Should this preponderance of the cortex over the medullary portion not occur in the human, that is, if the proportions remain like those of other animals, the brain fails to develop properly, or an entirely brainless monster is generated.

It will also be seen that the shaft is a hollow cylinder, formed of compact tissue, enclosing a cavity called the medullary canal, which is filled with a pulpy, yellow fat called marrow.

At the ends of a long bone, where it expands, there is no medullary canal, and the bony tissue is spongy, with only a thin layer of dense bone around it.

Short and irregular bones have no medullary canal, only a thin shell of dense bone filled with cancellous tissue.

A, membrane of the hair-follicle, cells with nuclei and pigmentary granules; B, external lining of the root sheath; C, internal lining of the root sheath; D, cortical or fibrous portion of the hair shaft; E, medullary portion (pith) of shaft; F, hair-bulb, showing its development from cells from A. ]

These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules.

Note on the cut surfaces, on the outer side, the darker cortical portion, and on the inner side, the smooth, pale, medullary portion.

This core is surrounded by the white substance of Schwann, or medullary sheath, which gives the nerve its characteristic ivory-white appearance.

The medullary sheath, on the other hand, is broken at intervals of about 1/25 of an inch, and at the same intervals nuclei are found along the fiber, around each of which is a minute protoplasmic mass.

Some nerve fibers have no inner sheath (medullary), the outer alone protecting the axis cylinder.

These are known as the non-medullary fibers.

They are gray, while the ordinary medullary fibers are white in appearance.

A, a medullated nerve fiber, showing the subdivision of the medullary sheath into cylindrical sections imbricated with their ends, a nerve corpuscle with an oval nucleus is seen between the neurilemma and the medullary sheath; B, a medullated nerve fiber at a node or constriction of Ranvier, the axis cylinder passes uninterruptedly from one segment into the other, but the medullary sheath is interrupted.

A, a medullated nerve fiber, showing the subdivision of the medullary sheath into cylindrical sections imbricated with their ends, a nerve corpuscle with an oval nucleus is seen between the neurilemma and the medullary sheath; B, a medullated nerve fiber at a node or constriction of Ranvier, the axis cylinder passes uninterruptedly from one segment into the other, but the medullary sheath is interrupted.

A, a medullated nerve fiber, showing the subdivision of the medullary sheath into cylindrical sections imbricated with their ends, a nerve corpuscle with an oval nucleus is seen between the neurilemma and the medullary sheath; B, a medullated nerve fiber at a node or constriction of Ranvier, the axis cylinder passes uninterruptedly from one segment into the other, but the medullary sheath is interrupted.

Here we have three bones whose medullary cavity is extremely smallalmost nil, in factwhich explains in some measure how easy it is when suppuration exists to get necrosis and exfoliation of, say, portions of the os pedis.

Inflammatory changes occurring in the medulla we may pass without consideration, for in the bones of the foot the medullary cavity is so small, and the changes taking place in it of such minor importance, that we may do this without in any way seriously prejudicing our work.

The ends of the bones are thus exposed, and their medullary cavities exposed to infection.

In Figs. 11 and 12, which show a few tracheæ and medullary rays of the ligneous bands of the same plant, we observe the same phenomenon.

The direction of rupture is, according to Jaccard, not influenced by the distribution of the medullary rays.

140-141): "The sides of the medullary rays sometimes produce planes of least resistance varying in size with the height of the rays.

The medullary rays assume a direction more or less parallel to the lumen of the cells on which they border; the latter curve to the right or left to make room for the ray and then close again beyond it.

If the force acts parallel to the axis of growth, the tracheids are more likely to be displaced if the marginal cells of the medullary rays are provided with weak walls that are readily compressed.

This explains why on the radial surface of the test blocks the plane of rupture passes in a direction nearly following a medullary ray, whereas on the tangential surface the direction of the plane of rupture is obliquebut with an obliquity varying with the species and determined by the pitch of the spirals along which the medullary rays are distributed in the stem."

This explains why on the radial surface of the test blocks the plane of rupture passes in a direction nearly following a medullary ray, whereas on the tangential surface the direction of the plane of rupture is obliquebut with an obliquity varying with the species and determined by the pitch of the spirals along which the medullary rays are distributed in the stem."