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TRANSACTIONS

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THE ZOOLOGICAL SOCIETY

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I. On the Development of the Skeleton of the Tuatara, • Sptyenodon p^actatus ;
with EemarJcs on the Egg, on the Hatching, and on the ^Hatched, %oyng.. By
G. B. HOWES, LL.D., F.B.S., and H. H. SwimKV^^' ^6.^aY^U''^(^olar,
R. Coll. Sci. Lond. (From the Huxley Eesearcfi Laboratory.)

Eeceived May 21, 1900 ; read May 22, 1900.
[With Plates I.-VI. and 18 text-illustrations.]

CONTENTS. Page

1. Introduction 1

2. Material 4

3. Methods aud Reconstruction ' 7

4. Observations on the Egg, on Hatching, and on the Hatched Young .... 8

5. The Axial Skeleton , 10

*•*%)

General, and as to Terminology 10

Vertebral Column 11

Ribs and Sternum 27

" Abdominal Ribs " (Gastralia) 34

The Skull and Visceral Arches 37

Cranio-facial Membrane-Bones 51

6. The Appendicular Skeleton 58

The Pectoral Girdle 58

The Pelvic Girdle 58

The Long Bones 60

The Carpus and Tarsus, with Phalanges 60

7. The Dentition 63

8. Summary and Conclusions 67

9. List of the more important Memoirs dealing with Sphenodon 71

10. Explanation of the Plates 75

1. INTRODUCTION.

ALL work in "Reptilian Morphology during the last thirty years has increased the
interest attaching to the creation in 1867 by Dr. Giinther of the Order Rhyncho-
VOL. xvi. — PART i. No. 1. — February, 1901. B

889981

2 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE

cephalia, which now, in its extended form, would appear to embrace a series of
genera and species occupying a truly central position among the terrestrial vertebrates.
Since the publication of Dr. Giinther's memoir on Sphenodon, the discovery by Baur
and others of its vomerine teeth, and by Spencer of its parietal-eye, have more especially
increased our knowledge of this remarkable animal beyond that which is ordinary.
One of its most distinctive characters is the forward prolongation of the pterygoids
to meet the vomers with apposition in the middle line. The mere forward prolongation
referred to is a feature already recognizable among the Batrachia and Stegocephalia ;
but special interest attaches to the median apposition, as there is little room for
doubt that in that there lies the clue to the reduction and suppression of the para-
sphenoid in the ascending series of the Amniota. This important Rhynchocephalian
character,, long recJog&rzed in the Crocodilia and Dinosauria, has during recent years
been^is;qc>v^e*d'ih|th]e;*-Ichthyosauria1 and the Plesiosauria 2 by Lydekker and others,
and probably in the Pterosauria by Newton 3, and it justifies the conclusion that
the living Sphenodon may be the sole surviving representative of an early and
widely ancestral amniote type. While the recent confirmation by Menzbier 4 and
Pycraft5 of Brandt's discovery in 1839 6 that the Avian pterygoid may reach the
vomer, with their further demonstration, that while this is a permanent feature of
some Ratitaj and the Tinamous among the higher birds, this Rhynchocephalian
character becomes lost during ontogeny under secondary segmentation and co-
ossification of parts, as the progressively modified facial skeleton comes into closer
relationship with the basis cranii, would seem to indicate an origin for the class Aves
from some more primitive reptilian type than might otherwise have been supposed 7 —
from something lower than the Dinosauria. Beyond this, Cope in 1870 8, and Seeley
in 1874 9, have drawn attention to certain Chelonian resemblances in the Rhyncho-
cephalia. In this they have been more recently followed by Boulenger, who regards 10

1 Lydekker, R. : Brit. Mus. Cat. Fossil Rept. & Amphib., Part 2, 1889, p. 5. Cf. also Baur, G. : Anat. Anz.
Bd. x. 1895, p. 456 ; and (concerning the Rhynchocephalian affinity) Americ. Nat. vol. xxi. 1887, p. 337.

3 Lydekker, R. : originally in PL dolichodints, ibid. p. 257. Of. also Andrews, C. "W.: on Peloneustes,
Ann. & Mag. Nat. Hist. (6) vol. xvi. 1895, p. 248, and on " The Structure of the Plesiosaurian Skull " in
Jouru. Geol. Soc. vol. lii. 1896, p. 246.

3 Newton, E. T. : Phil. Trans, vol. 179 B. 1888, p. 503.

4 Menzbier, M. v. : Bull. Soc. Imp. Nat. Moscou (n. s.), tome i. 1887, p. 492.
-' Pycraft, W. P. : P. Z. S. 1898, pp. 973-974.

6 Brandt, J. : Mem Acad. Sci. St. Petersb. (vi.), Sci. Nat. tome iii. p. 81, & espec. pi. xvii. fig. 3 (RJiyncops),

7 Provided the so-called " hemipterygoid " has the value claimed for it. It must not be forgotten that
Archceopteryx appears to have had "abdominal ribs" (Dames, Palaeontol. Abhandlg. Berlin, 1884, Bd. 2,
p. 144), and that " intercentra " occur in most of the groups of non-Passeres among living birds (Beddard,
P. Z. 8. 1897, p. 465).

8 Cope, E. D. : Proc. Americ. Assoc. vol. xix. 1870, p. 233.

9 Seeley, H. G.: Journ. Linn. Soc., Zool. vol. xi. 1876. p. 183.

13 Boulenger, G. A. : Brit. Mus. Cat. Crocodilia and Chelonia, 1889, p. 1.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 3

" the affinities of the Rhynchocephalia to the Chelonians as at least as great as to the
Lacertilia; " while almost the first observation made in the development of the Tuatara
was that by Dendy (98, and 99 b. p. 66) of the post-am niotic canal, which, though
probably of wide occurrence, was originally discovered l and is at present known
elsewhere only in the Chelonia, and of the horny " shell-breaker," which, being of the
Chelonian type 2, places Sphenodon in sharp contrast to the Lacertilia, which, so far
as is known, develop a calcified " egg-tooth." 3

Far reaching as is thus the interest arising from a comparison of the recent Sphenodon
with representative members of the living orders of Reptiles, that with certain extinct
orders and suborders other than those already alluded to is even more suggestive.
The discovery by Credner in the Permian deposits of Saxony of the assemblage of
vertebrate forms he has so aptly termed4 the " Eotetrapoda," and more particularly the
genus he has less aptly named Palseohatteria, has materially lessened the structural
gap between the Reptilia and the Stegocephalia ; while the description by Lortet, eight
years ago, of Rhynchocephalian remains 5 from the Upper Jurassic of the Rhone Basin
which reveal new cranial characters, with that of Crocodilian resemblances in Champ-
sosaurus 6, which, like Acrosaurus 7, is believed to have been aquatic in habit, shows
the Rhynchocephalian Order, now all but extinct, to have been in the past extensive
and subject to considerable modification. It is now generally conceded that the
Anomodontia (Theriodontia and Pariasauria) in some respects stand on an even lower
structural level than the Rhynchocephalia ; and, this being so, the recognition among
these of Rhynchocephalian characters — originally by Seeley in Procolophon in 1878 8 —
only the more fully justifies the belief in the primitive nature of the Rhynchocephalian

1 Hitsukuri, K. : Journ. Sci. Coll. Tokyo, vol. iv. 91, p. 10. Cf. also Dendy, 99 c. pp. 251 & 255.

2 Cf. Dendy, A., 99C. pp. 56 & 59, and Parker, W. K., 'Challenger' Reports. Zool. vol. i. pi. 3. fig. 1.

3 Cf. Ley-dig, F. : ' Die in Deutschl. lebend. Arten d. Saurier/ Tubingen, 1872, p. 110 ; and Boulenger, G. A. :
on the Ophidian Aipysurus annulatus, in Willey's ' Zoolog. Results,' Cambridge, 1899, p. 57.

4 Credner, H. : Allgem.-Yerhandl. Naturwiss. Abhandlg. Berlin, Hft. xv. 1891, pp. 1-52.

5 Lortet, L. : Archv. Mus. Hist. Nat. Lyon, Bd. v. 1892, pp. 139. It is interesting to note that Sauranodon
possessed proccelous vertebrae.

6 Dollo, L. : Bull. Soc. Beige d. Geol., tome v. 1891, p. 151.

7 Andrew, A. : Ber. Senckenbg. Naturf. Gesellach. 1893, p. 21.

8 Seeley, H. G. : Quart. Journ. Geol. Soc. vol. xxxiv. 1878, p. 803. The pterygo-vonierine relationship is
now known to be lihynchocephalian among Anomodonts in Procolophon and Galesaurus (A. S. Woodward,
' Outlines of Yertebr. Palseont.,' Camb. 1898, pp. 148 & 152), and it is probably so in Pariasaurus also (cf.
Seeley, Phil. Trans, vol. 183 B. 1892, p. 317). The description of a post-palatine fossa, which in all probability
received a median tonsil (" bursa pharyngea ") like that observed by Killian (Morph. Jahrb. Bd. xiv. 1888,
pp. 659-690) for living reptiles, as the posterior nares, and of the true posterior nares (p. 317) as " anterior
comma-shaped palatal vacuities," is erroneous. The study of the palatal region of this animal needs re-
investigation.

B2

4 PHOF. G. B. HOWES AND MR. H. H. SWINNEETON ON THE

Order, and of Sphenodon, its living representative. Since Sphenodon thus occupies
the afore-mentioned primitive position among living reptiles — not to say among the
Sauropsida as a whole — and since our classificatory systems of the Vertebrata, to be of
avail, must be primarily based upon facts concerning parts capable of fossilization, the
special interest attaching to the study of the development of the Sphenodon skeleton
becomes sufficiently evident. And, as involving the Ord.er Rhynchocephalia, the fact
that in one of the most recent, and that which we have found the most rational and
serviceable of classifications thereof1, a distinction has become possible between a
higher and a lower sub-order, in itself raises the interesting question whether in the
development of Sphenodon, a member of the higher sub-order, there may not be passed
through phases characteristic of the lower, to-day unrepresented.

During the thirty years afore-named no available opportunity has been lost by
workers of all nationalities to study the habits and anatomy of Sphenodon, and a list
of the resulting papers is appended to this Memoir (infra, p. 71). Most organs and
systems have received attention. The most exhaustive contribution is that of the
Japanese Osawa, which is a laborious anatomical treatise extending over 438 pp.
of the Archiv fur Mikroskopische Anatomic (cf. list, Osawa, 96-98) ; and, while
grateful to him for this, it is with much astonishment that we have to record his
final conclusion (98 b. p. 352, and 98 c) that Sphenodon is an Agamid — a reversion to
the view of Gray (1831), adopted and afterwards forsaken by Cope 2, revived by
Peters (70), and rejected by Giinther (69. p. 624) 3.

2. MATERIAL.

In 1894, when Professor Dendy was appointed to the Chair of Biology in the
Canterbury College of the New Zealand University, one of us, in regular correspondence
with him, sought to impress upon him the desirability of doing all in his power to
secure without delay material for the study of the development of Sphenodon, not
knowing at the time that our mutual friend, Prof. Baldwin Spencer, F.R.S., of
Melbourne, had also approached him on the subject. With what enthusiasm and at
what personal cost he responded to the desire, his published memoirs (Dendy, 98,
99% 99b) amply testify. On hearing of his success in the field, no time was lost

1 Boulenger, G. A. : Ann. & Mag. Nat. Hist. (6) vol. xi. 1893, p. 204.

3 Cope, E. D. : cf. Proc. Acad. N. S. Philad. 186-1, p. 227, and Proc. Americ. Assoc. vol. xix. 1870,
p. 233.

3 It has always been to me inexplicable why Huxley should have refused to admit the validity of the Order
Ithynchocephalia. Well do I remember how, in conversation, he once remarked to me that " Sphenodon is a
lizard and only a lizard ! " but, this notwithstanding, his final printed statement and proposal to create, for the
reception of Hyperodapedon, Rhyncliosaurus, and Sphenodon, the group of the " Sphenodontina " (Quart.
Journ. Geol. Soc. vol. xliii. 1891, p. 691) would seem indicative of a compromise suggestive of an approaching
conviction. — G. B. H.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 5

in drawing his attention to certain of the more interesting problems (duly set forth
in the pages of this Memoir) presented more especially by the skeleton and teeth
of the adult animal. In reply, he expressed the hope that one of us would undertake
this portion of the work, and offered, with a generosity and friendly appreciation for
which we tender him our heartiest thanks, to give all the necessary material he could
command if we would acquiesce. There accordingly reached us in the autumn of
1898 a large series of specimens, treated, for the younger stages with corrosive
sublimate and alcohol, for the older with alcohol alone. From these, after preliminary
examination, the undermentioned were selected, as embracing the period of skeleto-
genesis ; and, concerning those which remain, Prof. Dendy has very generously
acquiesced to the proposal that Dr. Elliot Smith and Mr. E. J. Bles, of Cambridge,
should work out respectively the development of the brain and urinogenital organs.

List of Young Specimens Investigated (15 in all).

Stage. No. Date of removal from Egg.

P 87. Jan. 25, 1898.

P* 39 a. Unknown.

Q*t 52a. Jan. 30, 1899.

Q la. End of Jan. 1897.

R 142. March 8, 1898.

R 154. April 5, 1898.

R 159. May 12, 1898.

R 162. June 24, 1898.

R-Sf I.

Sf II.

st iv.

S* la. Hatched Dec. 8-9, 1898.

S* 19a. „ Dec. 27, 1898.

S 138. No details.

Tf III.

The following are the details concerning the individuals incubated and afterwards
reared in our own Laboratory.

Stage. Length in cms. Remarks.

R-S1- 6'3 Died in egg, 13.11.98.

( Hatched prematurely with
mi. 7-5 J

I excessive yolk, 22.11.98.

Tm- 15 Hatched 14.1, died 1.5.99.

J Found decomposed in egg,

I 14.1.99.

Ty- 15 Hatched 19.1, died 18.5.99.

TVI- . 17 „ 24.1, died 18.5.99.

6 PEOF. G. B. HOWES AND ME. H. H. 8W1NNEJJTON ON THE

In the foregoing list the stages and numbers are those of Dendy's series, described
in the Quart. Journ. Microsc. Sci. vol. xlii. p. 10. Those marked * were found requisite
as our investigation advanced, and were very kindly supplied by him at our request,
and those marked f were incubated in our own Laboratory from unhatched eggs. The
latter, six in number, packed close in moist sand in a 1-lb. canister with a perforated lid,
were brought over by Mrs. Dendy and kept during the voyage from New Zealand in her
cabin. One only decomposed, and of the five which remained, three ran the full deve-
lopmental period, the enclosed young making good their own escape. These lived from
three to four months, and for their reception we have added to Dendy's series a Stage T.
At this stage the coloration is the same as at S, but as an advance upon that there is
a complete absence of all traces of the yolk-sac and shell-breaker, and the appearance
in the thoraco-lumbar region of the all characteristic median dorsal languets (spines,
auct.\ such as are already present at Stage S in the so-called " nuchal " and the caudal
tracts. These appendages, whose existence is expressed in the native name Tuatara x,
are liable to no slight individual variation. Three tracts are present in the adult, viz.
" nuchal," thoraco-lumbar (" dorsal "), and caudal, as recognized by Boulenger in his,
the latest, diagnosis (89. p. 2), with consequent scapular and sacral intervals. Buller
(76. p. 324) and Newman (77. p. 230) have called attention to the existence in the
region of the cervical space of a conspicuous pigment-patch ; and, concerning the
numerical variation of the " spines " in the adult, they give for the " nuchal " series
10-14, for the thoraco-lumbar 15-20. From examination of eleven specimens present
in our own collection and that of the British Museum of Natural History, we find the
extremes range from 6 to 14 for the " nuchal" and 15 to 24 for the thoraco-lumbar
series. In two specimens of our Stage T they number 10 and 18 respectively.

With a view to ascertaining the limits of individual variation, and thereby
rendering the present memoir as complete as possible anatomically, we have examined
all the dried skeletons within our reach — viz., the complete skeletons of nine adults,
fragments of some six to eight others, and the complete skeleton of a half-grown
individual in the possession of the Royal College of Science, Dublin. For the
privilege of examining all but two, which are at South Kensington, we are
indebted to Prof. A. C. Haddon, F.R.S., to Prof. C. Stewart, F.R.S., of the Royal
College of Surgeons Museum, to Dr. R. F. ScharfF, Keeper of the Natural History
Department of the Science and Art Museum at Dublin, and to our friends in the
British Museum of Natural History.

Beyond this, we have had recourse where necessary to dissection of six spirit-
specimens in the Teaching Collection of the Royal College of Science, two of which
were presented by Prof. Dendy in the spring of 1899.

1 Of. Newman (Taylor tit.), 77, p. 222.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 7

3. METHODS AND RECONSTRUCTION.

Methods. — Dissection was resorted to only in the later stages, and wherever the
elements under consideration were fully formed. Throughout the earlier stages, and
in the later where necessary, microscopic sections were relied upon ; and further, as
for example at Stage S and in dealing with the carpus and tarsus, dissection was duly
checked by section, as a means of ensuring accuracy of detail.

The microscopic sections were in all cases mounted serially, the plane of section
being determined by the object in view (as set forth in the accompanying description
of the Plates). After preliminary experiment with the Green Lizard (Lacerta viridis),
it was found that diiferentiation of the skeletogenous tissues could best be obtained
by staining in bulk with Ehrlich's haematoxylin, and afterwards on the slide with
Griibler's orange G. For this suggestion and much subsequent aid we are indebted
to Mr. M. F. Woodward, Demonstrator of Zoology, Royal College of Science, London,
than whom no better manipulator or master of micro-chemical technique exists ; and
we found, as our work proceeded, that much time is to be saved by dissolving the
orange in 70 p. c. alcohol, with the addition of a few drops of glacial acetic acid,
thus eliminating the tedium arising out of the use of a mere aqueous solution. The
results of this method are exceedingly satisfactory, cartilage being as a rule differen-
tiated blue, bone in all its forms deep yellow, while the other tissues behave each in
its own way.

Reconstruction. — Since the time has nor.v arrived at which mere dissection is
insufficient for the study of the facts of skeletogenesis, recourse was had to the
so-called Bornean method of reconstruction from microscopic sections 1. We were
under the necessity of working with thin plates, and found that if made of the
Bornean mixture of beeswax and turpentine there was difficulty in preparation and
liability to snap. By substituting vaseline for turpentine, we entirely overcame all
this, and we can confidently recommend our mixture as reliable.

The figures which constitute PL III. and figs. 7 and 10 of PI. VI. are all from
models prepared from plates thus made. For the most part the sections of the animal
were cut to a uniform thickness of 10 /u, and each plate made to that of 1 millim.
Tracings were then drawn upon the plates, by means of the camera lucida, of sections
at regular intervals, determined by the degree of magnification (every fourth section
for a magnification of 25, every third for that of 33, and so on). In cutting out the
tracings, trabecula? were left where necessary for holding the parts together during
reconstruction, and afterwards cut away. For the process of cutting, the best results
were obtained by the use of a needle, the plates being laid upon glass.

1 Earlier achievement in the same direction must not be overlooked. In England it stands memorably
associated with the Huxleyean traditions: c/.E. T. Newton, " On a New Method of Preparing a Dissected Model
of an Insect's Brain from Microscopic Sections,'' Journ. Quekett Microscop. Club (I.), vol. v. 1878, p. 150, and
Qu. Journ. Micr. Sci. (u. s.) vol. six. p. 340.

8 PROF. G. B. HOWES AND ME. H. H. SWINNERTON ON THE

The tracings, as cut out, were laid fiat in superposition, adhesion being effected by
carefully running a heated wire along their edges. The use of colour was deemed
desirable, but a possibility of error seemed likely to arise were the models coloured
after completion. This, however, was obviated by colouring the tracings before they
were cut out ; and a perfectly reliable result was obtained by the use of ordinary
oil-paint dissolved in xylol, to secure rapidity in drying. In plates thus treated, the
melting together of their edges ensured the diffusion of the colour necessary to
produce the final realistic result.

4. OBSERVATIONS ON THE EGG, ON HATCHING, AND ON THE HATCHED YOUNG.

Dining the period of Prof. Dendy's activity, both as collector and investigator, which
led to the publication of his two pioneer memoirs on the Development of Sphenodon
(Dendy, 98b, 98 c), there arrived in New Zealand two German naturalists — one Dr. H.
Schauinsland, of the Bremen Museum, the other Prof. G. Thilenius, of Strasburg ; one,
if not both, of them sent out under the auspices of the Berlin Academy. Each has
since published preliminary reports upon his investigations (cf. List, p. 74), without,
however, in any way alluding to Dendy's work ; and this is the more regrettable, since
in matters of small detail their statements both differ from and supplement his — while
it is the more unaccountable, since one of them was permitted by the New Zealand
Government to explore the same island as Dendy, with the aid of the very collector he
had employed. Since neither of them has written upon the skeleton, we omit further
reference to their work, except so far as it concerns the newly-hatched young. Dendy,
in defining his Stage S, inclined (99 a. p. 59) to the belief that the yolk is still pendant
at hatching, and was unable to decide definitely upon his surmise (pp. 79-80) that the
olfactory cellular-plugs which he discovered are at that period " removed." Schauins-
land, on the contrary, both figures the yolk and describes the nasal plug as absorbed
shortly before hatching (98°. p. 312), and there can be no doubt he is correct. It is
but just, however, to Prof. Dendy to state that in a letter to one of us, antedating the
publication of Schauinsland's notes, he had corrected his former statements (cf. letter
to ' Nature,' vol. lix. p. 340), having discovered that the embryos which had led him to
believe that both yolk and plug might be present on leaving the egg had been
prematurely hatched.

Concerning the newly-hatched young, he further points out that the pineal eye is
" plainly indicated by an irregular scale, surrounded by eight or nine others, radially
arranged, and all much larger than the surrounding granules," an observation which
we can confirm. And to this we \vould add that the supra-pineal area of the skin of
the head is at hatching transparent and pigmentless, and that it remained in that
condition throughout the four months our young ones were alive.

Before passing to the main subject of this Memoir, we desire to record some
observations pertinent to those communicated by us, in conjunction with Dr. Dendy,

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 9

in the above-mentioned letter to ' Nature.' Firstly as to the rupture of the egg-shell,
to the symmetrical "clean cleft" character of which we drew attention. The
following is a drawing of the shell of one of the eggs therein referred to which ran
the full time ; and in correspondence with Prof. Dendy concerning it and our
suggestion that it seemed to indicate that the shell-breaker may be an actual cutting-
instrument, he has authorized us to state his own view, since formed, on opening an
egg at Stage S, nearly ready to hatch. He observed that the moment a small
puncture is made in the shell, that " splits of itself, very suddenly and with almost
explosive violence, reminding one of the bursting of a seed-vessel ; " and he remarks
that it has been suggested to him that the splitting may have been assisted by

Fig. 1.

Ruptured egg-shell of Sphenodon after the escape of the enclosed young.
Full time. Nat. size.

absorption of moisture from without, by the allantoic fluid 1. He reverts to the analogy
of the well-known " Prince Rupert's drops," and concludes that " the function of the
very sharp shell-breaker is probably to make the small incision ;" and that when that
is done, the egg, being in a condition of high tension, simply bursts open. And he is
the more inclined to this view from having noted that the shell of an egg contained
in sand which had been " somewhat excessively moistened " prematurely burst, and
revealed within its interior a dead embryo in an insufficiently advanced stage of
development.

In the afore-mentioned letter to 'Nature 'we recorded certain details concerning
the treatment up to the time of hatching of the eggs brought us by Mrs. Dendy. The
three young Sphenodons which from these we successfully hatched out were kept in
confinement in the incubator (Hearson's, size A I.), at the temperature at which they
were hatched — viz. 25° Centigr. They were fed upon mealworms, small earthworms,
cockroaches, and flies, as best obtainable. For these the individual taste was
observed to vary somewhat. One little creature exhibited a decided preference for
mealworms, and a " tug-of-war " for the possession of an earthworm or cockroach was
a not unfrequent occurrence.

1 Cf. also Dendy, 99 c. p. 251,

VOL. xvi. — PART i. No. 2.— February, 190]. c

10 PROF. G. B. HOWES AND MR. II. H. SWINNERTON ON THE

The bottom of the vivarium was covered with coarse sand to a depth of about one
inch, and in one corner a water-bath was sunk ; while a piece of corky-bark was
introduced, which presented to the little captives a vaulted retreat. While to the
latter they would readily retire, they exhibited a decided preference for the darker
recesses of the chamber. Their movements during the day-time were very active, the
passing of a finger-tip, the point of a pencil, or a piece of india-rubber tubing over the
glass front of their dwelling, being sufficient to entice them forward. The tendency to
burrow evinced itself during the second month — the actual date of the first effort being
March 9th in one case observed. They exhibited a fondness for reclining in the water,
in which they would lie at full length, the top of the head being usually kept above
the surface. It was noticed that when, on leaving the water, the whole body was wet,
an area surrounding the pineal eye always remained dry ; and, concerning the use of the
" bath," it was observed that if an earthworm seized by the Lizard happened to be
beset by sandy particles, recourse was had to the water and a " washing " of it before
it was devoured. The prey was never swallowed as soon as seized, but always at first
held between the jaws and more or less masticated.

The first ecdysis in the case of the largest specimen (TVL p. 5) was observed to take
place about March 9th, — i. e. about 7 weeks after hatching.

Under the conditions above-described our little Sphenodons thrived and grew fat ;
i. e. they increased in length during the four months we kept them alive from 8 cm.
to 15-17 cm. The near occurrence and manner of their decease, however (all three
having died in the "bath" within a period of 17 days), points to a common cause of
death. We suspect that this may have arisen from our having unconsciously con-
tinued to liberally feed them into the period normal to hibernation (April to middle of
August l) ; but, on the other hand, it may have been the mere result of over-feeding
on our part (if indeed that may not have been in turn aided by the attentions of night-
watchers and others who were "interested"). Whichever be the case, the salient
feature of the dead animals was a superabundance of fat ; and we found post mortem
that this was evident externally in life, had we but known it, in the great enlargement
and tenseness — due to its accumulation — of the dorsal languets and certain irregular
folds of the skin originally described by Gray 2 ; i. e. that undue distension of these
may be an index of over-feeding — an observation to be borne in mind by those who
may yet be so fortunate as to rear this species in captivity.

5. THE AXIAL SKELETON.

General and as to Terminology. — The adult skeleton of Sphenodon has been so fully
described in its modern aspects by Siebenrock (93) and Osawa(98°) that recapitulation
of its general features is here unnecessary. Before, however, we proceed to details

1 Of. Schauinsland, 98, p. 702 (for Stephen's Island).
s Of. Gray, 42. p. 72.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 11

and the study of its development, we desire to deal briefly with certain facts
and matters of terminology which are necessary to render clear our method of
procedure. Admitting for the vertebral column of all terrestrial vertebrata a primary
classification of the parts in relation to the sacrum, the time-honoured classification
of the prae-sacral portion of that of the Amniota into cervical, so-called "dorsal" or
thoracic, and lumbar regions, is now wholly insufficient for purposes of accurate
description and comparison. The term '* dorsal," being one of orientation, is mis-
applied. " Thoracic," although applicable to the middle region in the mammal — as
embodying the region enclosed by elongated rotatable ribs and bounded posteriorly by
the diaphragm — cannot with precision be applied to that of the lower Amniota, inasmuch
as it presupposes the existence of a post-cardiac septum (diaphragm). The so-called
" diaphragm " of birds (Huxley's " oblique septum ") is prae-cardiac, and the subdivision
of their ccelom into pulmonary and cardio-abdominal compartments is in marked
contrast to that of mammals, which is pulmo-cardiac (or thoracic) and post-cardiac (or
abdominal). Further, when it is remembered that within the reptilian series various
modes of ccelomic subdivision occur, and that free ribs in both birds and reptiles may
extend beyond the limits of the pulmo-cardiac region, the application of the term
" thoracic " to the whole of that portion of the body which bears them is apt to lead to
confusion. And when, in addition, there are considered the presence of free ribs in
the lumbar region of at least the young of seme mammals1, the great variation of the
ribs both in the lumbar and cervical regions of the Amniota generally, and especially
that of the sternum in all its relationships, simplicity and greater uniformity in our
ideas are to be ensured by enumerating the several segments of their prse-sacral
vertebral skeleton by reference to the sternum — and we accordingly propose to substitute
the terms prcesternal, sternal, and poststernal, for the more familiar but arbitrary
" cervical," " thoracic," and " lumbar," delimitating the regions by reference to the one
organ which renders a series of terms necessary2.

Vertebral Column. — Concerning the adult vertebral column as a whole, we have not
met with any numerical variation of its parts beyond that involving the relationships
of the sternum duly considered in the sequel. For the caudal region the maximum
number of vertebrae observed by us was 34 (two less than that originally recorded by
Gunther [67. p. 605]), and for the praecaudal we found it always 27, viz., prsesternal 8,
sternal 3-4, poststernal 13-14, sacral 2, with one exception for the praesternal series.
To an exceptional condition of the sacrum in another individual we shall return.

