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COMPARATIVE OSTEOLOGY
OF THE SNAKE FAMILIES
TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

TRE LIBRARY OF Tae
DEC 21 1966

Digitized by the Internet Archive
in 2011 with funding from
University of Illinois Urbana-Champaign

http://www.archive.org/details/comparativeosteos6list

COMPARATIVE OSTEOLOGY
OF THE SNAKE FAMILIES
TYPHLOPIDAE

AND LEPTOTYPHLOPIDAE

JAMES CARL LIST

ILLINOIS BIOLOGICAL MONOGRAPHS

36

THE UNIVERSITY OF ILLINOIS PRESS - URBANA AND LONDON .- 1966

Board of Editors:

James G. Sternburg, Bernard C. Abbott, Robert S. Bader,
Hobart M. Smith, Dale M. Steffensen, and Ralph S. Wolfe

THIS MONOGRAPH IS A CONTRIBUTION FROM THE DEPARTMENT OF ZOOLOGY,
UNIVERSITY OF ILLINOIS. ISSUED OCTOBER, 1966

© 1966 by the Board of Trustees of the University of
Illinois. Manufactured in the United States of America.
Library of Congress Catalog Card No. 66-63773.

ACKNOWLEDGMENTS

The writer is particularly grateful to Dr. Hobart M. Smith of the De-
partment of Zoology of the University of Illinois for suggestions and
direction throughout the course of this work. Both the Department of
Zoology and the Museum of Natural History of the University of Illinois
aided in various ways, as did the Department of Biology of Loyola Uni-
versity, Chicago, where much of the work was done.

Thanks are due to the following museums and institutions for loans
of specimens: the Australian Museum, Sydney, N.S.W.; the California
Academy of Sciences at San Francisco; the Chicago Natural History Mu-
seum; the Museum of Comparative Zoology of Harvard University; the
National Museums, Colombo, Ceylon; the University of Illinois Museum
of Natural History; the U.S. National Museum; and the Zoological Society
of San Diego.

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CONTENTS

INTRODUCTION 1

THE SKULL 4

THE LOWER JAW 19

THE VERTEBRAL COLUMN AND RIBS 25
THE HYOID 38

THE PELVIC GIRDLE 43

DISCUSSION 45

SUMMARY 56

ABBREVIATIONS USED IN PLATES 59
PLATES 60

LITERATURE CITED 104

MATERIALS EXAMINED 106

INDEX 109

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INTRODUCTION

The Typhlopidae and Leptotyphlopidae (auctorum) are families of
peculiar, small, burrowing snakes, most of them being less than a foot
long when mature. They are found throughout the warmer parts of the
world in both tropical forest and semi-desert conditions. They are quite
secretive and, aside from food habits, very little has been reported of
their natural history.

Interest in them has lain chiefly in their numerous and often extreme
burrowing modifications and in their primitive, lizard-like features. Their
scales, for example, are so polished and close-fitting that scale counts are
made with difficulty. Some of the enlarged head scales in particular have
such fine and closely applied edges that the outline of a scale can be
determined only by critical angles of lighting. The tail is very short; the
snout is sometimes flattened and spadelike; the eyes are quite reduced
and lie beneath the skin, hence the name “typhlops” (clouded eyes) and
the common name of “blind snakes.” Skeletal modifications associated
with burrowing are discussed in the various sections to follow. Primitive
features include the presence of pelvic vestiges, a coronoid, a tabular,
paired parietals, a distinct proatlas, etc.

The two families differ from each other in several basic respects and
have long been distinguished on the basis of skeletal characters. Within
the Typhlopidae, however, so little is known of the anatomy of the rarer
forms that scalation has been the only generic criterion. The skeletons of
Helminthophis and Typhlopis are still not figured or adequately de-
scribed. The usual arrangement of the genera is as follows:

A. Usually with well-developed pelvic vestiges; maxilla toothless—

Leptotyphlopidae. A single genus, Leptotyphlops:

bo

OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

AA. Pelvis usually reduced to a pair of ischia; maxilla bearing teeth—
Typhlopidae.
B. Head with small scales like those on body; rostral scale reduced,
invisible from above—Typhlophis.
BB. Head with enlarged scales; rostral large, visible from above.
C. Two enlarged preanal scales; a loreal scale present—Anoma-
lepis.
CC. No enlarged preanals; loreal absent or fused with upper nasal.
D. Prefrontal scale fused with upper nasals; rostral and
frontal scale in contact—Typhlops.
DD. Separate prefrontals.
E. Prefrontal scales in contact between rostral and
frontal—Helminthophis.
EE. Prefrontals separated by rostro-frontal contact—Lio-
typhlops.

The genus Leptotyphlops includes approximately fifty species, which
occur in Africa and from southwestern U.S. south through Mexico to
Argentina. There are very few Asian and no Australian species. Typhlops,
the largest of the genera, includes about 180 species, some twenty of
which are found in Mexico, the West Indies, and south to Argentina. The
others are Old World forms found in Africa and the Mediterranean
region, eastward through Madagascar and southern Asia to Australia, the
Philippines, and other South Pacific islands. The most widely distributed
and best known species, T. braminus, is native to Ceylon, India, and the
Philippines. It seems to have become established recently in Guam,
Hawaii, Mexico, and, in the opposite direction, the Mascarenes. There
are five species of Anomalepis (found from Panama to Peru), three of
Helminthophis (from Costa Rica to Venezuela), one of Typhlophis (in
Brazil and the Guianas), and ten of Liotyphlops (from Costa Rica to
Paraguay). There is thus a total of almost 250 species of these blind
snakes, and, although a number of names have been reduced to
synonymy, the list continues to grow by the description of one or two
new species nearly every year.

Of this number, not more than 10 per cent have been examined for
internal features. Relatively few studies have considered the soft anat-
omy. Haas’s work (1930) on the head musculature and Robb’s work
(1960) on the general internal anatomy are outstanding exceptions.
Nakamura (1941) reported on the circulatory system of T. braminus.
Aota (1940) reported a histological study of the skin and its sense organs
in one species. Brongersma (1958) reported on the respiratory and
circulatory systems. Mosauer (1935) included Typhlops in his work on
the trunk musculature of snakes. For the most part it is the skeleton
which has received attention, and even these descriptions are often

INTRODUCTION 3

incomplete or involve only a part of the skeleton such as the pelvic girdle.
Only Evans (1955) has adequately described the entire skeleton of a
species, utilizing a series of specimens to determine possible variations. A
number of papers dealing with parts of the skeleton will be mentioned
later in their respective sections. Some of the more extensive works,
however, may be summarized briefly at this point. Duerden and Essex
(1923) and Essex (1927) described the pelvic vestiges of a number of
species. Haas (1930) thoroughly described the skulls of two species
of Typhlops and one of Leptotyphlops. Brock (1932) described the skull
of Leptotyphlops nigricans. Mahendra (1936) reported several unique
features of the skeleton of T. braminus. Dunn (1941), Dunn and Tihen
(1944), and Tihen (1945) have authored the only papers on the
skeletons of Anomalepis and Liotyphlops. McDowell and Bogert (1954)
in their work on Lanthanotus included considerable discussion of the
blind snakes and proposed removal of all the blind snakes except
Leptotyphlops from the Ophidia. Underwood (1957) has criticized this
proposal as well as other parts of the Lanthanotus paper.

However, even these studies were sometimes based on a single
specimen or on one or two species. Also, much of the early work was
done on dried skeletal materials in which small sutures are often
obscured and where superficial bones like the orbitals might have been
lost with removal of the skin. In view of the significant position these
snakes must occupy near the base of any classification of the Ophidia, it
seems worthwhile to review past work and to add to our still meager
knowledge of the anatomy of the groups with the aim of clarifying the
phylogenetic relationships of the blind snakes with each other and with
the lizards.

The approach has been: (1) to review previous descriptions and _re-
examine the described species; (2) to examine species whose skeleton
had been unknown to date; and (3) to determine the degree of intra-
and interspecific variation of the skeleton, especially of those characters
on which previous taxonomic conclusions have been based.

This study developed a number of unexpected contradictions with
previous descriptions. In some cases these are no doubt due to different
methods of preparation of the specimens. In other cases simply better
lighting or more completely cleared specimens might account for the
differences. Other factors include variability of the structures and
differences of interpretation.

Besides adding to our picture of the interrelationships of the blind
snakes, this examination of a series of specimens has (1) revealed further
correlations between their skeletal structure and their burrowing mode of
life, and (2) suggested a reinterpretation of the homologies of certain of
their skeletal elements.

4 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

A word of explanation may be said here about certain terms which are
used in the following pages. “Blind snakes” will serve as a collective term
for all six genera. “Typhlopid” here refers to the genus Typhlops only.
“Leptotyphlopid” likewise refers to the single genus. “Anomalepid”
includes the four remaining genera: Anomalepis, Liotyphlops, Hel-
minthophis, and Typhlophis.

The work is based on examination of seventy-five specimens, represent-
ing thirty-two species of Typhlops, Leptotyphlops, and Liotyphlops.
Identification of each specimen was checked by means of an appropriate
key wherever possible. Most of the others were certified personally by the
lending curator. At first, the sexes were determined. In these snakes this
requires dissection, and the practice was discontinued because of the
tendency of dissected areas to disintegrate too rapidly during subsequent
treatment in potassium hydroxide.

The skeletons were prepared for examination by a modification of the
technique described by Davis and Gore (1936) and others. The
specimens are macerated in 1 to 4% potassium hydroxide, heavily
pigmented ones bleached in 114% hydrogen peroxide, the skeleton
stained with Alizarine Red S (alizarine sulfonate of sodium), and the
specimen further cleared by storage in glycerine. This method is one of
the best for the study of small skeletons in situ. Every bone and tooth was
quite distinct in one specimen in which the skull was less than two
millimeters long.

In some cases clear observation required some dissection and removal
of skin and other tissues. In order to avoid inadvertant removal of any
superficial bones like the orbitals this dissection was done only after
clearing and staining.

Observations were made with a binocular dissecting microscope.
Figures are by the author and were drawn on cross-ruled paper with the
aid of a Whipple micrometer disc in an ocular of the microscope.

THE SKULL

The snakes are a group of highly specialized reptiles whose affinities
with the rest of the class have been the subject of much speculation. They
are commonly accepted as highly modified lizards. If they are an offshoot
of the Lacertilia, one might expect to find lizard-like features in the more
primitive snakes like the boids, aniliids, xenopeltids, uropeltids, and the
blind snakes. Interest in the relationships between snakes and lizards has
led to frequent examinations of the skulls of these various groups,

THE SKULL 5

especially the blind snakes. The earliest description of the skulls of the
latter seems to be that of Muller (1831) of Typhlops lumbricalis.
Duméril and Bibron (1834-54) illustrated the skulls of T. reticulatus and
Stenostome (= Leptotyphlops) deux-raies. Jan and Sordelli (1860-66 )
figured the skulls of T. braminus and richardi and Leptotyphlops
dimidiata and albifrons. Peters (1882) figured the skull of T. dinga
(=schlegeli) and L. macrolepis. Boulenger (1890, 1893) figured the
skulls of T. diardi and T. lumbricalis.

Many of the early illustrations are quite generalized, with the result
that small sutures and relationships of some bones are often obscure.
Later studies, of which Haas’s is perhaps the best example, have utilized
serial sections, minute dissections, or alizarin preparations, and most of
our detailed knowledge of the anatomy of these snakes dates from these
studies. Haas’s work (1930) on the skull and jaw musculature of the
blind snakes is quite detailed, with numerous very well-executed figures
of the skulls of T. punctatus, braminus, and Leptotyphlops albifrons,
including serial sections. Brock (1932) reconstructed the skull of Lepto-
typhlops nigricans from serial sections, reporting the presence of a tiny
tabular bone between the quadrate and the otic capsule. Mookerjee and
Das (1932) noted the paired parietals of T. braminus. Mahendra (1936 )
dissected and figured four alizarin-stained specimens of T. braminus,
recording for the first time in the blind snakes the presence of small
postfrontals. Dunn (1941) described the skeleton of an alizarin-stained
Anomalepis aspinosus, figuring the jaw mechanism and parts of the
skull, including free orbital bones. Dunn and Tihen (1944) described
and figured the skull of Liotyphlops albirostris from three similarly
prepared specimens, noting the close resemblance between this genus
and Anomalepis. Tihen (1945) added to Dunn’s description of Ano-
malepis and made comparisons of skeletal features in Typhlops, Lepto-
typhlops, Liotyphlops, and Anomalepis. Smit (1949) figured sections
and reconstructions of the skull of T. delalandii. McDowell and Bogert
(1954) discussed at length the cranial features of the blind snakes
(including figures of T. punctatus and Leptotyphlops dimidiata) and
concluded that the Typhlopidae have had a saurian ancestry separate
from the leptotyphlopids and higher snakes and are sufficiently distinct
to be removed from the Ophidia.

The detailed descriptions and figures in these later papers make
extensive repetitions unnecessary here. However, each of the studies is
largely based on an examination of a single species, or at the most, three
or four species out of the two hundred or more known kinds of blind
snakes. It is worthwhile to summarize the preceding work and to point
out a number of variations, discrepancies, and contradictions that have
come to light in the course of the present study of thirty-two species.

6 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

This in itself is a small sample, of course, but a good one nevertheless in
view of the scarcity of most species in collections (many are known only
from type specimens or type series) and the reluctance of museums to
loan scarce materials for a procedure which destroys all parts of the
specimen except the skeleton.

The occipital region of the skull of these snakes shows a great deal of
interspecific variation. A basioccipital and paired exoccipitals are always
present, but the supraoccipital may be single, paired, or fused with the
exoccipitals (or absent). The basioccipital in Typhlops is flat and
roughly triangular, with its apex directed posteriad. The anterior edge
(the base of the triangle) is straight or slightly concave and meets the
rear edge of the basisphenoid. Laterally the bone is bordered by the
lower edges of the exoccipitals and prootics. A single median foramen is
present in some species. The posterior end enters into the formation of
the foramen magnum to varying degrees, tending to be crowded out by
approximation of the postero-ventral tips of the exoccipitals dorsal to it.
This posterior end of the basioccipital normally articulates with the
hypocentrum of the atlas, fitting against a calcified cartilage facet of the
latter. Of the species of Typhlops examined here, the basioccipital is
completely excluded from the foramen only in braminus, the exoccipitals
in this case meeting each other behind the former.

The basioccipital of Liotyphlops is very much the same as in
Typhlops: roughly triangular, the posterior tip articulating with the
hypocentrum and entering into the formation of the foramen magnum.

In Leptotyphlops this bone has the same general form and relation-
ships as in the typhlopids. It is more likely, however, to be completely
excluded from the foramen magnum by posterior extensions of the
exoccipitals. It is thus excluded in L. nigricans, emini, bakewelli, and
magnamaculata. There is an interesting correlation between this exclu-
sion from the foramen and the great reduction or absence of the
hypocentrum of the atlas. In the four species just mentioned the hypo-
centrum is absent or quite vestigial. In other species, where the basioc-
cipital participates in the foramen, the hypocentrum is relatively well
developed.

The exoccipitals are irregular bones, the major part of each forming the
lateral wall of the foramen magnum and of the occipital region of the
skull. This central portion of the bone may be thought of as having three
extensions. (1) Curving toward the midline is a dorsal piece which, with
its opposite, forms the roof of the foramen magnum. This dorsal piece is
usually separated from the opposite one by a considerable gap. (2) The
second extension is a postero-ventral piece which also curves toward the
midline, lying above the basioccipital and tending to exclude it from
the foramen. The end of this extension articulates with an anterior facet on

THE SKULL 1

the corresponding side of the atlas. (3) The third is a slender antero-
ventral piece of variable length which lies along the lateral edge of the
basioccipital, separating the latter in part from the prootic above. Near
the base of this extension of the exoccipital is a foramen of variable size,
through which exit the seventh, ninth, and tenth cranial nerves.

In Typhlops the relationship between the exoccipital and adjacent
bones is varied. In most species the exoccipital is separate, meeting the
prootic firmly but separated from the supraoccipitals by a gap. In other
species it is fused with the supraoccipital (T. braminus and boettgeri),
and in T. lineatus it is fused with both the supraoccipital and prootic. In
Liotyphlops it is fused with the prootic. In all the species of Leptotyph-
lops examined here it is a separate bone with approximately the same
shape and relationships as in most Typhlops.

