.i/. .1 \ />. 



The anterior extremity advances in a curve to neor tlic optic fossa. 



In aged animals, there arc sometimes found on the faces of the falx 

 eeivbri, especially towards its posterior extremity, small yellow granules. 

 known as the PaccJiii'iiinii ijlaitds. They are little nuclei of connective 

 tissue that arise from the subnrachnoideal tissm ; ///< ///</< nl o-.////////'r/i/x 

 would bo a better designation for them than that of glands. 



6. The tent<>rinni </ /*/.< 1U is composed of two lateral laminae, which form 

 a transverse partition between the cerebellum and the posterior extremities 

 of the cerebral lobes. 



Each lamina, coursed internally by one of the transverse sinuses, offers : 

 an adherent convex border, attached to tho parieto-tcmporal crest; a free 

 concave border, turned inwards and a little forwards, remarkable for its 

 thickness and solidity, and, with the second lamina, circumscribing an oval 

 opening through which the encephalic isthmus passes ; a superior extremity, 

 attached to the parietal protuberance ; an inferior extremity, which 

 disappears above the Gasserian ganglion, near the fold that surrounds tho 

 pituitary gland. 



Of the two faces of these lamina?, the anterior corresponds to the cerebral 



a, the posterior to the cerebellum. 



c. The zuprasjrficnoidal, or pituitary fold, is a thick, slightly salient, and 

 almost circular pad, channeled internally by the cavernous sinus, and 

 circumscribing the sella turcica by enveloping the pituitary gland laterally 

 and posteriorly. 



2. The Arachnoid Membrane. 



The arachnoid presents the same disposition as all the splanchnic serous 

 membranes, in being resolved into two layers a parietal and a visceral, 

 both constituting a perfectly closed sac, outside which the cerebro-spinal 

 is contained. The cavity of this sac is traversed by the roots of nerves, 

 the vessels of the brain and cord, and filaments and cellular lamella- which 

 pass from tho pia mater to the dura mater ; around all these its layers form 

 sheaths by becoming continuous with one another. 



Kach of these layers exhibits an adherent and a free face. The adherent 

 face of tho parietal layer is united, as we have already seen, to tho dm a 

 mater. That of the visceral layer covers the nervous axis in spreading 

 itself over tho pia mater, but without accompanying it into the anfractnosi- 

 f the central mass ; it is beneath this face of the visceral layer that tho 

 <( ]-i bro-spinal (or subarachnoid) fluid is confined in spaces which will bo 

 studied hen aft< r. P.y their fr, > fiu'i; which is smooth and moist, like that 

 of all serous membranes, tho arachnoid layers are in contact with each 

 other. 



STBUCTOBE. The structure of this membrane resembles that of all others 

 of the some nature. The meshes of elastic fibres are most abundant in tho 

 cranial portion. Everywhere tho parietal layer is only composed of a 

 simple layer of epithelium. The arachnoid has no proper vessels or 

 nerves; those which pass through it only accompany each other. 



SPINAI, AliAi'iiNoiD MKMJ-.IIANR. Tho parit-tnl /<//< r presents nothing of 

 int rest. Tin- riwi-al /'// r is separated from the spinal coid. throughout 

 ^tclit, by a some\\h;ii considerable space (the xnlmr<i<-hiini<l \, in \\ hieh 

 tlie suliarucimoid fluid is collect- d : this >j.ace is greatest posteriorly, 

 around the terminal extremity of the cord and the nerves of tho can. la 

 cquina. 



The adherent face of this membrane is only connccte.l \\ith the c.\' 