During the past fifteen to sixteen years the study of the detailed constitution and early
development of the vertebral column has received an altogether exceptional amount of

1 Ex. Homo, juv. : Rosenberg, Horph. Jahrb. Bd. i. p. 111.

2 On the other hand, it has been pointed out by one of us ('Xature,' vol. Ivii. p. 577) that in the Batrachia,
in the absence of a costal sternum, delimitation becomes possible only in relation to the sacrum, whereupon
the praesacral vertebras are best dealt with collectively. The same principle applies to those Amniota in which
the sternum has been lost ; while in the absence of a sacrum, as in the Ophidia, the course is obvious.

c2

12 PKOF. G. B. HOWES AND ME. H. H. SWINNERTON ON THE

attention, mainly as the result of palaeontological discovery by Cope 1, Gaudry 2, and
Fritsch 3 ; leading to the recognition of the so-called rhachitomous, embolomerons, and
other similar conditions, which hive received at the hands of subsequent investigators
correspondingly appropriate names. Both on the embryological and the palteonto-
logical sides, a considerable amount of evidence has been brought forward for the

0 "

belief that some such complex type of vertebra as these, i. e. one in which each vertebral
segment was made up of a series of paired elements, was the ancestral one, and that
the various l;ypes of vertebral structures characteristic of the living groups may have
resulted from diverse modification (inequality of growth and suppression) of these.
And, in the attempt to substantiate this belief. Manner, in the latest paper 4 on the
subject, has sought to show that from the first period of its differentiation in cellular
tissue, the individual " sclerotome " of the Lacertilian is a compound structure. Goette,
basing his arguments, like Manner, mainly upon the study of the Reptilian backbone,
has concluded5 that the vertebra of the living " digitata" have arisen from the embo-
lomerous type, and he regards the rhachitomous type as " neither primitive nor
independent, but transitional. ' If, however, the relationships of these are really direct,
we would rather transpose the order, since we regard the greater extension of the
skeletogenous tissues, and consequent deeper constriction of the notochord, occurring in
the embolomerous type as indicative of advance upon the rhachitomous, as already
pointed out by Gadow 6. He, working on this basis, has simplified our conceptions of
the fundamental constitution of the diverse forms of vertebral structure represented
among the living vertebrata, beyond his predecessors, by the introduction of a
systematic terminology based on the supposition that all surviving forms of vertebrae
are constituted more or less of two pairs of dorsal and two of ventral elements
symmetrically disposed, and that 7 " the solution of the composition of the vertebral
column is given by the metameric repetition " of these, " the origin of which can be
traced in fishes." His terms " basi- " and " inter-" " dorsalia," " basi- " and " inter- "
" ventralia," are most welcome ; and the arguments and conclusions drawn by him
certainly furnish a possible explanation of some of the great anomalies arising out of
the mere study of the adult vertebral column among living forms — as, for example, the
intervertebra] disposition and independence of the " chevron bones " of the Amniota,
and the vertebral disposition and confluence with the vertebral bodies of the " hsemal
arches " of the Urodela.

1 Cope, E. D. : Americ. Nat. 1878, p. 327 ; Proc. Americ. Philos. Soc. vol. xvii. 1878, pp. 510-526; Trans.
Americ. Philos. Soc. vol. xvi. 1886, p. 243.

'2 Gaudry, A. : Enchainements d. Monde anim. Foss. Prim., torn. i. (Paris, 1883), p. 263.
:! Fritsch, A. : Fauna d. Gaskohle d. Permform. Bohmens, Bd. ii. 1889, pp. 14 & 24. Of. also Baur, G. :
Biol. Central!)!. Bd. vi. 1886, pp. 332 & 353.

4 Manner, H. : Zeitschr. wiss. Zool. Bd. Ixvi. 1899, p. 43.
' Goette, A. : Zeitschr. wiss. Zool. Bd. Ixii. 3897, p. 390.
' Gadow? H. : Phil. Trans, vol. 187 B. 1896, p. 1.
7 Op. cit. p. 50.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 13

Certain it is that this subject, as it now stands, forms one of the most fascinating
chapters in the vertebrate morphology of our time. Our own researches begin at the
period of differentiation of actual skeletogenous tissue, and while, concerning the
supposed original complexity and general uniformity in origin of the parts of the
vertebral body, we retain an open mind, we question if, in matters of detail to be
referred to in the sequel, theories, in their growth, have not been at times unconsciously
read into the supposed record of facts.

First differentiation of the Skeletogenous Tissue. — The earliest stage which we have
investigated is Dendy's P, and a median longitudinal section through any portion of the
skeletal axis at this stage reveals the presence of a central notochord, ensheathed in a
thin structureless and deeply staining cuticle or chordal sheath (elastica externa of Gadow
[nc.s., PI. I. fig. 2]). This is seen to be in turn invested by a continuous skeletogenous
sheath, composed of a thickly disposed mass of small cells, containing relatively large
nuclei. There are some 9-10 rows of these, and their close compression gives to the
tissue, when examined under a low magnifying power, the appearance of being feebly
longitudinally striate. The notochord itself consists at this stage of comparatively
small vacuolated cells, arranged in an irregular manner, and differentiated peripherally
into the usual chordal epithelium (nc.e.). Central or othei: differentiation there is
none.

Comparing with the foregoing a lateral longitudinal section, the superficial cell-
rows of the skeletogenous layer are seen to be more closely approximated than the rest,
and in addition there are (fig. 1) differentiated within the area of this more closely
aggregated stratum a series of metamerically recurrent masses (i.p.) of cells, generally
more rounded than the rest. They are the developing intercentra; wherefore it follows
that in order of differentiation these are the first formed skeletal elements.

"When the corresponding parts are viewed in transverse section, the skeletogenous
layer is seen to completely encircle the notochord, constituting a skeletogenous sheath,
the aggregation afore-named being apparent (i.p.} as a couple of symmetrical tracts
which are ventro-lateral, widely separated in the trunk -region (cf. fig. 2), closely
approximated in the ventral line in the caudal (fig. 3). The neural arches are at this
stage first differentiated, in the form of bilaterally symmetrical upgrowths of the
skeletogenous sheath (fig. 3, n.a.), separated by a wide interval in the mid-dorsal line.

Stage Q. — A transverse section through an intervertebral region at this stage shows
that, concerning the skeletogenous sheath (t.a., text-fig. 2 and PI. I. fig. 6), the cells
remain practically unchanged, their nuclei when examined under a high power presenting
the oval contour indicative of mutual apposition, so characteristic of the earlier stage
afore-described.

Comparison of a similar section through a vertebral region shows (text-fig. 3) that
chondrification has there set in, but not at all points — for, while laterally hyaline
cartilage is now present, in the form of paired masses (c.v.\ continuous with the
now cartilaginous neural arches (n.a.) and confined to the superficial layers of the

14

PEOF. G. B. HOWES AND ME. H. H. SW1NNERTON ON THE

skeletogenous sheath, in both dorsal and ventral middle lines the latter (s.s.) has
remained unchanged.

Comparison with the foregoing of a lateral longitudinal section at a slightly later
stage, shows (PI. I. figs. 7 & 8, c.v.) that these lateral chondrites encroach upon the
skeletogenous sheath from without inwards, rapidly involving its deeper layers, until its
innermost limit is reached. They also effect the replacement of the afore-mentioned
median portions, but by union within the deeper layers and subsequent extension in
the opposite direction — ?. e. from within outwards, as is seen at c.v. in PL I. fig. 6,
which is that of a median longitudinal section at this period.

The above described processes continue until chondrification of the vertebral portions of
the skeletogenous sheath is complete, and there thus results a metameric segmentation

Fig. 2. Fig. 3.

vy

n.a

n.c.s

n,a

nc.s

Transverse sections through the poststernal region of the trunk of SpUenodon. 2. Intervertebral ; 3. Vertebral,

drawn for comparison. Camera lucida X 70.

c.v. Cartilaginous vertebra ; i.p., primitive paired intercentrum ; my,, myelon ; n.a., neural arch ; nc.e.,
notochordal epithelium: nc.s., chordal sheath; r.t., trunk rib; s.s. skeletogenous sheath; t.a., inter-
articular tissue (intervertebral portion of skeletogeuous sheath).

of the vertebral axis, whereby a series of segments become recognizable, each comprising
a centrum, an intercentrum, and a pair of neural arches ; and the facts justify our
regarding the centrum as of paired origin — a view which lends support to Gadow's
conclusion that it represents the fused " interventralia " of the lower vertebrate forms.

As is well-known, the chevrons and praesternal or cervical intercentra present in
most Lacertilia may, by shifting, come into secondary relationship either with the
vertebrae in front of them l (by which they may even be carried down on autogenous
hypapophyses, as in the neck of the Mosasaur Tylosaurus 2), or with those behind

1 Ex. Anguidap, Varanidae, Helodermatidse ; and, with co-ossification, Mosasaurus, some Varanida?, and
Pseudopus. (Of. Boulenger, P. Z. 8. 1891, p. 113, and Gadow, Phil. Trans, vol. 187 B. 1896, p. 30).

2 Cf. Osborn, H. F. : Mem. Americ. Mus. Nat. Hist. vol. i. 1899, p. 171 ; and also Americ. Nat. vol. xxxiv.
1900, p. 1.

DEVELOPMENT OF THE SKELETON OF THE TTJATARA. 15

them, as in Tupinambis 1. This notwithstanding, since the anterior element of the whole
series (that lying between the skull and first vertebra) is the first intercentrum, pre-
cision and uniformity are gained by enumerating it in correlation with the centrum
behind it, and so on for the whole series which follow — as has been done, for example
by Gadow, for the chevrons, though not with that uniformity which is desirable. The
method mostly adopted, especially in illustrations, of associating with the numeral
indicative of a given chevron that denoting the vertebra in front of it, as has been done
with descriptions of the skeleton of the adult Sphenodon from Giinther to Osawa, leads
to confusion and must be given up.

Passing now to the intercentra, a marked advance is seen to have taken place in
those of the anterior twelve body-segments and the tail. At Stage P the intercentral
bodies are everywhere paired. At Q, fusion in the mid- ventral line has come about in the
anterior region (rf. PL I. fig. 8, i.p'.J. In the case of the first four bodies, the contour
of the fused product gives no indication of its paired origin, but from the fifth to about
the twelfth (as determined by very careful examination of serial longitudinal sections)
a median depression remains. These facts are embodied in column Q of our table on
p. 27, and perusal of them would seem to indicate that fusion of the paired intercentra
takes place antero-posteriorly.

At Stage P, owing to the absence of demarcation between the cranial and vertebral
portions of the differentiating tissues, the enumeration of the centra had to be
determined by reference to the sacral region, i. e. the segments had to be worked out
in postero-anterior succession. The numerous practical difficulties arising from this
necessity, leave us in doubt whether the first and second intercentra are or are not
represented at this stage. Hence the 1 in our table, column P (p. 27). This con-
sideration would seem to throw some doubt upon the paired origin of these first
two intercentra; but, judging from the fact that from segments 12 to 5 the unpaired
intercentra at Stage Q still show traces of paired origin, and that in segments 4 and 3
these elements are proved to be beyond doubt originally paired, we deem it fair to
conclude that the same conditions apply to segments 2 and 1.

It may be remarked that at this stage (Q) the union of the first centrum with
adjacent parts is effected. While it fuses (fig. 8 a) completely with the second inter-
centrum (i j/.), it does so only peripherally with the second centrum, and that so as to
enclose at* a central mass of undifferentiated tissue.

The neural arches have at this stage completely united in the dorsal middle line and
are fully chondrified.

Passing to the caudal region, the intercentra of its fourth and succeeding vertebral
segments, by an astonishing rapidity of growth, have acquired a characteristic elongation,
each extending downwardly into (PL I. fig. 7, i. p.'1) the substance of the tail, but
without meeting its fellow. Although they are chondrified, and at this stage differ-
entiated in advance of their homologues — the paired intercentra — in front, their cells

1 Cf. Boulenger, G. A. : op. cit. p. 114.

16 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE

are still more closely aggregated than those of the centra, wherefore they appear under
the microscope dark and highly conspicuous.

Stage E. — This stage is most noteworthy for the completion of chondrification in
the median plane (cf. PL II. fig. 11) of the vertebral bodies, throughout the whole
length of the column, and for the lateral extension of these. Ossification of them has
now set in, chiefly in the dorsal and ventral surfaces as seen in transverse section
(PI. II. fig. 11, o.v.). The neural arches begin to ossify independently of each other
and the centrum, by an identical and similarly superficial process, as represented (for
Stage S) at PL II. figs. 4-6.

At this stage a remarkable change, for which we were not prepared, is undergone
by the intercentra of the segments numbering 11 to 29 (i. e. those between and
including the third sternal and second caudal segments), viz., the complete disappearance
of those belonging to segments 13 to 25 (cf. table, column R, p. 27) ; and the tendency
to disappearance, to an extent which renders it difficult to identify their presence,
for segments 11 and 12 and 26 to 29. We are unable to say at this stage by what
process this removal is effected, whether by absorption into the intervertebral tissues
or otherwise ; but, in view of the discovery of this remarkable fact, it is the more
astonishing to note that while one pair (viz. those of the third caudal segment)
remain in their primitive condition, those which follow this in order of succession
behind, while still unossified, have coalesced distally, enclosing the caudal canal, to
form the so-called " chevrons," — which are thus proved to be the direct derivatives of
primary paired intercentra.

Stage S. — Viewed in median longitudinal section, the salient advances at this period
are seen to be four in number. Firstly, the ossific tracts, described in the previous
stage (PL I. fig. 10, o.v.), when viewed in transverse section (PL II. figs. 4 & 5), are
seen to be extending into the lateral cartilaginous expansions, which are being rapidly
absorbed over the areas marked f . Internally to these ossific centres and immediately
surrounding the notochord, there are marked signs of calcification revealed by the
selective action of our reagent. Exactly the same processes take place in the ossifica-
tion of the centrum of the atlas (os odontoideum) as of an ordinary vertebra (cf. PL I.
fig. 9V).

The advance in ossification of the vertebral bodies (o.v., PL I. fig. 10) is seen to go
on hand in hand with the assumption of a more truly hyaline character by those
portions which are still cartilaginous. These (as viewed in longitudinal section) are
seen at the same time to undergo a marked change in shape, becoming thinned
over the centre of bony deposition and thickened at and towards their extremities—
i. e., an inverse development of bone and cartilage is recognizable, in proportion as the
centre of each developing vertebra is approached.

In the intervertebral regions (t.a.t PL I. fig. 10) the cells of the skeletogenous sheath,
still closely crowded, retain, in the elongation of their nuclei, a character originally

DEVELOPMENT OF THE SKELETON OF THE TUATAKA. IT

common to the whole sheath ; but there has appeared around them a feebly hyaline
matrix. The now clearly recognizable differences in the parts generally admit of the
application of the term inter articular tissue to these intervertebral areas ; and we desire
to emphasize the fact that though they are feebly hyaline, " intervertebral disks " are not
present — the hyaline matrix, dense and resistant for the vertebral bodies, diminishes
markedly as the extremities of the centra are reached, and at these fades into the mure
flexible interarticular tissue, there being no hard and sharp line between the two.

The process of differentiation at this stage is most noteworthy for the full formation
of an important, constituent of the individual vertebra, which it so happens our
reagents differentiate with startling effect. This, which we propose to term the chordal
plate, is located transversely in the central and most constricted part of the developing
vertebra. We have encountered it (PI. I. fig. 10, n.p.} in all regions of the column,
from the first (odontoid) vertebra (fig. 9) to well into the region of the tail. Micro-
chemically, it reacts in a totally different manner to the reagents we have employed to
anything else thus far described, wherefore there is no room for ambiguity concerning
it. Its general matrix, which is extensive, stains a deeper blue than any other form of
skeletogenous tissue which is present, and when examined under a high power its very
conspicuous appearance is found to be due to the extent of its matrix and the presence
of regular circular spaces, each filled by a cell which hardly stains at all and contains
a conspicuous rounded nucleus. From its general appearance and disposition we
have no doubt that it represents the so-called chordal cartilage described by Gegenbaur
in 1862 1 in the Urodela and Reptilia, and since observed by Field, Fraser, and Stohr
in certain allied forms and by Goette in the Anura.

Gadow has given (op. cit.) an admirable summary of the work of these investigators,
all of whom regard this as chordal in origin, and of others who seek to disprove that.
With the latter he is himself agreed. He deals with the question in full in Lacerta
and the Geckos among Lacertilia, and since we are dealing with Sphenodon, it is with
his statements that we are alone concerned in detail. Having referred (op. cit. p. 11)
to an " occasional perforation of the elastica externa " in the Urodela, he is most
emphatic as to the rending asunder and destruction of the chorda (p. 26) during the
formation of the plate in certain Lacertilia. He describes this plate as a septum
of which the cells "retain the appearance of young or embryonic cartilage." Dealing
with the embryonic Lacerta, he asserts (p. 24) that he is " absolutely certain this so-
called chordal cartilage does not exist, if thereby be understood cartilage which

is produced by the conversion of chorda cells ; nor does this cartilage invade the
chorda." His context shows this statement to be based mainly upon the examination
of transverse sections, of which he says that they " allow the elastica externa to be
traced as a continuous, unbroken line, which becomes irregularly folded, or creased, as

1 Gegenbaur, C. : Untersuchg. z. vergleichd. Anat. d. Wirbelsaule b. Amphib. und Itept. 4to. Leipzig,
1862.

VOL. xvi. — PART i. No. 3. — February p, 1901. D

18 PKOF. G. B. HOWES AND ME. H. H. SWINNEKTON ON THE

the sections approach the septum " ; and he adds that " the cartilage of the latter is
nowhere in direct contact with the cells of the chorda." The figures which illustrate
his memoir are unfortunately diagrammatic, but that of a longitudinal section of the
caudal vertebra of an adult Haplodactylus (p. 26), taken conjointly with the descriptive
text and the associated remark that " in Phyllodactylus the chorda is only constricted,"
leaves little doubt in our minds that he would regard the chordal plate as ectochordal.
We, on the other hand, are as emphatic to the contrary as concerning Sphenodon 1,
since we are convinced that in that animal it is endochordal and intimately associated
with the chordal epithelium in origin, as asserted by Gegenbaur.

It first appears at Stage E. (PI. II. fig. 11, n.p.) at the periphery of the chorda, and
entirely within the chordal sheath, which by our method of treatment stains at all
points light yellow as opposed to the blue of the chordal plate. On comparison of
Stage S with E, (fig. 11), it will be seen (PI. II. fig. 12) that the plate increases by a
process of inward proliferation. When at S it is worked out in detail in longitudinal
section, two important facts are very evident, which are wholly irreconcilable with the
theory of an ectochordal origin — viz., in the first place, that the tissue of which the plate
is peripherally composed can be traced into continuity with the chordal epithelium,
in a manner which suggests that it arises from this by special activity of its cells ; and,
in the second place, that its antero- posterior faces show no sharp line of demarcation
from the substance of the notochord, but rather, on the contrary, a passage into it — the
faces of the plate being irregular, and, as it were, sending prolongations of the matrix
into the chorda (cf. PI. I. fig. 10). The matrix of the plate is often seen to be feebly
differentiated as its centre is reached, and in median longitudinal section a gradual
transition into the central cells of the chorda may be observed 2.

Interesting, in consideration of recent discovery concerning the truncal origin of
the amniote occiput, is the fact that at this stage there is present, wholly within the
central tissues of the chorda (as it were in very testimony to the origin from this of the
plate-tissue), a similar differentiation ; and the fact that the distance between it and
the chordal plate of the os odontoideum is about equal (cf. PI. I. fig. 9, n.p.} to that
between the latter and the plate next in order of succession behind, is not without
significance. Going back to Stage R, we find this intrachordal mass represented
by an essentially similar, though somewhat irregular, differentiation of the chordal
epithelium, over the whole length of the iritracranial notochord (PI. I. fig. 9), with

1 Cf. our footnote and reference to Zykoff, on p. 22.

2 Dr. Gadow has courteously allowed us to compare his sections with our OWN. We can confirm his discovery
of the ectochordal origin of the plates in Lacerta. His sections of Gecko, however, are in complete agreement
with ours of Sphenodon. We conclude that the plates may arise in two independent ways ; and we would
accordingly distinguish between the Lacertan type in which they arise by inward extension of the skeletogenous
tissues with accompanying constriction of the cuticular sheath (elastica) and the Gecko-Sphenodon type, in
which they are chordal and lie at. all stages within this. A most interesting result, but by no means without
parallel in the animal kingdom.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 19

accompanying indications of there having been a similar change in the general substance
of the chorda and the adjacent tip of the odontoid vertebra.

The neural arches at this stage call for no special comment. Turning to the inter-
centra, a further suppression of the primary paired series has to be recorded — viz., that
of the bodies related to segments 10 to 12 and 26 to 29, thus giving a condition of
the complete absence of these between and including 10 to 29. With careful focussing
the disappearing primary intercentra (the mode of removal of which we were unable
earlier to determine) can be at this stage observed to lie wholly within the substance
of the skeletogenous tissue (cf. isp.1, PL I. figs. 9 & 10) ; and by comparison of the
several segments we have convinced ourselves that their disappearance is not due to a
process of absorption and decay, but to one which may best be described as a sharing
in the progressive differentiation of the skeletogenous tissues — i. e., there is no loss
of substance, but merely a histological change, leading to a loss of individuality.

On the completion of this remarkable process, the intercentra are present only for the
segments 1 to 9 and from the 30th backwards, i. e., in precisely those regions in which
in the Lacertilia they are most generally retained ; and, as concerning the more precise
limitations of this intercentrumless area, this comparison becomes more close as the
development of Sphenodon advances — until a passing condition is reached in which,
as regards its intercentra, the backbone becomes, as it were, that of a Lacertilian. The
anterior intercentra remain unossified, but it is during this stage that the caudal ones
(chevrons) ossify, and that as the result of a superficial deposit, which in its early con-
dition, as is the case with the neural arches, forms a bony shell (cf. PI. II. fig. 13, i.p."9
and figs. 4 & 5, na.). Owing to the rapidity with which this process is effected, we
have not been able to ascertain whether ossification arises at more than a single
centre.

Stage T. — The most conspicuous feature of this, the first stage after hatching, is the
great extension of ossification and calcification, with accompanying constriction of
the mid-vertebral areas and a general dawning of the adult characters. The process
of ossification in the centra (ov., PI. I. fig. 13) has invaded all but the innermost two
to three rows of cells, which are still but calcified ; and it is densest at the point of
greatest constriction. Both within the intervertebral areas (t.a.) and the central
substance of the chorda! plates (n.p.) calcification has become highly conspicuous, and
in the case of the latter it extends into the processes afore-mentioned, which pass into
the chorda-tissue.

The cells of the skeletogenous tissue which mark the boundary-lines between the
intervertebral masses and the vertebrae have undergone a complicated rearrangement.
These lines are delimitable by the fact that the nuclei of their cells, which are small,
are vertically disposed in close aggregation, as compared with those of the central
intervertebral series which are larger and run parallel to the longitudinal axis. Those

D2

20 PBOF. G. E. HOWES AND MB. H. H. SWINNEBTON ON THE

of the ends of the vertebrae, which during the earlier stages were structurally uniform
with the cells adjacent, have at this stage become large and rounded, whereby their
matrix is less conspicuous. Once again there are no structures recognizable which
merit the term " intervertebral disks," nor is there any discontinuity of parts.

At this stage a still further numerical reduction of the primary intercentra goes on,
their disappearance involving segments 5 to 9 and segment 30 (cf. table, column T,
p. 27), leaving only four present in the prsesacral region and traces of a fifth. The
third, and probably the second and first, at the same time commence to ossify, which
they do endogenously. For certain of the segments which have lost all traces of their
primary intercentra, there now takes place the formation of an entirely new set of parts,
remarkable no less for their time of appearance than for their detailed structure. These,
which arise in relation to segments 9 to 13, appear wholly beneath, though in close
apposition medially with, the interarticular masses (£.#., PI. 1. figs. 13, 14), but with
them they have at first no sort of connection. Laterally quite free of them, they lie
between them and a tract of coarse fibrous tissue which (f.t.) besets the ventral face
of the vertebral column. Each of these secondary intercentra stains deep yellow, as
does ordinary bone. The most remarkable character of them, however, is the presence
of a very dark and deeply-staining central portion (cf. fig. 14), which is highly con-
spicuous under a high power of the microscope, and into which there pass convergently
coarse fibres arising from the underlying tissue, which by their refractability are easy of
observation and impart to the bodies a highly distinctive character. These secondary
intercentra are from the first median and transverse, and in this they differ in toto
from the primary, which arise in pairs.

. Adult Vertebral Axis. — On the anatomy of this we have nothing that is general to
add. Develop mentally, the most noteworthy advances, apart from the mere com-
pletion of the vertebral bodies, notochordal plates, and chorda, concern the inter-
articular tracts (which have become more distinctly fibrous) and the intercentra
(which now are finally present along the whole length of the vertebral column). The
tail-vertebrse and their special peculiarities will be considered later.

Goette has recently briefly described l the detailed structure of the fully-formed
vertebra of Sphenodon, but that imperfectly, and judging by his figures from apparently
none too well-preserved material. He omits mention of the chordal plate, and describes
the chorda remnant as passing continuously through the vertebra?. He further remarks
upon the peculiar constitution of the osseous tissue of the vertebra, which he regards
as " no true bone," but rather to be compared in part to a poorly-celled calcified
cartilage, with enclosed medullary nests, and of an exceptional type for the living
Amniota.

We figure longitudinal sections from the sternal region of the adult backbone,
stained with haematoxylin (PI. I. tig. 15). The intervertebral tissues are now strongly
1 Goette, A. : Zeitschr. wiss. Zool. Bd. Ixii. 1897, p. 364.

DEVELOPMENT OF THE SKELETON OF THE TUATARA.

21

fibrous, and on the ventral side they, together with the subvertebral fibrous tissue (f.t.),
have attained to full differentiation. Their cells are arranged in parallel series, with
an accompanying loss of individuality, the tissues having the appearance of being
permeated by widely-separated parallel rows of small and elongated nuclei. While
peripherally this parallel arrangement becomes more conspicuous, in the deeper layers
the fibres become stronger, their attachments to the bony vertebrae appearing more
marked, as the result of their greater avidity for the stain. Owing to the increase in
thickness of the bony shell of the vertebral body (still largely composed throughout
its inner moiety of calcified cartilage), the chordal plates (PI. I. fig. 15 and text-fig. 4,
n.p.} are comparatively insignificant as compared with the earlier stages. They are,
however, present, and, owing to their completely septate nature, the chorda is now
broken up into a series of elongated and recurrent interseptal segments, each of which
is seen to be bounded not by the chordal epithelium hitherto recognizable, but by a
deeply-staining and structureless cuticle, which passes into the faces of the plates, the
superficial portions of which stain correspondingly with it.

Fig. 4.

nc.s.

Median longitudinal section of the adult vertebral column (caudal region) of Sphenodon, to show the tunica
chordse (i.e.) and its relationships to the chordal sheath and plate. Camera lucida, x 70.

i.sg., interseptal segment of chorda: n.c.s., chordal sheath; n.p., chordal plate; o.v., osseous vertebra;

£.c. tunica chordae.

This cuticle, which we propose to term the tunica chorda? (text-fig. 4, i.e.), would
appear to represent the chordal epithelium ; but that it underlies and is independent
of the chordal sheath («0..v.) is proved by the fact that this stains lightly and can

22 PEOE. G. B. HOWES AKD ME. H. H. 8WINNEETOX ON THE

therefore be easily traced and seen to be continuous along the whole length of the
vertebral column. We have searched in vain for evidence of the " occasional breaking-
down " of the cuticular sheath (el. interna) in the vertebral regions as supposed by
Zykoff for Siredon (Bull. Soc. Nat. Moscou, Bd. vii. 1893, p. 34).

The main cells of the chorda do not undergo any marked change, but in the centre
of each interseptal mass, at the point coincident with that of greatest flexibility,
there has now arisen, apparently by accumulation of a fluid contents, a conspicuous
globular vesicle (PI. I. fig. 15, v.c.), which we propose to term the vesicula centralis,
and assume to be in some way associated with facilitating the movements of the
parts.

