian optic lobes or nates.' One or two fissures of the cerebrum make folds that project into the hemispheral cavity or ventricle, e. g. the hippocampal and, in Man, the posthippocampal: most are confined to its crust or wall, and of these, as I showed in 1833, some, from their relative constancy, depth, and symmetry, may be termed 'primary,' while others are of secondary' or inferior rank.

The following are those which are noted by figures in the illustrations of the present work:

CEREBRAL FISSURES, in the order mainly of their constancy in the Mammalia.

8. Supersylvian.

15.

Subfalcial.

16.

8'. Ectosylvian

9. Postsylvian.

18.

Entotentorial.

18". Ectotentorial.

19.

Septal.

19. Superseptal.

19"". Postseptal.

Orbital or Postorbital. 19". Subseptal. 16. Midorbital.

The following are the cerebral folds which are indicated by letters in the illustrations of the present work, with the synonyms of original labourers in this field of anatomy :-

EBRAL FOLDS IN THE ORDER OF THEIR CONSTANCY IN MAMMALS.

Circ. cristato: gyrus fornicatus, Arnold.

c. del margine degli emisferi