CONTENTS.

On the Areas of the Axis Cylinder and Medullary Sheath as

seen in Cross Sections of the Spinal Nerves of Verte-
brates. By HENRY H. DONALDSON and G. W. HOKE.
(From the Neurological Laboratory of the University of
Chicago.) With one figure.

On the Number and Relations of the Ganglion Cells and Medul-
lated Nerve Fibers in the Spinal Nerves of Frogs of Dif-
ferent Ages. By IRVING HARDESTY. (From the Hearst
Anatomical Laboratory of the University of California.)

Editorial

Psychology and Neurology.

The International Commission on Brain Research.

Literary Notices.

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DENISON UNIVERSITY, GRANVILLE, OHIO

Comparative Neurology and Psychology

Volume XV

1905

Number 2

OBSERVATIONS ON THE SPINAL CORD OF THE EMU AND ITS SEGMENTATION.

By IRVING HARDESTY.

(From the Hearst Anatomical Laboratory of the University of California.)

With four figures in the text.

Some months ago a zoo in San Francisco lost by sudden death two specimens of Emu (Dromaeus novae-hollandiae) and the management very kindly delivered the carcasses to me within a few hours after death. The birds were immediately dissected and, with certain of the other organs, the central nervous system of each was removed and preserved in 10% formalin.

The specimens were full grown and considered of large size, being nearly as large as the adult ostrich. With the exception of the head and upper part of the neck, the bird resembles the Cassowaries; but it is larger, its neck relatively longer and it belongs to a different genus. In general size of the body it is intermediate between the Rhea, or South American ostrich, and the ordinary or African ostrich (Struthio camelus). The head, though less bare, is very similar to that of the ostrich, while most of the neck, unlike the ostrich, is covered with the long streaming plumage common to the rest of the body. The wings are even more rudimentary than those of the ostrich, being nothing more than slender stubs entirely hidden in the plumage and even void of spiny rudiments of wing feathers. Similar to the ostrich, the legs are bare but somewhat shorter in proportion than those of the ostrich and are relatively more stout, the "drumstick" being nearly as large in circumference as the thigh of a medium sized man.

The spinal cord of such an animal necessarily presents features of unique interest and preparations were made with the intention of describing it. Meanwhile, however, the paper of STREETER ('04) appeared giving a description of the spinal cord of the ostrich'and on comparison it was found that the spinal cord of the emu, in its general features, is apparently so similar to that of the ostrich that a full description of it was deemed unnecessary. STREETER'S desrcription of the one may be referred to for the most part as a description of the other.

This paper, therefore, may be limited to a few of the features presented in the spinal cord of the emu not touched upon by STREETER for the ostrich and to some further observations upon one or two points less fully treated by him.

In the lumbar enlargement alone STREETER mentions having observed a segmented appearance ("neuromeres") in the ostrich cord. He does not refer to such as present in other localities and little more than mentions it in the lumbar region. After noting a few of the general macroscropic features of the emu cord, some attention will be given here to the appearance of evident segmental enlargements in other localities, as well as in the lumbar region. In this respect it may differ from the spinal cord of the ostrich.

Lying in the vertebral canal, the spinal cord of the emu is surrounded by an epidural cavity which is somewhat larger in proportion than is usual in the more commonly studied mammals. The dura mater has an unusually smooth outer surface. Between the nerve pairs of the adjacent segments it appears thicker along the ventral and ventro-lateral aspects of the cord than along the dorsal aspect, while at the levels at which the nerves are attached it appears thicker along the lateral surfaces. From a number of measurements, made later from stained sections, the thickness of the dura mater was found to vary from 87 μ to 146 μ, withan average thickness of 113 μ. The arachnoidea is similar in proportional thicknesss and arrangement to that usually found in the mammals. The pia, however, is relatively thick as compared with that of the mammalian cord. It is well defined as to its outer surface and so thick as to be easily stripped from