PACCHIONIAN BODIES AND MOVEMENTS OF THE BRAIN. 727 



vibrator)- impulses it insulates the nerve-roots, and has important relations to the quantity of 

 blood in the brain and the cerebral circulation (Chemical Composition, 198).] 



[Spina bifida. Sometimes the lamina? of the vertebrae in the lumbar or other region of the 

 spinal column are imperfectly developed, in which case the membranes project through as 

 a tumour distended by cerebro-spinal fluid and covered by skin. The effects of rapid tapping 

 or compressing the sac are readily studied in such cases.] 



The Pacchionian bodies, or granulations, are connective-tissue villi, which serve for the out- 

 flow of lymph from the subdural and subarachnoid spaces into the sinuses of the dura mater, 

 especially the longitudinal sinus. The subarachnoid space also communicates with the spaces in 

 the spongy bone of the skull, and with the veins of the skull and surface of the face (Kollmann). 

 The subdural space also communicates with the lymphatic spaces in the dura, while the 

 latter communicate directly with the veins of the dura. Both the subdural and subarachnoid 

 lymphatic spaces communicate with the lymphatics of the nasal mucous membrane. The space 

 outside the dura of the spinal cord is called the epidural space, and may be regarded as 

 lymphatic in its nature ; the pleural and peritoneal cavities may be filled from it ; but it does 

 not communicate with the cavity of the skull. The plexuses of blood-vessels are surrounded 

 by undeveloped connective-tissue. The telae choroideae in the new-born are still covered with 

 ciliated epithelium. 



Movements of the Brain. The pulsations of the large basal cerebral vessels 

 communicate their pulsatile movements ( 79, 6) to the brain the respiratory 

 movements also affect it, so that the brain rises during expiration and sinks during 

 inspiration. Lastly, there are slight alternating vascular elevations and depressions, 

 occurring 2 to 6 times per minute, due to the periodic dilatation and contraction of 

 the blood-vessels ( 371). Psychical excitement influences these, and they are most 

 regular during sleep. The movements are best seen especially where the membranes 

 of the brain offer little resistance, e.g., over the fontanelles in children, and where 

 the membranes have been exposed by trephining. The presence of the cerebro- 

 spinal fluid is most important for the occurrence of these movements, as it propa- 

 gates the pressure uniformly, so that every systolic and expiratory dilatation of the 

 blood-vessels is concentrated upon those parts of the cerebral membrane which do 

 not offer any resistance (Bonders). When the fluid escapes, the movements may 

 almost disappear. 



Mental excitement increases the pulsations of the brain. At the moment of awaking, the 

 amount of blood in the brain diminishes ; sensory stimuli applied during sleep, so that the 

 sleeper does not awake, increase the amount of blood. As the arteries within the rigid skull- 

 case change their volume with each pulse-beat, the veins (sinuses) exhibit at every beat a 

 pulsatile variation in volume, the opposite of that occurring in the arteries (Mosso). 



The Cerebral Blood- Vessels. The blood-vessels of the pia, of course, are regulated by the 

 vaso-motor nerves ( 356, A, 3), and their calibre may also be influenced by the stimulation of 

 more distant parts of the body ( 347). Donders trephined the skull so as to make a round 

 hole, and filled it with a piece of glass, so that with a microscope he could observe changes in 

 the calibre of the blood-vessels. Paralysis of the vaso-motor nerves and narcotics dilate the 

 blood-vessels; they become greatly contracted at death (373, I.). The blood-vessels are 

 dilated during cerebral activity ( 100, A), as well as during sleep. Increased pressure within 

 the skull causes great derangement of the cerebral activity laboured respiration ( 368, B), 

 unconsciousness even to coma, and paralytic phenomena ail of which may in part be referable 

 to disturbances of the circulation. If all the cranial arteries be ligatured suddenly, there is 

 immediate loss of consciousness, together with strong stimulation of the medulla oblongata and 

 its centres, and death takes place rapidly with convulsions (compare 373). 



By the free anastomosis which takes place at the base of the brain, forming the circle of 

 Willis (fig. 510), the individual parts of the brain are preserved from want of blood, when one 

 or other blood-vessels is compressed or ligatured. Within the brain, the arteries are distributed 

 as "terminal" arteries, i.e., the terminal branches of any one artery end in their own area, and 

 do not anastomose with those of adjoining areas (Cohnheim). On the other hand, the peripheral 

 arteries (arteries of the corpus callosum, Sylvian fissure, and deep cerebral) which run externally 

 on the brain, form free anastomoses {Tichomiroiv). 



[The nutrient or gangHonic arteries for the central ganglia arise in groups from the circle 

 of Willis, or from the first two centimetres of its trunks. The antero-median group (1) supplies 

 the anterior part of the head of the caudate nucleus. The postero-median (2) enter the 

 posterior perforated space and supply the internal surface of the optic thalami and the walls of 

 the third ventricle. The antero-lateral groups (3, 3) from the middle cerebral enter the 

 anterior perforated space, supply the corpora striata, the anterior part of the optic thalamus, 

 and the internal capsule. These branches are apt to rupture. The postero-lateral (4, 4) 