Goette, by an ingenious argument, has drawn the conclusion (op. cit. p. 366),
primarily from the study of the caudal region, that in Sphenodon the vertebrae are not
truly amphiccelous. He extends this conclusion with qualification to the trunk-
vertebrae, which he figures as transmitting an uninterrupted notochord. Osawa has
adopted his view and applied it to the vertebral column generally (98 a. p. 104).
We defer consideration of the caudal region, which is specialized on its own lines, till
later, but acceptation of Goette's view nevertheless depends entirely upon what we are
to understand by an amphiccelous vertebra. As constituted ill many bony fishes, this
type of vertebra, at first sight solid, at its central and most completely constricted
region, is in reality perforated by a minute aperture or canalis dicentralis, for transmission
of a delicate thread-like process of the notochord connecting the adjacent inter-
vertebral masses. If such be termed an amphiccelous vertebra, as is customary, the
mere continuity of this notochord in Sphenodon would be no justification for dis-
regarding the accustomed terminology under which its vertebrae are described as
amphiccelous. If, on the other hand, by an amphiccelous vertebra be meant one
centrally solid and with excavated extremities, — i. e., a vertebra of which one or both
articular faces have not become condylar or flattened — then the term may be applied to
Sphenodon, the peculiar characters of its vertebrae being in this case the great depth
of its concavities. Inasmuch as we have shown the chordal plates to be notochordal
derivatives, we agree with Goette, in a sense, as to the presence of a continuous
notochord, which on the whole simplifies the customary conception of the Rhyncho-
cephalian vertebra. If, however, for argument's sake we dismiss the chordal plate
with the rest of the chorda, the characters of the Sphenodon-vertebra become more
nearly comparable to those of the cylindroidal type to which Credner has specially
drawn attention in Palaeohatteria (oj). cit. p. 492), which may or may not have been
plate-bearing. Viewed from this standpoint, the extension of Goette's argument by
Osawa, instead of supporting his defence of the supposed Agamid affinities of
Sphenodon, weakens it to an unexpected degree.

Passing now to the caudal region, the most important facts concerning the

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 23

vertebral axis (apart from outstanding processes and chevrons) lie in the study of the
" splitting " phenomenon and the intervertebral chorda. Since the days of Cuvier,
a good deal of interest has centred in the study of this process, by which the
Lacertilian tail may be cast off. Hyrtl, Gegenbaur, Miiller *, and Leydig have more
especially studied its details, which involve to a conspicuous degree the chordal plate,
as Gegenbaur first pointed out. Gadow has recently summarized our knowledge of
the nature and extent of the subdivision-line recognizable on the exterior of the
vertebra capable of " splitting " among certain Lizards ; and perusal of his statements
will show that as to its position and relationships to the neural arch and transverse
processes variability may be recognized, the " split " subdividing the vertebra in some
cases into equal, in others into unequal portions. In Sphenodon this suture usually
first appears on the caudal vertebrae numbering 6 to 8, and it may be present for all
posterior to it. Gunther, who first described it in Sphenodon, states (67. p. 606)
that it " passes through the middle and behind the transverse process." Gadow, on
the other hand, figures it as passing in front and subdividing the vertebra into
approximately equal halves, of which the posterior bears both transverse processes and
neural spine. With this we are in agreement (of. PI. I. fig. 18), but we have noted
that while the suture may occasionally pass through the expanded base of the trans-
verse process 2, it may also subdivide the neural spine (as in PI. I. fig. 20) in a manner
anticipatory of the more symmetrical division which, according to Gadow (p. 29,
figs. 22 and 23), appears to involve the anterior neural spine3 of Lacerta ocellata.
And further, the characters of the first three suture-bearing vertebrae prove conclusively
that although an elongation is effected when the suture is present, it is a subdivision
and not a duplication which has taken place, since in vertebrae which are in all other
respects identical with those immediately in front, the suture, which is restricted to
the centrum in nos. 9 and 10, passes gradually up to the arch, assuming the condition
characteristic of those behind.

We have noted that in the adult vertebral column both halves of the splitting
vertebra send down minute but definite autogenous hypophyses, which have not before
been described. These (ha.', PI. I. fig. 18), when examined in situ, are found
(fig. 19) to extend into the walls of the haemal canal, to which they act as extra
supports.

1 Miiller, H. : Ueber Regeneration d. Wirbelsaule u. d. Riickenmarks b. Triton u. Eidechsen. 4to. Frankfurt,
1864. For other references, see Gadow, op. tit.

- "We consider Cligny in error in his recent argument (" Miscell. Biologiques," Travaux d. 1. Station Zool.
d. AVimereux, torn. vii. 1899, p. 432), that the power of fracture and the " double pleurapophysis " are associated
with ancestral characters. The probability that the centra of the Amniota are compounded of the " intra-
ventralia " alone is completely opposed to it.

3 So called by Cope in Dipsosaurus and Sauromalus, Proc. Amer. Phil. Soc. vol. xxx. 1892, pp. 202-205.
Comparison with Sphenodon renders it extremely doubtful if this is a product of division, as assumed by
Boulenger (P. Z. S. 1891, p. 169). We would rather regard it as a secondarily formed outgrowth like the
autogenous hypapophyses which we herein describe.

24 PEOF. GK B. HOWES AND MR. H. H. SWINNBRTON ON THE

Equally significant, as proving that the splitting phenomenon is secondary, is the
fact, already pointed out by Gegenbaur in 18G4, that the changes which render it
possible appear as, by ossification, the vertebra is assuming the adult condition ; and in
support of this we are able to state that the bony centrum and chordal plate (both of
which become split as the adult condition is realized) are in the developmental stages
complete. The first appearance of subdivision is at Stage T. In fortunate sections of
the adult we have been able to determine the probable method of splitting, and that it
is, at least to a large extent, due to invasion of the bony vertebra and ultimately of the
chordal plate itself (cf. np., PI. I. fig. 17) by the surrounding tissues, with accompanying
absorption, since in sections in which the process was going on we find an inward
extension of these tissues into the parts already ossified, with an accompanying peri-
vertebral striation radiating from the split (cf. PL I. fig. 17, #.) such as we have
encountered nowhere else. The bony vertebrae, however, continue to thicken after the
first appearance of the split, and nowhere more so than at its opposite edges ; wherefore
it follows that by this, which is a growth process, the split is extended outwards.

We find in the intervertebral regions of the tail that a series of changes of a some-
what remarkable and intensely interesting order are undergone. Goette has recently
described them in part. He calls attention (op. cit. p. 365) to the fact that in the
caudal region the opposite ends of the vertebrae, which in the trunk are usually directed
outwards, are inwardly thickened, and that they so constrict the vertebral canal that it
is most spacious within the vertebra and narrowest at its extremities. In this respect
the caudal vertebra presents a striking contrast with that of the trunk-region, in which
the ends are widely open and the centre is contracted. He asserts that correlatively
with this constriction an ingrowth of the intervertebral mass, already foreshadowed in
the trunk-region, has effected a complete blocking of the intervertebral area, with
accompanying segmentation of the chorda. When first examined, the intervertebral
regions of the tail of a mature Sphenodon do appear to be compact, as Goette asserts ;
but when further investigated in well-preserved material the parts there present are
seen to be complex, and to bear to one another a relationship essentially similar to that
which the chordal plate bears intracentrally to the vertebral body. The interseptal
chordal segment (PI. I. fig. 17, i.sg.) becomes divided throughout its intervertebral region
by a cartilaginous plate (n.p.1) lying wholly within the chordal sheath, continuous with the
tunica chordae, and having essentially the same structure and evidently the same origin
as the chordal plate (n.p.). Indeed, the first indications of this are met with at Stage T,
as a well-marked thickening of the tunica chordae and its associated cellular tissue.
As fully differentiated, this, which we propose to term the intervertebral chordal plate,
in contradistinction to the chordal plate which is mtravertcbral, reveals terminal calci-
fications, and a centrally less dense area at the point where movement of the parts
is greatest, which, while providing for the necessary flexibility, furnishes additional
support. It would thus appear that under the weakening influence associated with the

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. .25

splitting of the strongest part of the vertebral complex, a compensating development is
deliberately initiated in the intervertebral — a process to which the term of Dohrn
and Kleinenberg, " substitution of organs," may be not inappropriately applied; and
beyond the extent to which these intervertebral plates may furnish support and be
concerned in determining points of muscular attachment, we are inclined to regard the
in tra vertebral plates us direct agents in the formation of the axis of the reproduced
tail. This matter, however, requires further investigation. There remain only for
consideration the definitive intercentra of the region of disappearance of those of
the primary series, viz. segments 5 C?)-6 to 30. The intervertebral region of each of
these shows an intercentrum of considerable proportions (PL I. fig. 15, i.s.). This, the
secondary intercentrum^ agrees with those already described (antea, p. 20) in lying
outside the skeletogenous tissues, as figured by Goette (op. cit. pi. xvii. fig. 25, x).
Not wholly so, however ! The most distinctive character of these remarkable bodies is
a sharp demarcation into a greater feebly-staining outer portion and a lesser inner one,
which differentiates darkly and, when viewed in section, tapers into the intervertebral
mass. The cells of their inner moiety are more numerous and much larger than those
of their outer ; and since in the mode of disposition these are linear with those of
the intervertebral mass, they would appear to be derived from it. If this be so, these
definitive secondary intercentra would appear to represent those to which we originally
applied the term, but with a superaddition of parts derived from the intervertebral
tissues. Be this as it may, their formation finally completes the series of inter-
centra, which are now present throughout the whole length of the column.

Typically these secondary intercentra arise singly, as median and transverse masses.
In one case, however (i.s., PL I. fig. 16), we have noted that for segments 12, 13, and
16 to 20 (7 in all) they are paired. Boulenger has drawn attention (P. Z. S. 1891, p. 170)
to the existence in Lacerta ocellata of paired intercentra in the posterior sacral and
anterior caudal regions, and Leydig has figured a similarly-paired condition of one of
the prsesternal intercentra of L. agilis (op. cit. pi. iv. fig. 53). In the absence of any
knowledge of secondary intercentra in the Lacertilia, we conclude that while in both
species the paired elements are of primary order, in our exceptional Sphenodon
those of the post-sternal region, which are paired, would seem to be of secondary,
and that these may therefore be variable as to their median or paired nature.

Comparison of the caudal region of Sphenodon with that of Lacerta ocellata as
described by Boulenger would seem to justify the conclusion that in the chevrons
primary intercentra are alone represented. We find, however, that in the case of the
first 4-5 this is not wholly so. In the adult Sphenodon, these are characterized by the
fact that their proximal ends are united, as pointed out by Dollo in 1888 *, whereby
they appear to overarch the caudal canal. Credner has confirmed this observation, and

1 Dollo : Bull. Mus. Hist. Nat. Belg. torn. ii. 1883, p. 324.

VOL. xvi. — PART T. No. 4. — February, 1901. E

26 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

with equal acumen has made it the basis (op. tit. p. 501) of determination of the
isolated chevrons of Palseohatteria as median caudal.

Seeking the explanation of this overarching in Sphenodon, it occurred to us, having
proved the chevrons proper to be permanent primary intercentra, that their united
"" proximal ends," being serial with our secondary intercentra, may be the homologues of
those and that the anterior 4-5 chevons are therefore complex 1. In support of this con-
clusion we would point out that at those stages at which the secondary intercentra are
undeveloped (PL I. fig. 12 and PI. II. fig. 13) the extremities of the chevrons in question
are in no way united ; and proof of its accuracy has come to us in a specimen belonging
to the Dublin Museum, in which (PI. I. fig. 21) the right half of the anterior chevron
{i.p-") and the overarching lobe (our secondary intercentrum) have remained distinct.

We append, in tabular form (p. 27), a synopsis of the complicated series of changes
undergone by the successively formed sets of intercentra ; and in conclusion desire
once again to emphasize the fact that in the most fully differentiated state the bony
vertebrae and the fibro-cartilaginous interarticular masses of Sphenodon are organically
continuous.

We are constrained to do this as Cope more particularly 2, and Gadow, though with
greater caution 3 (reading as we believe theory and expectation into fact), have referred
to the intervertebral masses in terms applicable only to discontinuous skeletal parts.

The so-called " Pro-atlas." — The most recent view expressed as to the morphology of
these debateable elements is that of Gadow, who (op. tit. pp. 12, 13, and 37) has come
to regard them as parts of the atlas — the serial homologues of his " supradorsalia " of
the supposed ancestrally composite vertebra. In the conclusion that the atlas was
thus originally more complex than has hitherto been supposed, and that the atlas and
" pro-atlas " represent one vertebra, he has been followed by Osborn (op. tit. p. 173),
who, from the study of the palaeontology of the Reptilia, has come to regard the atlas
as composed of five pieces and " persistently rhachitomous." Despite all attempts to
discover facts which might help further to elucidate this question, we have failed.
Appeal to the nerves availed us nothing, and all that we can add is that the " pro-
atlas " so-called is praeformed in paired cartilages (PL II. fig. 3,p.a.), which at Stage Q
arise independently of both the cranium and the rest of the vertebral column, and are
imbedded in the tendons of the dorsal skeletal muscles, near the point of attachment
of these to the exoccipital, and that their articulation upon the skull is secondarily
acquired (cf. Howes, 90, p. 357).

1 We fully concur in Boulenger's refutation (Ann. & Mag. Nat. Hist. ser. 6, vol. xii. 1893, p. 60) of Dollo's
hypothesis that " hsemapophyses are homologous in all Yertebrata."

2 Cope, E. D. : Trans. Americ. Philos. Soc. vol. xvi. 1886, p. 248.

3 Gadow, H. : Phil. Trans, vol. 187 B. (1896), pp. 33 & 51. The term " intervertebral disks " is apt to
create the impression of existence of independent elements.

DEVELOPMENT OF THE SKELETON OF THE TUATARA.

27

P.

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Fig. 5. — Tabular statement of the order of arrangement and succession of intercentra for

Stages P to T and the adult.

P. Primary paired iutercentra. U. Unpaired intercentra of primary order. — Intercentra absent.
F. Secondary intercentra. Chev. Chevrons, f Medially constricted.

Ribs and Sternum. — Ribs were attributed by Giinther to the segments between and
including the fourth praesternal (cervical) and the second sacral. Discriminating
between the osseous rib as a " pleuropophysis " and its unossified ventral portion as a
"haBmapophysis," he further distinguished between those vertebrae in which the latter
is fully developed as " dorsal " and those in which it is reduced as " cervical " and
" lumbar " respectively.

For the caudal region he describes the presence of " transverse processes " and

E 2

28 PEOF. G. B. HOWES AJSTD ME. H. H. SWINNEETON ON THE

rightly records a transverse disposition of the first and second and the forwardly-directed
one of those Avhich follow (loc. cit. p. 606). In attributing the first cervical rib to the
fourth vertebra he was in agreement with Owen, who first discovered this 1. Baur,
however, later described in an individual specimen the presence of a free rib upon the
third vertebra, and showed at the same time that (86 c. p. 736) the so-called caudal
" transverse processes " of the adult represent co-ossified ribs. Osawa (98a. p. 485)
declares his inability to confirm the presence of the latter ; but, with Gadow, we can
do so, and can confirm the occasional presence of a rib to the third praesternal vertebra.
Neither Gadow nor Baur state the number of caudal ribs observed. Our own investi-
gation shows them to be present (PI. I. fig. 12) for at least the eight anterior caudal
vertebrae. Posteriorly to these, according to Giinther, the " transverse processes "
become rudimentary, and we have no material to prove whether they do or do not
ossify separately. The osseous rib-formula may accordingly now be rendered as
follows, allowing for the possible presence of additional caudal ribs yet to be
discovered : —

Prsesternal 5-6

Sternal 3-4

Poststernal 13-14

Sacral 2 with variation.

Caudal 8 observed at Stage S.

Average 33

In the adult animal the anterior prsesternal ribs alone stand related to both inter-
vertebral and vertebral bodies (cf. PL II. figs. 1 & 2), the rest either articulating or, as
in the case of the caudal and apparently in individual cases of the last three post-
sternal, becoming co-ossified with the vertebrae alone. Baur, in describing the prae-
sternal ribs, has drawn attention to the existence of supposed ligamentous homologues
in relation to the first and second vertebral segments, and to the third where an osseous
rib is absent. Of these ligaments, he describes the first as single-headed and attached
to the first intercentrum, the second and third as double-headed and attached to both
intercentrum and transverse process of their corresponding vertebrae (i. e. those behind),
and he points out that in its attachment to the intervertebral body the lower liga-
mentous tract agrees with the capitulum of the rib borne upon the fourth vertebra,
which he, with Owen and Giinther, describes as two-headed. Of the fifth rib, he
rightly points out that it is the capitulum which is reduced, wherefore it follows that if
his identification of these ligamentous tracts as vestigial ribs is correct, the first and
fifth are diversely modified.

We can confirm (cf. PI. II. fig. 2) the general accuracy of his description and

1 Owen, K. : Cat. Osteol. Series E. Coll. Surgeons Mus. vol. i. 1853, p. 142.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 29

can extend his discovery of an osseous rib for the third vertebra to an individual of
Dendy's Stage S (PI. II. fig. 1) and to adult specimens in the R. College of Surgeons
and British Museum. If his " ligamentous ribs " are really such, it is reasonable to
suspect that at some developmental stage they may be either definitely skeletogenous
or may show traces of their supposed skeletal origin. After careful search, we are only
able in support of this conclusion to point to the existence within the third ligament
of an individual of Stage S of an insignificant cartilaginous nodule. The fact that no
trace of a corresponding nodule was forthcoming in the two specimens of Stage R
examined, leads us to regard the afore-mentioned case as an individual one of the
presence of a vestigial rib.

Concerning the relationships of these supposed ligamentous ribs, there is a detail
not recorded by Baur. As viewed at first sight (fig. 2), the double attachment would
seem suggestive of a two-headed rib ; but, in the case of the most distinctly two-
headed osseous rib (viz., that of the fourth praesternal segment), the osseous capitulum
and the supposed ligamentous one coexist, while for both this rib and those behind it,
in which the capitulum is unrepresented in bone, the supposed ligamentous portion of
the rib, instead of passing into the substance of the osseous one, as should be the case
were it a constituent of the rib, merely skirts the lower border of that with an
accompanying attachment of its fibres. Throughout the region of insertion anteriorly
of the muscles termed by Osawa " costo-cervical," it leaves the rib and passes on as an
independent structure, in the manner delineated in PI. II. fig. 2, m' — in exactly the
manner which would result from an intimacy of mechanical relationship. When to
this is added the disproportionate development of the first of the so-called " liga-
mentous ribs," which is in reality for the most part a muscular mass, we doubt how
far these structures really represent ribs wholly or in part, and confess ourselves
unable to definitely decide the question either way 1.

Turning now to the rest of the praesacral ribs, as concerning their heads and
articulations alone, we find as we pass back from the fifth cervical the distinction
between tuberculum and capitulum becomes gradually lost. With this simplification
there takes place a reduction of the transverse process, which, never strong, disappears
in the anterior sternal region, and, as pointed out by Osawa (98a. p. 735), is formed by

1 At the outset of our investigation into the " cervical " region, mindful of the belief in the Chelonian
affinity of Spheuodon and the assertion by W. K. Parker (' Challenger ' Reports, Zoology, vol. i. pp. 47 & 50)
that in the embryo of the Green Turtle the somatomes of the neck and tail are more numerous than later, and
undergo numerical reduction by abortion, we kept a look-out, in vain, for probable evidence of a similar
process, so far as it might involve the skeleton in Sphenodon, in the hope of being able to obtain some clue
to the meaning of the numerical variation of the reptilian pnesternal segments so conspicuous among the
Dolichosauria and Mosasauria. From the discovery of facts concerning the variation in relationship of the
sternum which we herein describe (infra, p. 34), we are disposed to regard numerical variation among the
praesternal vertebra?, if not the poststernal also, as associated rather with a shifting of the sternum than an
excalation of segments, as Parker's allegation would seem to suggest.

30 PKOF. G. B. HOWES A^D MK. H. H. SW1NNERTON ON THE

both the centrum and the arch. Giinther describes the heads of the ribs as " low and
compressed," and attributes to them a wholly central articulation. Baur has more
correctly shown (86. p. 735) that the connection is rather with the arch, but he never-
theless insists that " in reality the rib never completely forsakes the centrum."

We can confirm the details of Baur's description and extend them to Stage S.

Of the so-called " lumbar " ribs, i. e., the posterior two to four of the praesacral
series, the head of the last one may show increased expansion, and in this way that
may become in a sense transitional to the sacral rib, the special feature of which
(PI. II. fig. 5, r.s.) is its general robustness and greater attachment to the centrum.
Except to point out that the sacral ribs are ossified in the mariner of the prassacral
(PL II., cf. figs. 4 & 5), we have nothing to add tc recorded descriptions concerning
them. There are usually two pairs, of which the anterior are the more slender and
transversely disposed, the posterior the more robust and forwardly directed (PI. I.
fig. 12, r.s.). The iliac articulation is usually furnished by their united outer carti-
laginous extremities.

Fig 6.

Sacrum with hip-girdle of an adult Splienodon, bearing on the left side an abnormal set of ribs.

c.a., articular cartilage ; i7., ilium ; is., ischium ; pb., pubis ; r.cd.\ first caudal rib ;
r.s.1, r.s.2, sacral ribs. Nat. size.

In view of the frequent existence of three sacral ribs in many living Lacertilia !, of
more than two in the Chelonia, of the occasional presence of a third in recent Cro-
codilia2, and particularly of that of at fewest three pairs in Palreohatteria3, interest
attaches to a skeleton preserved in the Dublin Museum of an adult Sphenodon (text-
fig. 6) having on the left side a trisegmental sacrum, on the right a sacrum and hip-
girdle normal in all respects. The third sacral rib on the left (r.cd.1) is seen to be the
first caudal, enlarged and expanded. Externally it was in life continuous by its outer

1 Stellio and Chamseleo, Credner, H. : op. tit. p. 505. Phrynocephalus, Cope, E. D. : Proc. Amer. Philos.
Soc. vol. xxx 1892, p. 207. For other examples cf. Siebenrock, F. : Ann. naturhist. Hofmus. Wien, Bd. vii.
p. 373, and Sitzb. Akad.Wiss. Wien, Bd. civ. p. 67.

2 Baur, G. : Zoolog. Anz. Bd. xii. 1889, p. 240.

3 Credner, H. op. cit. p. 505.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 31

cartilaginous border with that of the second sacral rib. This was stouter than usual,
while the first rib, reduced externally to a degree proportionate to the extension of the
first caudal into the sacrum, was reduced to the calibre of a praesacral rib. The
combined cartilaginous heads of the three ribs, by union, furnished the iliac articulation,
and there can be no doubt that the determining cause of this abnormality was the
backward rotation of the left ilium, well marked. It may be a case of " vertebral
assimilation " 1, but its interest is none the less if so.

We have only to add, concerning the caudal region, that at Stage S, when ossification
is setting in, the detailed relationships of the caudal rib to its centrum and arch are
closely identical with those of the sacral vertebrae (cf. PL II. figs. 5 & 6), and that at
this stage comparison with the prsesternal region (fig. 4) shows that the interarticular
tissue between the rib and its vertebra is far less differentiated than there.

The most conspicuous difference recognizable on a survey of the whole series of rib-
heads in the adult and the later developmental stages of Sphenodon, is the fact that
while the individual rib is for the most part obliquely attached or articulated upon the
anterior end of its related centrum, in the case of the third and fourth praesternal ribs,
which are two-headed, this antero-ventral extension is more marked and involves the
interceritrum, the capitular head abutting against that. For this an explanation has to
be sought.

Examination of the posterior trunk, sacral, and tail vertebrae, at the period of
chondrification, would seem to indicate (cf. figs.) that the ribs arise only in relation to
the vertebral bodies, and that they may be derivative of either their arch system, as
originally believed for the higher Vertebrata by Gegenbaur, Goette, and others ; or of
their transverse processes, as argued by Glaus, and more recently by Corning2 and
others — i. e.9 that in any case they would appear to be vertebral in origin, as has been
more recently maintained for the ribs of the Vertebrata generally by Dollo 3. Hofmann,
in a memorable paper published in 18784, from the study of both the anatomy and
development of adequate representatives of all the amniote classes but birds, deduced
the final conclusion that the ribs of these animals are primarily intervertebral. Baur
has further sought to support this view 5, and Gadow, among most recent investigators,
has done likewise, in his final conclusion (96. p. 50) that the ribs of the Amniota are
lateral outgrowths and the chevrons and haBmapophyses ventral outgrowths of his
" basiventralia," which give rise to the intercentra 6.

1 Cf. Siebenrock, F. : A.nn. naturhist. Hofmus. Wien, Bd. vii. 1892, p. 373.

a Corning, H. K. : Horph. Jahrb. Bd. xvii. 1891, p. 611 ; cf. also Goeppert, ibid. Bd. xxv. 1897, p. 247.

3 Dollo, L. : Bull. Sci. Fr. & Belg. torn. xxiv. 1892, p. 113. For other references, see Hofmann, infra.

4 Hofmann, C. K. : Niederld. Archiv, Bd. iv. 1878, p. 199.
8 Baur, G. : Amer. Nat. vol. xxi. 1887, p. 942.

6 Psychologically interesting in this association is the conclusion of Dollo (op. cit. p. 128), who, though
apparently in error concerning the vertebral origin, regards the " ribs " as dorsal ribs, the " hsemapophyses ''
as ventral.

32 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE

On examination of transverse sections through the developing vertebral column
of Sphenodon at Stage P, at which the parts of the cartilaginous vertebrae are as yet
undifferentiated, the tissue giving rise (PI. I. figs. 3 & 4) to the paired intercentra
(i.p.1) — which, it will be remembered, are the first, and at this stage the only components
of the vertebral column recognizable — is seen to be continuous with that differentiating
into the ribs (r.cd.). Figs. 3 and 4 represent the first and sixth sections across an
individual caudal segment ; and comparison of those which intervene has shown us
that even here, when the vertebral body is not yet differentiated, the disposition of the
proximal end of the rib is oblique, involving ventrally and anteriorly the intercentrum,
dorsally and posteriorly the region of the future centrum and arch. Comparison with
the adult cervical rib reveals a close similarity of relationship ; and since with later
development the connection with the intercentrum is lost, the primary relationship of
the rib is proved to be intervertebral.

Cope in 1878 first drew attention l to the existence in certain Permian Pelycosauria
of a two-headed condition of the rib, with accompanying intercentral articulation of
the capitulum ; and Baur, eight years later, in his afore-mentioned paper on the
cervical ribs of Sphenodon (prompted by Cope's announcement), sought to emphasize
the importance of this. Cope, immediately afterwards, in dealing with the structural
resemblances between these creatures, prompted by Hofmann's brilliant generalization
afore-mentioned, penned the remarkable paragraph 2 : " The passage of time has
seen in the Reptilia generally " a modification " in the mode of attachment of the
rib," in which, "in passing from front to back, the intercentral articulation is
lost", and finally the head of the rib disappears." The facts we have just described
render this well-nigh prophetic ; and it remains to be ascertained how far the sup-
position, deduced from the study of longitudinal sections alone, that the ribs of the
Amniota, and of the Reptilia in particular, arise in exclusive relationship to the
transverse process, centrum, or arch, will stand the test of examination in other
planes, and, as deduced from that of developmental stages at which chondrification
is more or less advanced, will bear further comparison with the earlier ones of pro-
cartilage differentiation.

Concerning the bodies of the ribs, we have nothing to add to the descriptions
of Giinther, Maurer (96), Osawa, and others, except as regarding the so-called
" uncinate processes." Giinther in his original description accords the first of these to
the last praesternal rib, Osawa to the penultimate, but neither state their posterior
limitations. Like those of the Ratite birds, they are apt to be easily lost in maceration ;
but in carefully prepared specimens we have been able to trace them back, with

1 Cope, E. D. : Proc. Amer. Philos. Soc. vol. xvii. 1878, pp. 518 et seq.; and Proc. Amer. Assoc. Adv. Sci.
1884, pt. ii. p. 474.

2 Cope, E. D. : Trans. Amer. Philos. Soc. vol. xvi. 1886, p. 249.

DEVELOPMENT OF THE SKELETON OF THE TUATAKA. 3o

progressive diminution in length, to the llth-12th poststernal rib. They are longest
throughout the middle of the series, and they arise late at Stage Q, after the ribs have
become chondrified, by independent concentration of the cells which go to form the
intermuscular septa. They also chondrify independently at Stage R (PI. II. tig. 7,
u.p.), at which the ribs are well ossified. Jeffery Parker has already called attention 1
to their similar independence in Apteryx, and we accordingly follow him in the usage
of the term uncinates.

There can be no doubt that the process borne by the last prsesternal rib is a true
uncinate, since our sections at Stages Q and R reveal its independent origin. We
find that the " process " borne by the penultimate rib, which Giinther (67. p. 607)
believed to be homologous with the uncinates and which Osawa definitely refers to
them, may by elongation assume the size and shape of one in its most pronounced
form, as contrasted with its condition described by Giinther of a mere " dilated
baemapophysis." On the study of this he was led to regard the uncinates as
hsemapophysial in origin, " separate and removed from the distal end of the pleur-
apophyses as the latter increase in length." At our Stage R, at which the ribs are
beginning to ossify and the uncinates proper are still distinct from them, the penulti-
mate rib and its supposed uncinate are continuous, while a similar but feebly developed
process is present on the antepenultimate rib. At the period of continuity, the
penultimate rib and process may in some sections present appearances suggestive of a
possible precocious union ; but, inasmuch as we are unable definitely to detect
its presence at an earlier stage or in a wholly free state, we leave it an open question
whether the " process " may or may not be a mere outgrowth of the cartilaginous rib.
If the non-extension of the osseous rib into the uncinate zone be due to loss of connec-
tion with the sternum, the former conclusion would be the more likely; if, on the
contrary, it be not so, it may well be that, under the extension of the unossified moiety
into the zone, the plastic cartilage has been seized upon as available for extension and
support under the mechanical conditions at work.

