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| Gournal of Anatomp and Pbpsiologp.
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| ON THE DEVELOPMENT AND HOMOLOGY OF THE
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| MAMMALIAN CEREBELLAR FISSURES! By oO.
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| CHARNOCK BRADLEY, M.B., Professor of Anatomy, Royal
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| Veterinary College, Edinburgh. (PLATESs XVII-XXIIL)
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|
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| PART II.— Pic.
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|
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| 40 days embryo, 52 mm. long (figs. 54, 55 and 56).—At this
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| stage the cerebellum of the pig embryo bears a certain likeness
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| to that of the rabbit on the 20th day of gestation. No fissures
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| are visible to the naked eye, but when sections are made and
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| microscopically examined there is noticed a somewhat thin liplike plate projecting from the lower posterior corner of the
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| section of the cerebellar lamina (fig. 56). This is comparable
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| in every respect to the same feature in the rabbit’s brain on
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| the 20th day, and there develops a homologous lobe in connection with it.
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|
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| 44 days embryo, 64 mm. long (figs. 57, 58 and 59).—Development has proceeded rapidly during the interval betweën the
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| last stage and the present. A naked-eye examination shows a
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| sufficiently clear distinction between the future vermis and
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| hemispheres. There is also visible on the anterior slope a
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| fissure (IL.) of considerable length (fig. 58). Microscopie sagittal
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| sections show fissure IV. as before, and fissure II. of some depth.
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| There are also possibly faint indications of two other fissures
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| in that part of the vermis lying between II. and IV. There is
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| as yet no trace of a separation of a paraflocculus from the
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| hemisphere.
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|
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| 48 days embryo, 80 mm. long (figs. 60, 61 and 62)-—Develop
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| 1 The work, of which the present paper is the outcome, was done by the
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| writer as a Research Student of the University of Edinburgh.
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|
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| VOL. XXXVII. (N.S. VOL. XVIIL.)—APRIL 1903. 16
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| 222 PROFESSOR O. CHARNOCK BRADLEY.
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|
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| 4
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| “
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|
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| ment has again progressed rapidly ; indeed, it is something of
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| a misfortune that a stage intermediate between 44 and 48 days
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| could not be obtained. But though this is a misfortune, it is
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| not one which offers any insuperable difficulty in the solution
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| of the problem before us.
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|
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| An examination of a 48 days cerebellum reveals a fissure (IL)
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| which is prolonged for some distance into the hemisphere.
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| Below it the two othér fissures are faintly marked. These
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| develop into fissures I. and c. On the posterior slope there
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| are two faint fissures in the vermis. Subsequent development
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| shows that these become fissures III. and d. In the hemisphere
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| there is an indication of a fissure, which, growing inwards from
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| the lateral part of this portion of the cerebellum, ultimately
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| demarcates the paraflocculus. Another faint foreshadowing of
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| a fissure is also seen indenting the margin of the hemisphere
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| anterior to the one just mentioned. This latter, growing inwards, ultimately forms part of fissure a (fig. 60, a).
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|
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| Microscopie sections afford additional evidence as to the
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| actuality of the faint depressions seen with the naked eye
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| (fig. 62). They also show that a number of fissures are about
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| to complicate that portion of lobe À which lies below fissure c
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| (lobule A,). Lobe E has increased in volume, and is now, in
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| consequence, sharply defined from the posterior medullary
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| velum. A flocculus is becoming evident, and its development
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| from the boundary of the lateral recess is clearly indicated. Its
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| boundaries are not as yet rigidly set down, but it reveals itself
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| as a thickening and bulging in the region in which, in the
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| future, it is to become conspicuous (fig. 61).
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|
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| Embryo, 86 mm. long.—In the cerebellum of an embryo of
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| 86 mm. in length (of which the age is not certainly known,
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| but is estimated at about 50 days) the anterior surface is quite
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| richly fissured. Fissure IT. now reaches the extreme margin of
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| the hemisphere, and fissure I. almost does 80. On the posterior
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| slope, fissure &« runs completely across the cerebellum, but is
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| shallow at the junction of vermis and hemisphere. Fissure III.
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| crosses the vermis and invades the groove between it and the
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| hemisphere. The fissure which is about to cut off the paraflocculus is deep, and is growing inwards towards fissure III.
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| of the vermis, with which it finally becomes continuous.
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| THE MAMMALIAN CEREBELLAR FISSURES. 223
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|
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| Fissure d is, if anything, rather longer than fissure III. The
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| parafloceulus forms a distinct projection, and is now clearly
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| separated from the flocculus. Sections show that lobe B is
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| becoming divided by a shallow transverse fissure.
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|
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| 51 days embryo, 88 mm. long (figs. 63, 64 and 65).—The
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| difference between this and the above stage is only one of depth
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| of fissures.
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|
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| 55 daus embryo, 100 mm. long (fig. 66).—To the naked eye
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| the fissures have obviously deepened since the 51st day, but no
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| new ones can be made out. Sections, however, show that a
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| fissure, 6, has begun to invade that part of lobe C which is in
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| the vermis. It seems likely that this fissure first made its
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| appearance, on the anterior slope of the hemisphere, about the
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| 48th day (fig. 61), and that the two parts gradually grew
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| together in the vermis. It is interesting to notice at what
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| an early period fissure a came into existence, and how comparatively late fissure b is in making its appearance in the
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| vermis. This should be compared with the constancy of the
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| former fissure in the cerebella of the type of the rabbit, and
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| the inconstancy or difficulty of determination of fissure b in
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| the cerebella of the same order of complexity.
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|
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| The fissures in lobule A, are now of considerable depth.
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| Lobule A, retains its comparatively small size. Lobe B is
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| larger, and contains a moderately deep fissure, which is the
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| forerunner of a like feature in the adult brain.
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|
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| 59 days embryo, 118 mm. long (figs. 67, 68 and 69).—As in
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| the rabbit, the anterior part of the pig’s cerebellum has advanced
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| more rapidly than the posterior part during the earlier stages
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| of development. By the 59th day the anterior surface is bearing a strong resemblance to the adult condition, but the
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| posterior part is still comparatively simple. Fissure à is now
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| of some depth and can readily be recognised by the unaïded eye.
