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necessitated a development of two anterior lateral branches of the azygos vessel into the two lateral anterior cerebral arteries, and that with this has progressively gone on a shortening of the fusion of the two vessels and an atrophy of the azygos terminal, until finally we find the human type of this vessel, the anterior communicating artery, and the two lateral cerebrals. The fact that we occasionally meet with a median vessel, with fusion of

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FIG. 4. Photograph of a dissection showing the two lateral anterior cerebral arteries and a large median anterior cerebral artery with a typical distribution.

the two anterior cerebrals, and other anomalies of this set of vessels, I think may be accounted for on the principle of reversions and anomalies so frequently found among the insane.

The median anterior cerebral artery has been found in all forms of mental diseases, possibly a little more frequently in forms of dementia. In 400 cases of mental disease, 42 instances of the abnormal vessel were found; 11 were in senile dementia, 7 in chronic

dementia, 5 in epileptic dementia, 5 in arteriosclerotic dementia, 4 in paresis, 3 in chronic melancholia, 2 in dementia praecox, and 1 case each in manic-depressive insanity, organic dementia, acute delirious mania,acute mania, and idiocy. Twenty-five of these cases were in white males, 11 in colored males, 4 in colored females and 2 in white females. The disproportion between the cases examined of each color and sex makes this of relatively little value.

I do not see that there can be any special relationship between the mental disease per se and the presence of this anomalous vessel, but on the supervention of arterial diseases some very interesting cerebral conditions might be caused. In most instances, cerebral arterial anomalies are compensated for before the develop

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FIG. 5. Diagram of the Circle of Willis with a typical median anterior cerebral artery.

ment of the psychosis, the anomaly being then only indicative of ill development.

In these days of bold operations upon the vessels and even on structures at the base of the brain, it might be well for the surgeon to bear in mind the existence of these anomalies. In fact the main object of the paper of Grünbaum and Sherrington, quoted from above, was to call attention to the surgical relations of the inequalities of cross anastomosis of the circulation in anomalies of this anterior arterial system. Illustrative of these dangers may be mentioned one of my own cases in which thrombosis of the intracranial portion of the carotid artery resulted in death of the

whole left hemisphere on account of small size and sclerotic obstruction of the anterior communicating artery and the left posterior cerebral artery.

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FIG. 6. Photograph of the base of the brain showing the origin of a large median anterior cerebral artery.

The conclusions which I think we may reach with certainty are as follows:

1. There is a gradual development of the lower mammalian form of azygos anterior cerebral artery into the perfect Circulus Willisii of the human type.

2. The frequent variations of this system of vessels suggest instability of ontogeny, and of phylogeny.

3. The anomalies of these arteries together with the presence

of the median anterior cerebral artery are frequent among the insane.

4. That in keeping with other anomalies of the brain among the insane it is probable that many of these variations are in the direction of reversion to the primitive type, and that it is reasonable that the frequently found arteria termatica is one of these reversions or survivals such as are not uncommon in other organs.

Accepted by the Wistar Institute of Anatomy and Biology, March 24, 1910. Printed July 7, 1910.

CONTRIBUTIONS FROM THE ZOÖLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOÖLOGY AT HARVARD COLLEGE. E. L. MARK, DIRECTOR. No. 208.

DEGENERATION IN THE GANGLION CELLS OF THE CRAYFISH CAMBARUS BARTONII GIR.

HANSFORD MACCURDY

WITH NINE FIGURES

INTRODUCTION

Much of our knowledge of the changes occurring in the central roots of nerves and their ganglia after the nerve trunks have been severed has accumulated during the last two decades. In the earlier observations and experiments, attention was directed chiefly to the nerve roots and their related ganglia. From various causes, including the complex character of the nerve centers, the earlier investigations did not include the ganglion cells. Only comparatively recently has attention been directed specially to the ganglion cells and the changes occurring in them.

It was suggested to me by Professor G. H. Parker that the large nerve cells of the abdominal ganglia of the eastern crayfish, Cambarus bartonii, would afford favorable material for the study of the changes in the ganglion cells after their nerve fibers had been severed. Inasmuch as the investigations hitherto reported have been on the nerve cells of vertebrates, the additional purpose of extending our knowledge to an invertebrated animal would also be served.

As it is well known, Waller held that only those parts of the nerve fibers degenerate which are separated from their nerve centers. For many years this view prevailed. In time, however, from observations made in cases where limbs had been amputated which revealed an altered condition of the nerve roots and their ganglia, doubts arose as to whether Waller was correct in limiting the changes to the peripheral parts of the affected nerves. The

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