The supraoccipitals in nearly all the blind snakes are paired, ovoid or
rectangular, and rather widely separated from the surrounding bones.
The only exceptions are the single median supraoccipital of Liotyphlops,
Anomalepis, and Leptotyphlops dimidiata, and the previously noted
instances of fusion with the exoccipitals. Of course, in those instances
where the supra- and exoccipitals seem to be fused the former may
actually be absent, for there are no visible lines or other evidences of
fusion. As can be seen in the accompanying plates, however, in these
specimens the single bone covers about as much area dorsally as do the
separate bones in other species. If the supraoccipital is in fact absent,
the exoccipital has expanded anteriad to replace it. The pairing of the
supraoccipitals is in itself a rare condition in vertebrates, and it has been
suggested (McDowell and Bogert, 1954) that such a supraoccipital is
merely an unfused part of the exoccipital (if paired ) or a sort of fontanel
bone (if median), the true supraoccipitals being absent. As in other
doubtful situations in these snakes, embryological observations would be
quite helpful.

The prootics are rather large convex bones covering the otic region,
meeting all three occipital bones to the rear and the parietal and
basisphenoid in front. They are closely applied to the exoccipitals but
often widely separated from the others. The maxillary and mandibular
branches of the trigeminal nerve exit by an especially large gap between
the prootic and parietal where they approach the basisphenoid. In
another smaller gap between the prootic and exoccipital (largely a notch
in the edge of the latter) a very minute columella may be visible. Its
presence in or absence from some species could not be definitely
determined. The prootics are separate bones in Leptotyphlops, Ano-
malepis, and most Typhlops, but are fused with the exoccipitals in a few
Typhlops and in Liotyphlops. Such fusion of the prootics and exoccipitals
is common in lizards but among snakes seems to be limited to these few

8 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

cases. It has been reported in T. richardi, braminus, and bituberculatus.
In the specimens of richardi and braminus available to me, however, the
prootics are quite separate. Mahendra (1936) noted the same discrep-
ancy with respect to braminus. As mentioned previously, in T. lineatus
the prootics are fused with both the ex- and supraoccipitals.

The parietals of Typhlops are the largest bones of the skull. They are
bordered by the frontals, basisphenoid, prootics, and supraoccipitals and
are rather widely separated from all of them. The chief characteristic of
the parietals here is the downgrowth of their lateral edges to meet the
basisphenoid. They thus form the side walls as well as the roof of this
region of the skull. Such extreme downgrowth is typical and quite
characteristic of all snakes, although the same arrangement occurs in
amphisbaenid and dibamid lizards. Ordinarily, the parietals of snakes are
fused into a single large unit, and early comparative anatomists,
including even Williston (1925), spoke of the parietals of the Ophidia as
“always fused.” The paired condition of the parietals of many of the
blind snakes is thus an unusual feature. Mookerjee and Das (1932)
called attention to the paired parietals of T. braminus, but Haas and
others even as early as Jan and Sordelli had previously figured this
condition. Most species have them fused, but even in the most common,
fused conditions they usually show various degrees of mid-dorsal
notches, grooves, fissures, etc. (Plates 1, 4, 7, 10). In the early develop-
mental stages it is likely that the parietals are separate in all Typhlops.
One discrepancy between the present studies and a statement in the
literature may be mentioned: T. richardi was figured by Jan and Sordelli
with paired parietals, but in the one specimen of richardi available to me
they are well fused. In view of the numerous evidences of embryological
fusion mentioned above, one might expect to find some intraspecific
variations in this respect, although none were encountered in the
specimens at hand.

In Liotyphlops and Anomalepis the parietals are paired. In Leptotyph-
lops they are nearly always well fused; only in L. emini are they separate.
A peculiar feature of the parietals of L. humilis (noted also by McDowell
and Bogert) is a large unossified central area which often contains
scattered calcareous granules (Plate 10). Upon dissection, the area seems
as firm as the surrounding bone although it does not stain with alizarin.

Separate, paired parietals, as paired skull bones in general, are usually
considered to be primitive in comparison with their single fused
homologue. Fossil evidence supports this, although Mehely (1907) in a
review of the Lacertidae believes that paired conditions may appear in
descendants of ancestors having the fused condition. The value of this
opinion may be somewhat reduced, however, by the fact that several
other tenets of his review contradict generally held ideas of lizard

THE SKULL 9

evolution. In this connection, a very novel situation has been noted by
Grobman (1943) in the salamander Gyrinophilus porphyriticus, where
the anterior ramus of the premaxillary is continuous with its opposite
member in the larva but becomes separated by a suture or fissure in the
adult.

With respect to the parietals of the blind snakes, at least, it seems safe
to consider the paired condition as the primitive one. The greater
tendency for fusion of those bones in Leptotyphlops, both in per cent of
species and degree of fusion, goes along with the other features that they
share with more advanced snakes.

The basisphenoid is the chief bone of the floor of the cranium. It is
broad posteriad where it meets the basioccipital, prootics, and parietals,
tapering to a point anteriad between the ventral parts of the frontals. In
its relationship to the surrounding bones it shows the same wide fissures
which characterize the bones of the dorsal occipital region. McDowell
and Bogert (1954) attached some significance to this fissure between the
parietal and basisphenoid as a peculiarity of Typhlops, stating that in
typical snakes and Leptotyphlops “the ventral extremity of the parietal
forms a firm suture with the lateral edge of the basisphenoid.” However,
in all but one of the species (maximus) of Leptotyphlops examined by
me the fissure between these two bones is quite as pronounced as in the
average Typhlops. A second difference in the basisphenoids of these two
genera noted by the above authors is the shape of the anterior tip and the
relative length of the bone: “In snakes and leptotpyhlopids the basi-
sphenoid is pointed anteriorly, extends as far forward as does the frontal,
and meets the vomer. In the typhlopids the basisphenoid is truncated or
emarginated anteriorly, does not extend nearly so far forward as does the
frontal and is separated from the vomer by a median vacuity.” This
distinction is generally true, but examination of other species again shows
a number of exceptions and intermediate conditions. In seven species of
Typhlops, for example, the anterior end is quite pointed and in at least
three it reaches the vomers. On the other hand, in some Leptotyphlops
the basisphenoid is bluntly rounded and does not reach the vomers,
leaving a small fontanel in the cranial floor. This part of the basisphenoid
in Liotyphlops has an unusually long contact with the parietal and a very
broad anterior tip which narrows abruptly as it approaches the vomers.
In all three of these genera the tip of the bone is often cleft by a median
fissure.

The frontals of the blind snakes are always paired, as in other snakes,
and, like the parietals, extend ventrally to the basisphenoid, separating
the orbits and forming the side walls of this part of the skull. They vary
somewhat in detail, however, among the genera. One difference is in the
manner of formation of the interorbital partition. In Leptotyphlops there

10 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

is an extensive descending portion which is more or less vertical in plane,
and which turns down sharply from the dorsal horizontal plate. This
angle between the dorsal and vertical processes extends forward to a
posterior “finger” of the prefrontal. In Typhlops and Liotyphlops the
descending process curves ventrally more gradually, thus is not so
sharply defined from the dorsal part, and the posterior tip (orbital
process) of the prefrontal is very low in the orbit (Plates 2, 5, 8).
McDowell and Bogert feel that the low position of this orbital process
indicates a very small descending plate of the frontal, saying, “we must
rely on this (the orbital process) to distinguish between the descending
lamina and dorsal plate of the frontal, for the frontal bone itself shows no
sharp angulation or supraorbital shelf”; and that the interorbital cavity
here is formed not by the descending processes but “by the outward
inflation and billowing of the dorsal plate of the frontal.” In most
Typhlops, however, there is a fairly well-defined crest along the frontal
above the orbit. Lateral to this ridge the bone does not turn directly
ventral as in Leptotyphlops, but curves ventro-laterally. It seems best to
consider this low crest as the line between the dorsal and descending
plates and the latter portion of the bone as differing from that of
Leptotyphlops only in being convex rather than plane. The presence of a
very small descending plate is indeed suggested by the lower direction of
the orbital process of the prefrontal in Typhlops, but there is no crest or
angle on the frontal in this low position and it seems unlikely that this
orbital process would follow so exactly the movement of the line of
division between these two regions of the bone. It is more likely that the
slight difference in orientation of the prefrontal is associated with the un-
usually expanded nasal region of Typhlops. The flaring, swollen outline of
the nasal region of the skull is quite distinctive in this genus.

A second variation of the frontals is the extent to which they approach
each other in the mid-ventral line. The previously mentioned descending
processes turn medially just dorsal to the basisphenoid and approach
each other. In most of the blind snakes the opposite processes do not
meet, although they come close in Liotyphlops, but in a few species of
Leptotyphlops these parts of the frontals are in contact with each other
for some distance immediately dorsal to the basisphenoid, completely
encircling the brain at this level (Plate 12). The dorsal part of the frontal
varies considerably in relative length among these three genera. It is
longest in Typhlops and also rather constricted in the center, flaring
laterally where it meets the parietal behind it and the nasal region ahead.
The frontal is notably shorter in Leptotyphlops and not at all widened
anteriad. It is unusually short in Liotyphlops.

The presence or absence of postfrontals in Typhlops has been an
unsettled matter for some time. None of the early writers made any

THE SKULL ll

mention of them. Haas remarked that both the Typhlopidae and
Leptotyphlopidae lack “das Supratemporale (Squamosum), das Trans-
versum, und das Postfrontale.” Mahendra (1936) reported tiny bones in
T. braminus, “Perhaps . . . representing both the postfrontals and post-
orbitals,” and expressed some surprise that previous workers had missed
them. These bones in his preparations occurred “in the form of three or
fewer small pieces at the anterior outer borders of the parietals.”
Mahendra was apparently the first to use the clearing and alizarin
procedure in preparing his specimens of Typhlops and he attributed the
demonstration of these tiny pieces to this technique. My experience in
the present study leads me to conclude that these bones are of very
infrequent and irregular occurrence, even within a species. For example,
using the same alizarin technique and excellent lighting I could not find
any such structures in several specimens of the same species (braminus )
from various parts of the world. Mahendra’s photograph (1936, fig. 1, D)
is not at all clear in this respect, and I had about concluded that he was
mistaken when similar small pieces were noted in a specimen of T.
reticulatus. In this latter specimen (Plate 4) the structures are not true
bone but calcified cartilage. They appear to be functionless. One is
separate, lying just at the antero-lateral corner of the parietal; the
opposite one is attached to that point of the parietal. This single
specimen, out of some fifty Typhlops examined, was the only one to show
these bones. The location of these rudimentary pieces makes it most
likely that they represent postfrontals rather than postorbitals, since the
latter in lizards are normally more posterior. Leptotyphlops is apparently
completely lacking in postfrontals or other free bones in the orbital
region.

Both Liotyphlops and Anomalepis, on the other hand, have a well-
developed pair of orbital bones on either side, noted first in A. aspinosus
by Dunn (1941). One of these two bones lies horizontally above the eye
parallel to the edge of the frontal, its posterior end resting on a
conspicuous postorbital process of the frontal and its anterior end
curving down slightly in front of the eye. The second orbital bone in
aspinosus is somewhat larger. One curved part lies below and behind the
eye and from this a slender process extends directly posteriad to a point
lateral to the parietal. It lies free, with no contact with any other bone.
These bones of the orbital region were tentatively homologized by Dunn
with, respectively, the supraorbital and the posterior orbital (= fused
postorbital and postfrontal ) of varanid lizards. Dunn’s reference specimen
had been damaged and the articular relationships of these bones were
not clear. Tihen later (1945) found in a well-preserved specimen of A.
dentatus a supraorbital and a postorbital “nearly identical” with those
described by Dunn. He noted in addition that the anterior end of the

12 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

supraorbital is forked, contacts the dorsal part of the maxilla, and serves
as a pivot for the latter, which is moved forward and backward by the
pterygoid-ectopterygoid combination. The posterior end of the supraor-
bital is well braced against the lateral projection from the frontal. Dunn
and Tihen had previously (1944) noted an identical kinetic arrangement
of the maxilla and supraorbital of Liotyphlops albirostris. The supraor-
bital of this genus is quite like that of Anomalepis, but its posterior orbital
is much smaller and less complex, a simple curved rod lying lateral to the
supraorbital. The specimens of L. albirostris examined by me confirm
Tihen’s descriptions.

A different and well-supported interpretation of the homologies of
these orbital bones has been suggested by McDowell and Bogert.
Pythons and a few other snakes have a supraorbital, but it bears no close
resemblance in shape or position to that bone of the anomalepids. On the
other hand, examination of the bones of the orbital region of lizards
shows a pair of bones there with relationships that strongly suggest the
anomalepid supraorbital. The first is the palpebral (anteriormost supra-
ocular osteoderm) which extends across the lateral surface of the
prefrontal to approach or make contact with the ascending facial process
of the maxilla. The second is the postfrontal, a bone lying above and
behind the eye and attached to a lateral postorbital extension of the
frontal (and the parietal). The possibility is suggested, therefore, that
the dorsal orbital bone of Anomalepis and Liotyphlops “represents a
fusion of the palpebral with the postfrontal,” the anterior end (which
articulates with the maxilla) being the palpebral, the posterior end
(which meets the frontal) being the postfrontal.

With respect to the second of these orbital bones of the anomalepids it
seems quite likely that it also represents a fusion of two bones present in
lizards: the jugal and the postorbital. The jugal in anguinid lizards lies in
exactly the same position as the anterior part of the Anomalepis
“postorbital.” That is, it lies in part below the eye, curving up behind it to
meet the postfrontal. In its form and position the long posterior extension
of the “postorbital” is highly suggestive of the true postorbital of lizards.
In Liotyphlops this slender posterior piece is missing and the smaller and
simpler “postorbital” here has very much the same form and relationships
as the jugal in anguinid lizards.

The maxilla of the anomalepids is a rather flat, triangular, freely
movable bone. The base of the triangle is transversely oriented and bears
four or five teeth. The apex of the triangle extends forward and dorsad
alongside the prefrontal, ending in a shallow fork which articulates with
the palpebral portion of the “supraorbital.” It does not contact the
prefrontal and, in Liotyphlops, at least, upon manipulation seems to be
only loosely attached, if at all, to the latter. A small projection on the

THE SKULL 13

posterior side of the tooth-bearing portion fits into the forked end of the
ectopterygoid.

The maxillary teeth of Liotyphlops have an unusual form that seems to
have escaped notice to date. Rather than the slender, finely pointed,
recurved teeth of higher snakes (typical also of the other blind snakes ),
Liotyphlops has a spade-shaped tooth: its broad, somewhat flattened,
obtusely pointed tip is notably wider than the base of the tooth (Plate 3).
Teeth with a similar outline are seen in Iguana, at least, and probably
other lizards, although it is by no means the typical lizard tooth.

The maxilla of Typhlops is basically the same as in anomalepids in
form and position. Although freely movable it is connected by way of a
ligament from its dorsal part to the side of the prefrontal and the
septomaxilla. In the absence of the support afforded by the palpebral in
the anomalepids this ligamentous attachment serves as a pivot for the
maxilla. The tooth-bearing base of the maxilla here is also oriented
transversely, with from three to seven curved teeth. The teeth are
apparently replaced often, for in several specimens a tooth (red with
alizarin ) was noted in the intestine. The type of replacement is the same
as that of leptotyphlopids, higher snakes, and anguinomorphan lizards.
The young tooth develops beside the older one, rather than below it, and
forces it out from the side.

The maxilla of Leptotyphlops is of an entirely different type. It is
lizard-like, immovable, and closely attached to the bones of the lateral
nasal region, chiefly the septomaxilla, although it may also contact the
premaxilla, the prefrontal, or the vomer. Compared to the maxilla of
Typhlops the facial plate here is reduced. This maxilla, therefore, is more
like that of typical snakes which is reduced to a slender rod (tooth-
bearing, however ). It does not bear teeth, and its shape is irregular and
variable from species to species. In most, however, it bears two
characteristic processes. One is a prominent posterior extension which
may be slender and rodlike or rather broad and flattened in a horizontal
plane. The second is a vertical crest along the ventral edge of the bone,
irregularly notched and perforated by two to four holes. McDowell and
Bogert noticed an encircling suture separating the posterior process from
the main part of the maxilla in L. dimidiata and suggested that the
posterior portion represents the ectopterygoid. More will be said of this
shortly. Undoubtedly the ventral edge of the maxilla formerly bore teeth,
and its present ragged and perforated margin suggests degenerate tooth
sockets.