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| Fissure a has gained considerably in depth. Fissure III. has
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| become continuous with the lateral fissures, which, making an
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| early appearance, first indicated the limits of the paraflocculus.
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|
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| Fissure d is of great lateral extent, being indeed the longest
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| fissure of the cerebellum at this stage (with the possible
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| doubtful exception of fissure IL, which has a curved course).
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| Fissure d, it should be noted, is growing forwards into the
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| 224 PROFESSOR O0. CHARNOCK BRADLEY.
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|
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| paraflocculus, which is, by it, being divided into an upper and
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| a lower part, connected together in front (fig. 67). It is desired
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| to emphasise the fact that there is a strong, well marked
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| connection between lobe D and the paraflocculus This
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| connection at this stage is not confined to the part of lobe D
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| above fissure d (lobule D,), but belongs to the entire lobe.
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| Nothing could show more clearly that the paraflocculus and
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| lobe D are parts of one and the same morphologie unit. This
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| point is illustrated much better in the pig than it was in the
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| rabbit.
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|
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| The paraflocculus has enlarged, and its anterior surface shows
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| signs of foliation (fig. 68).
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|
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| 65 days embryo, 132 mm. long (figs. 70, 71, 72, 73 and 74).—
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| The anterior surface has now very closely approached the adult
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| condition, both in its external appearance and also in those
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| features which can only be adéquately appreciated by means
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| of sagittal sections. |
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|
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| Fissure IL. is of great depth, its lowest part being not far
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| removed from the summit of the roof of the 4th ventricle
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| (fig. 74). Lobe B shows definite evidence of its future bipartite
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| condition. Lobule A, has now lost its former arrangement of
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| indefinitely arranged folia, and has collected them into three
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| sub-lobules such as are found in the adult brain. Fissure b
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| is now of some depth, and fissure a makes an important
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| landmark on the posterior slope. Fissure d is deeper than
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| fissure III, and both parts of lobe D are becoming foliated
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| (fig. 74). Lobe E remains relatively small and simple, but
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| is now separated from the posterior medullary velum by a
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| conspicuous fissure.
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|
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| The paraflocculus is now divided into two parts, both of
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| which are now foliated. The whole lobule now closely
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| resembles the same lobule in the adult squirrel. The division
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| into two parts has obviously been brought about by an extension in a forward direction of fissure d. This extension
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| was beginning in the previous stage. The upper part of the
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| paraflocculus is connected with lobule D, by a rounded nonfoliated ridge. The connection between lobule D, and the
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| lower half of the paraflocculus has almost become obliterated,
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| but it should be kept in mind that such a connection did at
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| THE MAMMALIAN CEREBELLAR FISSURES. 225
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|
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| one time exist. The flocculus is small and, to the naked eye,
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| not yet provided with folia. On examining microscopic sections,
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| however, slight fissures are found to exist.
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|
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| 70 days embryo, 150 mm. long (fig. 75).—Except in richness
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| of foliation, no marked change has occurred in that part of the
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| cerebellum which is anterior to fissure II. The posterior
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| portion of the organ, however, has now entered into a more
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| active phase of development, and is rapidly assuming the adult
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| appearance. That part of lobe C which is anterior to fissure a
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| (lobules C, and C,) has grown considerably in a lateral
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| direction. Further, the vermis portion has also grown so much
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| in an antero-posterior direction that it can no longer be
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| accommodated in the strict mesial plane, but has become
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| distorted by being thrust over to one side. Fissure b is now
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| a very important feature. It extends all the way across the
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| cerebellum. Lobule C, has also altered considerably in appearance. It no longer forms a band of practically uniform width,
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| running from one margin of the cerebellum to the other. It
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| now fails to extend as far laterally as the more anterior part
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| of lobe C. Its vermis portion has increased in volume in a
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| sagittal direction, and, like that part of the vermis immediately
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| in front of it, is now distorted by being pushed to one side.
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| The hemisphere portions, too, have enlarged in a sagittal
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| direction, and are now in the form of rounded masses, connected
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| with the vermis by a comparatively narrow isthmus. This
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| lobule has therefore come to resemble that of the squirrel.
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|
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| The two parts of lobe D have also enlarged, and their folia
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| are more numerous. The connection between lobule D, and
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| the corresponding part of the paraflocculus is still smooth.
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| Lobe E remains small, and to the naked eye appears to have
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| no connection with the flocculus beyond that established by
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| means of the posterior medullary velum. But microscopic
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| sections show that there is still a low smooth ridge running
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| between the two structures.
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|
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| The parañlocculus has not increased much in size, and,
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| because of the lateral expansion of lobe C, is now not 80
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| prominent a feature on the lateral surface of the hemisphere.
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| The flocculus is still small, and to the naked eye smooth.
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|
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| Embryo, 165 mm. long, age unknown (figs. 76, 77, 78, 79
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| 226 PROFESSOR O. CHARNOCK BRADLEY.
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|
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| and 80).—This is the last embryonic stage which it is necessary
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| to examine, as it brings us within a short distance of the
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| condition of the adult cerebellum. Lobule A, is now certainly
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| composed of three sub-lobules, the uppermost of which has
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| beyond doubt an extension into the hemisphere. One single
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| small folium still adheres to the anterior medullary velum,
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| and therefore may possibly be looked upon as an attenuated
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| example of a lingula. Lobule A, is relatively small, and has a
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| rather shallow fissure dividing it into two parts. Fissure IT.
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| begins on the dorsal surface of the vermis; curving forwards
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| at the lateral boundary of the vermis, it runs obliquely down
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| the anterior surface. Lobe B is divided into upper and lower
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| portions by a fairly deep fissure, whose advent has been noted
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| in earlier stages. Lobe C has again made great advances. So
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| much is this the case that lobule C, is very considerably
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| distorted. Lobule C, is now clearly divided into three parts—
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| one in the vermis and one in each hemisphere—connected by
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| narrow bands. The connection between lobule D, and the
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| upper part of the paraflocculus is becoming slightly marked
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| by fissures, and has become in part hidden by the posterior
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| extremity of lobe C.
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|
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| The paraflocculus is now quite complicated, from the presence
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| of numerous folia; but there is no difficulty in recognising its
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| constitution as two tiers. The flocculus is now foliated.
