. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 636 NERVOUS SYSTEM. (NERVOUS CENTRES. THE MENINGES.) sabulous matter consists chiefly of phos- phate of lime with a small proportion of phos- phate of magnesia, a trace of carbonate of lime, and a small quantity of animal matter. The pia mater adheres very closely to the surface of the brain, coming for the most part into contact with grey matter. When a portion of it is raised carefully in a fresh brain, num- berless extremely minute bloodvessels are seen passing from it into the cerebral substance. These are the princi
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 636 NERVOUS SYSTEM. (NERVOUS CENTRES. THE MENINGES.) sabulous matter consists chiefly of phos- phate of lime with a small proportion of phos- phate of magnesia, a trace of carbonate of lime, and a small quantity of animal matter. The pia mater adheres very closely to the surface of the brain, coming for the most part into contact with grey matter. When a portion of it is raised carefully in a fresh brain, num- berless extremely minute bloodvessels are seen passing from it into the cerebral substance. These are the principal nutrient vessels of the brain. On its outside the pia mater adheres partially to the arachnoid membrane. At those points which correspond to the convex portions of the convolutions the adhesion of arachnoid to pia mater is close; but at other places the latter membrane separates completely from the former. The pia mater of the brain differs from that of the spinal cord in its great delicacy and tenuity ; it wants the strength and density of the latter membrane. This is owing to its being composed almost entirely of extremely minute and delicate bloodvessels, whilst the spinal membrane consists chiefly of white fibrous tissue. The bloodvessels of the former are in- finitely more numerous than those of the latter, and the reason of this probably is that the cerebral membrane is chiefly in contact with grey matter, which requires a great quantity of blood, but the spinal membrane immediately embraces white matter, which is much less vascular. It is important, in a pathological point of view, to notice that this membrane is the me- dium of nutrition, not merely to the nervous matter of the brain and cord, but also to the arachnoid membrane which is immediately adherent to it, and to which it bears the same relative position as the sub-serous areolar tissues elsewhere to their respective serous membranes. Hence the difficulty, if not the impossibility, of adopting distinctions
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