The bones of the palatal region of the blind snakes vary interestingly
among the genera. The most primitive, yet somewhat unusual, arrange-
ment is that of Liotyphlops. Here the pterygoid is a simple slender rod
extending forward from the region of the exoccipital to contact a process

14 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

of the palatine. Its anterior part angles slightly mediad. Its posterior end
makes no articulation with the skull, lying free in the muscles below the
occipital region. The ectopterygoid is also a slender rodlike bone but
much shorter, lying along the anterior end of the pterygoid. Its posterior
end lies against the medial surface of the pterygoid, and for a short dis-
tance it extends forward parallel to the latter. It then angles laterad and
crosses above the pterygoid, terminating in a blunt fork which receives a
short process from the base (tooth-bearing portion) of the maxilla. Except
for its free posterior end the pterygoid has basically the same relationships
with other bones as in lizards: meeting both the ectopterygoid and the
palatine anteriad. The position of the ectopterygoid between the maxilla
and pterygoid is also normal. The rather loose connections between all
these bones is unusual, of course, in view of their normally rigid
articulations in other reptiles, and is associated with the mobility of the
maxilla. The palatine in lizards is a Y-shaped bone, its two anterior
processes meeting the vomer (and the opposite palatine) and the
maxilla, and the posterior process meeting the pterygoid. The palatine
of Liotyphlops seems easily derivable from this lizard type. The medial
process meets the posterior tip of the vomer and the opposite palatine.
The maxillary (antero-lateral) process, however, is quite short and is
unusual in its failure actually to contact the maxilla. The pterygoid
(posterior ) process of the palatine is slender and, in order to meet the
pterygoid, extends more ventrad than posteriad. A nearly identical set of
bones occurs in the maxillary kinetics of Anomalepis, with the possible
exception of the palatine, whose presence or absence was not certainly
determined in the specimens available to Dunn and Tihen.

In Typhlops the arrangement of these bones has been modified
through the loss of the ectopterygoid as a separate element. The palatine
here is more robust, its major portion extending in a slight curve from the
midline of the palate, where it abuts against the posterior tip of the
vomer, laterad and ventrad to the maxilla. Its rounded lateral end fits
into a pocket of the maxilla or, more often, into a foramen which
penetrates the bone. From about the center of the palatine a slender
process extends ventrad to meet the pterygoid. Dunn and Tihen noted
that the bone usually called “palatine” in this genus corresponds in its
relation to both the palatine and ectopterygoid of Liotyphlops and
suggested that the latter two bones have fused in Typhlops. McDowell
and Bogert supported this view: “For this there is some additional
evidence not cited by these authors. In Typhlops the pterygoid is
bilobate anteriorly, strongly suggesting the furcation seen in lizards and
many snakes into two processes, an external process for the ectopterygoid
and an internal process for the palatine. But the so-called ‘palatine’ of
Typhlops is attached not to the internal process but to the external

THE SKULL 15

(ectopterygoid) lobe. Yet the element cannot be a simple ectopterygoid,
for it extends inward to articulate with the vomer, as does the palatine in
other squamatans (except the majority of snakes ).”

I suggest an alternative explanation which seems to fit the observations
equally well. That is the possibility that the ectopterygoid has fused not
with the palatine, but with the pterygoid. In the first place, as will be
seen later in a consideration of the hyobranchium and the pelvic girdle,
although conditions in the anomalepids are generally more primitive they
are often too specialized to represent stages through which the corre-
sponding typhlopid structures have passed. Hence, the short maxillary
process of the palatine of Liotyphlops and its failure to meet the maxilla
need not have preceded the state of the palatine of Typhlops. Although
there are some unusual orientations and differences in sizes of processes
in this group of bones in the anomalepids, so far as their contacts with
each other are concerned the only point of departure from the normal liz-
ard relationships is the “most remarkable” lack of contact between palatine
and maxilla. It is possible that this short maxillary process is a condition
which has appeared since the separation of the anomalepid and typhlo-
pid lines and that in the latter the palatine has always bridged the space
between the vomer and maxilla, at the same time sending a process
posteriad to the pterygoid, as it does now in lizards. Further support is
given to this suggestion by the manner of articulation in Typhlops of the
end of the palatine fitting into a foramen of the maxilla. In Liotyphlops
the anterior end of the ectopterygoid is forked, receiving here a
projection of the maxilla. Were it still the ectopterygoid meeting the
maxilla in Typhlops, then a similar type of articulation would be
expected. The anterior end of the Typhlops pterygoid is always forked,
but between species it varies considerably in the length of the rami and
in its exact relationships to the palatine. The rami may be well developed
(as in T. lumbricalis ) with the pterygoid process of the palatine received
rather loosely between them. In this condition, with slender rami, the
anterior end of the pterygoid suggests the combined pterygoid and
ectopterygoid of Liotyphlops. A fusion and slight shortening of these two
bones in the latter genus would result in a structure quite like the
pterygoid of T. platycephalus, braminus, and especially lumbricalis. In
most species of Typhlops the rami of the pterygoid are shorter and
stouter and their articulation with the palatine becomes more complex.
McDowell and Bogert, as quoted above, describe the palatine of
Typhlops as attached not to the internal ramus but to the external. To
me, the opposite seems true: the pterygoid process (postero-ventral )
from the palatine contacts chiefly and most intimately the internal
(medial) ramus of the pterygoid, while the external ramus (= the
ectopterygoid?) extends somewhat laterad to brace against the base of

16 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

the pterygoid process or against the body of the palatine itself. In some
species a small secondary process is developed on the pterygoid process
of the palatine which fits between the two rami of the pterygoid.

The pterygoid-palatine-maxilla series in Leptotyphlops has yet a third
arrangement. The pterygoid is a slender, slightly curved bone, shorter
than in the other blind snakes, reaching posteriad no farther than the rear
of the basisphenoid. Posteriad it is unattached. Anteriad it is closely
applied to the pterygoid process of the palatine. The palatines in this
genus differ from the preceding in their form and in their larger size.
They are still basically triradiate, however, contacting the vomer, the
pterygoid, and (usually ) the maxilla. The body of the palatine is a broad
flat plate, usually perforated by a foramen. Its vomerine process is broad
and not well distinguished from the body of the palatine. It is expanded
and often curled ventrad as it abuts against the posterior tip of the
vomer. The pterygoid process is slender and lies against the ventro-
lateral surface of the anterior end of the pterygoid. The maxillary process
is slender and may not contact the maxilla. For those palatines which do
touch the maxilla (on its medial surface) there is no differentiated
articular facet for their reception (except in L. emini), although the
distal end of the maxillary process itself in one species (maximus) is
expanded where it meets the maxilla. With the rigid attachment of the
maxilla there is apparently no fore and aft movement possible in this
series of bones.

In the past, the ectopterygoid had been considered absent in Lepto-
typhlops. However, McDowell and Bogert noticed a definite suture
delimiting the peculiar posterior extension of the maxilla in L. dimidiata.
They suggested that this piece represents the ectopterygoid partially
fused to the maxilla. Certainly it is a logical position and there is
otherwise no counterpart in either snakes or lizards of this extension of
the maxilla. In most species this remnant of the ectopterygoid (if it is
such ) is completely fused to the maxilla. A suture between the two was
visible in only one of the species examined by me (Plate 12: maximus).

Mention may be made here of a pair of weakly calcified cartilages (?)
that are present in most of the species of Leptotyphlops in this study and
are noted here for the first time. They are rodlike, horizontal, variable in
size, quite flexible upon manipulation, and lie just below and more or less
parallel to the maxillary processes of the palatine bones (Plate 12). The
figures of Haas on the musculature of this region show no ligaments or
tendons here that might have sesamoid-like calcification. The only bones
from this area of the palate that might be represented by such rudiments
are the ectopterygoids, parts of which may be represented here by these
rather degenerate calcifications. More likely they are a sort of heterotopic
“bone” developed in the connective tissue of the palate and serving to

THE SKULL 17

strengthen it against the teeth of the dentary which lie below it in this
area.

The paired vomers of the blind snakes are all basically the same. In
ventral view each has a flat anterior expansion which curves posteriad and
ends in a hook. The middle section of the bone usually consists of a
smaller, hookless expansion. The posterior part of each vomer in
Liotyphlops is a slender, finger-like process, its tip barely in contact with
the respective palatines (which are braced chiefly against each other ). In
Typhlops and Leptotyphlops this posterior part is extended a short
distance ventrad as a vertical plate against which is braced the expanded
end of the palatine. The vomers in all these genera lie just ventral to the
medial edges of the septomaxillae. In cross section the horizontal portion
of each vomer is seen to have a short dorsal vertical plate, separated in
the midplane by a thin cartilaginous septum. Those of Leptotyphlops are
considerably larger and more closely applied to one another, even
partially fused in one specimen of nigricans.

These paired bones of the palate of lower tetrapods (here called
vomers ) have been subject to changes of terminology which are reflected
in some of the works pertaining to the blind snakes. “Vomer” was the
original name for these bones, which were believed to be homologous to
the single vomer of mammals. A later view held that the mammalian
vomer is the homologue of the parasphenoid of other vertebrates, and the
vomers of reptiles then became known as “prevomers.” Some of the
papers cited here use this latter term. Parrington and Westoll (1940)
have been followed by most comparative anatomists in a return to the
original view, holding that the parasphenoid of lower vertebrates has
been lost in mammals.

The septomaxillae are prominent bones in a ventral view of the skull,
although in Leptotyphlops they may be largely covered by expansions of
the vomers and maxillae. Each septomaxilla encloses one of the Jacob-
son’s organs. Ventrally it is overlapped by the edges of the vomer,
premaxilla, and prefrontal (it is fused with the latter in Liotyphlops)
and, in Leptotyphlops, the maxilla. Dorsad it is concealed by the
overlying frontal and nasal. To the rear it reaches the descending portion
of the frontal except in Leptotyphlops. Laterad it is largely concealed by
the prefrontal. Low on the lateral wall of the septomaxilla there is a
horizontal shelf which usually forms a small part of the bony anterior
naris. In Typhlops there is a tendency for the edge of this shelf to curve
upward, and in Leptotyphlops it is a highly developed ascending process
which is characteristically perforate where it enters the bony naris (Plate
11). A second characteristic of the bone in Leptotyphlops is its much
reduced contact with the premaxilla, a result of the expansion of the
vomer.

18 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

Finally, mention must be made of a pair of squarish bones apparently
unique to Liotyphlops and (possibly ) Anomalepis. First noted by Dunn
and Tihen in the former genus, they were tentatively identified by them
as extensions of the frontals, or as epipterygoids, or laterosphenoids (=
the very large orbitosphenoids of amphisbaenids?). Although the rela-
tionships of these bones to the adjacent ones are somewhat obscured by
the dense connective tissue of the palate, their arrangement in the two
specimens of Liotyphlops albirostris at hand does not agree with that
described by Dunn and Tihen. As figured by these authors (1944, fig. 4)
the bones correspond very well to what I see as antero-ventral extensions
of the frontals: i.e., they are directly above the palatines, posterior to the
vomers, and overlapped slightly by the anterior edge of the basisphenoid.
Yet in my two specimens I note a pair of apparently separate bones
which do not seem to be shown in Dunn and Tihen’s figure. These are in
a more anterior position, immediately ahead of the ventral extensions of
the frontals, and dorsal to the tips of the vomers. Each is definitely
separated from the frontal by a fissure, but their borders match closely
(Plate 3). They seem to meet the posterior extremities of the septomaxil-
lae, and it is not certain that they are separate from them. Whether they
are distinct bones, processes of the frontals, or septomaxillae, they have
no counterpart in the other blind snakes.

The prefrontals of the blind snakes are all rather similar. They are
separate bones except for their fusion with the septomaxillae in Liotyph-
lops. They cover the sides of the rostrum and, especially in Typhlops,
contribute as well to the floor of this region. Posteriad there is an orbital
process lying against the frontal. Anteriad in Typhlops and Liotyphlops
the prefrontal forms a part of the border of the naris, but in most
Leptotyphlops it has shortened to such an extent that the exposed
septomaxilla replaces it in the border (Plate 11).

Correlated with the burrowing mode of life, the nasal bones and
general nasal region are quite expanded, especially in Typhlops, less so in
Leptotyphlops. The nasals are separate in all the Typhlops examined and
in Anomalepis aspinosus. They are fused in Liotyphlops, several species
of Leptotyphlops, and A. dentatus. In cross section, a descending plate of
each bone is seen to form an internasal septum. The nasal always
contributes to the border of the bony naris. A slitlike extension of the
naris separating the nasal and the prefrontal was considered by Mc-
Dowell and Bogert to be characteristic of Leptotyphlops (and nearly all
higher snakes) but to be absent in Typhlops. Such a fissure between the
two bones is present, however, in several species of Typhlops. The rather
striking foramina in the nasals of the blind snakes are passages for the
exit of nerves to the numerous sense receptors in the skin of the rostrum.

An unusual feature of the nasals noted in Liotyphlops and in two

THE LOWER JAW 19

species of Leptotyphlops is the presence of a short and incomplete
transverse fissure near the rear of each bone. The appearance is that of a
partially fused fontanel bone. The condition may be correlated with the
greater length of the nasals in these two genera, for no such fissures were
noted in Typhlops, where these bones are much shorter. More likely, the
fissures are merely elongate foramina for the passage of sensory nerves.

The premaxillae, like the nasals, reflect the burrowing life of these
snakes in their great enlargement, which often suggests a shield across
the ventral edge of the rostrum. They are consistently fused in all the
blind snakes. The resulting bone forms the anterior face of the rostrum
(except in Liotyphlops) and curves ventrad where it meets the septo-
maxillae and vomers. In Typhlops it is in broad contact with the
septomaxillae and has a pointed posterior process, the tip of which
usually lies between the vomers but may or may not actually contact
them. On the other hand, in Leptotyphlops this posterior palatal process
is shorter and broader and firmly meets the much wider vomers. The
premaxilla-septomaxilla contact is considerably reduced, although there
is some interspecific variation here.

THE LOWER JAW

In a comparison of the genera of blind snakes the structure of the
lower jaw and its suspension seem particularly significant. Two funda-
mentally different types of mandibles occur, emphasizing, as much as any
other part of the skeleton, the distinctness of the leptotyphlopids and the
typhlopid-anomalepid group.

In Typhlops the rather flattened quadrate is connected to the exoccipi-
tal and extends forward and downward to its articulation with the
mandible. The relative shortness of the mandible here, and in other blind
snakes, necessitates this forward direction of the quadrate, which in
typical snakes is vertical or directed posteriad. The attachment of the
quadrate directly to the cranium is similar to that of lizards, the other
blind snakes, and a fossil snake Dinilysia, but differs from typical
snakes where a well-developed tabular bone is interposed. The anterior
part of the quadrate has a dorsal expansion in the form of a winglike
plate. This is a process absent in some of the other blind snakes and all
higher forms but suggestive of the outer conch of the quadrate in some
diploglossan lizards. The anterior articular end of the quadrate is
rounded, usually capped with calcified cartilage, and fits into a similarly
capped, concave facet of the mandible.

The major part of the mandible of Typhlops is a curved, bladelike

20 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

bone formerly called the articular. However, it has a number of variable
and indistinct lines, fissures, and foramina, and it is likely, as indicated by
McDowell and Bogert, that its composition includes the surangular and
prearticular as well as the articular, although the boundaries of these
elements are obscure. There is a retroarticular process of the mandible of
variable length (usually about half that of the quadrate) extending
below the quadrate.

At the anterior end of this compound “articular” is a group of three or
four bones, firmly attached to it and to each other. No movement among
themselves is possible for the bones in this group. The most prominent of
them is the coronoid, a flat, triangular bone lying against the medial
surface of the compound bone, its apex (the coronoid process) tall and
usually sharply pointed and lying just lateral to the maxilla when the
jaws are closed. McDowell and Bogert figure the horizontal base of
the coronoid in T. punctatus as emarginate near the center, a part of the
compound bone (surangular?) being thus exposed in medial view. They
attach some significance to this form of the coronoid since it resembles
the similarly notched coronoids of the anguinomorphan lizards. The
coronoid is indeed so notched in punctatus and schlegelii but in a few
other species it is so slightly notched that the compound bone is not
exposed and in most species the base is perfectly straight with not even a
slight emargination. In the general form of coronoid, Typhlops resembles
one of the two groups of anguinomorphan lizards (the diploglossa) but
differs from the other (the platynota) and the typical snakes. In the
snakes and platynotans the coronoid process arises from the posterior
portion of the bone, the anterior half of the bone having a more or less
horizontal upper border. In Typhlops and the diploglossans, on the other
hand, the coronoid process is more in the center of the bone and the
entire dorsal border is involved in the development of the process. There
is some interspecific variation in the form of the process (Plates 2, 5, 8).
It is pointed in some, rounded in others, the front may be concave or
convex, etc.