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|
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| Adult cerebellum (figs. 81, 82, 83 and 84).—Having traced
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| the development of the fissures and lobes up to an advanced
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| stage, it does not seem necessary to give an additional detailed
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| description of the adult organ. It will suffice to briefly indicate
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| the changes which have occurred since the 165 mm. stage.
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|
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| The cerebellum anterior to fissure II. has not undergone any
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| radical change. It has taken additional folia upon itself, but
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| that is all In the posterior part of the cerebellum more
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| decided changes have occurred. Fissure b is now very distinct
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| crossing vermis and hemisphere, and reaching the border of the
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| latter. A further displacement of the vermis portion of lobe
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| C has taken place, so that in the adult brain fissure à is
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| decidedly oblique. The connections between the vermis and
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| hemisphere portions of lobule C, have become very much reduced.
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| The upper part of lobe D has shared in the general distortion of
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| THE MAMMALIAN CEREBELLAR FISSURES. 227
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|
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| this region of the vermis. Its connection with the paraflocculus
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| now consists of a transversely foliated ridge (fig. 83). Lobule
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| D, has merely increased in size and become more thickly foliated.
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| Lobe E remains very small and inconspicuous (fig. 84).
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|
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| In many cerebella the paraflocculus has become a somewhat
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| jumbled collection of folia, but in most brains it has retained
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| a closer resemblance to its earlier condition. There is usually
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| little difficulty in tracing its two-tiered character, but it appears
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| as though the lower tier had been turned forwards at its posterior end. The flocculus in the adult is in the form of a row
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| of vertically placed folia, and runs in an antero-posterior direction, immediately below the paraflocculus. Its extremities only
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| are visible when the cerebellum is looked at from before or from
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| behind.
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|
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| Having now learnt the characters of the fissures and lobes in
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| the pig, we are in a position to examine those cerebella which are
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| constructed after a similar plan.
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|
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| Mustela furo (figs. 85, 86, 87 and 88).—In this animal is
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| a good example of the backward retreat that fissure II. makes in
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| some of the more complex cerebella. The vermis is about
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| equally voluminous in front of and behind this fissure, this
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| being the result of an increase in the number of lobules in the
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| more anterior section of the vermis.
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|
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| Lobe A is divided into two slightly unequal parts by a fissure,
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| e, which is almost entirely visible when the cerebellum is looked
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| at from the front, and which reaches the margin of the hemisphere. Lobule A, is divided into two parts, each carrÿing two
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| or three folia. Lobule A, is also divided into two portions, but
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| the fissure is not so deep as that in lobule A. Lobe B is cut
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| by a curved fissure which almost reaches its lateral boundaries.
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| It will be seen that lobes À and B are very similar to the
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| corresponding lobes in the pig, except that the lower component
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| of A is divided into two instead of three sub-lobules.
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|
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| Lobe C forms à very considerable constituent of the hemisphere. It has fissures a and 6, but the lobules in the vermis
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| between a and b and « and IIL are comparatively simple; 1e.
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| they are not developed to such an extent that their accommodation necessitates distortion of the vermis The connection
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| between vermis and hemisphere segments of lobule C, is very
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| 228 PROFESSOR O. CHARNÔOCK BRADLEY.
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|
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| narrow, as in the pig, and partly or wholly concealed. Lobes
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| D and E are confined to the vermis; and D is divided into two
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| lobules by a fissure, d.
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|
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| The paraflocculus is arranged in the form of two tiers of folia
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| joined together anteriorly. From the lower tier a lobulus
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| petrosus projects for some distance. The connection between
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| paraflocculus and lobe D cannot be made out in the adult. It is
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| somewhat difficult to satisfactorily distinguish a flocculus, but
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| it is apparently present, and visible when the cerebellum is
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| viewed from the side or from behind.
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|
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| Mustela erminea and M. vulgaris have both been examined,
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| but they so closely resemble M. furo that no further description
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| is necessary.
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|
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| Meles taxus (figs. 89, 90, 91 and 92).—As compared with
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| lobe B, lobe A is smaller in the badger than it is in the
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| pig. Only a comparatively small portion of it is visible on
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| the anterior surface of the cerebellum. Lobule A, is also small.
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| Below fissure c there are two groups of folia, that group lying
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| more inferiorly being further partially divided.
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|
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| Lobe B is large, and divided by a deep fissure into upper and
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| lower lobules, each of which is again somewhat deeply indented
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| by a fissure (fig. 92).
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|
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| In lobe C, fissure b extends to the border of the hemisphere,
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| as it does in the pig (fig. 90). Lobule C, consists of a vermis
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| portion, whose folia—unlike those of the pig—run transversely ;
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| and à hemisphere part, considerably removed from the vermis,
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| because of the large development of those parts of lobule C,
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| which belong to the hemisphere. The three segments of lobule
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| C, are very unequal in size, the hemisphere portions being
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| very extensive. There is practically no distortion of lobule C,
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| in the vermis (fig. 91). Lobes D and E call for no special remark.
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| The double character of the paraflocculus is very evident, the
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| two portions being arranged in an oblique plane, and very
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| clearly continuous in front (figs. 89 and 90). The connection
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| between paraflocculus and vermis is very difficult to establish.
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| In the brain examined, a very prominent lobulus petrosus was
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| present on the right side, and was received into a fossa formed
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| by the temporal bone. On the left side the corresponding
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| lobule was curved forwards underneath the lower part of the
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| THË MAMMALIAN CEREBELLAR FISSÜRES. 929
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|
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| paraflocculus (fig. 89). The question arises as to the possibility
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| of the lobulus petrosus always representing the posterior
| |
| extremity of the lower portion of the paraflocculus. This may
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| be the case. If we accept this as being a true interpretation
| |
| of the facts, then we should consider that, as the paraflocculus
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| increases in size in different animals, it tends to press forwards,
| |
| since the lobulus petrosus is often found in cerebella having
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| small paraflocculi.
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|
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| The flocculus consists of a single folium iying between the
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| lateral recess of the ventricle and the most posterior part of the
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| paraflocculus.
