Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species

Cases of rudimentary 12th rib in Man are not rare. When the last dorsal in this respect approaches to the lumbar type, the change of the articular process from dorsal to lumbar may take place higher than normally, as in STRUTHERS' Cases 1 and 2 (/. c. p. 54 and p. 57). In both of these the change was symmetrical, and in the first case it was abrupt and completed bet ween the llth and 12th dorsals, but in the second it was less complete. Though the place at which the change of articular processes takes place here varies in correlation with the diminution of the last ribs, both being higher than usual, such correlation is not always found, change in respect of either of those characters sometimes occurring alone.

1 Struthers points out that unless the cervical vertebrae above the rudimentary ribs are counted there can be no certainty that in any given case these ribs are not extra cervical ribs. !•;. Tli.- formation of inoveable ribs upon vertebrae normally beli.nv:iiiur i" til-- luiiil)jir groups is in Man rarer than reduction of tinliNi ill,- In thes,- i-ases the ribs may or may not coexist with M i ^iven by Struthers (/. c., p. 00), the change of articular pro-

17. TindiH'ereiici s lietwct-n the vertebrae of these regions are far more matters <>t degree than those between the members of other tinlumliais ma\ become (), and in thirase the 2nd sacral wholly or partially takes tincharacters proper !•• the 1st sacral, but this change i- not neci asarilj accompanied by union between the last p. t;M. (>ii tinother hand. th«- last lumbar may unite with the I ial. and sui-h union may IK- rithrr symmetrical or unilateral

onl\. 'ripaiiioiint t» which th<- ilium articulates with these ver- and tindegree to which tln-ir jn-<.c,--Nes are developed to support it aUn ]>n--i-nt many -hadi-s of variation. Similarly the Since all tlirM- chaiiL:' s anmanifestly ijiiestions of degree it v.onld he inteiv-ting tn know whetliejany particular positions in th' ••!' chan--e> are found nmi-e tiv|uently than others, but I know no liody of st.-ti i-t ic> iVoni which this might be determined. In the alis. -nee ,,( -uch determination thei-e is no reason to suppose the exist, nee of ]>i- ..... tiniiitv in thoe variations.

examples "I ihe occurrence "f llonnrosis lietween mem- l"-i- ••( ihe several re-ions we have now to pass to the more interesting <\\\>^\ \«\\ «[ the degree to \\ hirti | loino-osis in one part of the column ma\ l.e con-elated \\ith .similar llomo-oti.- \ariation in the other parts. |-', ,r though each of the part in i la r dian-es in tin- \:iri..M- regions may occur withoul correlated change in other '•h eonvlatioii nevertheless otteii occurs, and in am cmi- >ideiaiioi, of magnitude .,1 \'aiiati..n it is a ta.-tor <,f importance. In several ••!' the examples to !„• -i\,-n it \\ill In- seen that the redi-tril.ution ot regions LS aU.. associated with Meristie change in th. total iiMinln i pnents in the column. Et is obvious that in

the present place only the most summary notice of the various cases can be given. Amongst them can be recognized two groups, the first in which the Homoeosis is from before backwards, the second in which it is from behind forwards. A few words in explanation of the use of these terms are perhaps needed. In describing cases of such transformation in the series, it is usual to speak of structures, the pelvis for example, as " travelling forwards" or "travelling backwards." These modes of expression are to be avoided as introducing a false and confusing metaphor into the subject, for there is of course no movement of parts in either direction, and the natural process takes place by a development of certain segments in the likeness of structures which in the type occupy a different ordinal position in the series. In using the expression, Homceosis, we may in part avoid this confusion, and we may speak of the variation as occurring from before backwards or from behind forwards, according as the segment to whose form an approach is made stands in the normal series behind or in front of the segment whose variation is being considered. The formation of a cervical rib on the 7th vertebra is thus a backward Homoeosis, for the 7th vertebra thus makes an approach to the characters of the 8th. On the other hand development of ribs on the 20th vertebra (1st lumbar), is a forward Homceosis, for the 20th vertebra then forms itself after the pattern of the normal 19th1.

If each segment in the series of vertebrae were to be developed in the likeness of that which in the normal stands in the position next posterior to its own, we should expect the whole series to be one less than the normal. The following case makes an approach to this condition. *18. Skeleton of old woman. C 7, D 11, L 5, S 5, C 4 (5th and 6th cervicals partially ankylosed). The 7th cervical bore a pair of cervical ribs [of Gruber's class 2, see p. 108], that on the left being ankylosed to the 7th cervical. There were only 11 pairs of thoracic ribs. The 1st lumbar was a true lumbar. GRUBER, WENZEL, Mem. Ac. Sci. Pet, 1869, Ser. vn., XIIL, No. 2, p. 23. Here the 7th vertebra resembles a dorsal in having ribs, the 19th, which in the type is the last dorsal, resembles a lumbar in all respects, the 24th is the 1st sacral, and there is no 33rd vertebra.