The dentary is small and toothless, although, like the maxilla of
Leptotyphlops, its edge is sometimes ragged and irregular, suggesting
former tooth fossae. The dentaries are rigidly joined to each other in the
midline by ligaments or cartilage and little or no movement between
them is possible.

At least among reptiles, the splenial is unusual in its extensive lateral
exposure. It partially conceals the dentary in lateral view. It lies close
against the ventral surface of the latter, curving up around it both
laterally and medially. In lateral view it meets the compound bone
(surangular portion) in a long, oblique suture. In medial view it extends
somewhat farther posteriad to about the middle of the base of the

THE LOWER JAW 21

coronoid, lying below and forming a horizontal suture with the latter.
The length of the splenial and its extensive contact with the coronoid and
the dentary makes the mandible a rigid unit. Here again Typhlops
resembles the diploglossans and differs from the platynotans and snakes
(including Leptotyphlops) where the splenial is short and may even fail
to reach the coronoid, permitting the formation of a vertical hinge joint
here and of a more or less movable “foremandible” composed of the
dentary and splenial. There are some variations in the size of the splenial
of Typhlops, in the degree of its lateral exposure, and in its junction with
the compound bone (the latter may overlap it). It is extremely reduced in
T. braminus, having here almost none of the normal relationships.

The angular in Typhlops is even more variable. It lies below the
compound bone, its anterior end meeting or overlapping the posterior
end of the splenial, and is visible in both medial and lateral views. It is as
long as the splenial in some species, quite vestigial in others, and absent
(or fused with the compound bone) in still others (Plates 2, 5, 8). It is
longest in T. braminus where the splenial is so much reduced.

A small columella is present in all the species of Typhlops examined.
It barely extends through a small fenestra ovalis (a notch in the fissure
between the exoccipital and prootic), and in well-cleared specimens its
greatly expanded foot plate can be seen within the otic capsule. The
columella and fenestra are usually concealed in lateral view by the
posterior end of the quadrate. In a few species the columella is freely
movable upon touch, but in most the foot plate seems firmly attached
within the capsule.

No evidence of a tabular has been reported in any Typhlops, nor was
any noted in the present series.

In Liotyphlops the lower jaw is basically the same as in Typhlops, but
some notable differences can be mentioned. In the first place, there is a
small, inverted, comma-shaped bone near the posterior end of the
quadrate. Two interpretations of this bone have been made. Dunn and
Tihen called it the tabular, a bone that connects the parietal and
quadrate in the Squamata. McDowell and Bogert suggest that it is more
likely a reduced squamosal, insofar as it is “lateral to the quadrato-cranial
articulation, considerably anterior to the paroccipital process, and iso-
lated from the parietal. . . .” The squamosal is absent in snakes, but in
most lizards it occupies a position alongside and dorso-lateral to the tab-
ular. The posterior end of the squamosal extends down to meet the
quadrate while the other end goes forward and laterad to meet the
postorbital and form with it a strong temporal arch. The fact that
Anomalepis has a postorbital “makes it the more likely that the closely
related Liotyphlops might possess the other constituent of a temporal
arch, the squamosal.”

22, OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

McDowell and Bogert do not include Liotyphlops in their list of
material examined and presumably have relied on the figures and
descriptions of Dunn and Tihen. It is necessary, therefore, to note that on
the basis of the specimens in the present study the quadrate, tabular, and
compound bone of the lower jaw in Dunn and Tihen’s figure all seem
considerably displaced dorsad and anteriad and the tabular is more
horizontal than vertical. The tabular in the specimens at hand is not
“considerably anterior to the paroccipital process” but is only slightly, if
at all, anteriad. Also, it lies directly above the end of the quadrate and is
hardly more lateral than is the posterior end of the tabular of most
lizards. It is, indeed, “isolated from the parietal,” but were it a squamosal
it would be even farther removed from the presumed position of the
missing postorbital. The best evidence supporting the “tabular” interpreta-
tion of this bone is the close resemblance in both its form and orientation
in Liotyphlops to the ventrally curving posterior end of the tabular in
lizards, especially in those where the tabular is somewhat reduced in size.
The tabular of the gecko Coleonyx, for example, except for its remaining
contact with the parietal, is very similar to that of Liotyphlops. In this
gecko, however, the contact of the tabular is only with a long posterior
projection from the rear corner of the parietal which overlies the
otooccipital region. In the absence of this extension of the parietal,
the tabular of Coleonyx would have exactly the spatial relationships of
the bone in Liotyphlops.

The quadrate of Liotyphlops is like that of Typhlops in its suspension
and its orientation, but it differs somewhat in form. Except for a very
small anterior elevation, the prominent dorsal plate of the quadrate in
Typhlops is absent here, but a similar dorsal projection, smaller and not
so flattened, is present at the other (posterior) end of the quadrate. The
form of this rear end of the quadrate suggests a loose articulation with
the tabular (Plate 2), but such a connection could not be determined
certainly.

The compound bone of the mandible here is more slender than that of
Typhlops, the articular facet for the reception of the quadrate is poorly
developed, and the retroarticular process is extremely long, much longer
than the quadrate itself. The front of the coronoid is much more convex
and the coronoid process is directed more posteriad than in Typhlops.
The base of the coronoid is straight, with no emargination.

The bone here termed splenial in Liotyphlops has been figured as the
angular by Dunn and Tihen. From the relationship of the bone to
the dentary in this genus, and in view of the stages of reduction of the
angular to be seen in Typhlops, it seems more likely that the bone in
Liotyphlops is the splenial and that the angular is absent.

The dentary is similar to that of Typhlops except that it bears teeth.

THE LOWER JAW 23

Earlier workers, from Peters and Boulenger to Dunn, had overlooked
these teeth (Taylor, 1939, detected the teeth in Anomalepis). Dunn and
Tihen, however, reported the presence of a single tooth on the dentary.
There is apparently some variation in the number of teeth here, for in one
of the two specimens at hand there are two teeth on each dentary, and in
the other specimen there are three on each dentary. The specimen with
the two teeth per dentary is quite small (68 mm). Its teeth stand in a line
almost at right angles to the main axis of the skull (the medial tooth is
very slightly ahead of the lateral one) and both seem to be functional. In
the larger specimen (158 mm) two of the teeth are likewise in an almost
transverse line, are of approximately the same size, and seem to be
functional. The third tooth here is much smaller, apparently a replace-
ment tooth, and stands behind the lateral functional tooth. These teeth of
the dentary are rather bluntly pointed, only slightly curved, and do not
show the spadelike outline of the maxillary teeth.

A slightly movable columella is present, covered in lateral view by the
posterior end of the quadrate. It is relatively larger and better developed
than those of Typhlops.

The following description of the lower jaw of Anomalepis is based on
the papers by Dunn (1941) and Tihen (1945). As figured by Dunn the
quadrate of Anomalepis is intermediate in outline between that of
Typhlops and Liotyphlops, with a flat dorsal plate present in the middle
of the bone, giving it a low triangular shape. The slender compound bone
of the mandible here is similar to that of Liotyphlops also in the
possession of a very long retroarticular process. Tihen reported the
possible presence of a separate surangular in one imperfectly cleared and
stained specimen but “confirmation of this point is needed.” The coronoid
is concave in front, and has a low and broadly rounded dorsal process
and a slender anterior extension of the base, being thus rather distinct
from both Typhlops and Liotyphlops. The base is not emarginate. A bone
obviously comparable to the splenial of Liotyphlops is figured by Dunn
as the angular, but, as pointed out above, it is more likely a splenial, the
angular being absent. The dentary bears a single tooth in the two cleared
and stained specimens which have been examined by the above two
authors, but Dunn was unable to find teeth here in three out of four
untreated specimens. Their occurrence may thus be irregular.

With respect to Typhlophis and Helminthophis, the only published
descriptions of the skeletal anatomy are a few comments by McDowell
and Bogert, including reference to the lower jaw: Typhlophis lacks a
tabular, has a more pointed coronoid, and the dentary bears a single
tooth; Helminthophis likewise has a single tooth on the dentary.

The lower jaw and quadrate of Leptotyphlops differ considerably from
those just described. The quadrate is a longer, more slender, slightly

24 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

flattened bone, with no evidence of the dorsal wing so characteristic of
Typhlops, although its posterior end is often expanded in a manner
suggestive of the rear end of the quadrate of Liotyphlops (Plates 2, 11).
This expansion in Leptotyphlops is flat and, if well developed, is usually
perforated by a foramen. Other variations occur in this part of the
quadrate. A small piece of calcified cartilage may be present as a
separate element at the end of the quadrate, it may be fused with the
latter, or it may be attached but delimited by a suture. Brock (1932)
reported the presence of a tiny tabular in this area from a study of serial
sections of L. nigricans. As described by her, it is “wedged between the
quadrate and otic capsule,” but in the accompanying lateral view of the
skull (1932, fig. 1) it is visible on top of the posterior end of the quadrate.
No bone or calcification was noted between the quadrate and prootic in
any of the species on hand, including L. nigricans, even upon careful
dissection of well-cleared specimens. McDowell and Bogert likewise
found no sign of a tabular in their Leptotyphlops material, which also
included nigricans.

In the specimens examined in the present work, a number of things
suggest that in Leptotyphlops the tabular is in various stages of
degeneration and fusion with the quadrate: the fused or separate
calcified cartilage at the end of the quadrate, the frequent expansion of
this end of the bone, and especially its resemblance in some species to the
quadrate plus the tabular of Liotyphlops. The anterior end of the
quadrate is more highly modified for articulation with the mandible than
is that of Typhlops. The articular portion is saddle-shaped, rather like a
heterocoelous centrum, and fits into a similar but more concave “saddle”
of the compound bone of the mandible.

The latter is quite short and has a strangely distorted appearance, with
irregular protuberances and foramina of various sizes (Plates 2, 11). It
probably consists of the fused articular, prearticular, and surangular, but
no sutures are present and the limits of each of these components are
obscured. A very short retroarticular process is present.

The coronoid has a shortened and distorted appearance like the
compound bone. It lies largely on the medial surface of the latter, with
only the highly variable coronoid process visible in lateral view. The base
of the coronoid also is irregular without definite anterior and posterior
parts.

A separate angular is present, lying chiefly along the ventro-lateral
surface of the compound bone, its posterior end fused to the latter in L.
dulcis. This lateral exposure is unlike the angular of typical snakes, in
which the bone is limited to the medial surface of the mandible. Its
anterior end is bluntly rounded or flattened and meets the similarly
shaped posterior end of the splenial. The junction of these two bones is

THE VERTEBRAL COLUMN AND RIBS 25

usually visible in lateral view just posterior to the rear edge of the
dentary. However, the small splenial lies almost entirely against the
medial surface of the dentary and may be so short that it does not appear
at all in a lateral view. All or most of the dorsal edge of the splenial is
separated from the dentary by the open Meckelian groove, a charac-
teristic also of the typical snakes and platynotan lizards. The wide
separation of the splenial and coronoid in the development of the hinge
joint here is the most extreme of any snake or lizard.

The dentary is large and well developed compared to that of the other
blind snakes. It appears to be compressed antero-posteriorly. The teeth,
usually four or five in number, are limited to the anterior part of a
conspicuously enlarged flange. The teeth are usually sharply pointed and
slightly recurved, except in one puzzling case (a specimen of L.
magnamaculata) where they are short and perfectly square-cut (Plate
11). A postero-dorsal projection of the dentary extends back over the
compound bone.

The “foremandible” here, consisting of the dentary and splenial, is
freely movable. This vertical hinge is a major point of distinction
between Leptotyphlops and the other blind snakes, and is a point of
resemblance to the typical snakes and some groups of the platynota. The
articulation is chiefly between the ends of the splenial and the angular,
the postero-dorsal piece of the dentary serving to limit the dorsal
movement of the tooth-bearing dentary-splenial unit.

THE VERTEBRAL COLUMN AND RIBS

Locomotion in snakes is peculiar. The vertebral column, the ribs, the
costal and cutaneous musculature, and the ventral scutes have taken over
this function and the vertebrae show a number of correlated modifica-
tions. First, they are more numerous than in any other group of
vertebrates. Some living species have over 400 and in one extinct species,
Archaeophis proavus, 565 have been counted (there is some evidence
that Archaeophis may have been a fish (McDowell and Bogert, 1954) ).
Further, the division of the column into the usual regions (cervical,
thoracic, etc.) is not at all clear. Additional articulations, the zygosphenes
and zygantra, although not unique to snakes, are quite characteristic of
them (zygantral articulations are known in several families of lizards,
both living and fossil, but not in the amphisbaenids nor, apparently, in
any other snakelike lizard). Usually, all the precaudal vertebrae except
the atlas and axis bear ribs.

26 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

These modifications of the vertebrae have attracted the interest of
various investigators, and the general anatomy of the snake vertebral
column has been known for some time. Owen (1853) presented a
detailed account of the vertebrae of several snakes, and a number of
textbook writers have added to the subject: Huxley (1871), Williston
(1925), Kingsley (1925), Goodrich (1930), and others. A recent review
of these and other more specific papers is that of Sood (1948), which also
includes studies of serial sections.

With respect to the Typhlopidae and Leptotyphlopidae, Mookerjee
and Das (1933) reported the presence of ventral foramina in the
vertebral centra of Typhlops braminus. Mahendra (1936) noted the
separate hypocentrum of the atlas and the simpler zygosphene-zygan-
trum relationship in the same species. Dunn’s (1941) study of a cleared
and alizarin-stained specimen of Anomalepis found the vertebrae to
“closely resemble those of Typhlops braminus as figured by Mahendra.”
He also found that “the odontoid is a part of the axis and not a separate
bone,’ but did not mention a free hypocentrum. Dunn and Tihen (1944)
noted the presence of hypapophyses on the atlas, axis, and other anterior
vertebrae of Liotyphlops albirostris. Tihen (1945) noted the number of
vertebrae and ribs of a second cleared and stained specimen of
Anomalepis but did not clarify the atlas-axis arrangement. Hoffstetter
(1946) described the only known extinct species of Typhlops on the basis
of two collections of vertebrae: Typhlops grivensis from the Vindobonian
(Miocene) of France, and T. cariei from subfossil deposits on Mauritius
Island of the Mascarenes.

A. REGIONS OF THE VERTEBRAL COLUMN

The vertebral column of serpents has been variously interpreted with
respect to its natural divisions. Most early writers referred to only two
regions, a precaudal (or presacral) and a caudal (or postsacral),
although Rochebrune (1881) distinguished five parts on the basis of
slight and highly variable features: cervical, thoracic, pelvic, sacral, and
coccygeal. The most recent and most acceptable scheme is that of Sood
(1941, 1948), in which the major division into precaudal and caudal is
retained (in the absence of a definite sacrum the terms pre- and
postsacral seem inappropriate ). In each of these Sood recognizes three
subdivisions: cervical, thoracic, and lumbar, and antero-, mid-, and
postero-caudal.

However, applications of the names and criteria of Sood to the
vertebral column of the blind snakes would result in considerable
distortion of some of the terms. For example, in Sood’s scheme the
thoracic vertebrae are those with well-developed hypapophyses. In the
snakes considered here, this would include only five or six anterior

THE VERTEBRAL COLUMN AND RIBS 27

vertebrae, leaving 90 per cent of the column as “lumbar.” In view of this
difficulty I use here a terminology similar to that applied to the
Amphisbaenidae by Zangerl (1945). That is: (a) cervical, to include the
atlas and axis, (b) thoracolumbar, or those vertebrae following the axis
and bearing normal unforked ribs, (c) cloacal, those bearing forked ribs
or forked transverse processes, and (d) caudal, those with unforked
transverse processes. Although this system is satisfactory for these two
families of snakes, its use is limited by the fact that the regions are not
completely comparable to those of other vertebrates. Further, the
position of the hyoid in Typhlops, for example, suggests that several
additional vertebrae are true cervicals.

B. THe ATLAS AND AXIS

The atlas in the blind snakes is unusual in that its elements remain
separate even in the adult. It is basically the same in all three genera
considered here (Typhlops, Liotyphlops, and Leptotyphlops). There are
some differences in the atlas of Anomalepis, but the two published
descriptions of the anatomy of this genus have been incomplete in this
respect.

The separation of the three units comprising the atlas of these snakes
was first noted by Mahendra (1936). The two lateral elements (Plate 14)
apparently represent the neural arches. Ventrally, each arch is rather
expanded, with an articular surface anteriad for meeting the exoccipital
and one posteriad for meeting the broad face of the odontoid process.
Both anterior and posterior facets are turned slightly mesiad; they do not
face directly forward nor directly to the rear. These articular surfaces,
like most others in the skeletons of these snakes, are composed of
calcified cartilage. The upper part of each arch is flattened, curving over
the nerve cord toward the midline but not quite contacting the arch of
the opposite side and with no indication of a neural spine. These dorsal
units slightly overlap the anterior edge of the neural arch of the axis,
without any real articulation.