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|
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| Canis familiaris (figs. 93, 94, 95 and 96)-—The anterior
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| part of the cerebellum of the dog does not differ very materially
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| in the arrangement of its fissures and the disposition of its lobes
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| from the corresponding part of the badger’s cerebellum. In
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| lobes C and D, however, there are differences of sufficient
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| magnitude to warrant mention. Fissure b is present in a position
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| very similar to that of the badger. It can readily be followed
| |
| across the vermis and hemisphere to the border of the latter,
| |
| running almost parallel to fissure IT. Lobule C, has a very
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| considerably distorted vermis portion, and its hemisphere
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| dependencies show several fissures of some depth, which. give
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| the impression that it consists of several distinct sub-lobules.
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| The central segment of lobule C, is also much twisted, and on
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| superficial examination appears to have no connection with
| |
| those vertically elongated masses which form its hemisphere
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| segments. On opening up the groove between vermis and
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| hemisphere, however, the connection can be distinguished. The
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| displacement and sinuousness of the vermis in lobules C, and
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| C, only appears after birth. In a new-born dog the vermis is
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| perfectly straight and its folia entirely transverse.
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|
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| Lobule D is connected to the upper part of the paraflocculus
| |
| by a low white ridge, which can only be discovered by removing
| |
| the lowest and most posterior part of lobe C. The rest of lobe
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| D and lobe E call for no remark.
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|
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| The paraflocculus is relatively larger than that of the badger,
| |
| to which it bears a close resemblance in the manner in which
| |
| its two tiers are arranged. It has not, however, a lobulus
| |
| petrosus; or, at any rate, there is not more than the merest
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| 330 PROFESSOR O. CHARNOCK BRADLETY.
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|
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| attempt at the formation of one, this occurring at the posterior
| |
| end of the lower tier, and being only occasionally present. The
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| flocculus is small and consists of a few folia, placed, under cover
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| of the paraflocculus, at the most anterior limit of the lateral
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| recess of the ventricle (fig. 95).
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|
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| Canis vulpes (figs. 97, 98 and 99).—The general shape of the
| |
| cerebellum of the fox is very different from that found in the
| |
| dog. The fox’s cerebellum has a greater vertical height in comparison with its antero-posterior diameter. Its anterior surface
| |
| is depressed for the reception of the corpora quadrigemina, and
| |
| its posterior surface is also concave from above downwards.
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| The posterior concavity is rendered all the more obvious because
| |
| of the backward projection of lobe D over the medulla. This
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| projection is confined to lobule D,, and is so great that this
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| lobule can be seen very distinctly when the cerebellum is
| |
| viewed from above. These differences being recognised, the
| |
| cerebellum of the fox otherwise resembles that of the dog.
| |
| The only points to which it seems necessary to draw attention
| |
| are two, as follows: The vermis in the region of lobules C,
| |
| and C, is possibly a little shorter in an antero-posterior
| |
| direction, and somewhat less distorted in form. The lower
| |
| part of the paraflocculus carries a definite lobulus petrosus
| |
| (figs. 97 and 98).
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|
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| The flocculus is small in the fox, and only just visible from
| |
| behind (fig. 98).
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|
| |
| Felis domestica (figs. 100, 101 and 102).—In the domestic cat
| |
| the anterior part of the cerebellum is so similar to the same
| |
| portion in the dog, both as regards its superficial characters and
| |
| also its appearance in sections, that no detailed description is
| |
| needed. The most important features are those presented by
| |
| the organ when viewed from behind. Several cerebella of the
| |
| cat have been examined, and in all a very striking character is
| |
| the extreme to which the distortion of the central portions of
| |
| lobules C, and C, is carried (figs. 100 and 101). In the brain
| |
| from which the figures were made this distortion is very
| |
| marked, possibly more so than is the case in the average cerebellum ; but they serve to show to what lengths this twisting
| |
| of the vermis may go. It will be observed that lobules C, and
| |
| C,; are arranged in the form of an S-shaped curve, the bends of
| |
| THE MAMMALIAN CERÉBELLAR FISSURES. 931
| |
|
| |
| which are very abrupt. This curvature of the vermis is continued into lobe D, but here its bends are not so sudden (fig.
| |
| 101). There can be little doubt that this exaggerated dis-.
| |
| placement of the vermis is to be interpreted as meaning that,
| |
| in the cat, lobes C and D are relatively more developed (s0
| |
| far as those parts of them which belong to the vermis are concerned) than is the case in the other mammals examined. The
| |
| lateral parts of lobule C, are relatively smaller in the cat than
| |
| in the dog, badger, or fox (fig. 101). They do not extend 80
| |
| far downwards as to blot out the connection between paraflocculus and the vermis. This connection is in the form of
| |
| one or two folia, resting upon the medulla below, and in contact with the lowest part of lobule C, above.
| |
|
| |
| The paraflocculus resembles that structure in the dog. There
| |
| is considerable difficulty in distinguishing a flocculus with any
| |
| degree of certainty in the adult animal. That it is present is
| |
| undoubted from the observations made by Stroud on its
| |
| development. But its clear definition in the embryo appears
| |
| to become obscured at a later date.
| |
|
| |
| Goat and Sheep (figs. 103, 104 and 105)—In many respects
| |
| the cerebellum of ungulates departs, in the way of details,
| |
| from the plan found in those carnivora just described.
| |
|
| |
| When viewed from the front, the cerebella of the goat and
| |
| sheep show fissures c, I., II. and b very distinctly (fig. 103), all
| |
| of these reaching the margins of the hemisphere. Fissure c
| |
| crosses the vermis almost perfectly transversely. Lobule A,
| |
| has only a very imperfectly developed hemisphere portion;
| |
| indeed it is doubtful if the hemispheres can be considered to
| |
| extend into this region. Fissure I, possibly a little shallower
| |
| than c, has a curved direction. Fissure IL is very acutely
| |
| curved, as in the dog. Lobule A, and lobe B are almost entirelÿ
| |
| confined to the vermis, their lateral prolongations being very
| |
| small Indeed, in this region it is difficult to set definite bounds
| |
| between the vermis and the hemispheres. There is some
| |
| amount of lateral displacement, with consequent curvature, in
| |
| the vermis in lobules C, and C,, but this is not greater in
| |
| amount than that found in the dog.
