392 



CRANIAL NERVES. 



Fig. 175. \vhich is connected by a commissure of the 



u same matter. The form of the grey sub- 

 stance, as observed in the section, is that of 

 t\vo irregularly curved lines joined by a 

 transverse band. The extremities of the 

 curved lines correspond to the sulci of origin 

 of the anterior and posterior roots of the 

 nerves. The anterior extremities, larger than 

 the posterior, do not quite reach this surface ; but the posterior appear upon 

 the surface, and form a narrow grey line, the sulcus lateralis posterior. 



The white substance of the spinal cord is composed of parallel fibres, 

 which are collected into longitudinal laminae and extend throughout the 

 entire length of the cord. These laminae are various in breadth, and are 

 arranged in a radiated manner ; one border being thick and corresponding 

 with the surface of the cord, while the other is thin and lies in contact 

 with the grey substance of the interior. According to Rolando the white 

 substance constitutes a simple nervous membrane, which is folded into 

 longitudinal plaits, having the radiated disposition above described. The 

 anterior commissure, according to his description, is merely the continua- 

 tion of this nervous membrane from one lateral cord across the middle 

 line to the other. Moreover, Rolando considers that a thin lamina of pia 

 mater is received between each of the folds from the exterior, while a layer 

 of the grey substance is prolonged between them from \vithin. Cruveil- 

 hier is of opinion that each lamella is completely independent of its neigh- 

 bours, and he believes this statement to be confirmed by pathology, which 

 shows that a single lamella may be injured or atrophied, and at the same 

 time be surrounded by others perfectly sound. 



CRANIAL NERVES. 



There are nine pairs of cranial nerves. Taken in their order from 

 before, backwards, they are as follows : 



1st. Olfactory. 

 2d. Optic. 



3d. Motores oculonm. 

 4th. Pathetici (trochleares). 

 5th. Trifacial (trigemini). 

 6th. Abducentes. 

 - , ( Facial (portio dura, 

 ' I Auditory (portio mollis). 



* Sections of the spinal cord. After Arnold. A. A section made across the lower 

 part of the corpora olivaria. 1, 1. Corpora pyramidalia. 2. Fissura longitudinalis an- 

 terior. 3. The corpus olivare; in the section of which the zig-zag outline of the corpus 

 jentatum is seen. 4. The corpus restiforme. 5. The grey substance of the corpus 

 lestiforme. 6. The corpora pyramidalia posteriora. 7. The floor of the fourth von 

 tricle. 



B. A section made between the third and fourth cervical nerves. 1. The fissura 

 /ongitudinalis anterior. 2. An indentation corresponding in situation with the fissura 

 iongitudinalis posterior, which latter is not distinguishable at this part of the spinal 

 cord. 3, 3. The antero-lateral columns of the spinal cord. 4, 4. The posterior columns. 

 5. The anterior cornu of grey matter. 6. Its posterior cornu, terminating at 7, the snlrus 

 lateralis posterior. 8. The isthmus connecting the grey matter of the two sides of the 

 iord. 