The ventral element of this ring of three bones has been called
“odontoid” (Mahendra, 1936, and Sood, 1948) or simply “ventral bone”
(Dunn and Tihen, 1944). On the basis of its position and relationship to
the neural arches it almost certainly represents the hypocentrum of the
atlas, the pleurocentrum having fused with the axis to form the odontoid
process. Such separate hypocentra are known in the atlases of Seymouria,
Sphenodon, and Crocodilia, occasionally in amphisbaenids, other living
and extinct reptiles, and even in the developmental stages of the human
atlas. The hypocentrum of the blind snakes is slightly movable, bears a
blunt hypapophysis, and has two calcified cartilage articular surfaces,
one anteriad for meeting the basioccipital and one posteriad for meeting

28 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

the face of the odontoid. Both of these surfaces also face slightly dorsad.

The axis is a more typical vertebra, somewhat wider than it is high,
with a centrum, a complete neural arch, neural spine absent or very
poorly developed, a pair of postzygapophyses, a pair of zygantra, etc.
(Plate 14).

The nature of the odontoid process is not completely clear. There are
at least two possible explanations. First, the odontoid may be represented
by a small blunt knob of calcified cartilage immovably fixed to the
anterior face of the centrum of the axis. Its separate origin, however, is
clearly indicated by a groove which sets it off from the rest of the axis
(Plates 1, 14). These small knobs have been found in both species of
Typhlops which have been dissected for them (lineatus, richardi).
Because of the surrounding arches of the atlas and other obscuring
tissues, their presence in other species has not been determined.

The second possibility is that the odontoid is more like a separate
centrum, a broad piece as wide as the pleurocentrum of the axis and
bearing its own hypapophysis. It has an extensive, slightly convex articular
surface which meets both neural arches and the hypocentrum of the
atlas. It is completely fused with the true centrum of the axis. The knob
of calcified cartilage would then represent a proatlas, a piece which often
contributes to the formation of the axis of amniotes and which appears to
be the remains of a now extinct vertebra originally intercalated between
the present atlas and the skull. Like the separate hypocentrum of the
atlas, a separate proatlas (single or paired) is found in Sphenodon,
Crocodilia, and other living and extinct reptiles. Embryological studies
by Hayek (1923, 1924) indicate that in the Squamata and in mammals
the proatlas is attached to the anterior end of the odontoid process.

I am inclined to this second explanation, for several reasons: (1) The
body of the axis of these snakes projects beyond the anterior edge of the
neural arch, as if a piece had been added. (2) The axis is the only
vertebra which bears two hypapophyses, adding further to the impres-
sion of a duplication. (3) The ventral foramina of a thoracolumbar
vertebra occur in the anterior half of the centrum, at the base of the
hypapophysis, if it is present. When such foramina are present on the axis
they occur nearer the center, at the base of the second (posterior)
hypapophysis (Plates 3, 9). (4) When rudiments of axis ribs are present
they lie opposite the center of the vertebra, not at the anterior end as is
normal. (5) The odontoid of Amphisbaena is described and figured by
Zangerl (1945, pp. 765-766 ) as “very well developed, in fact as big as the
centrum of the axis proper and often wider than the latter.” Two
hypapophyses are shown in an accompanying figure, one on the odon-
toid, one on the axis proper. No proatlas is figured or reported for the
amphisbaenids.

THE VERTEBRAL COLUMN AND RIBS 29

The separate neural arches and hypocentrum of the atlas, and perhaps
the nature of the odontoid, is a primitive arrangement. Yet, its persistence
in other groups of reptiles reduces its significance as an indicator of
primitiveness within the class. Immature specimens of Thamnophis radix,
for example, among the most modern of the serpents, show basically the
same condition of the atlas and axis: a dorsally divided neural arch, a
distinct hypocentrum of the atlas, and two hypapophyses on the axis.

In most snakes the axis bears a pair of ribs, but these are usually absent
in the blind snakes. The following were the only instances noted in the
specimens considered here. One specimen of Leptotyphlops humilis
cahuilae had a pair of rudimentary ribs associated with the axis. These
did not articulate and were embedded in the tissues a short distance
lateral to the axis. Of two specimens of Typhlops lumbricalis, one had a
similar pair of small axis ribs (one-tenth normal length), the other had
none. One T. s. schlegelii had a pair of axis ribs of almost normal size.
One T. lineatus (Plate 1) had a tiny ossification to the left of the axis,
probably representing a rib vestige. One T. jamaicensis had here a small
pair of ribs about one-fourth normal length.

The cervical vertebrae as just described are typical of Typhlops.
Within the genus there is little variation. The paired ventral foramina are
present on the axis in some species, absent in most. A pronounced. neural
ridge is present in T. braminus. Otherwise, with the possible exception of
the proatlas, which was not sought in most specimens, all the above
features are present and about equally developed in all the Typhlops
examined.

In the two specimens of Liotyphlops available the atlas and axis are
essentially as in Typhlops (Plates 1-3). Neither bears ribs. The neural
arches are separate pieces. The hypapophysis on the hypocentrum of the
atlas is perhaps less well developed. Dunn and Tihen reported ribs on
the axes of three specimens of Liotyphlops albirostris. In two specimens
of the same species examined by me there is no evidence of axis ribs.
However, the ribs of the first thoracolumbar vertebra are quite small, and
the presence of ribs on the axis may well be a variable feature, as it seems
to be in Typhlops.

In Leptotyphlops there is the same general form and arrangement of
the cervical vertebrae (Plates 1-3, 10-12). There is considerable varia-
tion, however, in the degree of development of the hypocentrum of the
atlas and the hypapophyses of the axis. Both tend to be reduced in
comparison to those of Typhlops. The hypocentrum is of moderate size
in L. maximus, dulcis, and humilis, quite small in emini, and absent in
nigricans and magnamaculata. In no case does it have a well-developed
hypapophysis. The hypapophyses of the axis are usually present, but
small, and sometimes fused to form a single process (Plate 2).

80 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

In the two published descriptions of the skeleton of Anomalepis,
(Dunn, 194] and Tihen, 1945), the atlas is described as divided ventrad
but not dorsad. Dunn remarks that “the odontoid is part of the axis and
not [as in T. braminus (Mahendra, 1936)] a separate bone” and makes
no mention of any other separate bone. Presumably, then, the hypocen-
trum of the atlas is absent. In the specimen examined by Tihen the
ventral division of the atlas and other ventral features of the anterior
vertebrae could not be determined. In Dunn’s specimen hypapophyses
were “present on the odontoid, on the centrum of the axis, and on the
centra of the next three vertebrae.” The axis does not bear ribs.

The vertebral anatomy of the other genera, Helminthophis and
Typhlophis, has not been described.

C. THe THORACOLUMBAR REGION

These vertebrae make up most of the length of the column. They show
some trends and gradual changes from one end of the column to the other
but are basically the same throughout (Plate 13).

They differ from typical snake vertebrae chiefly in their depressed
form and in the absence of neural spines and hypapophyses (the latter
present only on the anterior few vertebrae). The centra are procoelous
and depressed, about twice as wide as they are high. The anterior
cotyloid cavity does not face directly forward but slightly ventrad. Also,
the posterior condyle faces slightly dorsad as well as to the rear.

The most notable feature of the centrum, one which has aroused some
interest, is the presence of obvious foramina on the ventral surface. These
openings are usually in the anterior half of the centrum, they may be
laterally paired or single and median, and they extend completely
through the centrum into the neural canal. They were noted in other
ophidian vertebrae by Owen (1866) but apparently escaped the atten-
tion of later authors. Mookerjee and Das, unaware of Owen’s statements,
could find no other reference to the apertures when they reported them
(single and median) in Typhlops braminus. Sections made by these
authors showed that in the anterior region of the body branches of the
vertebral artery pass through these openings rather than through the
intervertebral spaces with the spinal nerves. In the posterior regions
vessels from the dorsal aorta enter the foramina.

Similar, but paired, foramina are known in boids, colubrids, and
elapids among the snakes, and in several rather unrelated groups of
lizards (geckos, pygopodids, amphisbaenids, and some scincomorphs ).

Mahendra (1935) confirmed the presence of the median apertures in
T. braminus, but doubted that they were homologous to the paired ones
of lizards because of (1) their more anterior location on the centrum and
(2) their position at the apex of two slight converging ridges, rather than
on opposite sides of a median ridge as in lizards.

THE VERTEBRAL COLUMN AND RIBS 81

In the examination of the several species of Typhlops considered here,
almost all possible intermediate conditions were noted. In some species
(T. lumbricalis, reticulatus, rostellatus, and schlegelii) the foramina are
regulary paired throughout the thoracolumbar region. In T. flaviventer,
polygrammicus, platycephalus, and richardi (and others) their size
varies widely in successive vertebrae and even between the two sides of
the same vertebra. Often only one of the pair is present, and, although it
is not medial, it is usually larger in size, suggesting that arteries from
both sides pass through it. Occasional vertebrae lack any evidence of
foramina.

The position of the foramina also shows some variation relative to the
ends of the centra. In general, the apertures in middle and posterior
vertebrae are quite near the anterior end of the centrum; in the anterior
vertebrae the apertures are more nearly in the center.

Finally, in eight specimens of Typhlops braminus examined here, and
in T. vermicularis, the foramina are large and medial throughout most of
the column but smaller and paired in the anterior few vertebrae of the
same snake.

They are undoubtedly homologous to the paired foramina in the centra
of other snakes and lizards.

In Leptotyphlops there is a reduction in size of the foramina and a less
regular occurrence. They are well developed in L. emini, paired anteriad
and single (not medial) elsewhere. They are few in number (sometimes
a total of only five or six), small, and of irregular occurrence in most
species, and are completely absent in magnamaculata and some speci-
mens of humilis cahuilae.

One specimen of Liotyphlops albirostris has regular paired foramina
throughout the thoracolumbar region; a second has scattered foramina of
variable size.

For Anomalepis, Dunn reports “The more anterior vertebrae have a
‘subcentral foramen’—as reported for T. braminus. The posterior verte-
brae lack the foramen. The vertebrae in general closely resemble those of
T. braminus as figured by Mahendra.”

The vertebrae of Helminthophis and Typhlophis are undescribed.

It seems likely that these foramina mark the line of junction of the two
sclerotome halves which formed the vertebra. In a typical vertebrate
embryo the intersegmental arteries (paired dorsal branches of the dorsal
aorta) lie originally between the somites but come to be included
between the sclerotome halves of the developing vertebra.

These ventral vertebral foramina, if really intersegmental in position,
represent an unusual and primitive arrangement. Yet, like the primitive
features of the atlas, their persistence in the vertebrae of more modern
snakes like the elapids and colubrids (even Thamnophis) reduces their
special significance in Typhlops.

82 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

The body of the centrum varies somewhat in different parts of the
thoracolumbar region. The anterior centra are short and the more
posterior centra become progressively longer and more slender.

Hypapophyses are present on, at the most, the anterior four or five
thoracolumbar vertebrae. The more posterior of these hypapophyses are
quite reduced.

The neural arches are broad bands nearly as long as the centrum. The
rear edge of each overlaps the anterior edge of the succeeding arch both
dorsad and laterad down to the level of the zygapophyses. In lateral
view, therefore, the intervertebral opening is quite small, appearing only
below the zygapophyses. In most snakes a second portion of the opening
is visible above the zygapophyses. Disregarding their well-developed
processes, the neural arches are about as high as they are wide. The
neural canal is generally circular except for a somewhat flattened floor. In
an occasional axis or succeeding vertebra or two, a low mid-dorsal ridge
may be present. Otherwise, there is no evidence of a neural spine.

The processes borne on the neural arch are of three types: for the
articulation of ribs, for the articulation of one vertebra with another, and
for the attachment of muscles.

The pre- and postzygapophyses are large and prominent. They have
the usual articular relationships to each other: the former facing up,
toward the midline, and forward, the latter facing down, to the side, and
to the rear.

Very well developed in the blind snakes are the metapophyses or
mammillary processes, lateral extensions from the prezygapophyses
serving for muscle attachment. Each is a bluntly pointed projection from
the base of the prezygapophysis, lying below the level of the latter's
articular surface, and directed forward and laterad. They are present
throughout the thoracolumbar region, being largest in the middle and
posterior sections. Such processes in snakes were noted by Sood (1948),
who reported them in a number of families. Mosauer (1935) had
previously figured them under the name of “accessory processes.”

A pair of unusual intravertebral foramina were noticed in the neural
arches of T. lineatus and Leptotyphlops humilis. In lateral view each
foramen occurs at about the center of the arch (Plate 13). Although
small they seem to extend through to the neural canal, and they are of
regular occurrence throughout the thoracolumbar region. Their position
corresponds approximately to that of the ventral apertures of the centrum
and, while blood vessels are not visible in these cleared specimens, it
seems likely that small dorsal branches of the intersegmental arteries
(vertebral or intercostal) enter the neural canal through these fora-
mina.

These could not be found in the vertebrae of other species of blind

THE VERTEBRAL COLUMN AND RIBS 83

snakes. It is possible that they are present but obscure because of their
small size and the abundant muscles of this region. They are present in
the vertebrae of other snakes (Python and Thamnophis, for example).

The zygantra and zygosphenes have a rather simple arrangement in
the blind snakes. The first to comment upon and figure these articulations
in Typhlops was Mahendra (1936, fig. 7), using alizarin preparations of
T. braminus. However, his description and figure, showing the zygo-
sphenes overlapping the edge of the preceding neural arch, appear
erroneous. I have noted in several similarly prepared specimens that the
posterior edge of the neural arch is often thin, quite transparent, and
nearly invisible except under certain angles of lighting. In such cases the
underlying zygosphenes and the anterior edge of their neural arch are
plainly visible and do appear to lie at the surface.

The zygantra of most snakes are paired pockets in the mesial and
posterior surface of the neural arch. Each one receives a wedge-shaped
process, the zygosphene, from the anterior edge of the following arch,
but the articulation involves more than the pocket and wedge. Only the
tip of the zygosphene is accommodated by the pocket; the rest of its
articular surface (ventro-lateral) meets an oppositely directed facet on
the mesial surface of the preceding arch. This latter facet, although not
depressed, is continuous with the pocket and is here considered a part of
the zygantrum.

Sood (1948) in a study of serial sections of the vertebrae of T.
braminus remarked. “The zygosphene, consequently, does not appear to
fit into a cavity as in other snakes, but forms a pair of lateral articular
processes which lie under flap-like projections on the postzygapophysial
region of the preceding vertebra.”

In the species of Typhlops in which isolated vertebrae were examined
for these features, the articulations show little variation and are basically
the same as those of other groups of snakes (Plate 13). Both zygosphenes
and zygantra are relatively smaller, especially the actual pocket of the
zygantrum, but they are by no means rudimentary. They are more nearly
on a level with the zygapophyses, rather than dorsal to them.

The vertebrae of Liotyphlops (Plate 13) are almost identical with
those just described, the only apparent differences being a slightly more
depressed neural arch and less well-developed metapophyses.

The vertebrae of Leptotyphlops (Plate 13) are also basically like those
of Typhlops, but there are some quantitative differences. The neural arch
is not quite so depressed, and the neural canal is somewhat higher than it
is wide. The level of the zygantral articulations is slightly above that of
the zygapophyses. There is a broad and very slightly elevated neural
ridge. The reduction and irregularity of the ventral foramina has been
mentioned.

34 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

The significance of the ratio of number of vertebrae to number of scale
rows has been the subject of some debate. Stehli (1910) concluded from
a study of various lizards that the primitive arrangement is a single row
of scales for each body segment. Camp (1923, p. 400) presents
considerable evidence to the contrary and notes that Stehli’s view “would
involve the derivation of the normal zonurids from the degenerate
Chamaesaura, the normal teiids from the worm-like Bachia, and many
other equally startling cases.” He concludes: “The best evidence seems to
show that the most primitive features of the squamation of lizards are:
(1) uniform granular scales on all parts of the body ... ; (3) trans-
verse rows of ventral scales not in correspondence with each pair of
ribs. . . . The frequency of the lesser number of ventral skin segments
aligns itself with the frequency of attachments of the specially developed
layers of the rectus muscle concerned with serpentiform or worm-like
terrestrial locomotion.”

Camp’s theory seems applicable also to the snakes. Certainly the 1:1
ratio is typical of the more advanced families of snakes.