| |
|
| |
| In the sheep and goat, and in ungulates generally, the lateral
| |
| divisions of lobule C, are not nearly so large as they are in the
| |
| 339 PROFESSOR O. CHARNOCK BRADLEŸ
| |
|
| |
| carnivora. In the carnivora their uppermost ends are commonly
| |
| visible, either on one or both sides, when the cerebellum is
| |
| regarded from the front. This has never been found to obtain
| |
| in those ungulates which have been examined for the purposes
| |
| of this research. Again, these lobules do not reach so far down
| |
| as to touch the medulla, other than in exceptional cases. The
| |
| result of this vertical abbreviation is to allow of the connection
| |
| of the paraflocculus to be traced directly to the vermis, as is
| |
| the case in the simpler forms of cerebellum (fig. 104). As we
| |
| have seen, this connection is easily made out in the adult pig.
| |
| In the sheep and goat, however, it is not quite so evident on à
| |
| superficial examination ; it is necessary to open up the groove
| |
| between vermis and hemisphere.
| |
|
| |
| The form of lobule D, is somewhat peculiar in both the sheep
| |
| and goat (fig. 104). It has a central, well developed portion in
| |
| the vermis, and smaller offshoots reaching into the hemispheres,
| |
| a constriction of greater or less tenuity intervening.
| |
|
| |
| Lobe E is of larger size than in the pig and the carnivora.
| |
| The paraflocculus and flocculus resemble those parts of the
| |
| cerebellum of the pig.
| |
|
| |
| Bos taurus (fig. 106).—In the cerebellum of the cow, although
| |
| the same lines are followed as in the sheep and goat, the arrangement of fissures appears at first sight to be very complicated.
| |
| This remark applies only to the superior and posterior views,
| |
| as lobes À and B and lobule OC, are almost identical in form
| |
| with those parts in the average carnivore or ungulate brain. It
| |
| may be added that it is impossible to make out any hemisphere
| |
| in lobe A. Even in lobe B the hemisphere is very attenuated.
| |
|
| |
| On closely examining the posterior part of the cerebellum, it
| |
| is found that the complexity is more apparent than real, and is
| |
| due to a distortion which rivals that of the cat’s vermis. Apart
| |
| from this disturbance of form, there is little to which special
| |
| attention need be directed. It may be mentioned, however,
| |
| that the lateral parts of lobule C, commonly extend farther in
| |
| a downward direction than obtains in the sheep and goat, this
| |
| extension bringing them almost or quite in contact with the
| |
| medulla. Not infrequently lobe E is so large and projects s0
| |
| far backwards as to be visible as one or two folia on the posterior aspect of the cerebellum.
| |
| THE MAMMALIAN CEREBELLAR FISSURES. 233
| |
|
| |
| Equus caballus (figs. 107, 108 and 109)—A very striking
| |
| feature in the horse’s cerebellum is the comparatively posterior
| |
| position of fissure IL. Fissures c, I, IL. and b are distinct and
| |
| deep. Fissure c is of very considerable depth, and fissure I. is
| |
| almost as deep as fissure IT. (fig. 109). It should be noted—as
| |
| distinguishing the cerebellum of the horse from that of the
| |
| sheep and goat, and especially from that of the cow—that lobe
| |
| À is certainly, though not very strongly, continued into the
| |
| hemisphere.
| |
|
| |
| The posterior part of the horse’s cerebellum shows one or
| |
| two points of interest and importance. As in the ungulates
| |
| already mentioned, the lateral parts of lobule C, are small as
| |
| compared with the carnivora. In the horse their connections
| |
| with the vermis are not difficult to follow. There is, further,
| |
| no difficulty in making out the connecting link between lobule
| |
| D, and the paraflocculus (fig. 108).
| |
|
| |
| In some specimens lobule D, is continued into the hemisphere for a short distance, but this continuation has only once
| |
| been found on both sides in the same brain. Its presence,
| |
| though inconstant, is interesting, as being apparently the
| |
| remains of that undoubted connection which we have seen to
| |
| exist between lobule D, and the lower part of the paraflocculus
| |
| during the embryonic life of the pig. In the majority of
| |
| animals all trace of this primitive unity is lost as the brain
| |
| grows into its adult form; but in some, possibly in man, evidences remain.
| |
|
| |
| Lobule E is, if anything, smaller in the horse than it is in
| |
| the sheep, goat and cow. The paraflocculus shows its two-tier
| |
| character more clearly than in the other ungulates examined,
| |
| in this respect resembling the paraflocculus of the carnivora.
| |
| It should be remembered that in ungulates generally the lower
| |
| tier shows a tendency to curve forwards at its posterior end.
| |
| This is so well marked in the horse that there are practically
| |
| three tiers produced. In an earlier part of this paper the suggestion has been thrown out that possibly the lobulus petrosus of
| |
| the rabbit, etc. represents only the posterior extremity of the
| |
| lower part of the paraflocculus of more complex cerebella. It may
| |
| be asked, further, whether in those animals like the horse, in
| |
| which the paraflocculus turns forwards at its posterior end, this
| |
| 234 PROFESSOR O0. CHARNOCK BRADLEY.
| |
|
| |
| recurved extremity may not be equivalent to a lobulus petrosus,
| |
| unenclosed in a special fossa of bone. The supposition that this
| |
| may be so is strengthened when the condition found in the badger
| |
| is taken into account. In the cerebellum of Meles taæus, of
| |
| which a description has already been given, on one side a lobulus
| |
| petrosus was found; but on the other side the corresponding
| |
| part of the paraflocculus was turned forwards underneath the
| |
| lower tier. |
| |
|
| |
| The flocculus is usually easily distinguished in the horse, and
| |
| is visible from the side and from behind. In some specimens
| |
| a distinct white ridge, independent of the posterior medullary
| |
| velum, passes from the flocculus to lobe E of the vermis. This
| |
| ridge is indicated on the left side of fig. 108. It has not been
| |
| met with elsewhere than in the horse—possibly because an
| |
| insufficient number of cerebella have been examined—but its
| |
| occurrence in this animal is of importance, as showing evidence,
| |
| in the adult, of the embryonic unity of the structures between
| |
| which it passes.
