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The canal for the spinal chord is of remarkable width throughout the sacrum. 

 Its transverse diameter in the first lumbar vertebra is two inches and a half, and 

 its vertical diameter two inches. It progressively dilates to the middle of the 

 sacrum, after which it contracts. The lumbar nerves issued by lateral perfora- 

 tions in the continuous neurapophysial plate, which are a little in advance of the 

 intervertebral spaces. The fourth pair of nervous foramina, which is between 

 the last lumbar and first sacral vertebrae, has a more obhque direction, looking 

 downwards and outwards, and is situated nearer the body of the vertebra. EacK 

 of these foramina is formed by the confluence of two distinct canals. The fifth, 

 sixth, seventh, eighth, and ninth pairs of foramina for the sacral nerves look 

 nearly vertically downwards, open on the under or inner surface of the vertebras, 

 and progressively increase in size. A wide oblique canal is continued from the 

 fifth outwards and downwards. A corresponding canal extends from the sixth 

 directly outwards to the upper border of the great ischiadic foramen. The canal 

 from the seventh leads obliquely downwards to the border of the same foramen. 

 A small canal is continued from both these to the upper or outer surface of the 

 sacrum. The eighth and ninth wide foramina pierce the sacrum vertically. 



The neural arch of the first anchylosed sacral or last dorsal vertebra (fig. 1. ii.) 

 sends off" from its anterior part three articular or oblique processes. The upper- 

 most is the largest, is compressed, and slightly thickened at its free extremity ; 

 its direction is nearly vertical and a little inclined outwards. The second articular 

 process is nearly horizontal, depressed, and terminated by an obtuse convex 

 margin. The third, or lowest, projects directly forwards, in the form of a short 

 mammilloid process. The anchylosed rib or costal process (a) is strong, mode- 

 rately long, flattened and rough above, convex and smooth beneath, proceeding 

 outwards and a little backwards, with a slight downward curve, from the side of 

 the neural arch, from which it arises by two distinct roots ; the lower one being 

 continued from the anterior and outer part of the neural arch, between the 

 nervous foramen and the base of the two lower articular processes, whilst the 

 upper root extends from the posterior articular process to the uppermost of the 

 anterior articular processes. These two roots intercept at their junction a fora- 

 men or canal ten lines by eight in diameter, which thus traverses the base of 

 the process in a line almost parallel with the axis of the trunk*. This very re- 

 * A style is represented as passing through this canal on the left side in PI. X. fig. I. d. 16. 



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