The Sternum. — By way of descriptive detail, of the adult sternum we have nothing to
add to the statements of Giinther and Osawa, except to state that neither has recorded
the fact that even in the adult its posterior border is notched. At Stages R and T this
notch (PI. VI. figs. 5 & 6, s.n.) is very conspicuous, and inasmuch as at Stage Q the
two halves of the sternum are widely separated, the question arises whether or not the
notched region is one of non-union of its opposite halves.

Parker, in describing the developing sternum of Apteryx, in the adult of which
there are four pairs of sternal ribs, has shown 2 that the two anterior of these apparently
give rise to the sternum, and that the connection of this with the two posterior is
secondary and due to extension of both sternum and ribs. In Sphenodon three pairs

1 Parker, T. J. : Phil. Trans. 1891 B, p. 80.

2 Parker, T. J. : op. tit. cf. pp. 87 & 113.

VOL. xvi. — PART i. No. 5. — February, 1901. F

34 PfiOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

of sternal ribs have been hitherto described for the adult, but we find that four pairs may
be present, as, for example, in a skeleton in the Teaching Collection of the R. College
of Science, Dublin. Similarly, in the developmental stages, four pairs may occur, as at
PI. VI. fig. 6 (Stage T), or four on the left side only, as at PL VI. fig. 5, or on the
right, as in specimens of Stage S in our possession.

The earliest developmental stage of the sternum we have observed is at Q. In the
section of this figured (PL VI. fig. 4) but two ribs are seen to contribute to the
sternum, but examination of serially related sections proves that the third enters also
into its formation ; and, from what we have seen, we incline to the belief that when
a fourth is present it also has contributed.

In the latest stage figured, the organic continuity between ribs and sternum is still
uninterrupted, the " incisurae costse " being of late origin. As early as Stage R the
sulcus coracoideus (cor') is well indicated, and anteriorly the sternal plate is prolonged
into a couple of episternal cornua, which skirt the stem of the interclavicle and
contribute to the formation of the sulcus, in a manner which holds good for the adult,
but has been inadequately recognized in all previous descriptions.

In the specimen from the Dublin Museum, this last right praestevnal rib reaches
the sternum, and its cartilaginous segment, by elongation and enlargement, has the
characters of a normal sternal member. Its osseous segment is normal, and there are
no accompanying changes recognizable in the ribs in front of it. We have already
adverted to one point of interest attaching to this specimen (antea, p. 30) ; and if, as
there is reason to believe from what is known of the Mesozoic reptiles, the amniote
sternum in its ancestral condition, in which it was most certainly cartilaginous, was
more extensive than its more specialized homologue of the living forms 1, fluctuation
anteriorly and posteriorly such as we have recorded becomes the more readily
intelligible.

There are no indications of any elements, median or otherwise, entering into
the composition of the sternum, beyond those derivative of the ventral extremities
of the ribs.

The " Abdominal Ribs " ( Gastralia 2) .

These are in number 22 to 26, and they are alternately attached to the ventral
segments of the poststernal ribs and free, at any rate for the most part, as originally
pointed out by Giinther. Osawa records 24, of which he remarks the first is attached
to the first poststernal rib (98. p. 491), as are those behind corresponding to odd
numbers, back to the 21st. The 22nd, 23rd, and 24th, with those corresponding to even
numbers, he describes as free. We find, however, that regarding the first point there

1 Osborn has described fossil an expanded cartilaginous sternum arising from ten pairs of ribs in the
Mosasaur Tylosaurus dyspelor (op. cit. [antea, p. 14] p. 180).

2 Baur, G. : Anat. Anz. Bd. xiv. 1897, p. 150.

DEVELOPMENT OF THE SKELETON OF THE TUATABA. 35

is considerable variation. Boulenger has called attention l to the fact that " the
anterior extremity of the plastron overlaps the posterior extremity of the sternum," and
concerning this, two specimens we have examined yield interesting results. In each of
them there are two free gastralia in front of the first that is attached to the ribs ; and
while in one example (that possessed of four pairs of sternal ribs) these are short and
median, in the other (that in which the last " cervical " rib is sternal) the anterior
gastralium is represented by a symmetrically-arranged pair of rods.

Giinther originally described each gastralium as of three elements, and their natural
relations are generally those indicated in PI. II. fig. 10, no. 7. Not unfrequently union
in the middle line, as figured and described by him, may occur, and it would seem to
involve a forwardly-directed spur on the median element which is generally present
(of. PI. II. fig. 10, no. 11). Much interest attaches to Giinther's description of an
exceptional specimen, in which for the rib-connected gastralia the lateral elements were
attached to the central by transverse "joints," instead of being in oblique juxtaposition
with them as for the free gastralia and as is more generally the case throughout the
entire series. The fact that, in most specimens we have examined, individual gastralia
of both the attached and free order show both "jointing" and juxtaposition, and that
while in most cases one or two such "joints " may be present only on one side — there
being no regularity recognizable, — proves that no physiological significance is to be
attached to these variations.

Turning to the embryo, we find that the gastralia arise at Stage S, within previously
differentiated fibrous tracts of the subcutaneous tissues of the body-wall (g.t., PL II.
fig. 9), by a process of calcareous deposition, which proves them to be wholly
membranous in origin. Their connection with the myocommata of the body-wall is
fully established later, and with Gadow 2 we have failed to detect any traces of a
cartilaginous origin, believed by Schneider to be the case for the Crocodilia. Figs. 8
and 9 represent (8) the anterior (third to fifth), 9 the posterior (16th to 18th and more
highly magnified) gastralia of an example at Stage S. It will be observed that the
median element is present only anteriorly, and that while for two of the three segments
figured comparison with the adult shows its lateral cornua to be partly represented by
a series of minute calcifications, for the anterior segment it is composed of two pieces.
Anteriorly the lateral elements are seen to be fully formed, but on passing to the posterior
series two of the three figured are observed to be represented by a linear series of
distinct calcifications, the median element being undeveloped. The fact that in the
adult the gastralia which occupy the positions of those here figured are alike
symmetrical and only trisegmental, proves that with advancing development a union of
the calcifications such as are here figured must occur, and that the median elements

1 Boulenger, G. A.: Brit. IVIus. Cat. Chelonia, Rhynchoceph. & Emydos. 1889, p. 1.

2 Gadow, H. : Morphol. Jahrb. Bd. vii. 1882, p. 77.

F2

36 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

arise antero-posteriorly. It further indicates a compound origin for all the parts, median
and paired alike ; and concerning the anterior paired segments, which in the individual
figured were single, we find that in younger individuals at the same stage they may be
represented by a series of elements. The details point to the conclusion that union is
rapid and irregular.

A striking characteristic is this irregularity of calcification ! It leads to irregularity
of union ; and it is fair to assume that in this lies the explanation of the asymmetry
which the parts of the adult "plastron" are apt to assume. It explains the not
infrequent presence of but a single asymmetric element, and of so extraordinary
a condition as that of the triradiate or quadriradiate union delineated on PI. II.
fig. 10 (Stage T) — the most erratic we have observed. It also renders clear the sub-
stitution of transverse "joints" between, for oblique juxtaposition of, the median and
lateral elements described by Giinther, and the co-existence of these herein recorded,
while it presupposes other combinations yet to be discovered.

Interesting and unexpected as are these details ontogenetically, we have come to
attach a still greater importance to their probable phylogenetic significance.

One of the most distinctive characters of Credner's Palaeohatteria of the Permian is
the multisegmented condition of its " abdominal ribs," which, on careful examination of
the originals, he has shown to be also the condition in Von Meyer's famous Protero-
saurus and other genera to which he refers (op. cit. p. 538). In view of the obvious
similarity to the embryo Sphenodon suggested, it becomes the more interesting to find
that whereas in Palaeohatteria, according to Credner's original description, there appear
to have been three rows of calcifications present for each rib, in Proterosaurus there
were two or three. In a later paper, however, on Kadaliosaurus, an allied genus, he
gives 1 the number of " abdominal ribs " as regularly six for each vertebral segment
possessed of them ; and in instituting comparisons with Palaeohatteria, Proterosaurus,
Stereosternum, and Hyperodapedon, he gives the number present in them collectively
as from three to six. The calcifications in all these forms are regular and structurally
constant, whereas in Sphenodon they are developmentally irregular and inconstant.

Kadaliosaurus is further interesting in the light of the foregoing observations upon
the substernal extension of the " gastralia " in Sphenodon, as in it they are still more
nearly pectoral in extent and Stegocephalian. The facts suggest that the " plastron "
may be undergoing reduction in the living genus, a consideration which may perhaps
explain the irregular mode of calcification by which it is formed.

Boulenger, availing himself of these facts of palaeontology, has made them a basis
of classification of the Rhynchocephalian Order to which we alluded at the outset
(antea, p. 3), and he has drawn a sharp distinction between the higher suborder
of the Rhynchocephalia vera (91. p. 171) (Hatteriidae, Homeosauridae, Rhynchosauridee,

1 Credner, H. : Zeitschr. deutsch. geolog. Gesellsch. Bd. xli. 1889, p. 330.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 37

and Sauranodontidae), characterized by the triserial condition of the " abdominal
ribs," and the lower or Proterosauria (Palaeohatteriidae, Proterosauridae, and Champso-
sauridse), in which their segmentation is multiserial. The adult Sphenodon, if
classified by its " plastron," can only be referred to the former — the developing
Sphenodon might with justice be relegated to the latter and lower suborder ! In this,
Boulenger's far-sighted classification receives welcome support.

Moreover, the multisegmented condition of the " plastron " segments is nothing
short of a Stegocephalian character.

The Skull and Visceral Arches.

In compliance with passing custom, we have adopted in this section of our work the
reconstructional method, as before stated (antea, p. 7).

Beyond the memoirs of the late Kitchen Parker, and some recent preliminary notes
by Gaupp, together with the observations of Ley dig (op. cit.), Born, and Hofmann, duly
mentioned by him, little has been written upon the actual development of the
Lacertilian chondrocranium 1 ; and since in the absence of figures we find it difficult
to follow the details of Gaupp's descriptions, we deem it more prudent to describe
connectedly the processes taking place in Sphenodon, which are simple and straight-
forward, and highly instructive in themselves.

The Chondrocranium. — In Sphenodon the cartilaginous elements of the skull arise
before those of the greater part of the vertebral column, and the ossifications in
membrane before those in cartilage of both skull and vertebral column. The first
differentiation to form the primordial cranium which we have observed is at Stage P,
and it consists mainly of pro-cartilage. It can be resolved into two perfectly distinct
portions, excluding the mandibular arch — an anterior common to the olfactory and the
trabecular regions, a posterior involving the sphenoccipital and auditory regions2.
Dealing with these individually, the anterior portion is seen to embrace the trabeculae
(PI. III. figs. 1 & 2, tr.) and an ethmoidal constituent, consisting of an extensive
basal plate with two pairs of outgrowths — an anterior or olfactory pair (n.e.) and a
posterior pair — to be hereafter termed the ethmosphenoidal plates (e.s.), The trabeculse
(tr.\ widely separated and enclosing a spacious pituitary foramen (py.1), are already
hyaline, and pass gradually into the lateral edges of the basal ethmoid. The

1 Gaupp, E. : Verhandlg. anat. Gesellsch. Sammlg. v. (Anat. Anz. Bd. iii., Suppl.) pp. 114, 120 (1891), also
ibid. Sammlg. xii. (Anat. Anz. Bd. xiv., Suppl.) pp. 157-163 (1898), and Ber. naturf. Gesellsch. Freiburg i. B.
Bd. x. pp. 302-316 (1898).

- Left uncoloured in our illustrations. Concerning the embryo which furnished the sections for figs. 1
to 3, PI. III., it is regrettable that before investigating it we had handed it on to another, who, in
decapitating it for other use, had cut through the auditory region. We found, however, on examination
of slightly younger specimens, evidence sufficient for the extension of the differentiation into pro-cartilage
into the regions included in the dotted lines in the figs.

38 PEOI<\ G. B. HOWES AND ME. H. H. SWINNEETON ON THE

posterior portion, at this stage disposed at right angles to the anterior (its anterior
extremity being alone visible from above, as in fig. 2), is seen to similarly consist of a
basal or parachordal plate (par.) also bearing two pairs of outgrowths, viz. an anterior
(o.s.), to be hereafter termed the otosphenoidal plate, and a posterior, the auditory
capsule (c.au.), This posterior portion is hyaline only at the anterior and lateral
borders of the parachordal plate, the anterior chondrification extending into each of
the otosphenoidal tracts. The intracranial notochord, enclosed within the basal para-
chordal plate, terminates anteriorly in a minute freely-exposed apex (nc., fig. 2), and,
as already pointed out by Dendy for Stage N (99 a. p. 75), it takes a sinuous course.

Dismissing for the present the sensory capsules, which at this stage are simple and
cup-shaped, it becomes necessary for comparison of later stages to deal fully with the
ethmo- and oto-sphenoidal plates. The former (es.) are large and wing-like and bear
no outgrowths. The latter are complex and wholly distinct from the trabeculse.
Each of these otosphenoidal plates is seen to be extending upwards and outwards,
backwards and inwards, and directly forwards. Two apertures are enclosed by it — a
lower (j. Hi.), which transmits the third cranial nerve, and an upper (f. iv.), which
transmits the fourth 1. The processes to which it is giving rise (indicative of differen-
tiation along definite lines) are five in number (os.1 to os.5, PI. III. figs. 1, 2, 3).

Before passing on to a later stage, we wish to emphasize the simple rod-like
condition and non-extension into the cranial wall of the trabeculee, which, except for
their connection with the procartilaginous basal ethmoid, are disposed serially with
the mandibular arch (j)g.mk.\

At Stage Q, despite the short advance in time upon P, remarkable progress is seen
to have been made in the formation more particularly of the cranium, nearly all the
definitive components of which are now recognizable. The trabeculae have now fused
posteriorly with the parachordal — not by their ends as might be supposed, but by their
postero-internal borders, — and they appear to us now to give rise to the basipterygoid
outgrowths (bs.1, PI. III. fig. 6). An accompanying upward rotation of the parachordal
(associated with cranial flexure) has brought about a consequent approximation of
the otosphenoidal plates to the trabeculae, with an accompanying fusion involving the
first and fifth otosphenoidal processes. Of these, the latter, passing downwards,
unites with the outer trabecular border, and thereby shuts off (f.j., fig. 4) a jugular
foramen ; the former, uniting with the inner trabecular border, encloses a passage (f.a.)
for the ophthalmic artery.

More significant than the foreging is the change in position undergone by the
second and third otosphenoidal processes. Originally directed upwards, under the
combined influence of rotation and growth, they are now directed forwards, and, by
union with the posterior border of the sphenethmoidal plate, they have come to
bridge longitudinally the membranous lateral cranial wall. As the result of this, two

1 Gaupp (1898, Berichte, p. 8) describes these nerves in the Lacertilian as related to a common fcnestra.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 39

further fenestrse arise in the same vertical plane in front of those already described.
Of these the upper or lateral cranial fenestra (f.n., PL III. figs. 4, 6, 7) is wholly
membranous, transmitting nothing, the lower (f. n.) giving passage to the optic nerve.
It will further be noted that with the establishment of this union between the ethmo-
and otosphenoidal plates the parts most nearly related to the latter have become
expanded and carried up by growth of the basi-ethmoidal plate, together with which
they constitute a considerable cartilaginous interorbital septum.

The fourth otosphenoidal process, originally directed downwards (os.4, fig. 1), now
carried up, looks straight backwards (of. figs. 5 & 8), but it has remained free.

On appreciation of these important processes, which have effected so marked a
change in the configuration of the parts, it is evident that growth must be most rapid
in the otic border of the otosphenoidal plate.

The chrondrocranium at this stage, viewed from beneath, reveals changes which,
though less dominant than those described above, are in themselves remarkable.
Massive indeed have the basis cranii and auditory capsules become, under the accelerated
growth associated with the straightening of the basi-cranial axis and the marked
lateral expansion of the post-pituitary floor (cf. figs. 6 & 7). The occipital region
has now become conspicuous, by the upgrowth on either side (e.o., PI. III. figs. 6 & 7)
of a considerable cartilaginous lobe lying free of the auditory capsule, between which
and it there lies the huge interspace for the 9th, 10th, and llth cranial nerves (figs. 6
& 7,/. ix. to an.).

Anteriorly to the trabeculae the basal ethmoidal plate (cf. fig. 6), vertically extended
as has been seen, has undergone a forward growth — as is proved by the fact that its
length is now as great as that of the trabeculse themselves, and it has also undergone a
downward rotation, very marked as viewed from the side (PI. III. fig. 4).

The pituitary foramen at this stage (py.'t PI. III. figs. 6 & 7), compared with that
of Stage P, as represented in the accompanying figs. (cf. fig. 2), would seem to have
undergone considerable reduction with advancing growth. When, however, it is
remembered that the figure of Stage P (fig. 2) is magnified 13 times, that of Q
(figs. 6 & 7) but 8, it will be evident that under the growth-changes going on the
trabecular tracts which more directly bound the foramen have been well-nigh stationary,
and that such reduction of the foramen as has taken place would appear to be rather
due to the mode of union between the trabeculse and parachordal cartilages than to
actual cartilaginous invasion.

Finally, as to the sense-capsules — now both chondrified. With the olfactory capsule
complication has set in. Its capsular portion (nc.) has entered into a union with the
anterior border of the ethmosphenoidal plate, giving off dorsally a short supranasal
process (nc.', fig. 4) connected with the plate by an ethmonasal bar (e.b.) lying within
the outer border of the olfactory nerve foramen. At its anterior extremity it gives off
a prcenasal process (nc.'', fig. 4), which embraces the anterior wall of the nasal sac.

40 PEOF. G. B. HOWES AND MR. H. H. SWINNEETON ON THE

Somewhat similarly related to the postero-external wall of the sac is a large
quadrangular cartilage, the extranasal (ex.), and from this four processes arise. The
two anterior of these (ex. 1 & 2) are united to the ethmoidal bar so as to enclose
a fenestra (n.f.1). The two posterior are free, and the third (ex. 3), together with
the posterior half of the parent cartilage, disposed at a sharp angle to the external
half of this, contributes to the support of the anterior orbital wall, bounding
ventrally the ethmoidal foramen (f.e.), which transmits the ophthalmic branch of
the fifth nerve !.

In addition to these complex nasal supports, there is present at this stage in
the nasal floor a sheet of procartilage which, in order to complete our terminology,
we name the subnasal. This, to which we shall return, is wholly independent in
origin, and by analogy to the extranasal we suspect that this may also arise
independently.

The only remaining changes in the chondrocranium are mainly of the nature of
advancing completion of the parts now described. No new elements are added
after Stage Q. These perfecting processes, as they may aptly be termed, are most
conspicuous at Stages R and T, which may accordingly be dealt with independently.

Stage R. — A very striking feature of this, as compared with the earlier stages, is the
straightening out of the ethmosphenoidal region, which at Q was downwardly rotated
(cf. PL III. figs. 4 & 8). This straightening process affects most conspicuously the
median parts (internasal septum), which now appear as if withdrawn under cover
of the extranasal cartilage (ex., fig. 8).

Equally striking are changes involving the antorbital and otoccipital regions.
That taking place in the former is of the nature of extension most markedly dorsal-
wards of the interorbital septum (s.i.), by continuation of the process of elevation of
the basal ethmoid already alluded to (anted, p. 39). Under the combined influences
at work, growth has become more rapid with the ethmosphenoidal than with the
otosphenoidal plate ; and ready proof of this lies in the now upward direction of
the third otosphenoidal process (os.3, fig. 1), which at Stage Q (os.3, fig. 4) was arched
and reached the highest point. Of the fenestrse described at Q (which in life are
closed by membrane, except where they transmit nerves) only one has undergone
change, viz. that transmitting the fourth cranial nerve (f. 4, fig. 8). This is now
complicated, having become continuous with the fenestrse transmitting the third
cranial nerve, the jugular vein, and ophthalmic artery — all four being now closed
by one continuous membranous sheet. It is clear, on comparison with Stage Q,
that the cartilaginous bridges which originally separated these fenestrse (i. e., the fifth
otosphenoidal cartilage and its near neighbours) have been absorbed.

As an accompaniment of these changes, the small cartilaginous bar bounding at

1 Of. Osawa, 98 », p. 504.

DEVELOPMENT OF THE SKELETON OF THE TIJATABA. 41

Stage Q the front of the foramen for the fourth nerve has become much elongated
and brought into line with the second otosphenoidal process, so as to give the
appearance of a continuous bar. That this is not the case, however, is proved by
the fact that the second otosphenoidal process in reality is now represented by the
insignificant tract (fig. 8, os.2) lying between the ventral extremity of the cranial fenestra
(f.n.) above and the dorsal extremity of the optic fenestra (/.") below. Its apparent
forward continuation at this stage is due to the appearance in the cartilaginous inter-
orbital septum of yet another fenestra (f.i., PI. III. fig. 8), which is of necessity median.
Like the lateral cranial fenestra (f.n.}, it is wholly membranous, and it alone merits
the term inter orbital fenestra.

Turning to the occipital region, the foramen magnum is now seen to be completely
surrounded in cartilage, as the result of union between the upper ends of the occipital
cartilaginous lobes and the posterior walls of the auditory capsules, resulting (cf. PI. III.
fig. 9, e.o.) in the enclosure of the afore-mentioned interspace transmitting the
cranial nerves ix. to xi. above, and its conversion into a foramen. With these changes
another, probably correlated with the afore-mentioned upheaval of the ethmosphenoidal
plates, is recognizable, viz. the appearance in the postero-dorsal cranial roof of a
spatulate cartilage (so/, PI. III. figs. 8 & 11), which in its general relationships recalls
that figured and described by Parker l in Lacerta and Zootoca as " supra-occipital."
This is seen to arise posteriorly from a massive tract of cartilage overlying the foramen
magnum, which appears to us more extensively derived by the overarching of the
auditory capsules than of the occipital lobes. When the chondrocranium is viewed
from the side, at this stage, this " occipital " cartilage is seen to be arched, and to
follow, with the antero-dorsal border of the expanded ethmosphenoidal plate, the arc of
the circle described by the top of the head, which at the earlier stage was followed by
the third otosphenoidal process (os.3, PL III. fig. 5). In this respect, the two may be
said to have been correlatively modified in accommodation to the roofing-in of the brain,
now possible under the diminution in relative rapidity of the growth of the central
nervous system.

An interesting detail at this stage is the presence in the basi-occipital region of a
minute depression, involving the lower border of the foramen magnum. Conversely,
the ventro-lateral border is on either side rounded and convex, the whole giving to the
chondrocranium, especially when viewed from above (PL III. fig. 11) or from beneath
(fig. 12), the appearance (as has been pointed out by Gaupp 2 for the embryo lacertilian)
of being doubly condylar.

In the nasal region the extranasal cartilage (ex., PL III. fig. 8) has increased in
size, but it has undergone no conspicuous change, except for the elongation of the

1 Parker, W. K. : Phil. Trans, 1879, p. 595.

2 Gaupp, A. : 1898, Berichte, p. 6.

VOL. xvi. — PART i. No. 6. — February, 1901. G

42 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

fourth of its processes (ex.4), which now lies in an interspace between the palatine and
maxilla (cf. fig. X., ex.4) l. The subnasal sheet (sb.)9 now chondrified, wherefore it may
be termed the subnasal cartilage, has entered into continuity by means of a delicate
cartilaginous bar with the prsenasal process (nc.") of the primitive olfactory capsule,
and by a less considerable bar with the extranasal cartilage (ex., fig. 8). It extends
inwards, partly underlying the vomers, and effects (as indicated in fig. 12, s.b.) an
infolding of the outer lip of the posterior nares.

Stage T. — At this stage the characters of the definitive chondrocranium are all
present, and, owing to the increase in size, we found it unnecessary in dealing with it
to resort to microscopic sections and reconstruction. Fig. 10, PI. IV., delineates from
the left side this chondrocranium, divested of all dermal elements except the para-
sphenoid (ps.), now co-ossified with the basisphenoid (bs.). The most conspicuous
changes to be observed are two, (i.) the backward extension of the fourth otosphen-
oidal process (0s.4) and its fusion with the auditory capsule at the base of the supra-
occipital bridge, (ii.) the elongation of the ethmo-nasal region, which is a main factor
in the final realization of the adult proportions and shape of the skull. As the result
of the fusion above-named, the lateral chondrocranial wall is now in a condition of
uninterrupted continuity dorsally with the olfactory and auditory capsules, and the
passage transmitting the fifth cranial nerve now becomes a perforated fenestra. In
proportion, size, and shape, the fenestrae have undergone a considerable amount of change,
mainly associated with the cartilaginous extension of the interorbital septum (s.i.). By
the extension of the lateral cranial wall, the process of closing in of the roof has
advanced, but there is no change of importance as compared with the preceding stage.

The nasal capsule has become modified by the fenestration (n.f.") of the extranasal
cartilage.

The cartilage-bones (which appear at Stage R, but, owing to their then feeble
condition, are not represented in our accompanying figures of the models at that,
figs. 9 & 12, PI. III.) are seen assuming shape at S (figs. 4, 5, 6, & 7), but at T they
are in the condition most favourable for description. They are 9 in all — 3 median and
3 paired — and with the exception of the basisphenoid all are otoccipital.

When the skull is examined from beneath (PI. IV. fig. 6) the basisphenoid (b.s.) and
basi-occipital (b.o.) are seen to arise within the anterior and posterior regions of the
post-pituitary floor. The former extends laterally into the cartilaginous basipterygoid
processes (bs1.)2, which at Stage T terminate externally in dilated extremities, for
articulation of the pterygoid bones ; and it also extends forwardly into the trabecular

1 This is presumably the " processus maxillarius posterior " of Gaupp, which he aptly compares with the
" antorbital" or palatal bar of the Anura and Ranodon (1898, Berichte, p. 8).

3 "We have found traces in transverse section at Stages E-S of the paired ossification asseited by Baur (Zool.
Anz. Bd. xii. p. 45) to hold good for the basisphenoid and stated by Parker to be present in the Lacertilia
(' Morphology of Skull,' 1877, p. 216).

DEVELOPMENT OF THE SKELETON OF THE TUATARA.

43

region, so as to enclose the pituitary foramen, now undergrown by the parasphenoid
(cf. transverse section, PI. IV. fig. 3). The basi-occipital (b.o.) arises from a single
ossific centre. The exoccipitals arise as ossifications of the occipital lobes of the chondro-
cranium, and by extension reach the posterior boundary of the exit for the ninth to the
eleventh cranial nerves. Osawa has recently described (98 a. p. 494), with perfect
accuracy, the adult condition of the nerve-foramina which result from this, and concern-
ing the hypoglossal foramina he gives two as the number present. He also describes

Fig. 7. Fig. 8. Fig. 9.

n.xz?

TtSS

Fig. 10.

Figs. 7 to 10. — Sections through the occipital region of Sphenodon showing the hypoglossus nerve-foramina at
different stages of development, and the sustentacular ligaments of the medulla. 7 and 8. Lateral
longitudinal sections at Stage S, x 33. 9. Lateral longitudinal section at Stage Q, x 67. 10. Transverse
section at Stage R, x 33.

b.o., basioccpital ; e.o., exoccipital ; Z.s., sustentacular ligament ; Z.s.', its exoccipital support ; md., medulla
oblongata ; we., notochord ; n. xii., hypoglossal nerve-roots and foramina.

two nerve-roots. Gaupp accords a third hypoglossal foramen to the embryo Lacertilian
(Berichte, p. 5). Interesting this, in consideration of modern discovery concerning
the truncal origin of the hypoglossal nerve-bearing region of the skull. Still more
interesting when we record the fact that, whereas in Sphenodon, at Stage S, three hypo-
glossal foramina are present, with corresponding nerve-roots (n. xii., text-figs. 7 and 8),

G2

44 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

at Q (text-fig. 9) there are four foramina and five roots. It is certain that, during
ontogeny, two roots at least disappear, and further investigation is necessary to render
perfectly clear the detailed nature of those which remain a.

We may most fittingly refer here to a series of ligamentous supports which, so far as
we can ascertain, are new. We first detected them at Stage Q in the occipital region.
At S each is very conspicuous, and with its fellow of the opposite side is closely
applied to the under face of the medulla oblongata. It is strengthened at its bases by
ingrowths of the occipital cartilage (l.s.'9 text-figs. 7, 8, & 10), and in the floor of the
neural canal it enters into a loose fibrous connection with the dura mater (cf. fig. 10).
This remarkable structure is repeated seginentally throughout the trunk-region of the
vertebral column, and we propose to term it the sustentacular ligament.