1 The same terminology may conveniently be adopted in the case of the parts of flowers. Development of petals in the form of sepals being an outward Homueosis, while the formation of sepaloid petals would be thus called an inward Homoeosis, and so forth. *19. Male, in Cambridge Univ. Mus., No. 78. Preparation shews C7, Dll, and the 19th vertebra formed as tin- 1st lumbar: remainder nut preserved, but Professor A. ^lacalister kindly informs me that there were 5 lumbars and 5 sacrals, giving C 7, D 11, L 5, S 5. Tin- Ttli \eri.-bra has cervical ribs, the left being large and articulating with a tuberosity mi 1st thoracic rib, the right being considerably smaller, but now broken at the end. Only 11 pair* of thoracic ribs. Change of articular process from dorsal to lumbar Jns partially on the left side between 17th and 18th vertebra tin-lead of between 19th and 20th) and is complete on both sides between 18th and 19th. The 19th bears no rib. [Backward II 'inM-osis, greater on left side than on right, as seen in the tt'-r size of the left rib on the 7th vertebra, and in the change ..f pi-.-c.-sus beginning at a higher level on this side. As the coccyx i- not preserved it cannot be seen whether there is one :ii.-ni I--- ill the whole column, which would be the case were backward Homoeosis complete.]

Th'- I '.'Hi \iTti'l.ra lia\iii^ a transverse process on the left side re- ,l>lnr_' tli.-ii nf the MTtelira in-xt lid(i\v it, as ivg;ml> place of origin ami its upward slnpc, Imt i^ InM-vr than it l.y l\\\. and is nearly a thinl broader and ;iU" thi<-ker. < )n right side corresjionding part is in t \\ •• pi' Change "t' .-uticular processes coni|ilete lietwcen iSth ;md L 9th (instead of between I'.'ihand I'otln. '1'heL'lth vertebra is uniteil tn >;icnini, but i-- nf unusual sliapi-. dillering -really from a normal

ei-ved. Ihh rilis reduced. | in. long, 4.1 in. \\ith cartilage. 12th ril^ nidiineiitary, left 1 in., right ^ in. long, lireadth of each about i in. Artie, pi' change ehietly between isth and ll»th vertebr.-e. \- was r. marked in the case »\ backward Homoeosis, if each vertebra were to I..- developed in tinlikeness of the one which in the normal stands next behind it in ordinal sequence, we should expect such backward Homoeosis to be accompanied by reduction in the total number of vertebra ; so, conversely we should expect forward Homceosis to be accompanied by an increase in total number. This will be found to be sometimes the case (e.g. No. 26).

*24. Male. C 7, D 13, L 5, S 5 [C not recorded]. 13 ribs on each side. The right side differed considerably from the left. Right side. 1st rib resembled the usual supernumerary cervical, being moveable and extending f in. from its tubercle. Greater part of ixth nerve crossed the neck of the rib ; just before doing so it was joined by large branch of xth. The 2nd rib, borne by ninth vertebra, in all respects resembled a normal 1st rib. The 3rd rib articulated with sternum like a normal 2nd rib. In all, 8 ribs articulated with sternum on right side, as usual. The 13th rib (on 20th vertebra) was 4^ in. long.

Left side. The 1st rib articulated with body and transverse process of 8th vertebra, connecting with sternum in normal position, but differing much from a normal 1st rib, being nearly stra;ght with very slight horizontal curve. 2nd rib normal in form and direction; articulates with sternum J in. higher than right 3rd rib, owing to the lower margin of manubrium being directed slightly obliquely upwards and to the left. In all, 8 ribs articulated with sternum, all below the first being at a level slightly higher than that of the right ribs. The 13th rib (on 20th vertebra) was 4f in. long. LANE, W. ARBUTHNOT, J. Anat. Phys., 1885, p. 267 [full description and discussion].