| |
|
| |
| Equus asinus.—The cerebellum of the donkey is 80 like that
| |
| of the horse in all but the merest details that an extended
| |
| description is not necessary. It may perhaps be well to say
| |
| that lobule C, in the hemisphere carries several fairly deep
| |
| fissures, whose presence give the surface a complex appearance.
| |
| Lobule D, shows the tendency, remarked in the sheep and goat,
| |
| to extend into the hemispheres in the form of lateral appendages. The connection of this lobule with the paraflocculus is
| |
| not so superficially evident as it is in the horse. The flocculus
| |
| of the donkey has a greater antero-posterior extent than is the
| |
| case in the horse.
| |
|
| |
| In the foregoing pages the steps by which the fissures, and
| |
| consequent lobes and lobules, of the cerebellum came into
| |
| existence have been traced in two mammals. It has also been
| |
| sought to discover the simplest form of mammalian cerebellum,
| |
| and this having been done, to endeavour to recognise, in the
| |
| complex as well as in the simpler forms, a likeness to this
| |
| elementary pattern. Apparently the cerebellum in which the
| |
| fissures are fewest and the lobes smoothest belongs to the
| |
| shrew and the smaller bats. In the shrew there are four
| |
| THE MAMMALIAN CEREBELLAR FISSURES. 235
| |
|
| |
| fissures only ; and of these only one (the second, 4e. IL.) extends
| |
| through both vermis and hemisphere. The remaining three do
| |
| not belong to the hemisphere, being confined to the vermis or
| |
| its immediate neighbourhood.
| |
|
| |
| In following the development of the cerebellum of the rabbit,
| |
| it was found that this five-lobed and four-fissured stage was
| |
| reproduced. But in the adult rabbit the number of fissures is
| |
| increased. In the development of the pig, it appears possible
| |
| that the five-lobed condition may obtain in its simple form for
| |
| a time, but it quickly gives place to a much greater complex of
| |
| fissures. |
| |
|
| |
| In both rabbit and pig fissure IV. was the first to appear,
| |
| and this in association with the Rautenlippe, which, continuing
| |
| round the lateral recess of the ventricle, blends with the
| |
| Rautenlippe of the medulla The association of fissure IV.
| |
| originally seems beyond doubt. But as development goes on it
| |
| becomes more and more removed from the edge of the cerebellar
| |
| lamina, because of the growth of lobe E and the flocculus.
| |
|
| |
| In both rabbit and pig the second fissure to develop is
| |
| fissure II. which has been recognised by several writers to be
| |
| of paramount importance, and which is declared by both Stroud
| |
| and Kuithan to be the first fissure visible in the developing
| |
| cerebellum.
| |
|
| |
| The next fissures, in point of time of appearance and importance as dividing lines of the cerebellum, are fissure III. and
| |
| those demarcating the paraflocculus from the rest of the hemisphere. These three are in reality the three elements of. one
| |
| and the same fissure, which, becoming continuous, they ultimately
| |
| form.
| |
|
| |
| By the presence of the above mentioned fissures, the cerebellum
| |
| becomes divided transversely (but not completely as yet) into four
| |
| unequal portions. (1) À part anterior to fissure IL.; this becoming itself divided later into lobes A and B by fissure I. (2) Lobe
| |
| C, lying between fissure II. and fissure III. with its lateral
| |
| elements. (3) Lobe D, to which the parafiocculus belongs. And
| |
| (4) lobe E, of which the flocculus is an outlying dependency.
| |
|
| |
| Fissure I., separating lobes À and B, appears shortly after
| |
| fissure IIT. in the rabbit, and somewhere about the same timein the
| |
| pig. The other fissures, which are formed either at the same time
| |
| 236 PROFESSOR O. CHARNOCK BRADLEY.
| |
|
| |
| as some of the above (as in the pig), or at a somewhat later date
| |
| (as in the rabbit), may be considered as of secondary importance,
| |
| and have no representatives in the simplest type of mammalian
| |
| cerebellum.
| |
|
| |
| In those adult cerebella which have been examined, there
| |
| is quite clearly a common pattern running through the whole
| |
| series. But in many of them there are interwoven into this
| |
| fundamental pattern subsidiary ornaments, which tend, in a
| |
| measure at least, to obscure the simplicity of the cerebellum which has been taken as the starting-point. In all the
| |
| cerebella the five fundamental lobes can be recognised, and
| |
| their individual peculiarities and tendencies may be summarised
| |
| as follows :—
| |
|
| |
| Lobe A, in all but the very simplest forms, is divided into
| |
| two unequal parts by fissure c This fissure is wanting in the
| |
| shrew and indefinite in the hedgehog, but is constant in all
| |
| others. Lobule A, in the higher forms consists of three sublobules. In some there are apparently only two of these
| |
| divisions. It is possible that this complexity of the lobule may
| |
| be indicated even in the rabbit. Lobule A, is always smaller
| |
| than lobule A,, and is generally provided with a moderately
| |
| deep fissure, whose precursor may possibly be shown in the
| |
| rabbit.
| |
|
| |
| In the higher forms lobe B is divided into two parts, each of
| |
| which may be again divided. In the rabbit and hedgehog it
| |
| carries two folia, separated by a moderately deep fissure.
| |
|
| |
| Lobe C consists of three lobules, separated by fissures à and
| |
| b. Of these two fissures « is held to be much the more important morphologically, because of its earlier appearance in the
| |
| embryo and its more constant character in the adult. These
| |
| two fissures apparently develop in a manner peculiarly their
| |
| own. They both begin in the hemisphere, and grow towards
| |
| the middle line.
| |
|
| |
| Lobule C, must be considered as standing definitely apart
| |
| from the rest of lobe C. Its differentiation is early, especially
| |
| in the pig, and in all the adult animals described, from the
| |
| squirrel upwards, its individuality is very strongly asserted.
| |
|
| |
| Even in the rabbit there is an attempt at a division of lobe
| |
| D, but this is not accomplished until the squirrel is reached.
| |
| THE MAMMALIAN CEREBELLAR FISSURES. 237
| |
|
| |
| In the higher forms the division is embryonic and early. In
| |
| the ‘pig, fissure d appears about the same time as fissures III.
