Till: i 7.7,'/:/;/.'M..s/'/.\ |/. | \/>. .;,;:, 



brain, is alkaline, and contains but a sniiill quantity of albumen ; it varies 

 in quantity according to tin- ri lutive siy.e of tin- c. ivhro-spinal axis ami its 

 containing cavity, or with the amount of blood sent to thin region. By 

 finding, under all circumstances, an equable piessurc on tin- Itrain and 

 spinal cord, and the iitTves emanating from these, its importance as a hydro- 

 ageut is greatly enhanced. ) 



3. Tfie Pia Mater. 



The fin maler, the proper envelope of the cerebro-spinal axis, is a thin 

 membrane whoso framework, essentially connective, sustains on its external 

 face a very abundant network of blood-vessels and nerves. 



plied immediately to the surface of the encephalon and spinal cord, it 

 adheres timily to that surface and follows all its inequalities, penetrating 

 : he cerebral or cerebellnr convolutions, and forming in each inter- 

 mediate sulcus two layers that lie against each other. 



The external face of the pia mater, bathed in part of its extent by the 

 subaraehnoid fluid, adheres to the visceral layer of the arachnoid by means 

 of a more or less dense and close filamentous connective tissue. From it 

 the cellular c>v< -rings that constitute the neurilemma of the nerves. 

 It detaches a multitude of filamentous or lamellar prolongations to the 

 int rnal lace of the dura mater, which traverse the arachnoid cavity in the 

 same manner as the nerves and vessels, by being enveloped, like these, in a 

 sheath furnished by the arachnoid membrane. Always very short, these 

 prolongations simulate the adhesions established between the two layers of 

 that membrane. 



The internal face is united to the nervous substance by multitudes of 

 arterial and venous radicles or connective filaments, which leave the pia 

 mater to plunge into this substance. 



The vessels of the pia mater form a very close network, from which are 

 !u-d branches that reaoh the medulla and encephalon. They arc ac- 

 companied by nervous filaments, and surrounded \tjftiriwuaHaf canals, which 

 : <-w believed to be lymphatics. Certainly, in their interior a colour- 

 less fluid circulates, and which contains globules very like those of lymph. 



Snx.u. l'i v MATEU. Less vascular than the cranial pia mat r. with 

 which it is continuous towards the mi dnlla ohlongata. this membrane is 

 remark ,tl>!<- f ->r the arrangement of the prolongations that arise from its 

 



The liiti rnal prolongations form longitudinal lamiuro at the fissures of the 

 cord, and enter these fissures. 



The external prolongation* attach, as we have said, the pia mater t the 

 nal meninge. A very large nnml>er are filamentous in form, and are 

 Tsed over the superior and inferior surfaces of the cord. Otluis consti- 

 tute on each side of the organ, a fest-iom-d hand named the <L ntat<-<l /<''/"""/ 

 m ittiiiit ili-nlata, or dcnticulaium). These ligaments exist throughout the 



_'th of the m> dullary axis, between tin: superior and inferior n 

 roots: their inner border is confounded for its whoh: length with the pia 

 mater; and their outer margin, cut into festoons, attaches itself to the dura 

 mat<-r by the summit of the angles separating these festoons. 



inpl. t: tliis description of the spinal pia mater, there may be noticed 



a posterior or nx-i-i/ycal }irl >n'jutii>n (jilitm tcnuin il>)\ a very narrow process 



formed by this membrane at the posterior extremity of the cord, situated in 



the mid>t of the canda equiiia in rves. and attached to the lx;tt mi of the 



'/ 'l<--nac at the termination of th" dura m.i: 