The supra-occipital calls for no special comment.

The opisthotic (op., PI. IV. fig. 9), which Siebenrock has proved 2, to be an inde-
pendent element (the " paroccipital " of Owen), is at this stage remote from both the
prootic and exoccipital, and the ossific centre of the former is now beginning to
monopolize the feebly- developed cartilaginous parotic process (p-p-}, which appeared
at Stage Q and is still short. The prootic (" otosphenoid," auct.) (pro., figs. 8 & 10)
is a simple bone, and its processus anterius inferior, so characteristic of the adult 3, has
not yet appeared, nor has ossification yet encroached upon the processus anterius
superior, which, still hyaline, forms (cf. fig. 8, cj.) not only at this, but at Stages R
and S, a formidable projection.

The Mandihdar Arch. — This is first differentiated at Stage P, in the form of a
minutely procartilaginous mass having a body or quadrate portion (PL III. fig. 1, q.)
bearing three outgrowths : an antero-dorsal or pterygoid (p.g.1), a postero-dorsal — the
future epipterygoid (columella), epg., — and an antero-ventral, much the stronger of the
three, the Meckelian bar (mk.).

The main body or quadrate mass, at this stage somewhat squarish, is disposed
parallel with the parachordal (pc.), and throughout the later stages, at which the
rotation of the latter and the straightening out of the basis cranii already referred to
are effected, it retains this relationship, i. e., the absolutely distinctive characters of the
whole arch are present in procartilage. Chondrification is seen to be setting in
independently in its body and the Meckelian bar, and even at this early stage the
latter is connected with its fellow symphysially by a thin procartilaginous tract. At
Q advancing chondrification of the Meckel's cartilage invades the symphysial tract,
and the whole cartilaginous lower jaw becomes for the time a single hyaline mass.
It remains such until Stage T, when the definitive symphysis begins to appear.

1 Cf. Peter on Ichthyophis (footnote, infra p. 70).

a Siebenrock, F. : 1893, p. 304, English Transl.

3 Cf. Siebenrock, F. : Transl. cit. p. 307, & fig. 14, pi. 10. & Bruhl, < Zootomie aller Thier Kl.' pi. 149. fig. 5.

DEVELOPMENT OF THE SKELETON OF THE TUATAKA. 45

With advancing development, the chondrifying centre of the quadrate cartilage
extends into the pterygoid and epipterygoid processes in common, and with this
replacement there comes about the afore-mentioned rotation, under which the epi-
pterygoid process, originally directed backwards and downwards, comes to be upwardly
directed, the pterygoid bar being displaced accordingly. On the assumption of this
rotation and its definitive position, the quadrate portion elongates and develops two
processes — a dorsal or otic process (fig. 4, q.'), and a lower process, which appears
correlatively with the segmentation off of Meckel's cartilage. Anteriorly its pterygoid
portion turns suddenly outwards and expands (cf. espec. PL III. fig. 6, pg.1). Con-
tinuing to elongate, it comes at Stage R to overlie the pterygoid and the inner half
of the os transversum, tapering to a point. Gaupp describes this cartilage in the
Lacertilian as merely extending " in the direction of " the transversum. He points
out (Berichte, p. 9) that did it continue forwards it would enter the maxillary region
and that of the processus maxillarius posterior (our fourth extranasal process) of the
nasal capsule, it would realize the condition occurring in Ranodon and the Anura.
With this we fully agree ; but we regard the extension over the transversum as
indicative of the retention by Sphenodon of a more approximately batrachian condition
than that thus far known for the Lacertilia.

In Sphenodon the study of the nerves and all possible relationships leaves no doubt
that the epipterygoid process is the homologue of the processus ascendens of the
batrachian quadrate cartilage, as recognized by Gaupp. He, however, seems to us
somewhat in doubt l as to the actual occurrence in the Lacertilian embryo of a
cartilaginous connection between the epipterygoid " Anlage " and the quadrate.
In Sphenodon, so far from there being any doubt on this matter, not only are the
epipterygoid and quadrate originally prseformed in one continuous cartilaginous tract,
but, from Stage E, onwards, the portion of this which, after the establishment of these
two bones, remains, begins to ossify by extension of the quadrate centre, to form the
characteristic antero-dorsal quadrate lobe (PI. IV. fig. 11), the presence of which
accounts for the close relationship of the epipterygoid and the quadrate in the adult.
The difference with the reduction of the jugal arch and the liberation and freedom of
the quadrate associated in the Lacertilia is one in respect to which the gap between
these and the Ehynchocephalia is immensely greater than between them and the
Chelonia 2, to say nothing of the Crocodilia and other reptiles possessed of a fixed

1 Gaupp, E., especially in his paper in Anat. Anz. Bd. vi. 1891, p. 107, and Berichte cit. 1898, pp. 9-11.

a We can only express astonishment, mixed with regret, at the gratuitous assumption by Osawa (98 °.
p. 102), in seeking to explain away the Giintherian dictum concerning the relationships of the quadrate to
the pterygoid, that the latter arises from two ossific centres, of which the hinder has in Sphenodon become
co-ossified with the quadrate. There is no trace of any such posterior pterygoid bone actual or potential.

46 PKOF. G. B. HOWES AND ME. H. H. BWINNBBTON ON THE

quadrate. And in this connection it may be remarked that if the detailed configura-
tion of the cartilaginous upper jaw be a criterion of relationship, the fact that a near
approach to the condition occurring in Sphenodon is that of the Csecilian Ichthyophis
glutinosa as recently described by Winslow 1 is of great interest, when it is remembered
that these Apodal Batrachia, in the possession of dermal ossifications and other well-
known characters, are the most approximately Stegocephalian of all living forms 2.

The Hyoid and Columella auris. — Our observations concerning the hyoid apart from
its connection with the auditory apparatus are few. At the earliest stage we have
examined (viz. P) it has already appeared in procartilage in the form it assumes in the
adult, except for slight differences in general proportion, as is better seen at Stage Q
(PL III. fig. 4). We have no evidence pointing to a compound origin of its basal
portion such as that described by Gaupp 3 for the Amphibian, or of the complexity in
structure of the order described by Siebenrock 4 for the Chelonia.

It is only as concerning the vexed question of the relationship between the colu-
mella auris and the anterior cornu of the hyoid that we need proceed to details. The
nature of this in the adult has been so oft recapitulated that it will suffice to point
out once more that, apart from theories based on alternative interpretations of the
facts of adult anatomy and surmises necessary for their defence, the real question
develop mentally at issue is whether or not the hyoid cornu and the extrastapedial are
secondarily united, and whether the object called by Huxley suprastapedial does or
does not arise independently.

Huxley, in describing the parts of the adult, regarded5 the whole columellar
complex as hyoidean, and the extra- and suprastapedial processes as parts of its
expanded outer extremity. Peters, and all subsequent investigators 6, on the contrary,
with the exception of Versluys, who has recently argued 7 in favour of original con
tinuity, have assumed that the connection between the extrastapedial and the hyoid
cornu is secondary, while Peters more especially believed the suprastapedial to have
been originally distinct. As great testimony to the extreme care with which Huxley
worked at this problem, there stands the fact that he drew attention (op. cit. p. 398) to
the presence, on the inner side of the foramen (f.h.t text-fig. 11, which for brevity's
sake we associate with his name), of a fibrous differentiation included between the
extra- and suprastapedial processes.

1 Winslow, G. M. : Tuft's Coll. Stud. vol. i. no. 5, 1898, pi. iii. fig. 24.

2 Of. Boulenger, G. A. : P. Z. S. 1895, p. 402.

3 Gaupp, E. : Morph. Arbeiten, Jena, Bd. iii. 1894, p. 399.

* Siebenrock, F. : Ann. naturhist. Hofmus. Wien, Bd. xiii. 1898, p. 424.
5 Huxley, T. H. : P. Z. S. 1869, p. 391.

0 Peters, W. : Monatsber. Akad. Wiss. Berlin, 1870, p. 15, and ibid. 1874, p. 40. Of. also Baur, G. : Biol.
Centralbl. Bd. vi. 1887, p. 655 ; Killian, G. : Jen. Zeitschr. Bd. xxiv. 1890, p. 649 ; Osawa, G.: 98 a, p. 520.
7 Versluys, Jan. : Zool. Jahrb. Anat. Abth. Bd. xii. 1899, p. 167.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 47

Gadow alone among recent investigators has carefully examined a series of indi-
viduals, and he records further details. Chief among these is the discovery ] that the
Huxleyean foramen may be reduced to the size of a pin-hole or absent (op. cit. p. 467)
— facts which point to the conclusion that its condition is indicative of variation in
degree of extension of chondrification, especially when it is remembered that it
transmits nothing.

Huxley described the head of the suprastapedial process (p. 397) as connected
with the parotic cartilage of the skull. Gadow, on the other hand, records in one
example a ligamentous attachment to this ; he remarks of another that " it does not
touch the cranium " (p. 468) ; and of a third he writes, the hyoid is continued
" along the anterior and lower margin of the extra-columellar cartilage, upwards to
the parotic corner, when it does not fuse with, although it directly touches, the
cranial cartilage." Sufficient this to show that the suprastapedial is in its ultimate
attachment variable.

With these facts in mind, we were especially attentive to the extrastapedial region,
and concerning it the following : — Examined at Stage S, and onwards to those stages
in which the adult condition is assumed, lateral longitudinal sections through the
quadrate (PI. V. figs. 13 & 14) show that bone to be unossified dorsally. It is seen to
be overlain by the squamosal (sq.), and when successive sections are followed outwards
the extrastapedial process (e.c.) is seen in the inner series to pass (PL IV. fig. 13) into
the suprastapedial (s.st.}. As the sections become external the suprastapedial is seen
to approach the head of the quadrate and eventually to fuse with it, as in fig. 14
(s.st.), which passes through the Huxleyean foramen. Sections more superficial, as
regarding the continuity of the parts, combine the appearance of these two figures.
Examination of the whole series and dissection alike reveals (cf. PL IV. figs. 7 & 9)
an absence of cartilaginous connection with the skull ; and in the denial of this we are
in agreement with Gadow.

The foregoing observations would at first sight appear contradictory to Huxley's.
Examination of his fig. 4, however, reveals an error, in the fact that he has indicated
as the exoccipital the parotic process of the opisthotic, as is proved by his delinea-
tion of its articular extremity. Allowing for this correction, his " parotic cartilage "
can only represent the articular head of the quadrate ; and, if so, his description
amounts to that of a union between the suprastapedial and the quadrate, such as we
have described and have observed not only at Stage S but at T. And, as a con-
sequence of this, it follows that cartilaginous continuity between the suprastapedial
and the skull does not exist, and that the quadratic union applies to the adult as well
as to the young. Eesorting to the earlier stages, with a view of ascertaining whether
this union is or is not primary, we find in sections at Stage R that it does not

1 Gadow, H.: Phil. Trans. 179 B, 1889, p. 468.

48

PEOF. 0. B. HOWES AND ME. H. H. SWINNEETON ON THE

exist (cf. PI. V. fig. 12), the quadrate head (#'.) and suprastapedial process (s.st.)
being distinct though closely approximate. Passing to Stage Q (figs. 10 & 11), the
distance between the two is seen to be much greater, the nearest approximation

being that of fig. 11.

Turning now to the suprastapedial process, and the fibrous interval of Huxley. The
former arises at Stage Q as a simple upgrowth, seen in section at fig. 10, PI. V., s.st.
When Stage K is reached, this is seen to be still elongating (text-fig. 11, s.st.) and to
have given rise at the middle of its inner border to a recurrent process (s.st.'), which,
passing downwards and inwards, becomes apposed to the columella auris (st.), to
which it is tied by a series of fibres, which pass obliquely between the two. Between its
recurved lower extremity and the columella a non-hyaline tract is present (*, fig. 12)

Fig. 11.

Fig. 11. Drawing from a reconstructional model, showing the detailed characters of the columellar head of
SpTienodon and its derivative processes at Stage E, x 30. Fig. 12. Microscopic section through the same,
parallel to the columellar axis, x 75.
e.c., extrastapedial ; /A, foramen of Huxley ; h'., anterior cornu of hyoid ; ?</., ligamentous fibres ;

</., upper end of quadrate ; s.st., suprastapedial ; s.st'., recurrent process of the same.

which we conclude is that described by Huxley. It remains only to add that as the
process is absent at Stage Q it is of secondary occurrence.

As to the continuity between the hyoid cornu and the outer head of the columella
(extrastapedial process), we have evidence that for the earliest stages of differentiation
(P especially), when all the parts concerned are in the procartilaginous state, it is
complete ; but a very interesting detail arises — viz., that in some of a series of thick
sections which we possess there can be observed (PI. V. fig. 5,*) a very feeble
suggestion of jointing, so feeble that it would be likely to be overlooked by anyone
not familiar with the sections. This, however, cannot be regarded as evidence of
original discontinuity between the columella and the hyoid cornu ! It is seen to be
but a passing phase, indicative of either a probable ancestral or an incipient "jointing"
such as takes place elsewhere along the cornu (**) ; and, as compared with a later

DEVELOPMENT OP THE SKELETON OF THE TUATAEA. 49

differentiation occurring at the base of the extrastapedial (PI. V. fig. 12 £), the
primary independence of which has never been suggested 1, it is insignificant indeed.

Holding the foregoing facts proof sufficient that the columella, extra- and supra-
stapedial are but the products of specialization of the upper extremity of the hyoid
arch, with which they are at all stages continuous, we have in conclusion to direct
attention to some puzzling procartilaginous tracts, of which we have been unable to
detect a counterpart at a later stage. They are of the nature of two pairs of rounded
masses (one of which is represented in PI. V. fig. l,f) disposed serially between the
roof of the pharynx and the auditory capsule, ventrad of the fenestra ovalis region, and
we are unable to hazard a guess at their significance.

Concerning the chondrification of the columella and the related anterior cornu of
the hyoid, we find at Stage Q, when the procartilaginous tracts above described become
hyaline, that all traces of the "jointing" disappear. Examination of figs. 6 to 9
(PI. V.) shows this conclusively, and also that the hyoid cornu (h.'} passes continuously
into the extrastapedial (#£.), and through that into the columella (st.). The inner
head of the latter, seen at the procartilaginous stage (PI. V. figs. 3 & 4, st.) to merge
into the feebly differentiated mass (c.au.) giving rise to the auditory capsule, at the
period of chondrification is seen to be structurally continuous with that now hyaline,
and in section (PI. V. fig. 6, st.) delimitable only by a close approximation of its
peripheral cells. Later, it becomes free, and attached to the rim of the fenestra ovalis
by membrane, in the customary fashion (of. PI. V. fig. 12, st.). Its rod-like portion
commences to ossify superficially, in the manner of the parts of the vertebral column
and the otoccipital bones.

The Trabeculce. — One very conspicuous feature of the afore-described stages in the
development of the chondrocranium is the non-extension or incorporation of the
trabeculse into the lateral cranial wall. As pointed out (antea, p. 38), these remain
passive during the development of this.

Examination of the adult chondrocranium of Sphenodon, apart from a knowledge
of its development, might well arouse the supposition that its fenestree are due to
absorption of an originally continuous wall, of the cartilaginous fish type. One of the
most certain and fascinating of our results is the discovery that the cartilaginous
cranial bars are all due to continuous-growth processes, that the correlated fenestree
are in no way due to absorption, and that the trabeculse play no part in the formation
of the lateral cranial wall. From first to last these are simple rods, lost by union

1 Kingsley, the latest worker who has dared to deal with the subject of the general morphology of the
auditory ossicles (with which we are not concerned), expresses his conviction (Tufts Coll. Studies, No. 6, 1900,
pp. 215-216) that the Lacertilian hyoid and columella are originally continuous in the embryo. He claims
for the " extra columella " an independent origin, but since he uses the term in an unconventional sense and
his figure (which does not bear out his description) leaves us in doubt whether his " extra columella " may
not represent the supra-stapedial process, we feel justified in the above statement.

VOL. xvi. — PART i. No. 7. — February, 1901. H

60 PKOF. G. B. HOWES AND ME, H. H. SWINNEETON ON THE

anteriorly with the basal ethmoid, united by their postero-internal extremities with
the parachordal ; and, what is more, they are serially disposed at all stages with the
visceral skeletal arches.

Recent investigation by the reconstruction method has led to the conclusion that
the developmental processes occurring in the skull of Man himself are not easily
reconcilable with those generally believed to be passed through by even that of certain
other mammals 1.

As is well known, Salensky in 1878 described2 in the embryo Sturgeon a distinct
cartilaginous centre for the lateral cranial wall ; and Stohr, in 1880, discovering that
the parachordal of Triton3 appears in two pieces, in 1882 showed4 the basal portion of
the chondrocranium of Rana to be complex, if not actually composed of three pairs
of distinct elements — trabeculse, " mesotic cartilages," and " occipital plates " (para-
chordals). Miss Platt has later described in Necturus 5 the dorsal part of the " crista
trabeculae" as paired, and instituted, on consultation with Sewertzoif, a comparison
with the alisphenoidal cartilage originally described by him in Acanthias in 976.
While Peter, in the same year as Miss Platt, recorded the formation in Ichthyophis 7 of
so-called " dorsal trabeculae." Most important of all, however, is the full monograph
of Sewertzoff, which has appeared during the progress of our work, in which 8, bringing
the whole subject to a focus, he shows that in the Elasmobranch Acanthias the trabeculae
take an insignificant share in the formation of the lateral cranial wall, and that this is
mainly formed on either side from the above-mentioned distinct cartilages (termed by
him the alisphenoidal), the pair of which, uniting with the trabeculae, contribute what
he has termed the prochordal portion of the resulting chondrocranium. In his
memoir he meets the challenge that if this cartilage be of the importance he claims, it
should be more generally forthcoming, by showing reason for its being present in
Pristiurus, that W. K. Parker had seen it in the Salmon 9, and that other
observers, and more particularly Miss Platt and Peter referred to above, had probably
done so in other chordate forms. In view of this and of the similarity in posterior
extension of the trabeculae along the parachordal in Acanthias and Sphenodon, and of
the relationships of the latter to our otosphenoidal plate (PI. III. fig. 1), we consider
that this may perhaps represent SewertzofFs alisphenoidal cartilage 10.

1 Levi, G. : Archiv mikr. Anat. Bd. Iv. 1900, p. 407.

2 Salensky, W. : Zool. Anz. Bd. i. 1878, p. 289.

3 Stohr, Ph. : Zeitschr. wiss. Zool. Bd. xxxiii. 1880, p. 477.

4 Stohr, Ph. : Ibid. Bd, xxxvi. 1882, p. 91.

5 Platt, Miss Julia : Morph. Jahrb. Bd. xxv. 1897, p. 377.

6 Sewertzoff, A. : Anat. Anz. Bd. xiii. 1897, p. 413.

7 Peter, K. : Morph. Jahrb. Bd. xxv. 1898, p. 555.

8 Sewertzoff, A. : Kiipffer Festschrift, Jena, 1899. p. 281.

9 Parker, W. X. : Phil. Trans. 1883, p. 129, pi. v.

During the passage of this Memoir through the press, Sewertzoff has announced details concerning the
development of the skull in the Gecko (Ascahabotes fascicularis) which fully supports this conclusion (cf. Anat.
Anz. Bot. xviii. p. 36, 1900).

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 51

Far reaching as is his discovery, and interesting as are its bearings on our own
work, we venture to think that the most rational interpretation -rtb '-be pn^ilpon the
behaviour of the trabeculse in Sphenodon is that of Huxley, jongiaally-ptit fe>?ward in
his Hunterian Lectures in 18G4, that they represent a pair 'of prse-oral" visceraT arches.
Huxley reiterated this conclusion in 1874, in his suggestive note on Amphioxus 1, and
von Kiipffer gave it consideration and support in 1893 2, in his discovery of a pair of
prse-oral visceral diverticula in the embryo Sturgeon. Further consideration of this
very important topic is beyond the possibility of this memoir, but we hail with delight
the discovery, as our work was nearing its termination, by von Davidoif, of the
existence of this very pair of diverticula in the Lizards Platydactylus and Lacerta.

Cranio-facial Membrane-Bones.

The anatomy of these has been so fully dealt with by various authors, and most
recently by Osawa (98 a. p. 497), that we have little to add to their descriptions.
Developmentally, however, some interesting considerations arise. At Stage Q, the
earliest at which we have been able to observe membrane-bones, the vomers, palatines,
pterygoids, maxillae, postorbitals, squamosals, angularia, supra-angularia, and dentaries
are all present (PI. III. fig. 5) and remote from each other. By the time that R is
reached, all the membrane-bones present in the adult are represented (cf. PI. III.
figs. 10-12). Looking at the skull from the side, this does not at first sight appear
so, but when examined fully it is found that while the frontals are approximated in
the middle line, the parietals are widely divaricated and small and of a remarkable
angulated type. Examination of the skull at this stage shows that the frontal and
postfrontal, the prsefrontal, maxilla, jugal, and postorbital are all in close relation-
ship, first active development having apparently involved those elements which are
circumorbital — a fact which immediately impresses itself on the mind when, at this
stage, the skull is viewed either from above (fig. 11) or the side (fig. 10). And one is
led to speculate how far this may not be indicative of a first protection of the eye,
when it is remembered that the palaeontological record proves the circumorbital

1 Huxley, T. H. : Proc. Royal Soc. vol. xxiii. 1874, p. 131.

There is evidence among Huxley's unpublished notes that in the early 80's he was returning to this conception
and to work upon the skull. He was bringing to bear upon it the discovery in the Elasmobranchs of a fourth
branch of the trigeminal nerve, to have been termed the palato-nasal or Jiyporhinal. This term was intended
to express the fact that, in relation to the trabeculse, this branch of the fifth cranial nerve, together with the
ophthalmic (for which he had already introduced the correlative term orbito-nasal, in his article " Amphibia,"
Encyclop. Brit., Vol. i. Edit. 9, p. 767), repeats the condition of the other cranial nerves in relation to their
visceral arches and clefts, and thereby presupposes the existence of a prae-oral cleit. And, further, he was
building up an argument on this basis to show that in these facts there lies the explanation of the mode
and point of termination anteriorly of the notochord. — Gr. B. H.

2 Kiipffer, C. von : Stud. d. vergl. Entwick. Kopfes d. Kranioten, Hft. i. Acipenser: Miinchen, 1893, p. 89.

H2

52 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

region to have been the .first seat in order of time of the development of dermal
plates *. ; V- . '••' :. -

Passing. to the ptailaterit 'is seen that at this stage approximation is most marked in
front, for while the vomers have met in the middle line, the pterygoids are widely
divaricated behind. A noticeable feature is the fact that the palatines, which support
the orbital floor, have apparently shared in. the afore-mentioned rapidity of growth.
From this stage onwards, the salient feature in progressive development is the closing
in towards the middle line of the bones of both the cranial roof and palate, rendered
possible by the fact that the most rapid phases in the growth of the brain have now
passed. Comparison of PI. III. figs. 11 & 12, and PI. IV. figs. 5, 6, and 8, will
render clear the changes undergone in the individual bones during the process, which
it is not necessary to describe in words.

It is at the stage (R) that the parasphenoid first appears, in the form (PI. III.
fig. 12, p.s. ; in section in PI. IV. fig. 1) of a minute bony element which would most
certainly be lost to sight in ordinary dissection, lying freely beneath the antero-median
border of the post-pituitary plate. With advancing development it assumes an arrow-
head shape and a more intimate relationship with the basis cranii, fusing by its broad
posterior extremity at Stage S with the basisphenoids, and closing the pituitary foramen
as it does so by extension anteriorly (PI. IV. fig. 3).

We have already drawn attention (antea, p. 2) to the interest attaching to this bone.
It was overlooked by Giinther, Briihl, and others, and its discovery was first claimed
by Fritsch, who believed he had observed it as an independent element2. Baur
immediately challenged the alleged independence 3, and gave an accurate account of
its limitations in a young individual. Fritsch compared the supposed parasphenoid
with that of Hyloplesion, and comparison of his figure of this with that given by
Credner (op. cit. p. 513) of the presumed co-ossified basi- and praesphenoids of
Palseohatteria at once arouses suspicion by the close similarity in shape of the two ;
while further complication arises from the fact that Baur, commenting on Credner's
discovery, regards4 his basi-praesphenoid as a parasphenoid alone. Fritsch for
Sphenodon, and Credner for Palseohatteria, were dealing with the compound basi- and
parasphenoid, and were therefore in error. Baur was right only in his delimitation
of the parasphenoid of Sphenodon.

The pterygoids, as already remarked, are developed widely apart, apposition in the
middle line commencing anteriorly at Stage R, at which (PI. III. fig. 12, pg.) they
already reach the vomers — i. e., their forward extension is thus recognizable as soon as

1 Of. Newberry, J. S. : Monogr. U.S. Geol. Survey, vol. xvi. 1889, p. 103, pi. xliv. ; and Jajckel, 0. : Sitzb.
Ges. naturf. Fr. 1892, p. 90.

2 Fritsch, A. : Fauna d. Gaskohle d. Permform. d. Bohmen, Bd. ii. 1889, p. 58.

3 Baur, G. : Zoolog. Anzeiger, Bd. xii. 1889, p. 45.

4 Baur, G. : Amer. Journ. Sci. 1889, p. 311.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 53

the bones assume a mutual relationship, and is not brought about by ontogenetic
growth. At Stage E (PL III. fig. 12) it will be observed that the anterior edge of the
palatine (pa.) is transverse and that the vomers (vo.) lie wholly in front of them ;
whereas at Stage S (PI. IV. fig. 6) the palatine border is angulated and the vomers are
correspondingly modified. Proof that this change has arisen by backward elongation of
the vomers, lies in the study of the relationships to the posterior nares, and it therefore
follows that in the all-characteristic vomero-pterygoid apposition the vomer has played
a part. Boulenger, one of the advocates of the Ehynchocephalian affinities of the
Chelonia, has called special attention l to a similar apposition in this order ; but con-
cerning it the process is the reverse of that of the adult Ehynchocephalian, it being
the vomer which for the most part reaches back to the pterygoid. Judged by the
foregoing ontogenetic changes undergone by the developing Sphenodon, this feature,
instead of presenting, as might appear, a difficulty in the way of the acceptation of the
said affinity, strengthens it, since both bones are in both groups of animals involved
in the apposition, though in an inverse degree.

In Ichthyosaurus the vomers extend back divaricatingly behind the nares, and the
pterygoids, inserting themselves between them, extend forwards between the nares 2.
Taking the Stage E of Sphenodon as the starting point, the Ichthyosaur might well
represent one extreme of modification, the Chelonian, through the adult Sphenodon,
an opposite one ; and in consideration of accepted views of the Chelonian affinities of
the Plesiosauria 3, it is interesting indeed to find that in these they are the vomers
which longitudinally extend 4.

The interest in the pterygoid of Sphenodon does not stop here, for, on examining its
basicranial articulation we have found a synovial joint to be present and an indepen-
dent interarticular cartilage (PL 4, figs. 1 & 3, m.p.), which flanks the inner face of the
pterygoid and has a,n essential similarity to the meniscus mandibuli. We therefore
propose to term it the meniscus pterygoideus 5.

Cognate to the study of the pterygoid is the presence of a process of the squamosal
hitherto unrecognized, which (PL IV. fig. 11, sq.1) extends down wards and forwards
between the quadrate and pterygoid, and, together with a process arising from the
posterior border of the squamosal (sq.", PL IV. fig. 9 and PL V. fig. 13), embraces the
expanded otic head of the quadrate. Both are present in the adult, the hinder process
being the less conspicuous of the two.

1 Boulenger, G. A. : Brit. Mus. Catal. cit. p. 17.

2 Of. Baur, G. : Anat. Anz. Bd. x. 1895, p. 458, fig. 1.

3 Cf. Andrews, C. W. : Quart. Journ. Geol. Soc. vol. lii. 1896, p. 251, fig. 2.

4 Cf. Andrews, C. W. : Geol. Mag. (iv.) vol. iii. 1896, p. 4, and Ann. & Mag. IS'at. Hist. (6) vol. xv. 1896,
p. 345.

5 Parker has undoubtedly seen and figured this in Zootoca (Phil. Trans. 1879, p. 612, & pi. 45. fig. 4), but
his descriptive paragraph (§ 7) can hardly be said to adequately describe it.

54 PEOP. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

The " Squamosal" — This bone has been most fully described by Baur, who J has
accurately dealt with its relationships to the parietal, postorbital, jugal, quadrato-jugal,
quadrate, and paroccipital process. It is unnecessary here to recapitulate the details
of this association, which our figures render sufficiently clear, except to remark that
we have extended the relationship to the pterygoid.

