216 THE ESSENTIALS OF HISTOLOGY. 



LESSON XXXVIII. 



STRUCTURE OF THE SPINAL CORD. 



SECTIONS of the spinal cord from the cervical, dorsal, and lumbar regions. 

 As it is difficult to obtain the human spinal cord sufficiently fresh, that of a 

 dog, cat, or monkey may be used. It is to be hardened by suspending it 

 immediately after removal from the body in a tall jar of Miiller's fluid (see 

 Appendix). After a few hours the fluid is changed, and the cord is then left 

 for about a month, when it will be ready for sections. These are to be made 

 either with the freezing microtome or by the celloidin method. They may 

 be stained by the modified Pal method given in the Appendix, or by aniline 

 blue-black. The latter stains the nerve-cells and axis-cylinders, the former 

 the medullary sheath of the nerve-fibres. Carminate of ammonia may also 

 be employed to stain the nerve-cells and axis-cylinders. 



Notice the relative extent of the grey as compared with the white matter 

 in the different regions of the cord. 



Sketch a section from each region under a low power. Sketch also a small 

 portion of the white substance, two or three nerve-cells, and the central canal 

 with its lining epithelium and surrounding neuroglia under the high power. 



Measure the diameter of some of the nerve-fibres in the anterior columns, 

 n the lateral columns, and in the posterior columns. 



2. Tracts in the spinal cord. The conducting tracts of the spinal cord may 

 be studied in two ways, viz. : (1) by preparing sections of embryonic cords 

 (from the 5th to the 9th month), the sections being stained by the modified 

 Pal process ; (2) by preparing sections from the cord of an animal in which 

 either a complete section or a hemi -section has been performed about 10 days 

 before the animal is killed, and staining small pieces of the cord from below 

 and from above the section by placing them in a solution consisting of two 

 parts of Miiller's fluid and one part of 1 per cent, osmic acid (Marchi's 

 method). The cord must previously have been partly hardened by placing it 

 for a few days in Miiller's fluid. 



The spinal cord is composed of grey matter in the centre and of 

 white matter externally. It is closely invested by a layer of connective- 

 tissue containing numerous blood-vessels (pia mater), arid less closely 

 by two other membranes. One of these is an areolar membrane, 

 resembling a serous membrane in general structure, but non-vascular 

 and more delicate in texture (arachiioid). The other, which lines the 

 vertebral canal, is a strong fibrous membrane known as the dura mater. 

 At the middle of the anterior and posterior surfaces the pia mater dips 

 into the substance of the cord in the anterior and posterior median 

 fissures, so as to divide it almost completely into two lateral halves. 





