GLAKDUL2E PACCHIOXI. -BLOOD-VESSELS. 567 



may be regarded as continued into the terminal filament of the spinal 

 cord, which thus connects it to the dura mater at the lower end of the 

 sheath. (See Figures 341 and 342.) 



Structure, It consists of white fibrous tissue, mixed with many exceedingly fine 

 elastic fibres which are seen on applying acetic acid. It is obviously continuous 

 on the one hand with the fibrous tissue of the pia mater, and on the other with that 

 of the dura mater. 



The pia mater of the cord presents a conspicuous fibrous band, running 

 down in front over the anterior median fissure. This was named by Haller, 

 linea splendens. 



Glandules Pacchioni. Upon the external surface of the dura mater, in 

 the vicinity of the longitudinal sinus, are seen numerous small pulpy-looking 

 elevations, generally collected into clusters, named glands of Pacchioni. 

 The inner surface of the calvarium is marked by little pits, which receive 

 these eminences. Similar excrescences are seen on the internal surface of 

 the dura mater, and upon the pia mater on each side of the longitudinal 

 sinus, and also projecting into the interior of that sinus. Occasionally they 

 are found also in other situations. 



These bodies are not found at birth ; and according to the brothers 

 Wenzel, they exist only in very small number, if at all, before the third year. 

 After the seventh year they are usually found, and they increase in number 

 greatly as life advances ; in some cases, however, they are altogether want- 

 ing. In animals there appears to be no corresponding structure. 



On a careful examination of the connections of these bodies it will be 

 found that the elevations, found on the outer surface of the dura mater and 

 within the longitudinal sinus, in no instance take origin in those positions, 

 but that they are grape-like bodies which are attached more deeply, and in 

 their growth have perforated the dura mater. Their precise origin and nature 

 were long the subject of conflicting opinions, but it has been satisfactorily 

 shown by Luschka that they are only an enlarged condition of normal villi 

 of the arachnoid, and that no other structure is involved in their formation. 

 Their most prolific source is, as one may very soon discover, the cerebral or 

 generally acknowledged layer of the arachnoid, but they likewise arise in a 

 similar manner from the serous surface of the dura mater, and may some- 

 times be found of all sizes in the recesses into which that surface is thrown 

 in the neighbourhood of the longitudinal sinus. (Luschka, in Miiller's 

 Archiv. 1852 ; and " Die Adergeflechte des Menschlichen Gehirns," 1855. 

 See also Cleland " On Tumours of the Dura Mater, &c.," in the Glasgow 

 Medical Journal, 1863.) 



BLOOD- VESSELS OF THE BRAIN AND SPINAL CORD. 



The origin and course of these vessels have already been described in the 

 Section Angeiology. In passing to their distribution the several arteries, 

 having passed across the arachnoid cavity, enter the subarachnoid space an I 

 then divide and subdivide into branches, which, in their farther ramification 

 in the nervous centres, are supported by the pia mater, and, it may be 

 remarked, are more deeply placed in the various fissures and sulci than the 

 small veins, which do not accompany the arteries, but pursue a different 

 course and are seen upon the surface of the pia mater. 



Moreover, it is to be observed that, whilst the main branches of the 

 arteries are situated at the base of the brain, the principal veins tend 