In the progress of investigation into the comparative osteology of the fossil reptiles,
the varying conditions of the squamosal and supratemporal, one or both of which may
be present, have become the subject of much consideration. The presence of the two
has been regarded as a lowly characteristic, if only by way of analogy to the Stego-
cephalia. Cope and Baur are conspicuous among those who have utilized these bones
in the determination and discussion of affinity, and nothing short of a deplorable
confusion has arisen from their inconsistency in the usage of terms 2, and the fact that
while one of them arrived at an inversion of the order adopted by certain contemporary
writers, he finally complicated matters 3 by needlessly reviving for the reptilian
squamosal Owen's term " prosquamosal." A final agreement was never arrived at, and
the question therefore arises as to which of the two bones is for the future to be
regarded as the supra-temporal.

As a general rule these bones lie side by side in the same transverse plane. The
term supra-temporal was applied by Bakker to the inner one 4, in dealing with the fish
skull. Cuvier denoted the presumably homologous bone in reptiles the "mastoid "5; and
Owen, retaining this term, applied6 to the outer of the two (Cuvier's "temporal") the
term squamosal. To be consistent, therefore, on the assumption that the inner of the
two bones, having similar relationships in fishes and reptiles, is homologous,
convenience and precision are met by terming the inner the supra-temporal, the outer
the squamosal. And it is in this sense that we use these words 7.

Our knowledge of the paleeontological history of the Rhynchocephalia has during
recent years been materially advanced by the description by Lortet of remains from
the Jurassic of France. In his memoir already cited (antea, p. 3) he drew attention
in Saphgeosaurus (Sauranodon) to a " parieto-squamosal " complex, in respect to which

1 Baur, G. : Anat. Anz. Bd. x. 1895, p. 321.

2 Cf. Baur, G. : Anat. Anz. Bd. i. 1886, p. 349, and Bd. ii. 1887, p. 657 ! and, as an awful example, the
series of notes embodying the dispute between him and Cope in Amer. Nat. vols. xxix. & xxx.

3 Baur, G. : Anat. Anz. Bd. x. 1895, p. 320.

4 In Cuvier and Valenciennes, Hist. Nat. des Poissons, t. i. 1828, p. 338.
6 Cuvier, P. ; Ossemens Possiles, t. x. 1836, p. 14.

6 Owen, E. : Catal. Osteolog. Series E. Coll. Surgeons, vol. i. 1853 (table), p. xxxviii.

7 Concerning the afore- mentioned confusion, Praas for example, in his revisionary memoirs on the Ichthyo-
sauria and Stegocephalia, following in respect to the latter the lead of Huxley, Miall, Fritsch, and Credner,
refers to the inner bone as the squamosal, the outer as the supra-temporal. Zittel adopts the Huxleyean
order for the Eeptilia and Stegocephalia, with confusion arising out of the interpretation of the latter in the
Lacertilia as the quadrato-jugal. Briihl is still more glaringly inconsistent and contradictory ; while even

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 55

Bonlenger first showed him 1 to be probably in error. Baur, accepting Boulenger's
correction, has sought to show 2 that the bones regarded by him as the supra-temporal
and squamosal lie within the area of the " squamosal " of Sphenodon, and that that
bone is therefore compound. Shuffling the terms, he regarded the body of the latter
with its laterally visible processes as a " prosquamosal " ("squamosal" auct.) and its
posterior ascending process as the squamosal (" supra-temporal " auct.).

Seeking for evidence in support of this in the Tuatara, Baur admits that none was
forthcoming in a skull of 25 mm. in length (pp. cit. p. 321). Not only have we failed
in all attempts to detect any such separation, but also to observe at any period traces
of a second element. While we fully admit that this so-called " squamosal " of
Sphenodon combines the structural relationships of the supra-temporal and squamosal
as originally defined, failing the discovery of any trace of its supposed double nature,
we are disposed, on consideration of the behaviour and all detailed relationships of the
supra-temporal in the Lacertilia, to regard it as a squamosal, and to interpret its
ascending limb, which meets the parotic process of the parietal, as secondarily acquired.
The alternative would be the introduction of a new term, in which neither
"squamosal" nor "temporal" were compounded, but we have no wish to render
confusion more confounded. The future can only settle the question, and we are
content to leave it to that.

The Quadrato-jugaL — This bone, as is well known, was first recognized in Sphenodon
by Dollo 3, and later more fully described by Baur 4. We have nothing to add to their
descriptive account of it. Its most characteristic feature is its enclosure with
the quadrate (qu. & q.j.9 PI. IV. figs. 7 & 9) of a conspicuous foramen. Osawa, the
latest writer upon it, terms it (98 a. pp. 499 & 520) the "tympanic," presumably
on account of his inability to regard the mammalian tympanic as the homologue of the
quadrate ; and associated with the study of this bone there is a matter of no little
importance, if, as we believe, the tendency of our time is in error.

Baur, in 1889, argued5 against the generally accepted belief that the single

Smith Woodward is not uniform in his terminology. Boulenger, on the other hand, is so, and, like ourselves,
he retains the terms for the hones to which they were originally applied — i. e. for him, in both fishes and
reptiles, the inner is the supra-temporal, the outer the squamosal. Difficulty admittedly arises when but one
bone is present, and there is no doubt that in many such cases the problem can only be solved develop-
mentally ; but, on comparison of those lizards in which both bones are present, we believe him to be right in
regarding the bone which alone suspends the quadrate in the Ophidia (Brit. Mus. Cat. " Ophidia ") as the
supra-temporal, and not the squamosal as do Huxley and his followers.

1 Boulenger, G. A. : Ann. & Mag. Nat. Hist. (ser. 6) vol. xi. 1893, p. 209.

2 Baur, G. : Anat. Anz. Bd. x. 1895, p. 322, cf. also Amer. Nat. vol. xxx. 1896, p. 145.

3 Dollo, L. : BuU. Mus. E. Nat. Hist. Belg. t. ii. 1883, p. 235.
1 Baur, G. : Zool. Anz. Bd. ix. 1886, p. 685.

3 Baur, G. : Journ. of Morphol. vol. iii. 1889, p. 473.

56 PEOF. G. B. HOWES AND ME. H. H. SWINNEETON ON THE

temporal arch of the Squamata represents only the upper arch of the Rhynchocephalia,
basing his conclusions on the surmise that the quadrato-jugal is not unrepresented in
the former as is usually supposed, but that the bone generally termed the "squamosal"
is its homologue. Somewhat similar conclusions follow from the later determinations
of Gaupp, laborious but unconvincing, in which he seeks to show 1 that the bone
hitherto known as the quadrato-jugal in Batrachia and Birds must be for the future
termed the " quadrato-maxillary," and that for the quadrato-jugal in Crocodilia,
Chelonia, Rhynchocephalia, and Lacertilia, the term " paraquadrate " must be
employed.

Baur assumes that the Squamata " never possessed an infra-temporal fossa, but that
the broad arch was reduced from below in the same way as in the Testudinata " (op. cit.
p. 473). It is beyond the scope of this memoir to fully discuss this question,
voluminous in itself, but there tells strongly against the interpretation of the bone
which in the " Squamata " reaches the head of the quadrate with that which in the
Rhynchocephalia flanks its lower articular border, the fact, long ago pointed out by
Huxley 2, that in the living Lacertilia there is present a ligament having the relation-
ships of the latter. And, further, argument by analogy to the living Urodela, ill
which, while the maxillo-jugal arch is complete in bone only in the Eastern genus
Tylototriton 3, a similar representation is present in ligament which may extend even
into the maxillary region, places a further obstacle in the way of its acceptation. All
recent investigation has gone to show that the Reptilia and the Batrachia are the
diversely modified descendants of the Stegocephalia ; and the fact that in them the
supra-temporal, squamosal, and quadrato-jugal coexist in a transverse series tells with
great force against this seductive argument.

The " Septo-maxillary :" — This bone was originally described in Sphenodon by Osawa
(98 a. p. 503) as a small semicircular element attached by fibrous tissue to the vomer,
and he therefore named it a " turbinal." In this he was unquestionably in error. The
bone was figured and described by Parker in Zootoca4 as the septo-maxillary, and
under this name it has been more recently described by Gaupp in other lacertilian
embryos. Concerning its detailed relationship, he associates it with the support of the
septum nasi internally and with that of the border of the cartilage enclosing Jacobson's
organ superficially (op. cit. Ber. p. 10). The bone present in Sphenodon (PL IV. fig. 2,
s.mx.) is still more superficial in position and free of the nasal septum than this. In
consideration of the fact that whereas here the Jacobson's organ is completely roofed in
cartilage, in the lizard, according to Parker, the septo-maxillary fulfils that function 5,

1 Gaupp, G. : Morphol. Arbeiten, Jena, Ed. iv. 1895, p. 77.

2 Huxley, T. H. : Anat. of Vertebr. 1871, p. 190.

3 Eiese, H. : Zoolog.-Jahrb., Anat. Abth. Ed. v. 1892, p. 99.

4 Parker, W. K. : Phil. Trans. 1879, pt. ii. p. 609.

5 Parker, W. K. : Phil. Trans. 1879, pi. 44. fig. 5.

DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 57

we are disposed to regard the bone as its homologue. It is figured in the macerated
state at PL VI. fig. 1, s.mx., and, as remarked by Gaupp, is a membrane-bone.

The supposed " lachrymal " of Giinther (67. p. 597), accepted by Hofmann J>
Seeley (?) 2, and Credner 3, has no existence.

The Prce- and Postfrontal and Postorbital. — The two former are proved by their
development to be membrane-bones 4, and examination of PI. IV. fig. 10 shows that
they are neither of them compound and that there are no correlated chondro-cranial
ossifications.

The postorbital has the customay relationships of that bone and is very large 5.

1 Hofmann, C. K. : Bronn's Klass. u. Ordng. d. Thier-Keichs, Bd. vi. Abth. 3, pi. 66. fig. 5.

2 Seeley, H. G. : Journ. Linn. Soc., Zool. vol. xii. 1876, p. 184. " In front is a small lachrymal, which is
not found in Chelonians." The context is not clear.

3 Credner, H. r op. tit. p. 510. Baur has pointed out the error here, Amer. Journ. Sci. vol. xxxvii. 1889,
p. 311.

4 "We retain the term praef rental, as one now in general use. It is, however, unfortunate (since it was
originally applied by St.-Hilaire, in 1807, to a cartilage-bone, which Cuvier in his 'Legons' defined as trans-
mitting the olfactory nerve) that it should have become applied indifferently to various cartilage and membrane
bones occurring in the prsefrontal region. A great confusion exists with respect to the modern usage of the
term, but it does not materially affect our work.

5 The study of the postorbital in Sphenodon is intimately bound up with Gunther's work upon the living
Crocodilia, which possess but a single so-called " postfrontal." On the basis of comparison with this he came
to regard the postorbital of Sphenodon (which, following Stannius, he termed " quadrato-jugal ") as "a
detached portion of the postfrontal " (67. p. 598). Baur discovered in 1886 (Zool. Anz. Bd. ix. p. 740)
that both postfrontal and postorbital are present in Belodon, and accepted Giinther's conclusion concerning
Sphenodon. Their reasoning suggests an origin of the postorbital from the postfrontal, rather than that both
bones were originally distinct, and that the presence of one or both is due to variation by co-ossification with
age. And, as bearing upon this, we submit the following observation : — Cuvier showed that in the Iguana
('Lecons,' t. x. p. 14) there are two bones occupying the region of the postfrontal of other Lizards. He
applied to both this term, and figured them as attached side by side to the postorbital process of the frontal.
In our own example the hinder bone alone has this relationship, the former being pushed forwards in front of
the process named. Comparison with the single " postfrontal " bone present in many Lizards — e. y., the
familiar backwardly-pointed bone of Yaranus — shows this to have the detailed relationships of Cuvier's two
" postfrontals " in Iguana, wherefore suspicion arises that it is perhaps compound. That this may be the
case is proved by the skull of a young Tupinambis in our possession, in which, as Mr. M. F. Woodward has
shown us, two bones are present in its place. Contrary to what happens in Iguana, the postfrontal is alone
attached to the frontal and the postorbital to it. This notwithstanding, it follows that the bones described by
Cuvier in Iguana are the postfrontal and postorbital, and that they are both represented in the varanoid type
(cf. also Gaupp on the embryo Lacerta, in Morph. Arbeiten, Bd. iv. p. 77, pi. vi. fig. 9), We are also
indebted to Mr. Woodward for drawing our attention to a skull of the Green Turtle (Chelone mydas) in our
Teaching Collection, in which that portion of the " postorbital" suturally conuected with the anterior two-
thirds of the frontal is on the left side distinct — i. e., an independent postfrontal is present.

These facts go far to prove that in the Reptilia generally, where either a single " postfrontal" or " post-
orbital" is alone present, it may be a compound of these two ; and they certainly suggest that the postfrontal
of the living Crocodilia may have gone elsewhere than over to the frontal, as surmised by Baur.

VOL. xvi. — PART i. No. 8. — February, 1901. i

58 PEOF. G. B. HOWES AND ME. H. II. SWINNEETON ON THE

The Mandible. — The mandibular ramus has been shown by Baur to consist (95 a.
p. 413) of the six elements usually present in that of other Reptilia. He originally
described it in 18911 as resembling most closely that of those Chelonia in which the
angular and supra-angular, apposed behind the splenial, under-arch the articular, and
as destitute of the 7th element or " praesplenial " described by him in these animals.
We have only to add that at the latest stage observed by us (T) the articular has not
yet appeared, the articular region being still cartilaginous, and that at Stage S the
angular and supra-angular (s.a., PI. IV. fig. 4) are still separated by the splenial (sp.).

6. THE APPENDICULAR SKELETON.

The Pectoral Girdle. — Concerning this we have little to record. The simplicity of
the coracoid was pointed out by Giinther, in the remark (67. p. 611) that it has
" no notch whatever." Furbringer, in a passing allusion seven years later 2, commented
on the rounded border and feebly ossified state of this (PI. VI. fig. 6, cor.), and there
can be no doubt that in respect to these features it simplifies the Lacertilian type. As
pointed out by Furbringer, however, the Chameleons approximate to a similar con-
dition, but it may be questioned whether the " simplification " in them is not due to
secondary causes. Ossification takes place during Stages S and T, on lines common to
both the Batrachia and Reptilia. An interesting detail is the early appearance of the
clavicle, viz. at Stage Q (PI. VI. fig. 4, cl.), at which no cartilage-bones are anywhere
present in the axial skeleton. The interclavicle appears later. We have failed in all
attempts to find evidence of a cartilaginous predecessor of these bones.

The relationships to the sternum we have already described (antea, p. 33).

The Pelvic Girdle. — Giinther accurately described the adult girdle, except that he
applies to the ileo-pectineal process the term "uncinate" (67. p. 615). Like the
shoulder-girdle, it is at Stage Q fully chondrified. Its two halves (PI. VI. fig. 7) are
united, and there is a considerable cartilaginous symphysis (c.i.p.) which in the mid-
ventral line separates the cordiform fenestree (f.c.). With later growth (at Stage R)
a backwardly-directed median process (the hypoischium of Mehnert3) becomes con-
spicuous, but it is never segmented off or ossified to form an " os cloaca?" as in
Lacerta. The epipubic cartilage (e.) like it is simple — i. e., there is nothing to
suggest those processes of bifurcation and subdivision recorded for certain Lacertilia.

Interest attaches to the ligamentum medianum pelvis, from the fact that while
Wiedersheim has described 4 in its place in the adult a cartilaginous tract uninter-

1 In his 1895 notes he admits a transposition in those of 1891 of the terms angular and splenial, but it
does not affect his comparison.

2 Furbringer, M. : Morph. Jahrb. Bd. i. 1876, p. 643.

3 Mehnert, E. : Morph. Jahrb. Bd. xvii. 1891, p. 123.

4 Wiedersheim, E. : Zeitschr. wiss. Zool. Bd. liii. 1892, p. 54.

DEVELOPMENT OF THE SKELETON OF THE TTJATAKA. 59

ruptedly continuous with the epipubis and hypoischium, Mehnert has denied (op. tit.
p. 142) a " skeleto-vicarious " significance to this ligament for Lacerta. Our develop-
mental material shows that Wiedersheim was in error, since the ligament is already
present (PL VI. fig. 8, l.i.p.) at Stage R. Concerning Mehnert's conclusion, we can
only add that in Sphenodon the ligament is preformed in cartilage (PI. VI. fig. 7, c.i.p.)
at first of considerable extent, and that with advancing development, correlatively with
the expansion of the pelvis and widening of the cordiform fenestrse, this undergoes
a relative reduction with accompanying replacement in fibrous tissue. If Mehnert is
correct, the cartilaginous symphysis and the primarily small size of the fenestrse carry
Sphenodon so much nearer the Batrachia.

In the course of our work our attention became arrested by the fact that there are
apparently two types of hip-girdle represented in the adult. We append camera-lucida
figures of these. When viewed from beneath, it is evident that the essential difference

Fig. 13. Fig. 14.

Camera-lucida outline sketches of extreme types of the adult pelvis of Sphenodon.
13, least expanded ; 14, most expanded. Nat. size.

between them is one of increased length as compared with breadth. In the pelvis of
the least expanded type (text-fig. 13) the cordiform fenestrse are more rounded than in
the most expanded, in which they appear (fig. 14) angular ; and we find that whereas
in the least expanded type the transverse measurement across a-b is about equal
to that along c-d (fig. 13), in the most expanded (fig. 14) c-d is greater. We note,
however, that in all cases the distance between the opposite limits of the cordiform
fenestrse is equal to that of the symphysis ischii from the vertebral column and to the
transverse diameter of the sacrum.

For want of material undoubtedly mature upon which to base further comparison,
we are unable to decide how far this is or is not a sexual matter ; but we are disposed
to believe the contrary. The only other case known to us, which is at all analogous,
is that of the presence of two still more distinct types of scapulae in an extensive
collection of bones of the Australian Dugong brought home by Professor Haddon.
F.R.S., from Torres Straits in 1889, now in the custody of one of us.

i2

60 PROF. G. B. HOWES AND ME. H. H. SWINNERTON OJST THE

The Long Bones. — Under this head we include the humerus and femur, radius and
tibia, ulna and fibula. They have all been so often described, from Giinther to
Osawa, that detailed recognition by us would be superfluous. We would only add that
the condylar foramina of the humerus, originally observed by Dollo (84), are both
fully formed at Stage Q (PL VI. fig. 10, f.en.^f.ec.), and that the inner lias from the
first period of differentiation its canal-like character.

The long bones are the first of all the cartilage-bones to ossify.

Carpus and Tarsus, with Phalanges.

It is evident, from the study of both carpus and tarsus, that chondrification sets in
correspondingly (for the tarsus, cf. PI. VI. fig. 15). One inexplicable feature is the
long duration of the cartilaginous state of both. Ossification begins in both post-
axially (as is seen in fig. 14 for the carpus), but not until the rest of the limb is fully
ossified.

We have examined both carpus and tarsus at all stages of development back to Q,
where these elements are first chondrified. To make sure of detail, we have employed,
beyond clarified dissections, serial sections cut horizontally.

The Carpus. — Giinther described ten carpal elements, and in this he has been
followed by others. He appears to have missed one of the centralia, and to have
confused the other with the proximal elements, which he describes as five in number
(67. p. 612). Osawa, the latest writer on the subject, correctly records eleven
elements (98*. p. 528), the eleventh being the secend centrale, detected by Bayer
(84. p. 237), who first applied to the parts a rational terminology. It was, however,
independently discovered by Dollo arid Baur (86a. p. 188), the latter opposing Bayer's
conclusion that its supposed absence is due either to disappearance or union with
another carpal element. In this he was right, for we find it always present.

None of the afore-mentioned observers describe the precise size and relationships
of the two centralia to each other and the adjacent carpal elements. Osawa, however,
gives a very different delineation to the dorsal and ventral aspects of the same pair,
and figures the prseaxial as outwardly extended between the radiale and first carpale as
seen from the dorsal surface (08a. p. 527, figs. 13 & 14). While we can confirm the
accuracy of this, we are able to record further suggestive details. From a comparison
of our figs. 12 and 13 (PL VI.) which represent the opposite carpales of the same
individual, we find that the right (fig. 12) is normal but that the left (fig. 13) is
exceptional, in the fact that the preeaxial centrale (pr.c.) is smaller than the postaxial
(po.c.} and lies wholly between the radiale and the first carpale, instead of merely ex-
tending between them. The postaxial centrale, on the other hand, is correspondingly
enlarged, whereby it articulates with the second carpale, as well as with the third and
fourth, to which alone it is usually related. There is thus to be observed an inverse

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 61

proportion to that of the corresponding centralia of the other limb (fig. 12). Bayer has
suggested that in the presence of the double centrale Sphenodon exhibits a Batrachian
tendency, drawing attention to the great extent to which the living Urodela are doubly
centralial. One of us has, with another, attempted to show l that the presence of a
second centrale carpi is a diagnostic character of the Anura, and this goes to support
Bayer's argument. As to centralia, however,Wiedersheim has demonstrated2 the presence
of three in the Axolotl ; and with these facts in mind it occurred to us that the inequality
in development of the two centralia in Sphenodon might possibly be due to the presence
of a third, which had fused with the opposite fellow on the opposite sides in the pair
of limbs under discussion. At Stage Q the condition of the centralia was found to be
the same as in the normal adult; but in a young specimen belonging to the R. College
of Science, Dublin, the praeaxial centrale is on each side ossified from two independent
centres (PL VI. fig. 14, pr.c.), and in such a form that while co-ossification of them
would bring about the condition of the right limb (fig. 12), co-ossification of the
middle nucleus with the postaxial centrale (po.c.) would result in that of the left.

Bruhl, for some unaccountable reason, systematically terms 3 the pisiform of Reptiles
the " ulnar sesamoid " ! Concerning the rest of the proximal carpals and the centralia
we have nothing to add.

The distal carpals, stated by Giinther to be five in number, are by Bayer enumerated
as four. As he was dealing with a young animal he found only the 4th carpal ossified.
This is seen to be the case on the left side of our figs. 12 and 13, in which (Stage T)
the rest of the carpus is still cartilaginous (cf. previous statement on p. 60). Bayer
believed that the 5th carpale is to be sought in the cartilaginous head of the related
metacarpal (op. cit. p. 241) ; but in this he was mistaken, as pointed out by Baur
in that it is always present and distinct, though small (PL VI. figs. 11 to 14).

We have no variations or other matters to record concerning the phalanges of the
fore limb.

The Tarsus. — Giinther describes two proximal and two distal elements, and is doubtful
about a fifth — the fifth tarsal. He alludes without name to the " meniscus " of Born,
which we figure (PL VI. fig. 18, mn.). Osawa describes one proximal element, the
" proximal tarsale," and four distal — five in all. He regards the meniscus (p. 504) as the
first tarsale, while Born associates it in the Lacertilia4 with the centrale. Both are
in error, for whereas the meniscus does not appear till Stage S (when all the tarsal
elements have been formed), the first tarsal arises at Q (fig. 16) as a separate element
(I.), and at Stage R, when fully chondrified, unites with its metatarsal. The meniscus is
thus proved to be an accessory element (cf. Born, Morph. Jahrb. Bd. vi. 1880, p. 67).

1 Howes & Ridewood : P. Z. S. 1888, p. 177.

2 Wiedersheim, R. : Morph. Jahrb. Bd. vi. 1880, p. 581.

3 Briihl, C. B. : Zootomie aller Thier Kl., Wien 1880, pis. 31-34 and 53 & 54.

4 Born, G. : Morph. Jahrb. Bd. ii. 1876, p. 25.

62 PKOK G. B. HOWES AND ME. H. H. S WIJSIS1 EETOJN' ON THE

Born, as is well known, gave it as characteristic of the Lacertilia that tarsalia 1
and 2 were probably united with the corresponding metatarsals ; and in this lie has
been followed by Bayer (p. 24o), who claims a phylogenetic union for these ! Osawa
rightly figures the second tarsale of Sphenodon as distinct ; and we find that from
Stage Q (fig. 15) to the adult state this is present as an independent element (as in
fig. 18) which becomes extensively ossified.

Perrin asserts (95. pp. 44 & 97) that five separate distal tarsalia are present,
and his figure 9 may illustrate but does not adorn his text! We are at a loss to
understand what he has figured ; but one thing certain is that in ascribing three
phalanges to the fifth digit he is in agreement with Bayer, who is inclined to regard
the hooked bone, which by its angulated head articulates with the outer face of the
fourth tarsale, as the fifth of that series. As a salient objection to regarding this as a
metatarsal he seeks to show that on the Giintherian determination Sphenodon would
be an exception to the rule among Lizards in possessing more than three phalanges
to the fifth digit ; but it does not occur to him that this statement is tantamount to
admitting that the angulated bone is in most Lizards a metatarsal, and that it thereby
nullifies his argument. Dismissing for the moment the facts of development, the
discovery by us that a specimen preserved in the R. College of Surgeons Museum is
possessed of three phalanges on the outermost digit of one hind limb, and four on the
other, dispenses with the necessity for further discussion of this point, except to remark
that among the Chelonia, Pleurodira (Emydura) for example, we meet with a quadri-
phalangeate fifth toe. The matter is clearly one lying within the range of individual
variation.

Developmentally, this bone, angulated from the first period of its differentiation
(Stage Q, PI. VI. fig. 16, v.), ossifies at R (PL VI. fig. 17), at the same time and in
the same manner as the other metatarsals ; and we have already pointed out that the
tarsal elements do not ossify until T, when the metatarsals are formed. And were
further proof needed of its metatarsal homology, it is forthcoming in the totally
different manner of ossification of the carpus and tarsus and the metacarpals, meta-
tarsals, and phalanges — the former ossifying endosteally, the latter ectosteally.

There is no trace in Sphenodon of tarsale 5 actual or potential, and no evidence
developmentally for the belief of Baur that it is incorporated in the fourth tarsale
(Zool. Anz. Bd. ix. p. 189) 1. It seems to have vanished even from the ontogenetic
record.

Concerning the proximal tarsal series, Osawa describes one confluent element; and
Giinther evidently had to deal with a specimen in which they were just uniting, for
the " suture " to which he refers as " scarcely visible " is recognizable, as in our PI. VI.

1 We are disposed to believe, with Forsyth Major (Trans. Linn. Soc., ZooJ. vol. vii. 1890, p. 510), that the
compound nature of the " cuboid " is seriously open to doubt.

DEVELOPMENT OF THE SKELETON OF THE TUATAKA. 63

fig. 18, in all but old individuals. Bayer, finding the prseaxial moiety of the " astra-
galus " cartilaginous, regarded it as the tibiale, and the whole " astragalus " as con-
sisting of the centrale l and the intermedium, the " calcaneum " being to him the
fibulare (op. dt. p. 243). Perrin, going further, names the " astragalus " (op. cit.
p. 44) the " tibio-centro-intermediare."

Development at Stage Q shows (PI. VI. fig. 16) that at the chondrification period the
" astragalus " and " calcaneum " are independently chondrified, and a feeble ypsiloid
differentiation (accurately indicated in the fig.) may be observed at what would be
the apposition lines of the tibiale (£.), centrale (tc.), and intermediare (?'.), were they
distinct. In an earlier embryo of the same stage (fig. 15) we found the inter-
mediare -(i.) and fibulare (/.) chondrified and separated by a foramen apparently
homologous with that known as the f. arteria perforans mesopodii (/$.), the
centrale (tc.) and tibiale (t.) being procartilaginous, although in close apposition with
the intermediare and with each other. Bayer and Perrin had correctly surmised!

7. THE DENTITION.

The detailed study of the tooth-genesis does not fall within the scope of our work,
but we have one or two interesting anatomical facts to record.

Firstly, as to the vomerine teeth. No trace of them in a calcified form is forth-
coming up to Stage T, the oldest we have examined. We can add nothing to what is
recorded in the latest account given by Siebenrock2. It maybe that we have not
happened to deal with embryos in which they were developing, or, perhaps, that these
clearly vestigial organs attain their full development late.

Baur would seem to be wrong in the surmise (96 b. p. 437) that they exist in
young specimens and disappear in old age 3.

The Incisors. — These have been correctly shown by Dendy (99a. p. 77) to be repre-
sented in the young stage by three pairs of " distinct pointed conical teeth " above and
below, and not by two as believed by Giinther (67. p. 602) and Baur (p. 436). It is
worth remarking, however, that Knox had already recorded the supposed existence of
three pairs in the upper jaw (69. p. 18), and Newman in the lower (77. p. 234), the
former stating that they were confluent at their bases. This is the case at our Stage T

1 Baur's passing remark (Zool. Auz. Bd. ix. p. 189) that he found this represented by a piece of cartilage
which was " eingekeilt " is suggestive of begging the question.

