Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: arteries of the cortex are, therefore, terminal arteries in the sense of Cohnheim. In small areas of the cortex, depending only upon a single vessel, the latter has been found at autopsies obliterated, with consequent destruction of the area involved, while the surrounding regions were intact. The blood-vessels of the cortex enter its substance at a date subsequent to the development of the nerve elements, among which they penetrate and ramify. HISTOLOGY OF THE CORTEX The Component Tissues.—Within the cortical pulp are found two distinct varieties of elements, derived from tissues of widely different fietal origin—blood-vessels of mesoblastic origin, nerve cells with their dependencies, and neuroglia of epiblastic structure. Without a sufficient number of arterioles to nourish them and veins to carry off the used blood, the nerve elements could not grow and function. Accordingly, the vascular structures are of an importance hardly secondary to that of the nerve elemeuts themselves. Indeed, a prwri, it may be assumed that a badly organized or damaged nerve cell might function better than a well-developed cell with an inferior supply of nourishment. Let us therefore turn to the histology of the vessels before attempting that of the nerve cell. Within the cortex we find medium-sized and small arteries, terminal arterioles, and eventually capillaries and veins of all sizes. The structure of the larger and smaller arteries is essentially similar, only as they progressively diminish in size the several component coats lose their distinctness, until finally the capillary is reached with its single tunic. On examining a properly stained section of an artery we find the wall separable into four contiguous sheaths, surrounded externally by a space of considerable extent, t...