7. =Basal Vessels.= Anomalies in size and distribution, thickness and character of vessel-walls (sclerosis, atheroma, aneurism, calcification). Thrombosis, embolism, aneurism, sclerosis, atheroma, calcification, obliterative endarteritis due to syphilis, are the most common conditions. The changes in the middle cerebral arteries are of especial importance in cases of apoplexy, softening, etc. 8. =Inner Meninges.= The arachnoid, subarachnoid space and pia are usually considered together. The arachnoid bridges over the sulci, the pia dipping down following the brain substance. The contents of the subarachnoideal space are best seen, therefore, between the convolutions. The inner meninges are gray, delicate and transparent; the pial veins show plainly, the arteries are empty and lie deeper, while the more superficial veins are uniformly filled with blood. Sclerotic arteries run more superficially and are more prominent. The removal of the skull-cap often gives rise to the presence of air-bubbles in the pial vessels, and this should not be mistaken for any pathologic condition. Hypostasis likewise should not be regarded as a pathologic condition. Normally the membranes are moist; in increased intracranial pressure (tumors, hydrocephalus, hemorrhages) they are dry and dull. Inflammation is shown by a loss of transparency of the membrane and by the presence of exudate in the subarachnoideal space. Old thickenings are white and opaque. The amount of fluid in the subarachnoideal space may be so great as to cause the arachnoid to bulge out over the sulci. Note character of exudate (purulent, fibrinous, serous or hemorrhagic). In purulent meningitis greenish-yellow or yellowish-white collections of thin pus are found in the meshes of the arachnoid; in fibrinous inflammation the exudate is grayish or milky white. The normal fluid (cerebrospinal) of the subarachnoideal space is clear and small in amount. It is increased in œdema and congestion, as well as in serous inflammations. In inflammatory conditions the membranes are dull and cloudy and the fluid more or less turbid. Pathologic adhesions may exist between dura and inner meninges, and between the latter and the brain-substance. In the latter case the meninges do not strip easily, but pull off portions of the cortex. Over tumors, gummata, areas of softening, the meninges may be so adherent that they cannot be separated from each other. In old syphilitics, alcoholics, cachexias of old age, etc., the pia may be thickened, white and opaque (leptomeningitis chronica fibrosa). Aneurisms of the pia vessels are of great importance in cases of meningeal hemorrhage. They may be very small (size of pea) and often are found only after very careful search. Atheroma, infective emboli, etc., are also causes of meningeal hemorrhage. Meningeal tubercles are very common and often hard to recognize. They are usually best seen over the basal meninges. Often they can be demonstrated by stripping off the