In the blind snakes a number of different dorsal scales/vertebrae ratios
occur (Table 1). “Two scales per segment” has been reported by three
authors for Typhlops, Liotyphlops, and Anomalepis. In most species of
Typhlops, however, the ratio is nearer 1.7:1, varying from leas eto
2.2:1. Although not statistically significant, the figures suggest a correla-
tion between a high number of dorsal scales and a higher ratio. Only in
those species with about 400 scale rows (e.g., schlegelii and polygram-
micus) does the ratio reach 2:1.

Mahendra (1936) reported for T. braminus that “The ribs alternate
with two scale rows. . . .” In the specimens of braminus examined here
the ratio is considerably lower (1.6 to 1.7:1), and even Mahendra’s
photograph (1936, fig. 9) seems to show pairs of ribs covering slightly
less than two scale rows each. This lack of a definite 1:1 or 2:1
correlation between the scales and ribs of Typhlops may be a primitive
condition or just another special peculiarity. The reduction of the mid-
ventral scales of Typhlops, which are barely, if at all, distinguishable
from the adjacent dorsals, is no doubt an associated feature. Although the
mechanics of their burrowing seems not to have been studied, it is
doubtful that the “caterpillar” type of locomotion, accomplished in most
snakes by definite rib and ventral scute connections, would occur in these
blind snakes.

With respect to the vertebrae of Typhlops it is interesting to note an
apparent geographic variation in the number of thoracolumbar vertebrae
in the widely distributed T. braminus: Ceylon—172, 174; Madagascar—
176; Java—176, 177, 178; Thailand—175; Philippine Islands—168, 169;
Mexico—166. The close agreement between Mexican and Philippine

THE VERTEBRAL COLUMN AND RIBS 85

specimens is especially interesting in view of Taylor’s (1940) suggestion
that the Mexican population of braminus is of Philippine origin.

Dunn and Tihen (1944) report “two scales to each segment” in three
specimens of Liotyphlops albirostris, but scale counts are not given. In
the two specimens of albirostris examined here a ratio of 1.7:1 occurs,
agreeing well with most Typhlops.

Dunn’s cleared specimen of Anomalepis aspinosus had a ratio “close to
2:1,” although the vertebral count was not certain.

These ratios in Helminthophis and Typhlopis are as yet unknown, but
are probably close to those of the preceding genera.

Leptotyphlops is also reported to have two scales to each segment, but
the scales/vertebrae relationship noted in this investigation is almost
exactly 1:1. Minor departures from this ratio are most likely due to
errors in counting scales. In this feature the genus resembles the higher
snakes.

Vertebrae of the thoracolumbar region always bear ribs. These are
slender, curved, directed somewhat posteriad, and frequently cartilage-
tipped. They are basically single-headed (syncephalic ), articulating with
a rounded prominence, the synapophysis, situated low on the neural arch
(Plate 13). This terminology follows that of Remane (1936), the
synapophysis representing the fused diapophysis and parapophysis. The
articular facet of the typhlopid rib head is a simple shallow cup. This
facet is probably, for reasons given below, not so much a fusion of the
tuberculum and capitulum as it is a new formation between the much
reduced latter structures.

A small projection extends dorso-posteriad from the proximal end of
the rib (Plate 13), apparently representing a reduced tuberculum. It
does not articulate with the vertebra. An identical process occurs on the
ribs of garter snakes (Thamnophis radix). On the opposite side of the
articular cup of the rib in Typhlops is a smaller, poorly developed, blunt
process which, like the dorsal one, plays no part in the articulation of the
rib. In Thamnophis a similar, but well-developed, ventral process is
present and makes contact with a ventral extension of the synapophysis,
serving to brace the rib and restrict its movement toward the mid-ventral
line. The major part of the synapophysis here is a hemispherical
protuberance quite like that in Typhlops. These ventral projections from
the rib heads of both genera seem best interpreted as capitula. The great
reduction of the capitular process in Typhlops and the very simple rib-
vertebra articulation is further indication of the reduced role of the ribs
in the locomotion of the blind snakes.

The ribs of Liotyphlops and Leptotyphlops (Plate 13) are quite like
those just described for Typhlops. The only notable difference is a
greater reduction of the capitular process in Leptotyphlops.

86 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

D. THe CLoacaL REGION

The vertebrae of this region differ only slightly from the thoracolumbar
group. They are more compressed in appearance longitudinally, being
relatively higher and rather short. The ventral foramina are often present
but of irregular occurrence and size. Pre- and postzygapophyses are
present and well developed. Metapophyses are present but reduced in
size. Zygantra and zygosphenes are quite reduced or absent, especially in
the last vertebra or two. Hypapophyses are absent. The most notable
feature of this region of the column is the ribs. They are forked, the two
pieces first diverging and then curving toward each other, lying in a
vertical plane (Plates 19-22). Such forked ribs enclose lymph hearts and
are typical of snakes and some lizards. These forked ribs, or lympha-
pophyses, are usually fused with the vertebrae in the blind snakes, but the
anterior ones may be slightly movable. They vary in number from two to
five pairs in the species examined, but within a species are relatively
constant (Table 1). The thoracolumbar ribs just anterior to these forked
ones occasionally show tendencies toward the forked condition by
bearing a short dorsal process and by curving upward briefly before
continuing their normal ventro-lateral direction (Plates 19-22). The
posterior lymphapophyses decrease in size, especially the dorsal piece.
This latter finally becomes incorporated into the base of the lower one,
and the simple transverse process of the caudal vertebra appears. In this
antero-posterior transition the thoracolumbar rib seems to be homologous
to the ventral piece of the cloacal rib and to the transverse process of the
caudal vertebra.

In both Liotyphlops and Leptotyphlops the vertebrae and forked ribs
of this region are similar to those of Typhlops just described. Dunn
reported for Anomalepis three pairs of “immovable forked lateral
processes” similar to those of Typhlops.

E. THe CaupAL REGION

These vertebrae appear still more compressed from front to rear, often
being nearly twice as high as they are long in the mid-caudal region.
They are simplified, without zygantra and zygosphenes and with reduced
zygapophyses and metapophyses. There are occasional ventral foramina.
The open haemal arches, characteristic of the caudal vertebrae of most
snakes, are completely absent. Transverse processes are present on all
these vertebrae, but are quite reduced posteriad. The terminal two to
four vertebrae commonly fuse to form a blunt tip of the column, although
their processes and intervertebral foramina persist, indicating the number
of vertebrae involved.

The most unusual feature of the caudal region of the column is the

THE VERTEBRAL COLUMN AND RIBS S7

presence in some species of Typhlops of a mid-ventral rodlike ossification
associated with the fused terminal vertebrae (Plate 14). In T. polygram-
micus and vermicularis these structures are well developed; in T.
lineatus, rostellatus, and jamaicensis they are rudimentary. Their form
and location are reminiscent of the urostyle of frogs. They are directed
forward but the appearance of the fused terminal vertebrae in some of
the above species suggests that the tip of the vertebral column itself has
been bent down and forward. The major part of the frog urostyle
develops from an ossified hypochordal rod, and these structures in
Typhlops may have a similar embryonic origin. In spite of their well-
ossified nature in the first two species they appear to be functionless,
embedded in the tissue of the tail. No mention of any such structure in
snakes was encountered in the literature.

The preceding description applies quite well to the caudal vertebrae of
Liotyphlops and Leptotyphlops, except that no evidence of the “urostyle”
was seen here.

Table 1, which follows, shows the scales/vertebrae ratios of representa-
tive species of blind snakes. The usual system of counting dorsal scales in
the blind snakes is to begin with the rostral scale and include the mid-
dorsal head scales (prefrontal, frontal, interparietal, and interoccipital ).
However, in order to obtain a more valid ratio, the dorsal scale counts in
Table 1 begin immediately behind these head scales and continue to the
level of the anus. Figures in parentheses under precaudal vertebrae refer
to cervicals, thoracolumbars, and cloacals respectively; under caudal
vertebrae they refer to the separate ones and the fused terminal ones
respectively. The figures for Anomalepis are from data presented by
Dunn (1941); those for the last three specimens of Liotyphlops are from
Dunn and Tihen (1944). Dashes indicate that scale counts were not
recorded before the specimens were cleared.

TABLE 1
DORSAL SCALES/VERTEBRAE RATIOS

Sup- CaupaL
DorsaAL PRECAUDAL CAUDAL VERTE-
ScaLES VERTEBRAE Ratio ScALEs BRAE
Liotyphlops albirostris 344 207 (2—202-3) le7/ell 16 16(13-3)
a oe 353 208 (2-—203-3) Lyell 15 16(14-2)
ee ue - 252(2-245-5) alee - 8
of - - 238(2—-231-5) PE hes - 9
rh a - 234(2-227-5) A Ls - 10
Anomalepis aspinosus 328 173(2-168-3) feel - -
Typhlops braminus = 171(2-166-3) = = 10(7-3)
“ fe 172(2-168-2) - - 10(7-3)

a 282 174(2-169-3) 1.6:1 12 10(7-3)

38

OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

TaBLeE 1—Continued

Sus- CaupDAL
DorsaL PRECAUDAL CAUDAL VERTE-
SCALES VERTEBRAE Ratio SCALES BRAE

Typhlops braminus 300 177 (2-172-8) ileal 12 10(8-2)
as ee 292 179(2-174-3) 1.6:1 11 10(8-2)
g s 309 181 (2-176-3) L272 12 10(7-3)
« as - 181 (2-176-3) = = 11(8-3)
rs : Bly 180(2-175-3) iL ¢sil 12 11(8-3)
ee ‘ 300 182(2-177-3) 1.6:1 11 11(8-3)
ce op ~ 183 (2-178-3) - - 11(8-3)
- blanfordi lestradei 435 237 (2—231-4) 1.8:1 10 11(8-3)
- boettgerz 377 200(2-194—4) 1.9:1 8 7(4-8)

: flaviventer — 207 (2—201-4) - - 13(10-3)
af lineatus ~ 254(2-249-3) - ~ 8(5-3)
“ lumbricalis 279 169(2-164-3) L.7/eil 10 10(8-2)
i platycephalus 371 222 (2—215-5) He7/ Bi 11 11(7-4)

os polygrammicus - 221 (2-214-5) — - 18(15-3)

ae S 392 194(2-189-3) 2.0:1 19 16(13-3)

os 5 393 193 (2-188-3) 2.0:1 19 16(13-3)

WG 6 409 206 (2—201-3) 2.0:1 16 14(10-4)
a pusillus 290 158(2-153-3) 1.8:1 12 12(8—4)
as reticulatus 213 143 (2-138-3) 1.5:1 10 9(6-3)
a richardi 331 204(2-199-3) 1.6:1 13 13 (9-4)
vY rostellatus 320 183 (2-177—4) He7/ell 14 10(8-2)
i schlegelii schlegelii 407 189(2-182-5) POM 8 9(5-4)
a ef mMucruso 456 202 (2-195-5) 2.321 a 8(5-3)
re vermicularis 346 193 (2-187-4) 1.8:1 13 12(8—4)

Leptotyphlops dulcis dissectus = 216(2—210-4) — - 16(13-3)

ee a ee - 218(2-212-4) = = 16(13-3)

ft emini 242 224 (2-218-4) Patel: 21 25 (22-3)

ut humilis cahwilae ~ 259 (2-252-5) - - 21(19-2)

ss sf is ~ 269 (2263-4) - - 20(18-2)

“s magnamaculata 222 231 (2—225-4) 96:1 19 19(16-3)

se maximus 199 202 (2-196-4) 99:1 14 17(15-2)

wt nigricans 207 198(2-193-3) 1.0:1 28 29 (26-3)

THE HYOID

The hyoid of the blind snakes is quite varied in form and position and
has received the attention of several investigators. There are two distinct
types. One is a Y-shaped form somewhat like the hyoid of higher snakes,
but with the anterior median process highly developed and with the
posterior cornua more divergent (Plates 15-18). This type is found more
or less embedded in the base of the tongue in Typhlops and in a more
superficial position in Leptotyphlops. The second type, known in

THE HYOID 89

Anomalepis and Liotyphlops, is so unique that it was at first taken to be a
reduced scapulocoracoid. It is a slender, threadlike structure, superficial
in position, immediately behind the head, and has the form of an M with
its legs bent back upon themselves (Plates 2, 3, 17, 18).

A generally accepted scheme of homologies of the parts of these hyoids
has not yet been reached. Dunn and Tihen (1944), the discoverers of the
peculiar M-shaped hyoid of Liotyphlops, considered it a vestigial
pectoral girdle because of (1) its unusual, most unhyoid form, (2) its
resemblance to the girdle of the burrowing lizard Dibamus, and (3) the
presence at the anterior end of the trachea of a small inverted U-shaped
element which much more closely resembles the usual ophidian hyoid.
They did mention but discounted at that time an alternative explanation
which seems to be the correct one. That is, the small anterior element is
the cricoid cartilage, and the larger M-shaped thread is the hyoid.

Warner (1946) found the same M-shaped structure in Anomalepis and
established it as a hyoid by demonstrating that the muscles attached to it
are those normally originating or inserting on the hyoids of other snakes.
She considered the legs of the M as thyrohyals and the middle section as
the basihyal, following the usual terminology of ophidian hyoids.

In a later paper Smith and Warner (1948) discarded as inappropriate
the term thyrohyal for the legs of the M, instead calling them hypohyals
and homologizing them with the posterior cornua in all other snakes. In
this interpretation the middle “V” portion is the basihyal and the
recurved extensions of the legs (directed toward the angles of the jaws )
are ceratohyals, the entire structure thus being derived from the hyoid
(second visceral) arch.

McDowell and Bogert (1954) argue against this latter view, suggesting
that the M-shaped arch of Anomalepis and Liotyphlops represents a sort
of “floating” hypohyal (that is, free from the basihyal) as seen in the
anguinid lizard Celestus, for example, but differing from the latter in the
retention of ceratohyals and in the midline junction of the left and right
hypohyals. The more anterior U- or Y-shaped element in these genera,
between the rami of the lower jaw, then represents the basihyal.

This latter interpretation is in part unacceptable, insofar as the Y-
shaped element between the lower jaws cannot be the basihyal. An
identical structure is present in the same location in both Typhlops and
Leptotyphlops, genera which have also the larger and more typical
basihyal farther to the rear (Plate 17). This far anterior structure is
almost certainly the cricoid cartilage. It is partially calcified and is clearly
evident in most of the species of Typhlops and Leptotyphlops examined
by me. Its cricoid nature is indicated by its position below the glottis, its
shape, its occasional fusion with the adjacent tracheal rings (both are
derived from the sixth visceral arch), and its relationship to a pair of

40 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

dorsal arytenoid cartilages, which are also partially calcified (Plate
I).

Where then is the basihyal of Anomalepis and Liotyphlops? It may
indeed be missing. It seems to be absent in some burrowing snakes of
other families (Rhinophis, Cylindrophis, and Eryx) and in at least two
species of Typhlops examined in the present study (pusillus and
lumbricalis). In these forms, however, there is no tendency toward a
fusion of the remaining lateral pieces of the hyoid. If Liotyphlops and
Anomalepis are without a basihyal, then such an unusual fusion of lateral
hyoid elements has occurred.

An examination of Cope’s numerous figures of saurian hyoids (1900,
Plates 1-4) suggests still another interpretation of this M-shaped hyoid.
The hypohyals of lizards are, as McDowell and Bogert have pointed out,
directed forward from their point of junction with the basihyal. The
ceratohyals of lizards, on the other hand, whether fused with the
hypohyals or forming sharp-angled articulations with them, are always
directed posteriad. In several species of lizards the distal (posterior )
portions of the ceratohyals are recurved, terminating in an anteriorly
directed hook (Plate 18).

The following modification of Smith and Warner's terminology, there-
fore, seems to provide the most likely explanation. The middle “V”
portion of the M represents not the basihyal alone but the basihyal (only
the broad, shallow apex of the V) plus the hypohyals (the anteriorly
directed portions of the V). Each entire leg of the M, including its
recurved portion, then represents a ceratohyal. The chief difficulty in this
view is the unusual form of the section to be called basihyal—a simple
transverse rod, slightly convex posteriad. In lizards and in both Typhlops
and Leptotyphlops this part of the hyoid nearly always has a highly
developed anterior glossohyal process. The presence of such a process is
not an absolute criterion of the basihyal, however. The process is quite
reduced or completely absent in the typical snakes, and even in Typhlops
there is variation in its development (e.g., it is extremely short in T.
polygrammicus). In view of the above, and pending determinative
embryological work, it seems reasonable to call the small midsection of
this peculiar hyoid a basihyal rather than considering the latter structure
absent.