In this remarkable case, by the reduction of the 1st rib on the right side, the 8th vertebra shews a forward Homceosis so far as that side is concerned. The 20th vertebra, bearing a pair of 13th ribs, also shews a forward Homceosis, but this seems to have been a little greater on the left than on the right (cp. No. 20), the right rib being a ^ in. less in length. The fact that a large branch of the Xth nerve on the right side joined the brachial plexus instead of the usually minute fibre is specially noteworthy, as shewing a forward Homoeosis in the brachial plexus on the right side in correlation to the similar Homceosis appearing in the reduction of the 1st rib on the same side. (Compare Nos. 14 and 25.) 25. Skeleton C 7, D 12, L 6 [S and C not recorded]. First pair of ribs rudimentary, about 1^ in. long, exactly alike, as small horns attached to 8th vertebra. Scalene muscles wrere inserted into 2nd rib. The 25th vertebra was free, but the first lumbar (20th vertebra) had no trace of a rib. BELLAMY, E., /. Anat. Phys., 1885, p. 185.

[In this case there is forward Homceosis in the reduction of the first ribs and in the formation of the 25th vertebra as a lumbar, but there were no ribs on the 1st lumbar, which would •26. Mule, tet. 50. C 7, D 12, L U, S 5, C "3 or 4, probably 4. " Thirteen pairs of ribs, 13th ribs on 20th vertebra, nearly syiuni.-tiii-al. right 2 in. long; left 1£, and in breadth a little less than the li^ht. The <Hh lumbar, 2oth vertebra, had the characters of a ii.. rn. al laM lumbar (sc. 24th vertebra), including normal transverse | ..... Coccyx in 3 moveable pieces, the 3rd apparently

mposed of two. There is therefore probably one more than th,- ..... -ma! number in the whole series. STUUTHEHS, J. Anat. ril,-, normal. 20th vertebra normal, except that it has no trace •h \, rtel.ra ijuite free from sacrum, but articulating with ilium 1,\ Hnall facet "ii each side. The 1st coccygeal joined to sacrum. pi,, in 2oi h \ertebra, in separation of 2oth from sacrum, and lint though the variations of the vertebrae mav thus in great measure !„• i-due,-,l (,, system, there remain other eases, rare in M in l>iit n,.t \.-ry iineoiiinioii in lower (onus, \vhirh cannot be

^ight into ;n,\ system yel «le\ised. Such ,-a.ses shew that the liimt^ imposed 1,\ a system of individual homologies, het ween which \\e eoneeive the 'iirieiii-e of N'ariat ion, are not natural limits, and that they ma\ !,-• Bel aside in nature. In the following ease it ma\ In- es|» eially noted that X'ariatioii in the segmentation of the spinal nerves does not necessarily coincide with that of the vertebrae. 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 vertebras. 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. Phys. 1875, p. 72 and p 29. Here then the 7th vertebra shews backward Homceosis, imperfect on left side, but more complete on right. 19th having no ribs, shews the same, and this also appears in the absence of a •1th 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 redistributed piecemeal amongst a different total number of segments, 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 (7. c. p. 75) : " The variation in this case presents some complexity. To which region is the suppression of the vertebra to be referred ? 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 24 vertebra? above. The appearance of suppression of a vertebra in the neck, is met by .the consideration that the 7th vertebra carries ribs, imperfectly developed 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 is. Which. -\.-i- view be taken, this case is an interesting one, • •\hibith ir \ariation in every region of the spine, and as shewing tli.- importan.-.- "f i-x.-iiniiiing the entire spine before deciding as to

T . . ili.- Question, which vertebra is missing, there is no answer; >.r mi h< T tinan-wc-r is that there is no segment in this body • tl\ c..i T, -ponding tu the normal 7th, 20th, 2oth, &c.; that the diai.i'-t' i- "I t! ,.ial -.-gments are distributed afresh and ii|>"ii ii-> -trict, con-i-t.-nt plan among the segments of this body, ami that, therefore thenis no one segment missing from the li.-dv. Smvlv further efforts to answer questions like these ran lead t" inii-iTul result.

\>!.-iii|iu t" interpret Variation by the light of simple arithiii« -i if "nl\ i'» ol»ciiiv the real nature of Repetition and .:iii.-iital differentiation; for by constantly admitting to the miii'l tinfancy that this Dimple, subjective representation of these piifl ih«- right guide. and that the tangible complexity in which th<-\ present ili.-in^-lv.-x is ;i wrong one, we only become n-.-.l t«. an idea \\hifh i- IP. t trin- t' • tinfacts and the real difficulty

(In .-..i^id.'rincases -t' variation in the Cliinij.an/ee it should I).- biirni' in mind that th.-i.- .-in- >.-\,-r;il races and perhaps species in. 'hid. -d under this name, which have nut been clearly distinguished. I' ; il'l'-. iher.'fi.re, th.it xmie.if the \ariatimis recorded may I..- characteristic »t' th.--.- races and not actually individual variati"' "f i" CHAILLU'I T. calvua. It was received united by the natural liu'.-iiii.-nt, and DO vertebra therefore is lost. Cut. Cott. Swg., issj, n. \". t.

