SPINAL CORD. 97 



one ounce of water) for twenty-four or thirty-six hours, and then transfer it to a solution of 

 gum for twelve hours, and then cut it in the ordinary way with a freezing microtome. 



Stain the sections with logwood, carmine, or aniline blue-black, and mount them in 

 dammar. 



When investigating the structure of the nervous system, it is sometimes of importance 

 to have a section only partially cleared up. This may be done by examining a section in 

 Farrant's solution, though, for general purposes, mounting in dammar is to be preferred. 



Make transverse sections through the hardened cervical portion of the cord of a cat, rabbit, 

 or dog. Stain a section with carmine, or logwood, or preferably with aniline blue-black one 

 per cent solution, which stains the nerve-cells beautifully (p. xliv). Mount the sections in 

 dammar. 



Transverse Section of the Spinal Cord. EXAMINATION (L). Observe the pia mater 

 investing the cord. It consists of an outer part and an inner part, which latter sends numerous 

 processes or septa into the cord. Trace the passage of the outer layer into the anterior 

 median fissure, and a process of the inner layer into the posterior median fissure. 



Observe that the cord is essentially a bilateral, symmetrical organ, its two halves being 

 connected by a narrow bridge of tissue containing a small opening the central canal. Note 

 the broad, shallow, and well-defined anterior median fissure, and the narrow, deeper, and less 

 perfectly defined posterior median fi ssure, containing a process of the pia mater, often carrying 

 a blood-vessel. 



If the section has been made at the level of the origin of the nerve-roots, trace the fibres of 

 the anterior roots of a spinal nerve, leaving the cord by several bundles, whilst those of the 

 posterior root enter it as one bundle. 



White matter. Observe the white matter, composed of the cut ends of nerve-fibres of 

 the cord placed externally, and how each half is divided into an anterior, lateral, and posterior 

 column by the above-described arrangement of the nerve-roots. The posterior column is again 

 divided into two (in the cervical region), by a narrow band of connective tissue ; the narrow 

 inner part, which lies next the posterior median fissure, is known as the fasciculus cuneatus. 



Grey Matter. Observe the grey matter more deeply stained, and lying in the form of a 

 crescent in each half of the cord. Its extremities constitute the anterior and posterior horns 

 or cornua, though there is no well-marked limit between them. Note in the anterior horn 

 the numerous multipolar nerve-cells deeply stained, and observe the oval cap of deeply 

 stained matter the substantia gelatinosa which covers the posterior cornua. It is probably 

 non-nervous in its nature, and consists of a peculiar accumulation of ' neurogleia.' Observe 

 the bridge of tissue connecting, the two halves of the cord, and in it the central canal, lined 

 with columnar ciliated epithelium, in front and behind the canal, the anterior and posterior 

 grey commissures, also the nerve-fibres crossing in front of the anterior grey commissure, 

 forming the anterior white commissure. {Indicate the general arrangement in PI. XXIII., 

 Fig. i.) 



White Matter. (H). Observe the pia mater sending in septa ; trace these septa, becoming 

 continuous with a fine fibrous network the neurogleia lying between the nerve-fibres of the 

 white substance. Lying in the meshes of this network observe the cut ends of the nerve-fibres. 

 They are of different sizes : some are large, others of medium size, and some are very small. 

 Each axis-cylinder is deeply stained, and is surrounded by a clear, non-stained area, which 

 represents the white substance of Schwann, or myeline. In sections which have been 

 hardened for a long time in chromic acid, a well-marked concentric striation of the medulla 



O 