| |
| and ÏI. Particular attention has been called to the development of fissure d because of its forward extension and invasion
| |
| of the paraflocculus, which is, as a result, divided into two
| |
| parts, as is the rest of lobe D to which it belongs. Subsequent
| |
| development may obscure the continuity of the paraflocculus
| |
| with lobule D,, or, on the other hand, the connection may persist into adult life (eg. in the horse). The connection of the
| |
| paraflocculus with lobule D, is always lost in the adult, but
| |
| there may remain slight traces, such as are found in the horse.
| |
|
| |
| The embryonic continuity of lobe E and the flocculus, and
| |
| their morphologie unity, have already been commented upon.
| |
| This continuity early disappears, and there is usually no trace
| |
| of it apart from the posterior medullary velum. But in the
| |
| horse at least, as has been noted, some evidence may exist
| |
| even in the adult.
| |
|
| |
| The various fissures and lobes have been distinguished, up to
| |
| this, by letters and figures only. It would have been easy to
| |
| employ terms such as those used in human anatomy, but—as
| |
| Oliver Wendell Holmes has expressed it— words, from occupying for a long time the same place in language, become
| |
| ‘polarized.” So, in order to trammel the mind as little as
| |
| possible, it was thought better to avoid those terms which
| |
| would call up certain fixed and long-rooted conceptions.
| |
|
| |
| The purpose of keeping the judgment as unbiassed as possible
| |
| being now served, the letters and figures may give place to
| |
| terms such as are commonly employed. In order to do this,
| |
| the notion of the plan of the mammalian cerebellum, which has
| |
| been gained from the descriptions given herein, must be applied
| |
| to the cerebellum of man. Using the technicalities as employed
| |
| by Schäfer in Quain's Anatomy, the letters and figures may be
| |
| transmuted as follows :
| |
|
| |
| There can be little doubt that fissure IT. corresponds to sulous
| |
| preclivalis, fissure III. to sulcus postpyramidalis, and fissure IV.
| |
| to sulcus postnodularis. Fissures a and b correspond respectively
| |
| to sulci horizontalis magnus and postclivalis, and fissure & is
| |
| equivalent to sulcus prepyramidulis. That sulcus horizontalis
| |
| magnus should not be employed, as is done in human anatomy,
| |
|
| |
| VOL. XXXVII. (N.S. VOL. XVII.)—APRIL 1903. 17
| |
| 238 PROFESSOR O0. CHARNOCK BRADLEY.
| |
|
| |
| to divide the cerebellum into two primary parts, is evident, and
| |
| has been pointed out and insisted upon by Stroud. The comparative method clearly shows that sulcus preclivalis (furcal
| |
| suleus of Stroud) forms the real and fundamental dividing line.
| |
|
| |
| In that part of the cerebellum which falls anterior to fissure
| |
| IT. (suleus preclivalis), difficulties arise in the use of human
| |
| anatomical terms. For sulcus postcentralis of the human
| |
| anatomist corresponds to fissure c; a fissure secondary both in
| |
| point of time of appearance in the embryo and in morphologie
| |
| value. In the current descriptions of the human brain, as
| |
| given in this country, no suleus is mentioned as equivalent to
| |
| fissure I. The result is that the culmen of human anatomy
| |
| includes lobe B and lobule A, Lobule A, probably corresponds
| |
| to the “ascending part of the monticulus” of some German
| |
| writers (Flatau and Jacobsohn, for instance), but I am not
| |
| certain that the expression is used for lobule A, alone or
| |
| always.
| |
|
| |
| The following table shows the parts in the human brain
| |
| corresponding to the various divisions of the mammalian cerebellum as described in this paper.
| |
|
| |
| Fissuress. Loges.
| |
|
| |
| Lobus centralis.
| |
| c. Sulcus postcentralis
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| I. (Not named by Schäfer)
| |
|
| |
| A.
| |
| Lobus culminis
| |
|
| |
| B
| |
|
| |
| A;.
| |
| A>
| |
| IT. Sulcus preclivalis
| |
|
| |
| b. Sulcus postclivalis
| |
|
| |
|
| |
|
| |
| Lobus cacuminis. Cy } C.
| |
|
| |
| a. Suleus horizontalis magnus__ ’
| |
| Lobus tuberis. C..
| |
|
| |
| III. Sulcus postpyramidalis,
| |
|
| |
|
| |
|
| |
| |
| |
| |
| |
|
| |
|
| |
|
| |
|
| |
|
| |
| Lobus pyramidis. D,
| |
| d. Sulcus prepyramidalis D.
| |
| Lobus uvulæ. D.. ]
| |
| IV. Sulcus postnodularis
| |
| Lobus noduli. }E.
| |
|
| |
| It will be observed that I have only examined the cerebella
| |
| .of placental mammals. Lack of suitable material has precluded
| |
| a first-hand investigation of Monotremes and Marsupials. But,
| |
| THE MAMMALIAN CEREBELLAR FISSURES. 239
| |
|
| |
| judging from the descriptions and figures given by Ziehen (7),
| |
| it is clear that the scheme, as elaborated in the foregoing pages,
| |
| will apply to Marsupials at least. These mammals evidently
| |
| fall into the group of animals in which the cerebellum follows
| |
| the simpler type. Whether Monotremes also can be included
| |
| in this group is not so obvious from the descriptions available.
| |
| It seems not unlikely that their cerebella belong to a group
| |
| separate from the rest of the mammalia.
| |
|
| |
| In carrying out the work of this investigation, so much
| |
| assistance, in the form of material, has been afforded by 80
| |
| many persons, that it is impossible to make suitable acknowledgment without going to considerable length. Let it suffice to
| |
| say, that my debt of gratitude is not to be computed from the
| |
| extent of the avowal here made. Much of the microscopie
| |
| work has been done in the Physiological Laboratory of the
| |
| University of Edinburgh, where, through the courtesy of Professor
| |
| Schäfer and his assistants, every facility that could be wished
| |
| for has been afforded. , /
| |
|
| |
| REFERENCE.