Specimen having rudimentary ribs une,|ually de\ doped on the L'.'nli vertebra was transitional ..r lumb,, .sa.-ral in Jahrb., i. p. 1GO. 7'ables, Note 19. This case therefore shews forward Homoeosis in the presence of ribs on the 21st, also in the transitional character of the 25th, together with increase in total number. This increase is however not always found when the 25th is lumbo-sacral, for, on the contrary one sucli case quoted by Rosenberg had only 4 caudals (q.v.).

In this form the number of vertebrae articulating with the ilium varies, and the number uniting with the sacrum is also liable to alterations probably connected with age. ROSEXBERG, I. c. : Cat. Coll. Sury., 1884, n. p. 3. Gorilla savagii. C 7, D 13, occur in all skeletons of which I have found descriptions, making therefore one pair of ribs more than in Man1. The number of vertebra? articulating with the ilium and the number joining with the sacrum vary, perhaps with age. Cf. ROSENBERG, I.e.; Cat. Coll. Surg.; STRUTHERS, J.Anat. Phys., 1875, p. 79 note, &c.

*35. Adult female. C 7, D 12, L 4, S 5, C 3. This is a remarkable case. There is one rib-bearing vertebra less than usual, while the number of lumbo-sacrals is nine, as in the normal cases collected by Rosenberg. In a normal skeleton in the Camb. Mus. the articular processes change from the dorsal to the lumbar type between the 20th and 21st, but in this abnormal specimen the change is completed on the right side between the 19th and 20th as in Man, and on the left side, though the change has there also taken place, there is a curious irregularity in the fact that the posterior zygapophysis of the 19th is divided to form two processes which fit into two similar processes of the left anterior zygapophysis of the 20th vertebra. The rest is normal. Cambridge Univ. Mas., 1161, F. [There is here, therefore, a backward Homoeosis of all vertebrae from the 19th onwards; perhaps also an absolute diminution in the total number of segments. The simultaneous variation of both the number of ribs and the position of the

1 Since this account was written, STRUTHERS has published a valuable paper (Journ. Anat. Phys., 1892, xxvn. p. 131), giving particulars of twenty Gorilla skeletons. Of these the following are especially remarkable. Female, C 8, D 13, L 3. The seventh cervical is formed like a sixth, and the eighth is formed as a seventh, bearing no rib. The vertebrae 9 to 21 bear ribs, those of the 21st being well formed and coming close to iliac crest. The change of articular processes from dorsal to lumbar type occurred between 21st and 22nd, namely, one vertebra lower than usual. There is thus a forward Homceosis in absence of ribs on 8th, in presence of ribs on 21st, and in the variation of position of the articular change.

Out of 20 skeletons 3 have 14 pairs of ribs (on 8th to 21st) instead of 13 pairs. In one of these the articular change also occurred one vertebra lower than usual. On p. 136 a case is described in which there was a remarkable asymmetry in the structure of the articular processes, which as Dr Struthers has pointed out to me, is in some respects like that here described as No. 35 in the text. Struthers points out that it would be better in all cases to speak of the change of processes as from lumbar to dorsal instead of from dorsal to lumbar. I regret that this suggestion comes too late for me to adopt.

•al i- . l.-arly shewn by presence of pleurapophysial ossifications in tin- t ran>\ .-I >.- processes of the latter. Thus though Simla resembles Man in the number of ribs, it differs in the total number of prae- 1 I, but in the adult mention. 'd above, one of the coccygeal was and nl^ fniind in tlii- -emis arc n-i-nrdi-d in tin- Catalogue of the MU-. -uni of tin- ('ollt-iri- "f Surgeons, ifec.; since however the specific To the study of Variation of ih,. \n-tcliral iv-ions the phcnoinciia seen in tin- Sloths are of exceptional importance, and in attempts to trace the homologies ..f the segments special attention

particulars ..f il specimens of Bradypus &nd II of CAotepws seen by niv-elf in Kn^li-d, museums, and .if a few others of which descriptions ha\.- been published. To these is added a smmnarv "•' -K' specimena of Bradypus and n of Cholcepus in (J.-nnaii museums1 examined by WELCKER. Bis account is tnifortiinately not -i\.-i, in detail, Inn I ha\e tabulated his results so tar as i's possible. Welcker's list does not, I believe, include any of the specimens separately given in No. 44.