chap, in.] VERTEBRAE AND RIBS : MAN. 115 



spinal nerves does not necessarily coincide with that of the ver- 

 tebrae. This fact will be more fully illustrated in the section of 

 evidence respecting the spinal nerves. 

 '32. Female, cet. 40. As it stands, the grouping is C 6, D 12, L 6, 

 S 5, C 3; in all 32, viz. one less than usual. The vertebral artery 

 did not enter till 5th cervical (instead of 6th) on left side. The 

 7th vertebra bore a pair of ribs, left small, ceasing at middle of 

 shaft ; right has been sawn off, but has all the appearance of a rib 

 that would have reached the sternum. The 19th vertebra bore 

 no ribs, and has transverse processes like those of a normal 1st 

 lumbar. 23rd has transverse processes triangular and sloping 

 upwards, like those of normal last lumbar but one (sc. 23rd), 

 though in a less degree : pedicle thicker than usual for this 

 vertebra. 



The articular processes change in the normal space, between 

 19th and 20th vertebrae. Sacrum 5 ; Coccyx represented by 3 

 pieces ankylosed together. 



Two entire lumbar nerves went down from the lumbar region 

 to the sacral plexus. [Bones described in detail, q. v.] Struthers, 

 J. Anat. Phijs. 1875, p. 72 and p 29. 



Here then the 7th vertebra shews backward Homceosis, im- 

 perfect on left side, but more complete on right. 19th having no 

 ribs, shews the same, and this also appears in the absence of a 

 4th coccygeal. The fact that two entire lumbar nerves join the 

 sacral plexus is also a variation of the same kind. But if the 

 backward Homceosis were complete, the 24th vertebra should be 

 the 1st sacral, and the 29th should be joined to the coccygeal. 

 The change of articular processes moreover is in the normal place. 



An example like this brings out the difficulty that besets the 

 attempt to find an individual homology for each segment. If the 

 characters proper to each segment in the type may be thus re- 

 distributed piecemeal amongst a different total number of seg- 

 ments, the question, which in this body corresponds to any given 

 vertebra, say the 25th, in a normal body, cannot be answered. 

 The matter is thus clearly summed up by Struthers (I. c. p. 75): 



" The variation in this case presents some complexity. To which 

 region is the suppression of the vertebra to be referred 1 The lumbo- 

 sacral nerves would seem to indicate that the lowest lumbar vertebra 

 is the usual 1st sacral set free, thus accounting for the seemingly 

 deficient pelvic vertebra, and leaving 23 instead of 21 vertebrae above. 

 The appearance of suppression of a vertebra in the neck, is met by 

 the consideration that the 7th vertebra carries ribs, imperfectly de- 

 veloped on one side, like cervical ribs. 



"Then, although only 11 ribs remain, the next vertebra below, 



though rib-less, has the normal articular processes of a 12th dorsal 



(19th vertebra). If it is to be regarded as such, and not as the 



1st lumbar, then the suppressed vertebra would be really a lumbar, 



.although there are six free vertebrae between the thorax and the 



8—2 