2 Siebenrock, F. : Transl. cit. p. 309.

3 Further search is necessary to ascertain how far the vomerine teeth are or are not represented during
ontogeny, and a former pupil of mine, Mr. H. Spencer Harrison, has undertaken to immediately work out this and
other problems connected with the dentition of Sphenodon as the subject of a special communication to appear
in the Qu. Journ. Microscp. Science. — G. B. H.

64

PEOE. G. B. HOWES AND ME. H. H. SWINNERTON ON THE

(PL II. fig. 15), the outer tooth of each set being somewhat the larger of the three. At
Stage S (fig. 14) all are seen to be free, and the outer still large. Beyond the mere
inference of fusion, Dendy does not state the method by which he presumes these
pointed incisors to be converted into the tusks of the adult. As a rule each of the
upper tusks, when fully formed, is doubly pointed (or, as remarked by Giinther,
" notched") (cf. text-fig. 15), there being a smaller internal cone, and a larger external
one somewhat backwardly curved (text-fig. 16). In the lower jaw there are three cones
(text-fig. 16), a larger external and two smaller internal, the three teeth which are

Fig. 17.

Fig. 15.

Fig. 16.

Fig. 18.

Illustrations of the dentition of Sphenodon,

Fig. 15. Incisors, front aspect, old individual. Fig. 16. The same, younger individual, little worn. Both
nat. size. Fig. 17. Enlarged sketch of upper incisors of fig. 16, x 6. Fig. 18. Complete adult dentition :
nat. size, i, incisors ; t.a., cheek-teeth, alternating series ; t.u, cheek-teeth, structurally uniform series.

present having united with the mandible. That portion of the dentary element which
bears them becomes, with them, clothed in an enamel-like substance, which justifies
Giinther's remark (67. p. 602) that the alveolar edge of the mandible is polished.
Tomes l regards this substance as true bone.

In the embryonic upper jaw the middle incisor present early ceases to elongate
(cf. PI. II. fig. 15, t.m.) and at Stage T it becomes loose. The reason of this is
evident from the fact that longitudinal section (PI. II. fig. 16) shows it to be confluent

1 Tomes, C. : Dental Anatomy, ed. 4, 1894, p. 253.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 65

only externally with the premaxilla (p.x.) and not by its whole base, as is the case with
the other teeth. We suspect that this tooth is early shed, but unfortunately our material
does not embrace a specimen proving the point.

A possible source of error must not be here overlooked, in the fact that in the adult
there may be present a small pointed cusp (text-fig. 16, *) between the two upper
incisors, which at first suggests a persistent middle tooth. When, however, a tooth
thus constituted is examined under a lens, it is found that the minute cusp has a
counterpart (text-fig. 17) on the inner face of the inner tooth, and that, like this, it
is but the product of its base. And since the teeth, when first formed, are simple
cones, these lesser cusps must be due to secondary complication.

The palatal and maxillary teeth vary very greatly in appearance at different stages in
development and periods of life. One conspicuous feature which has not been recorded
is that at Stage S the maxillary teeth number 11 and the palatal 4-5 (cf. PI. IV.
figs. 4-6). These first-formed cheek-teeth usually alternate, a larger and a smaller
occurring in succession, and not infrequently they may be arranged in recurring sets of
three, a larger and two smaller to each. At Stage T the same numerical condition
obtains (allowing for individual variation, most marked for the palatine teeth), but
under the growth-processes at work the larger teeth have now increased in size.
From this period onwards the numerical increase in the teeth as a whole is due
to superaddition from behind forwards, and most of the teeth thus formed (t.u., text-
fig. 18) are uniform in size. Numerically they average about 6 on either side, and
for the palate about 4-5, giving a total number of about 16-17 maxillary teeth and
9-11 palatal1.

Passing to the mandibular series, we note an essential similarity to the maxillary, in
the arrangement of the teeth first formed. At Stage S (PI. IV. fig. 4) there are 11
alternating teeth as in the maxilla 2, but no others. On the assumption of Stage T
the teeth of the alternating series, unlike those of the upper jaw, apparently cease to
grow. Wear and tear supervening, and the development of the structurally uniform
teeth continuing apace, these (£.«., text-fig. 18) become predominant; and hence the
condition herein delineated, which is of short duration, as the teeth of the alternating
series (£.#.), now insignificant, become rapidly worn down.

Baur has described (95b. p. 436) a Sphenodon skull, 25 mm. in length, having two

1 The number of teeth recorded by different observers ranges for the maxillary from 6 (Knox) to 17 (Colenso),
and for the palatal from 5 (Knox) to 13 (Newman) ; for the mandibular from 13 (Colenso) to 19 (Giinther).
In the absence of detailed description and knowledge of degree of wear and tear, it is not possible to make
use of these figures.

2 This alternation is a striking feature. Among the Monitors it is often the case that in the fresh state the
cheek-teeth are similarly, though more markedly, alternate, the elongated teeth being fixed to thejaws alternately
with small ones which are freely displaceable at their bases. Can it be that there is a common determining
cause at work here ?

VOL. xvi. — PART i. No. 9. — February, 1901. K

CO PROF. G. B. HOWES AND ME. H. II. SWJNNEBTON ON THE

upper incisors and an eminence which he surmised suggested a third, and he remarked 1
that each of the inner incisors on either side had a very small successional tooth, which
he believed was never further developed. On examination of a series of sections of a
19 mm. example we find a similar tooth (PL II. fig. 16, td.) but behind the middle
tooth of the three that are present (t.m.), Baur's specimen appears to have suffered the
loss of the middle incisor, and to justify our conclusion that this is shed. And while
we are not sure whether our successional incisor is the same as his, or whether he and
we were dealing with members of a series which may be formed, his conclusion that
the tooth is never functional receives support from what we have observed 2.

In describing the cheek-teeth, Baur attributed to the fifth maxillary and the first
mandibular a successional tooth. This we have not been able to confirm. Passing to
the structurally uniform series (#.w.), we find these to mostly arise lineally. PL II.
fig. 17, in its outlined portion, is a reconstructional drawing from horizontal microscopic
sections at this period. The teeth drawn in outline (£/.) are fused to the maxilla and
palatine, as indicated. Those drawn in colour, together with the shaded portion of the
drawing, are from individual sections, the teeth which appear to represent the structurally
uniform series (coloured yellow) being delineated in the position in which they arise.

The teeth of the adult Sphenodon have been defined by Giinther (67. p. 601) as
" acrodout in the strictest meaning of the term." Boulenger (Brit. Mus. Cat. cit. p. 1)
regards them as " not implanted in alveoli " ; while Tomes, ignoring the incisors, has
written of the post-incisors that they are " acrodont," and he further suggests that
the glistening investment of the alveolar edges, which Giinther originally described and

showed to " perform the functions of teeth when these are ground down

in advanced age," is true bone. Baur refers (p. 437) to "alveoli" in his 25 mm.
specimens, but gives insufficient details.

If we may infer from the foregoing that Tomes, ignoring the incisors, was suspicious
of their being in the adult non-acrodont, we have to confirm his doubts. Thanks to
Mr. M. F. Woodward, we have been enabled to examine a series of microscopic sections
of both upper and lower incisors of the adult in situ ; and concerning the upper
there is evidence of surrounding bone — not as the result of a truly thecodont condition,
but of an apparent secondary overgrowth subsequent to the union between tooth and
jaw. Examination of PL II. fig. 18 shows in the case of a maudibular tooth that the
truly acrodont condition is assumed at Stage S ; and at Stage T the incisors show in
our sections a condition intermediate between this and that above described. Further
investigation of this topic is beyond the limits of our pledge to Professor Dendy,
but, pending detailed study of the tooth-genesis, we would distinguish the condition
occurring in at least the incisors as hyper acrodont.

1 As usual, he writes (line 8) " iimere " for " aussere/'

2 We have no material to show whether the embryo teeth which we herein describe do or do not become
later replaced.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 07

8. SUMMARY AND CONCLUSIONS.

Summary. — The following is a summary of the more important conclusions embodied
in Sections 5 to 7 of the present Memoir: —

1. That two kinds of intercentra are formed : primary intercentra, originally paired
and mostly preformed in cartilage ; and secondary intercentra, which replace those
throughout certain regions of the body, and are mostly median and arise by direct
ossification outside the vertebral column.

2. That the primary intercentra persist in the caudal region to form the chevrons,
and anteriorly for the first few segments, and that the secondary intercentra coexist
with them in the anterior caudal region alone.

3. That the hyaline cartilages which go to form the vertebral centra are paired in
origin.

4. That an intravertebral chordal plate is formed by transformation of the sub-
stance of the chorda within each vertebral centrum, and that the plate is continuous
with the chordal epithelium, which becomes converted into a tunica lying inside the
chordal sheath.

5. That during the final differentiation of the vertebrae the chorda becomes
metamerically segmented, and that there appears in each segment a central chordal
vesicle at the point of greatest flexibility.

6. That in that part of the caudal region modified for " splitting " there are formed,
by similar differentiation to that which gives rise to the intravertebral chordal plates,
a series of intervertebral plates, and that the intravertebral plates play an important
part in the casting of the tail, and may be possibly the seat of regenerative activity in
the formation of the renewed caudal axis.

7. That the ribs arise in procartilage, in relation to the primary intercentra, with
which they are the first differentiated skeletal elements ; and that they are differen-
tiated obliquely, the capitular portions in direct relationship with the intcrvertebrai
regions and the intercentra — the tubercular with the areas of differentiation of the
vertebral centra and arches of the vertebrae behind. That these relationships are lost
during later development for all but the third and fourth praesternal segments.

8. That the uncinates are separate in origin, with the possible exception of those of
the penultimate and antepenultimate praesternal ribs.

9. That the cartilaginous brain-case is a product of the union of distinct ethmo-
and orbito-sphenoidal plates, and that its bars and fenestrse are all attributable to
direct processes of growth — i. <?., that it is not a fenestrated cranium of the cartilaginous
fish type.

10. That the hypoglossus nerve-bearing region bears five pairs of nerves with four
pairs of foramina, and that during development these become reduced to two each.

11. That the trabeculae cranii play no part in the direct formation of the lateral
cranial wall, and that they represent a pair of prseoral visceral arches.

K2

f)8 PROF. G. B HOWES AND MR. H. H. SWINNERTON ON THE

12. That the epipterygoid bone is the product of ossification of the ascending process
of the pterygo-quadrate cartilage, and that the special feature of the quadrate bone is
an extension of its ossific head into the latter for approximation to the epipterygoid.

13. That the columella auris and stapedial processes are alike direct derivatives of
the hyoid arch, with which they are continuous at all stages, and that structural
complication is due to overgrowth of the same.

14. That the upper end of the hyoid cornu is attached to the quadrate only, and
that there is a fleeting "jointing " of the former throughout its course.

15. That in the meeting of the pterygoids and vomers, the latter play a part leading
up to the conditions occurring in the Chelonia and Plesiosauria.

16. The cartilaginous pterygo-quadrate is in its detailed characters most nearly
comparable to that of the Apodal Batrachian Ichthyophis.

17. That each of the three segments of each of the "abdominal ribs'' (gastralia)
arises by union of a number of calcifications, and that the median segment may be paired.
That the "plastron " is present in a degenerating form.

18. That in their early differentiation the membrane-bones of the head and face are
predominantly circumorbital in position.

19. That there is no supratemporal bone recognizable at any stage as a distinct
element.

20. That the hip-girdle in its development is of a lower type than the Lacertilian,
and that there are two types of pelvis present in adults.

21. That the fifth tarsale has no existence in ontogeny, and that the basal element
of the fifth digit of the hind limb is a metatarsal.

22. That there are apparently three centralia carpi represented during development,
and that a centrale is incorporated in the " astragalus."

23. That calcified vomerine teeth are not present during encapsulation within the
egg-shell.

24. That of the three pairs of upper incisors, the middle certainly disappear
and the inner may become tricuspid.

25. That the cheek-teeth appear to consist of two series — an early developed
alternating set, and a later posterior and structurally uniform set.

16. That there arise within the occipital region and the individual vertebral segments
sustentacular ligaments, for support of the medulla and spinal cord.

Conclusions. — Paragraphs 16, 17, 20, and 22 of our Summary add fresh testimony to
the belief in the Batrachian affinities of the living Sphenodon, while paragraph 15
strengthens the demonstration of its Chelonian resemblances and extends these to the
Plesiosauria. Paragraph 17 proves the creature to be a highly modified representative
of its Suborder, but at the same time to pass through a developmental phase realistic
of the lower Suborder of the Khynchocephalia, as now classified ; and the same is
true of paragraph 24, by comparison with the Proterosauria (especially Palaeohatteria).
Of the supposed Agamid affinities we have written enough (antea, pp. 4, 22, 46).

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 69

Sphenodon, judged from our standpoint, must be regarded as the surviving represen-
tative of that group of animals ancestral to all the living Sauropsida, and to at least the
Dinosauria, Pterodactyla, and Ichthyosauria, of the past — if not of the Mosasauria and
Dolichosauria also, and unquestionably intimately related to the Anomodontia. As
concerning the unmistakable Stegocephalian affinities of the Rhynchocephalia, it
becomes necessary to enquire more closely than hitherto into the sum of those
characters which constitute a Batrachian a Batrachian — a Rhynchocephalian a Reptile

Attention was in 1892 called by one of us (Journ. Anat. & Phys. vol. xxvi. p. 402)
to the fact that whereas no Batrachian living or extinct was then known to possess
more than two phalanges on each of its two innermost digits — the formula for the
Class being 22342, that of the Sauropsida being 23454 (or something minus that by
reduction), it would seem impossible to derive the Sauropsidan condition from that
of any known Batrachian, not excluding the Stegocephalia. Recent investigation,
however, has modified this aspect of the question. Firstly, there has been discovered
an undoubted Stegocephalian ally having on the second digit of its fore limb three
phalanges and on the third four, and for its hind limb the formula 2 3 4 4 3 1. And,
again, in Credner's Sclerocephaliis of the Permian, which, its massive quadrate notwith-
standing, he places among the Stegocephalia2, there existed a combination of the lowest
Stegocephalian type, amounting, in the structure of its dermal skeleton, almost to the
" Ganoidan," with a limb-skeleton (if the remains are rightly associated) of a veritable
lizard — the phalangeal formula being 2 3 4 5 4 for the hind limb, and that clawed 3.

Again, as to the sternum, it has also been pointed out by one of us (' Nature,'
vol. xlviii. p. 269, 1891) that a sharp distinction may be drawn between the coraco-sternum
of the Batrachia (an archisternum] and the costal sternum of the Amniota (a neosternum],
the existence of which in any Batrachian or Stegocephalian has not been proved.

And as to the skull, the now well-known fact that whereas in the Amniota the
hypoglossal nerve-bearing region, truncal in origin, is incorporated in the occiput, in
the Batrachia these nerves are postoccipital 4, once again opens the gap between the
Batrachia and Amniota — indeed, so markedly, that our ideas may be systematized by

1 Ceraterpeton galvani, A. S. Woodward, Geol. Mag. (dec. 4), vol. iv. p. 297 (1897).
- Credner, H. : Zeitschr. deutsch. geolog. Gesellsch. Bd. xiv. 1893, p. 639.

3 AVe are at a loss to understand the reason for the intercalation in the restored portions of the skeleton of
Pariasaurus in the British Museum of Natural History of a fourth phalanx to the second digit of the hind-
limh, especially as in the original description of the specimen it is the front-limb of which it is said (Phil.
Trans, vol. 183, B. p. 363) to be possible that one digit may have had four ! We fail to discover evidence of
more than three phalanges for any digit that is preserved.

4 Restricting the terms to the Terrestrial Verrebrata, we leave aside the question how far the vagus-bearing
portion of the skull may be truncal also, and that of the undoubted parallelism which exists between the
Amniota and certain Ichthyopsida, concerning the union of skull and vertebral column (cf. the masterly
Memoir by Furbringer, M. : Gegenbaur Festschrift, Leipzig, 1897).

70 PROF. G. B. HOWES AND MR. H. H. SW1NNERTON ON THE

applying to the former condition the term Arc/ticraniate1, and to the latter that of the
Syncraniate.

The characters of the occipital condyle and the presence of one, two, or, for the
matter of that, of three conclyles, no longer have the significance once attached to them
as criteria of affinity.

Judged from this point of view, the Rhynchocephalia may well be regarded as a
lowly group, ancestral to the Sauropsida as ordinarily defined, and intimately related
to the Anomodontia ; and while the latter, perhaps with or through the Pelycosauria of
Cope, on the one hand gave rise to the Mammalia, they were probably with the Rhyn-
chocephalia derived by diversity of modification from some common ancestral stock
which carries us towards a group which must have been either Batrachian Reptiles or
Reptilian Batrachians, as compared with forms extant — i. e.9 they either possessed a
coraco-sternum and an archicranium, or a costal-sternum and a syncranium, structural
combinations which go hand in hand. If they were of the latter type, the living
Batrachia must have suffered the loss of a costal-sternum and not a few of their
distinctive characters must be indicative of retrogression. The argument applies
equally to the quadrate and whether its representative in the living Batrachia is or is
not vestigial, and, as concerning the parasphenoid and pterygoids, the question arises
whether in these ancestral forms they did or did not reach the vomers.

On the other hand, it is possible that, in some manner yet to be discovered, the
ancestral series of Terrestrial Vertebrata may have combined the characters of the later
differentiated forms, as Gadow has surmised in his sagacious remark 2 that " the
Amphibia and Reptiles do not form a continuous line of development, but are two
divergent branches of a common stock of Palaeozoic Tetrapoda." If, with Credner, we
group together the Stegocephalia and " Proganosauria " as the " Eotetrapoda" 3, or with
Dawson and Baur4 associate a no less heterogeneous assemblage under the cognomen
" Microsauria," we but imply the conviction herein set forth.

Concerning the phalangeal problem, the discovery that certain living Chelonia are
hyperphalangeata5 ; that by Peters6' that in the Pleurodian Pelomedusa the numerical
reduction of the phalanges is in part due to fusion of more numerous elements during

1 Sewertzoff writes (Bull. Soc. Nat. Mosc. u. s. vol. ix. 1895, p. 180) : "Bei die Amphibien entspricht tier
Ganze Occipibalabschnitt einem ein/igen Segmente, dein einfachen Occipitalbogen, so dass die Amphibien in
dieser Hmsicht unter alien Cranioten, mit Ausnahmc der Petromyzonten, die einfachsten Zustand zeigen."
Intensely interesting in this association are the recent observations of Peter (op. cit. [antea, p. 50] pp. 590-
592), based on the discovery in Ichthyophis of a postvagal nerve, having, it would seem, an essential similarity
to the " spinal accessory " of the Amniota.

a Gadow, H. : Phil. Trans, vol. 187. 1896, p. 23.

3 Credner, H.: Allgem. Verstell. naturwiss. Abhandlg. Berlin, Hft. xv. 1891 (" Naturwiss. Wochenschr."),
pp. 1-52.

1 (?/. Baur, G. : Anat. Anz. Bd. xiv. 1897, p. 148, and Bd. xi. 1896, p. 657.

8 Of. Boulenger, G. A. : Brit. Mus. Cat. Chelonians, 1889, p. 240, espec. Chitra.

B Peters, W. : Reise nach Mossambique, Zool. iii. Berlin, 1882, p. 6.

DEVELOPMENT OF THE SKELETON OF THE TUATAHA. 71

ontogeny; the investigation of Kukenthal, which has brought to light the remarkable
fact l that the fourth and fifth digits of the Crocodilian fore limb are developmentally
hyperphalangeate — all testify to the great potentiality of the digital blastema 2, and do
away with the value of the mere numerical difference as a criterion of affinity.

The question thus resolves itself into this — are the Terrestrial Vertebrate the
descendants of the afore-defined Batrachian-Ileptilia or of Reptilian-Batrachia 1 The
problem for the immediate future lies in the study of the occiput, the sternal skeleton,
and the quadrate ; and, to our thinking, Sclerocephalus, with its multisegmented
and structurally simple " plastron," its " fanged " vomer, its elongated dentigerous
pterygoid 3, and its quadrate, points the way.

It is certain, but most unfortunate, that in its earliest forms, the sternum, known to
us only in its definitive conditions, was cartilaginous, and has been lost to us in the
palseontological record. The discovery by Osborn, however, of a cartilaginous sternum
in the fossil state 4, gives us hope. The decision must lie with the future.
Anatomist and palaeontologist must approach the question in the spirit of a combined
morphological brotherhood ; and its solution will mark an epoch in the progress of
the vertebrate morphology of the era of its discovery.

Addendum, Nov. 16, 1900.

Shortly after the proofs of this Memoir were revised for press, there reached us a recently
published paper on the organogeny of Sphenodon, by Professor H. Schauinsland, of Bremen
(Archv. Mikr. Anat. Bd. Ivi. pp. 447-867). Although it came to hand too late for comment in
our pages, we observe from its perusal that it is in places erroneous, and that we should have lost
nothing by its earlier appearance, since its author is insufficiently acquainted with the literature
of the subject, and apparently ignorant of the recent important papers by Deiidy, now more than
a year old.

LIST OF THE MORE IMPORTANT MEMOIRS DEALING WITH SPHENODON.

83a. ALBRECHT, P. Note sur la presence d'uu Rudiment de Proatlas sur un exemplaire de
Hatteria punctata. Bull. Mus. Belg. torn. ii. pp. 185-193. (First record of pro-atlas.)

83b. . Epiphyses osseuses sur les Apophyses epineuses des Vertebres d'un Reptile

(Hatteria punctata, Gray). Bruxelles, 1883. Pp. 1-6.

86a. BAUR, G. Die zwei Centralia im Carpus von Sphenodon (Hatteria) und die Wirbel von
Sphenodon und Gecko verticillatus, Laur. (G. verus, Gray) . Zoo/. Anz. Bd. ix. pp. 188-190.

1 Kukenthal, W. : Morphol. Jahrb. Bd. xix. 1893, p. 50.

2 In a manner akin to that of the passing "jointing'' of the hyoid cornu described in. the text (antea, p. 48).

3 It is unfortunate that its parasphenoid is unknown, but it must assuredly have possessed one, and that
probably dentigerous.

4 Osborn, H. F. : op. cit. antea, p. 14.

72 PROF. G. B. HOWES AND MR. H. H. 8WJNNERTON ON THE

86b. BAUR, G. Osteologische Notizen u'ber Reptilien. Zool. Anz. Bd. ix. pp. 685-690. (Cf.
Giinther, op. cit. p. 746, and Baur, G., ibid. Bd. x. pp. 120-121.)

86°. . Osteologische Notizen iiber Reptilien. Zool. Anz. Bd. ix. pp. 733-743.

86d. . The Ribs of Sphenodon (Hatteria). Amer. Natural, vol. xx. pp. 979-981.

87. . On the Morphology of Ribs. Amer. Natural, vol. xxi. pp. 942-945.

88. . Osteologische Notizen iiber Reptilien. Zool. Anz. Bd. xii. pp. 40-47. (Para-
sphenoid, epipterygoid, and alisphenoid.)

89. . Revision ineiner Mittheilungen im Zoologischen Anzeiger mit Nachtragen. ZooL

Anz. Bd. xii. pp. 238-243. (Quadratojugale and otic bones.)

91. — . The Lower Jaw of Sphenodon. Amer. Natural, vol. xxv. pp. 489-490.

95a. Ueber die Morphologic des Unterkiefers der Reptilien. Anat. Anz. Bd. xi.

pp. 410-115.
95b. . Das Gebiss von Sphenodon (Hatteria) mid einige Bemerkungeu iiber Prof. Rud.

Burckhardt's Arbeit iiber das Gebiss der Sauropsiden. Anat. Anz. Bd. xi. pp. 436-439.

84. BAYER, F. Ueber die Extremitiiten einer jungen Hatteria. Stzb. Akad. Wien, Bd. xc.

pp. 237-245.

87. BEMMELEN, J. F. Beitrage z. Kenntniss d. Halsgegend b. Reptilien. 1. Anat. Theil.

Bijdr. t. d. Nied. Dierkd. Ver. Amsterdam, 1887, pp. 102-146. (Contains an accurate

account of nerves, blood-vessels and glands of neck of Sphenodon.)
94. BERG, J. Zur Kenutniss der Briickeuechse. Zool. Garten, Bd. xxxv. pp. 102-105 and

pp. 146-150. (An admirable figure of Sphenodon.)
89. BOULENGER, G. A. Catalogue of the Chelonians, Rhynchocephalians, and Crocodiles in the

British Museum, 1889, pp. 1-3.
91. . On British Remains of Homoeosaurus, with Remarks on the Classification . of the

Rhynchocephalia. Proc. Zool. Soc. 1891, pp. 167-172.
93. . On some newly-described Jurassic and Cretaceous Lizards and Rhynchocephalians.

Ann. $ Mag. Nat. Hist. (ser. 6) vol. xi. pp. 204-210.

76. BULLER, W. L. Notes on the Tuatara Lizard (Sphenodon), with a Description of a supposed

new Species (S. giintheri). Trans. N. Zealand Inst. vol. ix. pp. 317-325.

77. . Notice of a new Variety of Tuatara Lizard (Sphenodon) from East Cape Island.

Trans. N. Zealand Inst. vol. x. pp. 220-221. (External characters of a live specimen
described, no name given.)

78. . Further Notes on the Habits of the Tuatara Lizard. Trans. N. Zealand Imt. vol. xi.

pp. 349-351. (Deals with individuals in captivity.)

98. BUSCH, C. H. Beitrage zur Kenntniss der Gaumenbildung bei den Reptilien. Zool.
Jahrb. (Anat. Abth.) Bd. xi. pp. 441-499.

85. COLENSO, W. Notes on the Bones of a Species of Sphenodon (S. diversum, Col.) apparently

distinct from the Species already known. Trans. N. Zealand Inst. vol. xviii. 1885,
pp. 118-123.

86. COPE, E. D. The Intel-centrum in Sphenodon. Amer. Natural, vol. xx. p. 175.

88. CORNET, J. Note sur le pretendu Pro-atlas des Mammiferes et de Hatteria punctata.

Bull. Ac. Belgique (se"r. 3), torn. xv. pp. 406-420.
98. DENDY, A. Summary of the principal Results obtained in a Study of the Development of

the Tuatara (Sphenodon punctatus). Proc. R. Soc. vol. Ixiii. pp. 440-443.
99a. • . Outlines of the Development of the Tuatara (Sphenodon punctatus). Quart. Jour n.

Micr. Sci> vol. xlii. pp. 1-87.

DEVELOPMENT OF THE SKELETON OF THE TUATARA. 73

99b. DENDY, A. On the Development of the Parietal Eye and adjacent Organs in Spheuodon.

Ibid. pp. 111-153.
99°. . The Life-History of Tuatara (Sphenodon punctatus). Trans. N. Zealand Inst.

vol. xxxi. pp. 249-255.

99. DENDY, A., and HOWES, G. B. The Hatching of Tuatara Eggs. Nature, vol. lix. p. 340.
84. DOLLO, L. Notes Erpetologiques. Zool. Anz. Bd. vii. pp. 547-548. (First description of

condylar foramina of humerus. More fully described with figures in Bull. Mus. Belg.

torn. iii. p. 151). (Cf. also Fiirbringer, Morph. Jahrb. Bd. xi. pp. 484-486.)

88. . Sur le Proatlas. Zool Jahrb. (Anat. Abth.} Bd. iii. pp. 433-416.

89. FRITSCH, A. Fauna der Gaskohle und der Kalksteine der Permformation Bohmens, Bd. ii.

Prag, 1889. (p. 58, parasphenoid ; p. 52, cervical vertebrae.) (A correction in Zool. Anz.
Bd. x. p. 115.)

88. GADOW, H. On the Modifications of the First and Second Visceral Arches, with especial
reference to the Homologues of the Auditory Ossicles. Phil. Trans, vol.. 179. pp. 451-
485.

96. . On the Evolution of the Vertebral Column of Amphibia and Amniota. Phil. Trans.

vol. 187, B. 1896, pp. 1-57.

98. . Zur Rettung von Hatteria. Anat. Anz. Bd. xv. pp. 41-43.

97. GOETTE, A. Ueber den Wirbelbau bei den Reptilien und eiuigen anderen Wirbelthiereu.

Zeitschr. wiss. Zool. Bd. Ixii. 1897, pp. 343-394.
31. GRAY, J. E. Note on a peculiar Structure in the Head of an Agama, Zool. Miscell. 1831,

p. 13. (Genus Sphenodon.)
42. . Descriptions of two hitherto unrecorded Species of Reptiles from New Zealand.

Zool. Miscell. 1842, p. 72.
69. . Sphenodon, Hatteria, and Rhynchocephalus. Ann. $ Mag. Nat. Hist. (ser. 4) vol. iii.

p. 167. (Gives history of three generic names.)
67. GUNTHER, A. Contribution to the Anatomy of Hatteria (Rhynchocephalus-, Owen). Phil.

Trans, vol. 167. pp. 595-629.

90. HOWES, G. B. Pro-atlas and Vomerine Teeth in Hatteria. Proc. Zool. Soc, 1890,

pp. 357-360.