The hyoids of Typhlops have in the past been described as simple Y-
shaped structures, buried in the tongue musculature, with the apex of the
Y directed forward and with rather divergent posterior horns. They are
small, usually 2 mm or less in length, and are located some distance
behind the head. This Y-shaped form is the only type observed in this
genus to date, It has been considered to be the fused basihyal and
hypohyals (Smith and Warner, 1948) and the basihyal alone (McDowell

THE HYOID 41

and Bogert, 1954). In the examination of the several species of Typhlops
included here, however, considerable interspecific variation of the hyoid
was found, with three distinct types present (Plates 15, 18).

The first is the Y-shaped type noted by previous authors. Such hyoids
in the blind snakes are usually composed of calcified cartilage, although
in two species (boettgeri and schlegelii) they appear to be true bone.
There is also variation in the relative size of the entire hyoid, in its
antero-posterior location, and in the degree of development of the
glossohyal process. In one species this latter process may be almost
absent, while in another it may comprise over half the total length of the
hyoid. The hyoid may barely cover one body segment or may extend
across five or six. Within a species, however, all of these features seem to
be quite constant. In every one of ten specimens of T. braminus, for
example, the hyoids were of indentical size and shape and lay between
ribs 8 and 14. The second type of hyoid in Typhlops is composed of this
Y-shaped calcified cartilage plus two slender bones, more or less parallel
and immediately behind the former structure. The third type consists of
the pair of parallel bones only, the Y-shaped cartilage being absent.

As in Anomalepis and Liotyphlops, a comparison of these hyoids of
Typhlops with those of lizards sheds considerable light on their homolo-
gies. In most lizards the hyoid consists of a basihyal plus anteriorly di-
rected hypohyals (cartilage ), posteriorly directed and sometimes recurved
ceratohyals (cartilage), and the first pair of ceratobranchials (almost
always bone) (Plate 18). An additional pair of cartilaginous rods is often
present. They represent the second pair of ceratobranchials and are at-
tached to the basihyal, lying between the first ceratobranchials. How-
ever, in the limbless lizards there is a decided tendency toward the
reduction of the hyoid—first a loss of ceratohyals, then of the hypohyals.
This leaves finally (as in Anniella pulchra) only a forked basihyal and
the first pair of ceratobranchials, exactly the situation found in some
Typhlops.

In view of these intermediate stages of hyoid reduction in lizards, the
basic hyoid elements in Typhlops clearly represent the basihyal and the
first pair of ceratobranchials. The three types of Typhlops hyoids seem to
represent further stages of simplification of the usual saurian hyoid. The
most primitive of the three types is that one composed of both the
calcified basihyal and the osseous first ceratobranchials, as in T. reticu-
latus and blanfordi. Further reduction of this stage has apparently
occurred through the loss of the basihyal, leaving the parallel ceratobran-
chials, as in lumbricalis and pusillus.

In the case of the simple Y-shaped hyoids (T. braminus, polygram-
micus, and others) the homologies are not so clear. There are at least
three possibilities, none of which is likely to be established without

42 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

embryological evidence. (1) The ceratobranchials may be absent, the
remaining Y representing an elongate basihyal alone. (2) The cerato-
branchials may have lost their usual osseous nature and fused with the
posterior extensions of the basihyal. (3) The Y may represent the
basihyal plus the second pair of ceratobranchials. I doubt these latter two
possibilities, inasmuch as there is no evidence of a fusion of parts in any
Y-shaped hyoid, nor is there any sign of the second ceratobranchials in
any Typhlops nor in any limbless lizard. The first suggestion has two
points in its favor: (1) the Y’s can be arranged in a series showing a
gradual increase in the development of their posterior extensions, from
the very short one of T. blanfordi (and Anniella) to the longer, more
typical ones; (2) where both basihyal and ceratobranchials are present,
the length of the posterior extensions of the basihyal is inversely
proportional to the length of the ceratobranchials, suggesting that the
basihyal extensions may become elongate in “compensation” for a
reduction of the ceratobranchials.

In Leptotyphlops the hyoid is much less variable (Plate 16). It is Y-
shaped and always composed of calcified cartilage. It differs from that of
Typhlops in the greater development of the posterior cornua and in their
more parallel positions. The parallel or slightly convergent relationship of
these parts is considered typical of the hyoids of higher snakes. However,
the posterior horns of some species of Leptotyphlops are quite divergent.
In this genus, at least, the degree of divergence seems generally
correlated with the relative length of the hyoid, the shorter ones being
the more divergent. This character of the ophidian hyoid may, therefore,
be primarily a reflection of its length.

Although the typical hyoid of Leptotyphlops is longer and the horns
usually more parallel than those of Typhlops, there are examples in both
genera of intermediate conditions. I believe, therefore, that the Y-shaped
hyoids of these two genera are perfectly homologous and that even the
long slender hyoid of L. dulcis represents only a basihyal with highly
developed processes. In the absence of contradictory embryological
evidence, this line of thought can be extended to include even the
slender, hairpin-like, calcified cartilage hyoids of the highest snakes,
which differ from those of Leptotyphlops chiefly in the reduction or
absence of the glossohyal process.

The relationship between the Y-shaped and M-shaped hyoids of the
blind snakes is not entirely clear. Both types are obviously derived from
the basic lizard hyoid, but it seems highly unlikely that either could have
given rise to the other. The anomalepid type is certainly the more
primitive in its retention of hypohyal and ceratohyal elements, but the
extreme reduction of its basihyal and the absence of ceratobranchials
precludes the derivation from it of the Typhlops or Leptotyphlops
types.

THE PELVIC GIRDLE 43

Hyoid structure, then, indicates the wide phylogenetic separation of
the Typhlops and the anomalepid lines. Leptotyphlops, of course, on the
basis of other features is rather far removed from both of these lines.

THE PELVIC GIRDLE

No known snake shows any trace of the pectoral limbs or girdle, but
the presence of vestigial elements of the pelvic girdle characterizes four
of the more primitive families (the Boidae, Aniliidae, Typhlopidae, and
Leptotyphlopidae ). The source of much of the early interest in the blind
snakes was the occurrence of these rudimentary girdles. They are figured
in some of the early herpetological works (e.g., Peters, 1882). Duerden
and Essex (1923) described and figured the girdles of Leptotyphlops
nigricans and four species of Typhlops, noting for the first time the
cartilaginous elements in the girdle of Typhlops and interpreting the
ossified rods here as ischia. Essex (1927) in connection with other studies
of degenerative evolution in reptiles, figured the girdles of eight
additional species of Typhlops and five of Leptotyphlops. His study
involved more than a hundred specimens and pointed out a number of
inter- and intraspecific variations. Later writers have commented on the
girdles of various species.

Leptotyphlops has by far the most elaborate pelvic girdle among blind
snakes. In most species separate pairs of bones representing ilia, ischia,
pubes, and even femora lie immediately anterior to the anus (Plates 19,
20). The three rod-shaped bones of each half of the girdle radiate from
an acetabular region, normally without fusion (the ilium and pubis are
fused in L. bakewelli). The ilia and the pubes are more consistently
ossified. The ilia are directed upward, to the rear, and slightly laterad.
They usually lie medial to the adjacent thoracolumbar ribs and have no
direct connection with the axial skeleton. The pubes may either converge
or diverge anteriad. The ischia vary considerably in their development
and may be true bone or calcified cartilage. They converge posteriorly
and are loosely connected in some species to form what has been
called a symphysis. Even in those cases where the ischia are quite close to
one another, however, each is separately movable so that symphysis, in
the proper sense of the word, does not exist. Nevertheless, their
connection with each other may be considered a primitive feature not
present in the girdles of other snakes. The distal end of any or all of these
bones may bear a slender calcified cartilage tip (Plates 19, 20). Whether
these bits of cartilage deserve recognition as hypoischia, for example, is
doubtful, in view of their occasional presence even on the femur. They

44 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

more likely represent an unossified portion of the cartilage precursor of
these replacement bones. Such cartilages are not figured by Essex,
although similar cartilages are shown on the ischia of his Typhlops.

The wholly cartilaginous girdle of Leptotyphlops albifrons is reduced
unusually. Each half is triradiate apparently representing the fused ilium,
ischium, and pubis. A femur is absent. Tihen (1945) quotes an oral
communication from Mr. Leonard Laufe to the effect that some species
of Leptotyphlops completely lack a girdle, but no examples are given.

The femur is a bone or calcified cartilage of variable shape and
development. At best it is unequally tripartite. One piece is directed
toward the acetabulum, another longer one ventrad and to the rear, and
the third upward, laterad, and to the rear. The latter projection bears a
cornified clawlike cap which may even extend to the surface by way of
a pore in the skin. Essex noted this condition in only one of nearly 100
dissected specimens of L. nigricans—a male with well-developed testes.
Essex suggested that the claw might be protruded only at the breeding
season, functioning in courtship as does the similar spur of some male
boids. However, the only specimen of the present series with such ex-
posed claws was an immature female L. dulcis dissectus. The claws were
undoubtedly better developed in the ancestors of this group, and their
present infrequent exposure seems best explained as merely an extreme
development of a now variable and nonfunctional structure (List, 1955).
The femur of some species is very small, may occur as two pieces, and
lacks a claw.

The girdle of Typhlops is much simpler, although a number of
interspecific and intraspecific variations may occur (Plates 19, 21, 2)
Normally a pair of bony rods, the ischia, lie more or less parallel to each
other just anterior to the anus. Additional cartilaginous elements repre-
sent ilia and pubes in some species. They are only rarely calcified or
osseous, and are never as prominent as the ischia. Evans (1955) reported
the first instance of an ossified (calcified?) pubis in Typhlops, finding it
in only one of seventeen specimens (T. jamaicensis). Three of his
specimens had ilia which were also osseous or calcified. A single specimen
(T. schlegelii) of the present series had a pair of tiny ossifications
representing ilia. The most unusual girdle was that of T. pusillus: a
robust, well-ossified bone with three processes, apparently the fused
ilium, ischium, and pubis. In a specimen of T. lineatus the girdle was
almost entirely cartilaginous. Only the left side was visible, consisting of
a slightly calcified ilium and ischium. Essex consistently figured a slender
or bluntly rounded cartilage, the hypoischium, at the posterior tip of each
ischium. These may have been present in the specimens examined by me,
but uncalcified cartilage is not easily visible in these cleared tissues, and
they were definitely observed in only two species.

DISCUSSION 45

Pelvic girdles have to date not yet been observed in the other genera of
blind snakes (Anomalepis, Helminthophis, Liotyphlops, and Typh-
lophis). However, the larger of the two specimens of Liotyphlops
albirostris in this series has a girdle in the form of a pair of broad
cartilages just anterior to the anus (Plate 19). Each lies chiefly in a
transverse plane, with a dorsal iliac process and a continuous ventral part
of doubtful homology which extends mediad and slightly forward
(suggesting a pubis, rather than an ischium). A single small granule of
calcification occurs in one of the cartilages. Like the cartilaginous ilia and
pubes of Typhlops, these pelvic bars of Liotyphlops are probably of

irregular occurrence.

DISCUSSION

The anatomy of the blind snakes shows an unusual mixture of
primitive and very specialized features. Most of the latter are obvious
reflections of the burrowing mode of life, are found in other fossorial
squamatans, and may thus be disregarded in consideration of evolution-
ary relationships. Their very short tail, for example, is a feature also of
most of the amphisbaenid lizards and such burrowing snakes as the
uropeltids. The shortened tail is extreme in some species of Typhlops,
where it may comprise only 1 per cent of the total length. The great
reduction or absence of neural spines and hypapophyses of the vertebrae
may also be considered as extremes of a trend in burrowers. Johnson
(1955) found some reduction of these processes to be characteristic of
other burrowing snakes, and the vertebrae of amphisbaenids are quite
like those of Typhlops in their lack of neural spines and hypapophyses,
except for the latter on a few anterior vertebrae. The broad premaxillae,
fused into a single unit, and the generally enlarged nasal region, again
most extreme in Typhlops, are further indications of a burrowing
existence. The unusual perforations in the nasal bones of Typhlops
facilitate the innervation of the abundant sense receptors in the skin of
the rostrum. Simplification of the hyoid apparatus of fossorial lizards is
also apparently correlated with burrowing, to judge from the reduction.
However, the functional significance of this latter trend is not clear, since
the tongue is not correspondingly reduced. The loss or reduction of
postfrontals is probably also a correlation since it is known in such
semiburrowers as the coral snakes and the burrowing vipers.

Some of the specialized skeletal features of the blind sakes which are
not obviously correlated with fossorial life include: (1) the rotation of

46 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

the maxilla to a transverse position in the typhlopids and anomalepids
and the highly unique suspension of the bone in the latter group; (2) the
reduction or loss of teeth and tooth-bearing bones in all the groups—
from the maxilla in Leptotyphlops, from the dentary in the others; (3)
the highly developed hinge in the mandible of Leptotyphlops; and (4)
the posterior migration of the hyoid in all but the anomalepids.

Basic primitive features, presumably retained from squamatan ances-
tors, include: (1) the pelvic vestiges, with even an ischiac “symphysis” in
an occasional Leptotyphlops; (2) lack of a definite scales/vertebrae ratio
in the typhlopids and anomalepids; (3) a distinct proatlas and three
separate elements comprising the atlas; (4) paired parietal bones,
especially frequent in Typhlops; and (5) the attachment of the quadrate
directly to the skull.

The first suggestion of a change in the classification of the blind snakes
since the original establishment of the Typhlopidae and Leptotyphlopi-
dae was Taylor’s (1939) proposed erection of the family Anomalepidae,
with Anomalepis as the monotypic genus: “This small group of snakes
associated in the genus Anomalepis differs from both the families
Typhlopidae and Leptotyphlopidae in such a way as to preclude their
inclusion in either family.” The basis for his proposal was the presence of
teeth on both the maxilla and dentary and the distinctive arrangement of
head shields.

Dunn (1941) disputed Taylor’s proposal, pointing out that it “disre-
gards entirely the obvious characters of scalation and dentition, disre-
gards the obvious relationship of Anomalepis to Helminthophis, and is
directly contradicted by the osteology,” which basically resembles that of
Typhlops.

Tihen (1945) agreed with Dunn that Taylor's action was premature
and that “recognition of a family Anomalepidae containing the single
genus Anomalepis is unwarranted.” He also felt, however, that there had
been a tendency “to minimize the importance of certain features in which
the Anomalepis-Liotyphlops compex differs from both Typhlops and
Leptotyphlops” and that the former genera plus Helminthophis are
worthy of consideration as a valid family or “more likely” a subfamily
group, the Anomalepinae.

Among the characters which are unique (with rare exceptions ) to one
or more of the anomalepid genera are: (1) the presence of bones in
the orbital region and their role in the kinetics of the maxilla; (2) the
presence of one, two, or three teeth on a reduced dentary; (3) the
presence of “laterosphenoids”; (4) independent ectopterygoids; (5) a
distinct tabular; (6) a separate surangular in A. aspinosus; (7) the
unusual W-shaped hyoid apparatus and its more anterior position; (8)
absence of an angular; (9) a very reduced and cartilaginous pelvic girdle

DISCUSSION 47

or none at all; (10) a single median supraoccipital; (11) nasals fused as a
single large plate; and (12) the odd maxillary teeth of Liotyphlops. The
first seven of these represent a more primitive state than the corre-
sponding conditions in Typhlops, where loss or fusion of various bones has
occurred. In spite of the greater reduction of the pelvic girdle and the
loss of the angular (the only features in which they are more advanced
than Typhlops), the anomalepids as a group are much more primitive
than their obvious relative Typhlops. That they are more nearly related
to Typhlops than to Leptotyphlops is indicated by their scalation, their
scales/vertebrae ratio, and especially such skeletal features as the
transversely oriented, toothed, movable maxilla, and the fundamental
correspondence of their lower jaws. In view of this closer relationship
between Typhlops and the anomalepids, Tihen felt that recognition of
three equivalent families of blind snakes was not warranted.

I believe, however, that the twelve features listed above, considered as
a whole, are sufficient justification for the establishment of the Anomale-
pidae, to include the genera: Anomalepis, Liotyphlops, Helminthophis
and Typhlophis. The latter two are placed here on the basis of statements
by McDowell and Bogert (1954) that “Typhlophis has a skull very
similar to that of Liotyphlops, differing in only a few minor details,” and
that Helminthophis has the anomalepid type of hyoid. This peculiar
anomalepid hyoid and the impossibility of deriving any of the typhlopid
types from it, or vice versa, is the character most suggestive of a rather
distant phylogenetic separation of the two lines.