| |
|
| |
| (7) Zienen, Tu, ‘Das Centralnervensystem der Monotremen und
| |
| Marsupialier. Thiel L. Macroscopische Anatomie,” Jenai’sche Dentkschriften, vi., 1897.
| |
|
| |
| PLATES XVII-XXIII.
| |
|
| |
| EXPLANATION OF FIGURES.
| |
| Fig. pa. Pig embryo, 40 days, 52 mm. Posterior view. x 2.
| |
|
| |
| Fig. 55 » 40 days, 52 mm. Left lateral view. x 2.
| |
| Fig. 56. » 40 days, 52 mm. Mesial sagittal section.
| |
| Fig. 57. 5 44 days, 64 mm. Posterior view. x 2,
| |
| Fig. 58. 5 44 days, 64 mm. Anterior view. x 2.
| |
| Fig. 59. » 44 days, 64 mm. Mesial sagittal section.
| |
| Fig. 60. » 48 days, 80 mm. Posterior view. x 2.
| |
| Fig. 61. 5 48 days, 80 mm. Anterior view. x 2.
| |
| Fig. 62. » 48 days, 80 mm. Mesial sagittal section.
| |
| Fig. 63. 5 51 days, 88 mm. Posterior view. x 2.
| |
|
| |
| Fig. 64. 5» 51 days, 88 mm. Anterior view, x 2.
| |
| 240
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
|
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
| Fig.
| |
|
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| THE MAMMALIAN CEREBELLAR FISSURES.
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| 65. Pig embryo, 51 days, 88 mm. Mesial sagittal section.
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| 66. 5 55 days, 100 mm. Mesial sagittal section.
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| 67. » 59 days, 118 mm. Superior posterior view.
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| 68. 5» 59 days, 118 mm. Anterior view. x 2.
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| 69. » 59 days, 118 mm. Mesial sagittal section.
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| 70, » 65 days, 132 mm. Posterior view. x 2.
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| 71. » 65 days, 132 mm. Superior view. x 2
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| 72. » 65 days, 132 mm. Anterior view. x 2.
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| 73. » 65 days, 132 mm. Left lateral view. x 2.
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| 74. » 65 days, 132 mm. Mesial sagittal section.
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| 75. » 70 days, 150 mm. Superior view. x 2.
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| 76. » 165 mm. Posterior view. x 2.
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| 77. mn 165 mm. Superior view. x 2.
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| 78. » 165 mm. Left lateral view. x 2.
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| 79. 5» 165 mm. Anterior view. x 2.
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| 80. » 165 mm. Mesial sagittal section.
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| 81. Pig, adult. Anterior surface. x 1.
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| 82. ,, 5 Superior view. x 1.
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| 63. » Posterior view. x 1.
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| 84. ,, 5 Mesial sagittal section. x I.
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| 85. Mustela furo. Anterior surface. x 2
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| 86. » Superior view. x 2.
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| 87. 5 Posterior view. x 2.
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| 88. » Mesial sagittal section,
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| 89. Meles taxus. Anterior surface. x 1
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| 90. 5 Superior view. x 1.
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| 91. » Posterior view. x 1.
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| 92. Mesial sagittal section.
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| 93. Canis familiaris. Anterior surface. x 1.
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| 94. » Superior view. x 1.
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| 95. » Inferior surface. x 1.
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| 96. » Mesial sagittal section.
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| 97. Canis vulpes. Superior view. x 1.
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| 98. » Posterior view. x 1.
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| 99. » Mesial sagittal section.
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| 100. Cat. Superior view. x 1.
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| 101. ,, Posterior view. x 1.
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| 102. ,, Mesial sagittal section. x 1.
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| 103. Ovis aries. Anterior view. x 1.
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| 104. » Posterior view. x 1.
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| 105. Goat. Mesial sagittal section. x 1.
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| 106. Bos taurus. Mesial sagittal section. x 4.
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| 107. Equus caballus. Anterior superior view. x à.
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| 108. » Posterior view. x à.
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| 109. » Mesial sagittal section. x à.
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| Journ. of Anat. and Physiology, Jan. 1903.] [PLATE XVII.
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| - Floccuivs PA
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| th
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| CAS
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| -Paraflocculuss.
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| Floceulus.
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| Fic. 52° Fenetre Fic. 53: WU.
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Journ. of nat. and Physiology, Jan. 1903.] [PLATE XVIII.
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| Fic. 55.
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| Fic. 57.
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| Fic. 58
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| a À
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| Fic. 60. ÿ
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| ---- Paraflaceulus.
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| J°----.Flocculus
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| Fic. 62. ' ä Fic. 64.
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Journ. of Anat. and Physiology, Jan. 1903.] [PLATE XIX.
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| --Paraflocculus,
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| Parafloceulus. --.
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| Floceulus, ..--k
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| a”
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| Fig. 70.
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| Poraflocovlus.
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| 0
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| 7) +. d.
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| Cf Le Floceulus,
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| V4 CET x
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| D
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| Fiü. 73:
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Journ. of Anat. and Physiology, Jan. 1903.] [PLATE XX.
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| Paroflocculus. .….. ‘
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| Flocculus 4...
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| Fic. 78.
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| % à rh è Fic. 81.
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| + Floceulu
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Jottrn. of Anat. and Physiology, Jan. 1903.] [PLATE XXI
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| IL.
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| . x Parofloceulus
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| D h ‘
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| d. GET y
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| Fic. 4 E , Fic. 85. e .
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| “1 É
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| 1 à
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| L': Parafloceulus @- à à
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| Ta. Pa rafloe eulus
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| Floceulus
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| Fic. 88. FL.
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| :Paraflocoulvs.
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Journ. of Anat. and Physiology, Jan. 1903.] [PLATE XXII.
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| .-Purofloceulus
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| Paraflocculus.
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| TS. Parafloceulus
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| "Floceulus.
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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| Journ. of Anat. and Physiology, Jan. 1903.] [PLATE XXIIT.
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| ---Paraflosculus
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| FiG. or.
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| ---Paraflocoulus.
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| Te Flocculus.
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| -Parafloceulus
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| Fic. 104.
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| 7 Flocculus.
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| Professor O. CHARNOCK BRADLEY on the Development and
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| Homology of the Mammalian Cerebellar Fissures.
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