69. HUXLEY, T. H. On the Representatives of the Malleus and the Incus of the Mammalia in
other Vertebrata. Proc. Zool. Soc. 1869, pp. 391-407.

98. KALLIUS, E. Ueber die Fovea centralis von Hatteria punctata. Anat. Anz. Bd. xiv. pp. 623-

624. (Reply by Osawa, ibid. Bd. xv. pp. 226-227.)
9.2. KLAATSCH, H. Zur Morphologic der Mesenterialbildungen am Darmkanal der Wirbelthiere.

Morphol. Jahrb. Bd. xviii. pp. 424-433. (Detailed description for Sphenodon.)
69. KNOX, F. J. On the Tuatara (Hatteria punctata, Gray), or Great Fringed Lizard of New

Zealand. Trans. N. Zealand Inst. vol. ii. pp. 17-20.
96. MAURER, F. Die ventrale Rumpf muskulatur einiger Reptilien. Festschrift zum siebenzigsten

Geburtstage von Carl Gegenbaur : Leipzig, 1896. Bd. i. pp. 183-256.
77. NEWMAN, A. K. Notes on the Physiology and Anatomy of the Tuatara (Sphenodon guntheri).

Trans. N. Zealand Inst. vol. x. pp. 222-239. (Includes description of habits.)
96a. OSAWA, G. Beitrag zur feineren Structur des Integumentes der Hatteria punctata. Archv.

mikr. Anat. Bd. xlvii. pp. 570-583.
VOL. xvi. — PART i. No. 10. — February, 1901.

74 DEVELOPMENT OF THE SKELETON OF THE TUATARA.

96b. OSAWA, G. Beitrage zur Lehre von den Eingeweiden der Hatteria punctata. Archv. mikr.

Anat, Bd. xlix. pp. 113-226.
98a. • — . Beitrage zur Anatomie der Hatteria punctata (Knochen, Muskeln, Nerven). Archv.

mikr. Anat. Bd. li. pp. 481-691.
98". . Beitrage zur Lehre von den Sinnesorgarien der Hatteria punctata. Archv. mikr.

Anat. Bd. lii. pp. 268-366.
98C. . Ueber die Stellung der Hatteria punctata in der Tierreihe. Verhandlg. Anat.

Gesellschaft, 1898 (Anat. Anz. Bd. xiv., Suppl.), pp. 100-106.
98d. . Erwiederung an Gadow auf den Aufsatz "Zur Rettung von Hatteria." Anat. Anz .

Bd. xv. pp. 289-291.

95. PERRIN, A. Recherches sur les Affinites zoologiques de THatteria punctata. Ann. Sci.

Nat. (ser. 7), Zool. torn. xx. pp. 33-102. (Mainly deals with hind limb.)
70. PETERS, H. W. Remarks on Exhibition of a Specimen of Sphenodon. Stzb. Ges. naturf.

Fr. Bwlin, 1870, p. 54.
74. . Ueber die Gehorknochelchen und ihr Verhaltniss zu dem ersten Zungenbeinbogen

bei Sphenodon punctatus. Monatsber. Ak. Wiss. Berlin, 1874, pp. 40-45.
81. REISCHEK, A. Notes on Zoological Researches made on the Chicken Islands, east coast

of the North Island, N.Z. Trans. N. Zealand Inst. vol. xiv. pp. 274-277. (Original

description of supposed commensal habit.)
90. ROSE, C. Beitrage zur vergleichenden Anatomie des Herzens der Wirbelthiere. Morphol.

Jahrb. Bd. xvi. pp. 27-96. (Deals with sinus venosus in detail.)

96. RUGE, G. Ueber das Peripherische Gebiet des Nervus facialis bei Wirbelthieren. Festschrift

zum siebenzigsten Geburstage von Carl Gegenbaur : Leipzig, 1896. Bd. iii. pp. 195-348.
98a. SCHAUINSLAND, H. Zur Entwickeluug von Hatteria. Stzb. Ak. Berlin, 1898, pp. 629-631.
(Preliminary account on general development, based on material obtained in Cook's

Island, Dec. 1896 to Jan. 1897.)
98". . Beitrage zur Biologic der Hatteria. Ibid. pp. 701-704. (Breeding-habits and

general development.)
98C. . Beitrage zur Biologic u. Entwickelung der Hatteria, nebst Bemerkungen u. d.

Entwickelung der Sauropsiden. Anat. Anz. Bd. xv. pp. 309-334.
93. SIEBENROCK, F. Zur Osteologie des Hatteria- Kopfes. Stzb. Akad. Wien, Bd. cii. Abth. i.

pp. 250-268. (English translation in Ann. $ Mag. Nat. Hist. (ser. 6) vol. xiii. pp. 297-

311.)
99. THILENIUS, G. Vorlaufiger Bericht tiber die Eiablage und erste Entwickeluug der Hatteria

punctata. Stzb. Akad. Berlin, Bd. xiv. pp. 247-256. (Apropos of investigations conducted

during 1898-1899 at Te Karewa, St. Stephen's Island, N.Z.)
90. THOMAS, A. P. W. Preliminary Note on the Development of the Tuatara (Sphenodon

punctatuin). Proc. R. Soc. London, vol. xlviii. pp. 152-156. (Records sexual differences

and gives a description of the egg.)
8.2. WARD. " The Hatteria (Sphenodon) punctatus/' Nat. Sci. Bull. vol. i. 1882, pp. 14-15.

(Mainly a popular account of an expedition to obtain the living animal.) (French

translation by Bonnier in Bull. Sci. Dep. Nord, torn. xix. pp. 89-97.)
93. WERNER, F. Beobachtungen an Sphenodon (Hatteria) punctatus. Zool. Garten, Bd. xxxiv.

pp. 335-339. (Observations on an adult in captivity.)

PLATE I.

76 DEVELOPMENT OF THE SKELETON OF THE TUATARA.

EXPLANATION OF THE PLATES1.

PLATE I

SPHENODON PUNCTATUS. — VERTEBRAL COLUMN AND RIBS.

a., arch of the atlas; a., body of atlas (odontoid peg) ; c.c., caudal canal; c.v., cartilaginous
vertebra; /./., fibrous tissue; h.a., accessory hypapophy sis; i.p., primary intercentrum ; i.p.', median
intercentrum ; i.p.", chevron-bone ; i.s., secondary intercentrum ; i.sg., interseptal segment ;
my., myelon (spinal cord); n.a., neural arch; nc.t notochord ; nc.e., chordal epithelium; nc.s.,
•chorda! sheath ; n.p., intravertebral chorda! plate ; n.p.', intervertebral chordal plate; n.sp., neural
«pine; oc.c., occipital condyle ; o.v., osseous vertebra; r.cd., caudal rib ; r.s., sacral rib ; r.t., trunk
rib; *./., splitting lamina; s.o., skeletogenous sheath; t..a., interarticular tissue; v.c., vesicula
centralis.

Fig. 1. Stage P. Vertebral Column : — Lateral longitudinal section at about the region of

vertebrae 6-8. X 50.

Fig. 2. Stage P. The same -. — Median longitudinal section through the region of fig. 1. x 50.
Fig. 3. Stage P. The same : — Transverse section through the intervertebral region of caudal

segments 2—3. x 40.

Fig. 4. Stage P. The same :— Section through a vertebral region — the 6th segment in front of

fig. 3. X 40.

Fig. 5. Stage Q. Vertebral Column : — Lateral longitudinal section in the region of vertebrae

20-23. x 40.

Fig. 6. Stage Q. The same : — Median longitudinal section through vertebrae 20-23. x 40.

Fig. 7. Stage Q. The same: — Longitudinal section (slightly oblique) through caudal vertebrae

3-6. x 40.

Fig. 8. Stage Q. The same : — Median longitudinal section through the basi-occipital and the

four anterior cervical vertebrae. x 40.

Fig. 9. StageS. Vertebral Column: — Longitudinal section through the basi-occipital and the

three anterior cervical vertebrae. X 25.

Fig. 10. Stage S. The same : — Median longitudinal section through vertebrae 13-15. x 25.

Fig. 11. Stage S. The same : — Transverse section through the intervertebral region 5-6. x 25.
Fig. 12. Stage S. The same : — Ventral aspect of the last presacral to the 9th caudal vertebrae

showing free caudal ribs. X 5.

Fig. 13. Stage T. Vertebral Column :— Median longitudinal section through vertebrae 7-10. X 18.
Fig. 14. Stage T. The same-.— Median longitudinal section through intercentrum 8-9 of fig. 13,

showing minute structure. x 50.

Fig. 15. Adult. Vertebral Column : — Median longitudinal section through vertebra 9-11. x 11.
Fig. 16. Adult. The same :— Ventral aspect of the 10th to the 20th vertebrae showing an abnormal

condition of the intercentra. | nat. size.

Fig. 17. Adult. The same :— Median longitudinal section at about the region of the 12th caudal

vertebra. v K

*"V C/ •

Fig. 18. Adult. The same :— Caudal vertebrae 7-12 from the left side. f nat. size.

Fig. 19. Adult. The same : — Transverse section through plane a-b of fig. 17. x 11.

Fig. 20. Adult. The same :— Caudal vertebra 11 from the left side. f nat. size.

Fig. 21. Adult. The same : — Caudal vertebra. £ nat. size.

1 In all the Plates, where colouring has been employed, blue indicates hyaline cartilage and yellow bone,
with the exception of PI. I. fig. 13.

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SPHENODON PUNCTATUS.
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PLATE II.

DEVELOPMENT OF THE SKELETON OF THE TUATABA.

PLATE II.

SPHEKODOX PUKCTATUS. — VEETEBRAL COLUMN A5D BIBS, GASTEALiA, A5D TEETH.

«., arch of atlas ; ab.f, abdominal rib, median portion ; ab.", abdominal rib, lateral portion ;
c.au., auditory capsule; d., dentary; e.o., exoccipital; g.t., gastralia tissue tracts; i.p.1, median
intercentrum ; ip*, chevron-bone; m., costo-cervical muscle; «.', ligament of costo-cervical
muscle ; mt., Meckel's cartilage ; «ur., maxilla ; my., myelon (spinal cord) ; *.', first spinal nerve ;
njcii., twelfth cranial nerve ; n.a., neural arch ; nc., notochord ; nc.e., chorda! epithelium ; ncj.,
chorda! sheath ; n.p., intravertebral chordal plate ; n*., neurocentral suture ; o.r.. osseous vertebra ;
p.a., pro-atlas ; px.y premaxilla ; r.c., cervical rib ; r.cd., caudal rib ; r*., sacral rib ; r./., trunk rib ;
/.a, interarticular tissue; txh., cheek-tooth; t.d., developing tooth; t.f., fully-formed tooth (fused
with bone) ; /.*., inner incisor ; /.*»., middle incisor ; t.o., outer incisor ; /./>., transpalatine ;
u.p.j nncinate process.

Fig. 1. StageS. Anterior cervical vertebra : — The first five vertebrae showing anterior cervical

ribs, lateral aspect. x 8.

Fig. 2. Stage T. The game : — The first 5-6 vertebrae showing osseous and so-called ligamentous

cervical ribs from left side, ventro-lateral aspect. x 4.

Fig. 3. Stage S. The "Pro-Atlas" : — Lateral longitudinal section, including the exoccipital.

x 20.

Fig. 4. Stage S. The Ribs : — Transverse section of last presacral vertebral segment. x 20.

Fig. 5. Stage S. The game : — Transverse section of the second sacral vertebral segment. x 20.
Fig. 6. Staff e S. The same : — Transverse section of the fourth caudal vertebral segment, x 20.
Fig. 7. Stage R. Uncinate process : — Section through a poststernal rib showing development of

nncinate process. x 25.

Fig. 8. Stage 8. Abdominal ribs : — Ventral aspect of ribs 3-5. x 8.

Fig. 9. Stage S. The game : — Ventral aspect of ribs 16-18 of right side. X 1 1.

Fig. 10. Stage T. The game : — Ventral aspect of ribs 7-16 showing irregular union of parts, x 2.
Fig. 11. Stage R. Notochordal plate : — Transverse section showing first origin. x 40.

Fig. 12. Stage S. The same : — Transverse section at full formation. x 25.

Fig. 13. Stage S. Chevron-bones : — Transverse section showing attachment to fourth caudal

vertebra. x 25.

Fig. 14. StageS. Incisor teeth : — Front aspect. X 5.

Fig. 15. Stage T. The same : — Front aspect. X 4.

Fig. 16. Stage T. The same : — Median longitudinal section through second upper incisor and

associated parts. x 23.

Fig. 17. Stage T. Maxillo-palatine teeth : — Combined drawing — the teeth already confluent with

the bone being indicated in outline, the developing teeth in colour. x 13.

Fig. 18. Stage S. Cheek-tooth : — Transverse section, including dentary and MeckeFs cartilage.

x 20.

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BPHENODON PUNCTATUS.
Vertebral Colixinn & Ribs, (xastralm & Teeth.

PLATE III.

SO DEVELOPMENT OF THE SKELETON Of THE Tl'ATARA.

PLATE III.

SPHE50DON PUlfCTATCS. — DEVELOPING SKULL, EARLIER STAGES-

The figures on this Plate are of wax models reconstructed from microscopic sections,
the skeletal parts being alone represented. The fenestrae and interspaces in the
chondrocranium are for the most part occupied by membrane (not indicated), except
in so far as they transmit nerves and blood-vessels (cf. PL IV. fig. 10).

«»., angular; ar., articular; A.*.', baaipterygoid process; c.', anterior semicircular canal;
.j auditory capsule ; c.r., coronoid ; d., dentary ; e.c., extrastapedial cartilage ; CM., external
; e.o., exoccipital; epg~, epipterygoid ; e*., ethmosphenoidal plate; ex., extranasal; ex.1-*,
extranasal processes ; /. i.-xii., foramina for exit of cranial nerves ; fjm^ foramen for ophthalmic
branch of the carotid; f.e., ethmoidal foramen; /.i., interorbital fenestra; /./"., foramen for jugular
rein; /.»., foramen magnum ; /.»., lateral cranial fenestra; fr.t frontal; k.t hyoid; k.'} anterior
cornu of the hyoid ; A.*, posterior cornu of the hyoid ; t ji., internal nares ; j^ jugal ; mk., Meckel's
cartilage; nur., maxilla ; nur/, maxillary process; n.a.p., alinasal process ; »r ., notochord ; a. c^ nasal
capsule; ».c/, supranasal process; n.e.*, prenasal process; »./.', nasal fenestra; n.paj)., naso-
palatine process; n.p.p., naso-premaxillary process; «*., nasal; n.r.p., inferior naso-romerine
process ; oc.c.. occipital condyle ; as., otosphenoidal plate ; a*.1-5, otosphenoidal processes;
p.t parietal ; pa., palatine ; par., parachordal ; />./., prefrontal ; py., pterygoid ; py.', pter _
process ; p.o.y postorhital ; po.f., postf rental ; p.p., parotic process ; p.y-, pteiygo-quadrate ;
pt.y presphenoidal cartilage ; p*.t parasphenoid ; px.t premaxilla ; py'. pituitary foramen ;
q.. quadrate; 9.', otic process of quadrate; q.j.. quadrato-jugal ; SM., supra-angular: #*., snhnasal;
* A, interorhital septum ; s.mje., septo-maxillary ; *.o/, supraocciphal cartilage ; 4$p., splenial ;
»y., sqnamosal ; tq.", posterior process of sqnamosal ; gM.. snprastapedial cartilage ; */., stapes ;
tf., transpalatine ; tr.} trabecula ; ro., Tomer.

Pig. 1 *. SJafft P. Dtrtltrp'mg chondrocrawiiun : — Left lateral aspect. The arrow indicates the

direction of the longitudinal axis of the embryo as it lay coiled.

Fig. 2 1. Stage P. The tame : — Ethmoidal, trabecular, and sphenoidal regions, dorsal aspect.

Fig. 3 \ Stage P. Tkt same : — Parachordal and auditory regions, dorsal aspect.

Fig. 4. Stage Q. Developing cko»drocraitimm : — Lateral aspect.

Fig. 5. Stage Q. Developing skmU : — Lateral aspect. x 8.

Fig. 6. Stage Q. Developing ckomdrocraminm :— Ventral aspect.

Fig. 7. Stage Q. The **me .-—Dorsal aspect, x 8.

Fig. 8. Siage R. Developing ckondrocra*i*m : — Lateral aspect.

Kg. 9. Stage R. Developing ***# :— Posterior aspect. x 8.

Fig. 10. Stage R. Tke tame :— Lateral aspect.

Fig. 11. Stage R. Tke tame :— Dorsal aspect. x 8.

Fig. 12. Stage R. Tke smme :— Ventral aspect. x 8.

1 In these figures the uncoloured areas represent pro-cntflage.

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SPHENODON PUNCTATUS.
.Developing skull, e curlier stages.

PLATE IV.

VOL. xvi. — PART i. No. 11. — February, 1901. M

82 DEVELOPMENT OF THE SKELETON OF THE THAT ABA.

PLATE IV.

SPHENODON PUNCTATUS. — DEVELOPING SKULL, LATER STAGES.

an., angular ; «r., articular ; b.o., basi-occipital ; b.s., basisphenoid ; b.sJ, basipterygoid
process ; c', anterior semicircular canal ; c.", posterior semicircular canal ; cr., coronoid ;
d., dentary ; e.c., extrastapedial cartilage ; e.n., external nares ; e.o., exoccipital ; e.p.g., epipterygoid ;
e.s., ethmosphenoidal plate; ex., extranasal; ex.l-ez.5, extranasal processes; f.i.-xii., foramina for
exit of cranial nerves /., fenestra in the suprastapedial cartilage ; f.e., ethmoidal foramen ;
/.i., interorbital fenestra ;/.;'., foramen for jugular vein; f.n., fenestra in the anterior wall of the
brain-case; f.p., parietal foramen; jr., frontal; h.' , anterior cornu of the hyoid; i.n., internal
nares; j., jugal; l.d., lachrymal duct; ink., Mocker's cartilage; mp., meniscus pterygoideus ;
mx., maxilla ; mx.', maxillary process ; n. v., vi., cranial nerves ; n.c., nasal capsule ; n.c.' ' , supra-
nasal process ; n.c.", prenasal process; nf.'} nf.", nasal fenestrse; ns., nasal; oc.c., occipital condyle;
op., opisthotic; o.s., otosphenoidal plate ; o.s.}~', otosphenoidal processes ; p., parietal ; pa., palatine ;
p.f.y prefrontal ; p.g., pterygoid ; p.g.', pterygoid process ; p.o., postorbital ; po.f., postfrontal ; p.p.,
parotic process ; pro., prootic ; ps., presphenoidal cartilage ; p.s., parasphenoid ; px., premaxilla ;
py., pituitary body ; q., quadrate; q.r, otic process of quadrate; q.j., quad rato-ju gal ; s.a., supra-
angular; sb., subnasal ; s.i., interorbital septum; s.mx., septo-maxillary ; s.o.} supra-occipital;
s.o.', supra-occipital cartilage; sp., splenial ; sg., squamosal ; sq.' , anterior process of squamosal;
sq.", posterior process of squamosal: s.st., suprastapedial cartilage; st., stapes; t.p., trans-
palatine ; vo., vomer.

Fig. 1 . Stage R-S. The head : — Transverse section through epipterygoid region (7-8 of fig. 4) .

X 6.
Fig. 2. Stage R-S. The same : — Combined figure of two transverse sections through the nasal

region (a-/3 of fig. 4), the left half several sections in front of the right, x 15.
Fig. 3. Stage R-S. The same : — Transverse sections showing detailed relations of pterygoid and

basisphenoid (seven sections in front of fig. 1). x 18.

Fig. 4. Stage S. Developing skull : — Lateral aspect. X 5.

Fig. 5. Stage S. The same : — Dorsal aspect. X 5.

Fig. 6. Stage S. The same : — Ventral aspect. x 5.

Fig. 7. StageS. The same: — Posterior aspect. x 5.

Fig. 8. Stage T. Developing skull : — Dorsal aspect. x 3.

Fig. 9. Stage T. The same : — Posterior aspect. X 3.

Fig. 10. Stage T. The chondrocranium : — With endostoses and the parasphenoid ; as seen after

removal of the mandibular skeletal arch. Left lateral aspect. x 3.

Fig, 11. Stage T. The left pterygo-quadrate arch and squamosal : — Lateral aspect. x 5.

V^.XVI.

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SPHENODO"N PUNCTATUS.
Developing skull, later stages.

PLATE V.

84 DEVELOPMENT OF THE SKELETON OF THE TUATARA.

PLATE V.

SPHENODON PUNCTATUS. — THE QUADRATE, HTOID, AND COLUMELLA AURIS.

an., angular; b., boundary between stapes and extrastapedial cartilage; b.a., branchial arch;
b.c., branchial cleft ; c.1", horizontal semicircular canal ; ca.} carotid artery ; ca.r, branch of carotid
artery; c.au., auditory capsule ; e.c., extrastapedial cartilage; eu., eustachian recess; fe., fenestra
in suprastapedial cartilage ; h.1, anterior cornu of the hyoid ; j.v., jugular vein ; mk.} Meckel's
cartilage; mt., mouth; n. v.-xi., cranial nerves; n.vii.', branch of chorda tympani; ph., pharynx;
p-p., parotic process; pq., pterygoquadrate ; q., quadrate; q.'t otic process of quadrate; s.a., supra-
angular ; sg.', anterior process of squamosal ; sq.", posterior process of squamosal ; s.st., supra-
stapedial cartilage ; st., columella (stapes) ; st.', boundary between columella and extrastapedial
cartilage.

Figs. 1—5. Stage P. A series of sections, in order from within outwards, showing the primary
relationships of the columella auris to the hyoid and quadrate. X 40.

Fig. 1. Represents the most internal section No. 1.

Fig. 2. Represents section No. 6.

Fig. 3. „ „ No. 8.

Fig. 4. „ „ No. 19.

Fig. 5. „ „ No. 27.

Fig. 6-11. Staff e Q. A similar series to the above. X 25.

Fig. 6. Represents the most internal section No. 1.

Fig. 7. Represents section No. 11.

Fig. 8. „ „ No. 26.

Fig. 9. „ „ No. 36.

Fig. 10. „ „ No. 46.

Fig. 11. „ „ No. 57.

Fig. 12. Stage R. Transverse section of auditory region passing through quadrate and columella

auris. x 25.

Figs. 13-14. Stage S. Sections, in the same order as figs. 1-5, showing the relation of the

suprastapedial cartilage to the quadrate. x 20.

Fig. 13. Represents the more internal section No. 1.

Fig. 14. Represents section No. 16.

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Ml\ Parker UU.

Geo W«rt *. Sons

SPHENODON PUNCTATUS.
The QuLcccLra,te, Hyoid, <5c Columella. a-uris

PLATE VI.

VOL. xvi. — PART i. No. 12. — February, 1901.

80 DEVELOPMENT OF THE SKELETON OF THE TUATAIiA.

PLATE VI.
SPHENODON PUNCTATUS. — CRANIO-FACIAL MEMBRANE-BONES AND APPENDICULAR SKELETON.

ac., acetabulum ; an., angular ; c., centrale ; c.i.p., ischio-pubic cartilage j cl., clavicle ;
cor., coracoid ; cor.', sulcus coracoideus ; cor.", foramen for supracoracoideus nerve ; d., deutary ;
e., epipubis ; ep., epiphysis; F., fibula; /., fibulare ; f.b., foramen for arteria perforans mesopodii;
f.c., foramen cordiforme ; f.ec., ectepicondylar foramen ; f.en., entepicondylar foramen ; f.o., obtu-
rator foramen; Jr., frontal; g.f., glenoid fossa; hp., hypoischium ; i., intermedium; i.e., inter-
clavicle; il., ilium; is., ischium ; j., jugal ; l.i.p., ischio-pubic ligament (ligamentum medianutn
pelvis); m.i., metischial process; mn., meniscus tarsale; mx., maxilla; mx.', maxillary process;
ns., nasal ; p., parietal ; pa., palatine ; ph., pubis ; pb.' , prepubic process ; p.f., prefrontal ; pg.,
pterygoid ; pi., pisiform; p.o., postorbital ; po.c., postaxial centrale; po.f., postfrontal; pr.c.,
preaxial centrale; pro. 1., proximal tarsal ; px., premaxilla ; q.j., quadrato-jugal ; R., radius;
rd., radiale ; r.t., trunk rib ; *., sternum ; s.a., supra-angular ; sc., scapula ; sc.', acromial process ;
sc.", suprascapula ; se., sesamoid; s.mx., septo-maxillary ; s.n., poststernal notch; sp., splenial;
sq., squamosal ; sq."., posterior process of squamosal ; T., tibia; /., tibiale; t.c., tarsal centrale;
t.p., transpalatine ; U., ulna; u., ulnare; vo., vomer; I.-V., metacarpals and metatarsals ;
1—5, carpals and tarsals.

Fig. 1. Stage S. The membrane-bones : — Bones from roof of skull and side of head. x 5

Fig. 2. Stage S. The same : — Bones from roof of mouth. x 5.

Fig. 3. Stage S. The same: — Bones from lower jaw. x 5.

Fig. 4. Stage Q. Pectoral girdle and sternum : — Longitudinal section with developing clavicle.

x 25.

Fig. 5. Stage R. Pectoral girdle and sternum : — Ventral aspect. x 8.

Fig. 6. Stage T. Pectoral girdle and sternum: — Ventral aspect. x 2.

Fig. 7. Stage Q. Pelvic girdle: — Ventral aspect (from wax model). x 8.

Fig. 8. Stage R. Pelvic girdle : — Ventral aspect. x 5.

Fig. 9. Stage T. Pelvic girdle : — Ventral aspect. x 2.

Fig. 10. Stage Q. Humerus : — Distal end, ventral aspect (from wax model). x 15.

Fig. 11. Stage Q. Right carpus : — Horizontal section. x 20.

Fig. 12. Stage T. Right carpus : — Dorsal aspect, showing normal condition of centralia. x 4.

Fig. 13. Stage T. Left carpus : — Dorsal aspect, showing abnormal condition of centralia from

same animal as fig. 10. x 4.

Fig. 14. Small Adult. Right carpus : — Dorsal aspect. x 2.

Fig. 15. Stage Q. Left tarsus: — Early period, horizontal section. x 20.

Fig. 16. Stage Q. Right carpus: — Late period, horizontal section. x 20.

Fig. 17. Stage R. Left tarsus : — Horizontal section. x 15.

Fig. 18. Adult. Right tarsus : — Dorsal aspect. X 2.

Fig. 19. Adult. Portion of left tarsus : — Dorsal aspect, showing ulnar sesamoid. X 2.

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VW.XVI. 3

H.H.S iel.
M.P. Parker lith.

SPHENODON PUNCTATUS.
Cranio-facial ineinbrane tones, & Appendicular Skeleton.

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CON T E N T S.

On the Development of the Skeleton of the Tuatara, Sphenodon puiictatus ;
with EC marks on the Egg, on the Hatching, and on the Hatched I
By G. B. HOWES, LL.D., F.E.S., and H. H. SWINNERTON, B.Sc., Marshal/
Scholar, JK. Coll. Sci. Lond. (From the Huxley Research Labor at v
(Plates I.-VI.) ?'•

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BSS transacted at the scientific meetings, but also all the papers read at such meetings and recom-
mended to be published in the " Proceedings " by the Committee of Publication. A large number
:' coloured plates and engravings are attached to each annual volume of the "Proceedings,
lustrate the new or otherwise remarkable species of animals described in them. Among such
lustrations, figures of the new or rare species acquired in a living state for the Society's (
re often given.

The "Proceedings" for each yenr are issued in four parts, on the first of the months of ,]
'Jgust, October, and April, the part published in April completing the volume for the }•.
ear.

The "Transactions" contain such of the r^ ore important communications made to the seieit
leetings of the So: <»n account of the nature of the plates required to illustrate them,

otter adapted for publication in the quarto form. They are issued at irregular intervals.

Fellows and Corresponding Members, upon payment of a Subscription of £1 Is. before the day of
ic Anniversary Meeting in each year, are entitled to receive all the Society's Publications for tin--
ear. They are likewise entitled to purchase the Publications of the Society at 25 per cent,
iian the price charged for them to the Public. A further reduction of 25 per cent, is made upon
nrchases of Publications issued prior to 1871, it -eed the value of five pounds.

Fellow* also have the privilege of subscribing to the Annual Volume of the 'Zoological Record '
or a sum of £1 (which includes delivery in the United Kingdom), but this privilege only holds
;ood if the subscription is paid before the First of December in each year.

Such of these publications as are in stock may be obtained at the Society's Office (3 Hanover
square, W.), at Messrs. Longmans', the Society's publishers (Paternoster Row, E.C.), or tlm
ikseller.

P. L. SCLATKK;
Secretary.

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SENfTONILL

APR 1 2 2002

U. C. BERKELEY

JUN 0 1 2004

DD20 1M 3-02