These three families of blind snakes are certainly not equally related to
each other. However, this argument against the third family loses force in
view of the current differences of opinion as to whether the typhlopids
and anomalepids even belong in the same suborder with the leptotyphlo-
pids and other snakes. Further, the “equivalence” of vertebrate families
or other taxonomic categories above the species can never be more than
approximate, even within a taxon, because the groups of any one
taxonomic level will vary in number of species, unique features, etc., and
because of the subjective value or weight placed on a taxonomic
criterion, such as the emphasis laid upon the hyoid in this present
discussion.

The second major conclusion from this study concerns the relationships
of the blind snakes to lizards, and their proper relation to the serpents.
Snakes are normally classified as the suborder Ophidia (Serpentes) of
the order Squamata, the other suborder including the lizards, the Sauria
(Lacertilia). Recently, Schmidt (1950) proposed the elevation of both
groups to ordinal rank, feeling that evolution in the snakes “both in
progressive lines and in adaptive radiation” justifies their equal rank with
their ancestral order. Similarly the birds and mammals are now accorded

48 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

equal rank with their ancestral class Reptilia. The fundamental relation
of the two groups to each other has long been recognized and is based on
a number of anatomical features which distinguish them from other
reptiles.

For the most part the snakes comprise a distinctive group, to be
distinguished from nearly all lizards by: (1) a greatly elongated body;
(2) complete absence of pectoral limbs and girdle, and absence or great
reduction of the pelvic limbs and girdle; (3) great flexibility of the jaws,
permitting the swallowing of large prey; (4) an immovable transparent
“spectacle” covering the eye; (5) a platytrabic skull; (6) zygosphenes
and zygantra; (7) an elongate and retractile tongue; (8) the down-
growth of the parietals to form a closed brain case; (9) enlarged
transverse ventral scales; (10) absence of an external ear; and other more
minor features.

The blind snakes, of course, unique in some respects, fit this general
picture. Until recently their taxonomic position in the Ophidia had not
been seriously questioned, although Mosauer (1935) referred to the
muscle arrangement of Typhlops punctatus as “so unlike that of any
other ophidian that its position within this group is certainly not
confirmed by myology.” The blind snakes have always been placed at or
near the base of the suborder Ophidia, but opinions have differed as to
their proper relationships to the other families. In Boulenger’s classifica-
tion (the first to be based on any comprehensive study ) the two families
of blind snakes as well as some other burrowers like the uropeltids and
aniliids were excluded from any direct ancestral position leading to later
forms because of their extreme fossorial adaptations. Other workers, from
Cope (1900) and Gadow (1901) to Schmidt (1950) have taken the same
view. The “classical” theory held by the early herpetologists placed the
boids as the most primitive of living snakes and suggested that the
original derivation of the ophidian stock was from a group of suprater-
ranean lizards having both limbs and eyelids. Camp (1923) and later
workers felt that this ancestral group had given rise to both the snakes
and the modern varanid lizards.

Mahendra (1938), however, considered the blind snakes to be the
most primitive groups, as apparently did Walls (1940, 1942). The latter
has become a leading exponent of an opposing theory of the evolutionary
origin of snakes, to the effect that the ancestral stock was a burrowing,
elongate, limbless lizard with vestigial eyes. Some of the unusual features
of the ophidian eye have suggested to him an evolutionary “recovery” of
the eye from some such degenerate condition as that of Typhlops.
Further support for at least the general aspects of this second theory of
the origin of snakes has come from a number of workers, particularly
Angus Bellairs and others in England.

DISCUSSION 49

A major change in thought on the taxonomic position of the blind
snakes is found in the recent extensive work of McDowell and Bogert
(1954) on Lanthanotus and the anguinomorphan lizards. In the first
place, several anatomical resemblances between Leptotyphlops and the
higher, typical snakes suggest that they represent a monophyletic group
that quite early branched into two lines, and “it would appear that the
Leptotyphlopidae are, if anything, even closer to the platynotan lizards,
particularly the group represented today by Lanthanotus, than are the
other snakes.” In the second place, McDowell and Bogert concluded that

“there is little to show that the typhlopids are related to the snakes and
Leptotyphlopids,” rather, they show evidence of relationship to the
diploglossan lizards. “It seems clear that the typhlopids should be
removed from the Ophidia or Serpentes. It is equally clear that the many
peculiar specializations of the typhlopids (particularly the unique upper
jaw mechanism) warrant their separation from the Diploglossa and,
indeed, from the Anguinomorpha. Whether these odd burrowers deserve
special subordinal rank or should be regarded as merely an infraorder of
the Sauria remains a matter for the judgment of the majority of
taxonomists.”

Before we comment on these conclusions, a brief characterization of
the pertinent groups of lizards may be helpful. The Anguinomorpha are
an infraorder of the Sauria, distinguished, among other things, by a
tongue which has a forked inelastic front portion. This portion may be
retracted into a sheath formed by an elastic rear portion. The infraorder
has two distinct superfamilies; the Platynota and the Diploglossa. In the
former the anterior bony naris extends backwards as a slit between the
nasal bone and the prefrontal, the jaws have a more or less distinct
intramandibular hinge and are primarily developed for the seizure of
prey, the splenial is shorter, and an open Meckelian groove lies above the
splenial. Most recent workers feel the Ophidia are most nearly related to
this superfamily. The Diploglossa lack the posterior slit of the naris, have
jaws primarily developed for crushing, a longer splenial, no open
Meckelian groove, and no indication of an intramandibular hinge. Three
families are included in this latter group: (1) the Anguinidae, (2) the
Anniellidae, and (3) the Xenosauridae.

It seems fairly certain that Leptotyphlops is properly a genus of the
Ophidia. Some of the more important resemblances between the lepto-
typhlopids and most other snakes are as follows:

1. The vertebral centra taper (very slightly) posteriad, and the
prezygapophyses extend considerably farther laterad than do the synapo-
physes.

2. Extensive lateral plates of the parietals meet the basisphenoid,
forming the side walls anterior to the prootic.

50 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

3. Lateral plates of the frontals separate the orbits and form an
anterior extension of the brain case.

4. The exoccipitals meet dorsally to exclude the supraoccipital from
the foramen magnum.

5. Both lacrimal and jugal bones are absent.

6. A median plate of each nasal bone separates the nasal cavities by a
double-layered septum.

7. The nasal is separated from the prefrontal by a slitlike posterior
extension of the anterior bony naris.

8. An extensive facial wing of the maxilla covers a large area of the
side of the snout in many platynotans and other lizards, but it is quite
reduced in Leptotyphlops and completely absent in other snakes.

9. Temporal arch elements are lacking.

10. The Meckelian groove is open above the splenial.

11. The surangular, prearticular, and articular are fused to form a
single unit.

12. The mandible is separated by more or less vertical sutures into a
fore part (dentary and splenial ) and a hind part.

These rather basic resemblances indicate a definite phylogenetic
relationship between the two groups. Of the above features, numbers 1,
3, 6, 7, 9, 10, and 12 are also common to platynotans (or at least
Lanthanotus), emphasizing the probably ancestral position of those
lizards.

That the leptotyphlopids are much too specialized to have given rise to
other snakes, however, is suggested by a number of their unusual
features:

1. Presence of the most highly developed intramandibular hinge joint
of any squamatan, resulting in a freely movable foremandible.

2. The loss of all maxillary teeth.

3. The slender rodlike form of the pterygoid and its dissociation from
the quadrate-mandible articulation.

4. Disappearance or great reduction of the tabular.

5. The extremely shortened mandible and the correspondingly long,
narrow, forward-directed quadrate.

6. Loss of the postfrontals.

7. Reduction or loss of the ectopterygoid.

8. In some species the exclusion of the basioccipital from the foramen
magnum.

A number of distinctly primitive, lizard-like features combine with
these specializations. In addition to those previously mentioned, which
are held in common with the other blind snakes, these include the rigid
attachment of the maxilla to the skull, the only slightly recurved teeth,

DISCUSSION 51

and the nearly vertical position (rather than horizontal) of replacement
teeth.

The most valid representation of the family Leptotyphlopidae on an
ophidian phylogenetic tree, therefore, would seem to be a small,
unbranched twig springing from the “proto-boid” stock at the very base
of the tree. Its inclusion is justified by its numerous ophidian features; a
position near the base is called for by its primitive features; and its
specializations preclude the descent of any other known snake from such
an ancestor.

The relationships of the typhlopids and anomalepids to the snakes are
much less clear. These groups superficially resemble the leptotyphlopids
and might be thought to be rather closely related to them and to occupy
a similar position on the ophidian tree, but basic skeletal differences
distantly separate the two lines. A few features remove the typhlopids
even further from Leptotyphlops than from the higher snakes. For
example, the snakes and typhlopids have a fenestra ovalis and exposed
columella while Leptotyphlops lacks them; there is an extensive contact
between the splenial and coronoid in Typhlops, a short contact in typical
snakes, and a wide gap between them in Leptotyphlops; the mandible of
Typhlops has no hinge, snakes have a suggestion of one, and Leptotyph-
lops has a freely movable one.

McDowell and Bogert have pointed out a number of important
anatomical features in which the typhlopids and anomalepids differ from
the typical snakes and Leptotyphlops. They state, however, that retention
of the former groups in the Ophidia might be justified if any one of three
hypotheses could be proven:

1. The typhlopids, though now very distinct from snakes, are derived
from snakes and represent only a much modified ophidian line.

2. The typhlopids are close to the ancestry of the ophidians, and their
numerous differences from the snakes and leptotyphlopids are but the
result of the retention in the typhlopids of ancestral characteristics lost by
other ophidians.

3. The typhlopids on one hand, the snakes and leptotyphlopids on the
other, have diverged from each other at an early date but are derived
from a common ancestor.

My work leads me to agree that the first hypothesis can be ruled out in
view of a number of primitive, lizard-like features of Typhlops and its
relatives which are unknown in the snakes and Leptotyphlops (e.g.,
retention of an immobile symphysis of the mandibles and, in the
anomalepids, retention of a jugal and of hypohyal and ceratohyal
elements of the hyobranchium). The second possibility is contradicted
by the presence in Typhlops of numerous specialized features (e.g., the
loss of much of the maxilla and its unique suspension, and loss of all

52 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

palatal, premaxillary, and most dentary teeth). If the third hypothesis
were true, the typhlopids would share with the other snakes a series of
characters indicative of this relationship and absent in other squamatans.
McDowell and Bogert feel, however, that this is not the case, “for the
characters common to typhlopids and to the other ‘Ophidia’ appear to be
either common to all Anguinomorpha and anguinomorph descendants or
of such general or capricious occurrence in the Squamata as to appear
valueless.” It is with this last opinion that I take issue.

Several of the distinctions between Typhlops and the other snakes,
leptotyphlopids, and platynotans pointed out by McDowell and Bogert
do not hold up when a number of species are examined:

1. The posterior prolongation of the external bony naris as a slit
between the nasal and the prefrontal is given as “the most distinctive and
diagnostic feature of the platynotan skull,” characteristic of typical
snakes and Leptotyphlops but absent in Typhlops and the diploglossans.
On the contrary, the slit is present in five species of Typhlops studied
here, and it is not present in all the species of Leptotyphlops (Plates 2, 8,
10).

2. In the typhlopids the manner of enclosure of the brain by the
parietals, frontals, and basisphenoid is held to have “no particular
resemblance” to that of snakes and leptotyphlopids. It is pointed out
specifically that (a) in Typhlops the parietal is separated from the
basisphenoid by a fissure but forms a suture with it in other snakes; (b)
the frontals of Typhlops have quite small descending processes and large
inflated dorsal plates, while in other snakes the brain enclosure in this
region and the separation of the orbits is accomplished chiefly by the
large descending processes of the frontals; and (c) in Typhlops the
basisphenoid is truncate or emarginate anteriorly and does not extend
forward to the vomers, leaving a median vacuity here (partially filled by
the laterosphenoids in Liotyphlops), while in other snakes it is directed
anteriad and does meet the vomers, eliminating the median vacuity. In
the description of the skull in the present work a number of contradic-
tions to (e.g., parietal-basisphenoid sutures in some Typhlops and
parietal-basisphenoid fissures in some Leptotyphlops), variations from
(e.g., in form and anterior extent of the basisphenoid ), and alternatives
to the points of view stated by McDowell and Bogert have been pointed
out. Collectively, they reduce considerably any distinctions between the
brain cases of the two groups. It is true that at least two other quite
unrelated groups of squamatans (Dibamus and the amphisbaenids ) may
have the brain case formed in about the same way and that this general
feature by itself is therefore no guarantee of snake affinities. However,
the specific manner of enclosure is not appreciably different in the
typhlopids and other snakes.

DISCUSSION 53

3. The septomaxilla of Typhlops is said to “show no resemblance to
that of the leptotyphlopids, snakes or platynotan lizards. There is no
ascending lateral process, but rather the lateral extremity of the bone is
horizontal and without upward flexure.” It is true that this bone in
Typhlops is greatly enlarged and has relationships not seen in these other
groups, but in some species the lateral edge is turned up, to varying
degrees, although not to the extent seen in Leptotyphlops (Plates 5, 8).

4. The coronoid of Typhlops is said to resemble that of both the
platynotans and diploglossans in that it possesses both anterior and
posterior descending processes, the notch between them exposing a
portion of the surangular. However, in about half of the species examined
here the base of the coronoid is more snakelike in being straight, with no
notch and thus no definite descending processes. The dorsal projection of
the bone, the coronoid process, arises in the middle of the bone in
Typhlops and diploglossans and from the posterior part in typical snakes
and platynotans. Of that of Typhlops it is said that “there is no
suggestion of the highly peculiar coronoid of the leptotyphlopids.” The
process in Leptotyphlops, although rather knobby and distorted like the
rest of the coronoid, definitely arises from the center of the bone and to
that extent it resembles that of Typhlops.

5. One of the more basic resemblances of the snakes and platynotans is
the posteriorly tapering centrum of the vertebra, with the condyle set off
by a constriction. Among snakes such vertebrae are known at least in the
Boidae and more primitive colubrids. The vertebrae of Leptotyphlops
are described as having centra which are tapered posteriorly, but in the
specimens at hand, this is only faintly indicated. Certainly the form of
their centra (and the rest of the vertebra as well) is much closer to that
in Typhlops than to that of a boid. The vertebrae of Typhlops are said to
show none of the platynotan-like features seen in the snakes (including
Leptotyphlops). There is no indication of the tapered centrum, but the
condyle is distinctly set off by a constriction (Plate 13).

6. Doubt arises concerning the homology of the zygantra and zygo-
sphenes of Typhlops to those of other snakes and Leptotyphlops because
in the latter two these articulations are well dorsal to the level of the
zygopophyseal joint, while in the former both joints are at the same level.
The difference in the levels of these articulations in the two groups is
extremely slight and insignificant. At the most, it is probably only a
reflection of the slightly higher neural arch of the leptotyphlopids (the
vertebrae in general are somewhat more depressed in Typhlops) (Plate
13));.

7. The typhlopids are said to differ from the snakes and leptotyphlo-
pids in the absence of ceratobranchial elements. However, as pointed out
in the preceding discussion of the hyoid, a hyobranchium consisting

54 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

solely of the first ceratobranchials occurs in some’ species of Typhlops.
This is beside the point, of course, if the hyoid of typical snakes consists
of only the basihyal, as was suggested earlier.

8. The pairing of the supraoccipitals in some species of Typhlops is
considered an anomalous condition since the bone is seldom if ever
anything but a median azygous bone in vertebrates. By an unusual
coincidence, every species of Leptotyphlops that has ever been figured,
from Jan and Sordelli’s work to that of McDowell and Bogert, has been a
species with a single, unpaired supraoccipital. Yet in all seven of the
species illustrated in the present book the supraoccipitals are paired, and
except for their slightly larger size, they are quite like those of Typhlops.
The two genera are therefore alike in sharing this highly unusual
characteristic (Plate 10).

The above considerations reduce the distinctions between the typhlo-
pid-anomalepid group and the other snakes considerably. Also, two
basically ophidian features of the blind snakes support the impression
that they are all truly snakes. One of these is mentioned by McDowell
and Bogert, but the significance of the other has apparently escaped the
attention of previous writers. The first is the fact that the exoccipitals
meet each other in the mid-dorsal line to exclude the supraoccipital(s )
from the foramen magnum. It has been suggested that the variability of
the bones of the occipital region reduces the significance of this feature.
But this variability is always with respect to the bones anterior to the
exoccipital—fusion with the prootics or with the supraoccipitals, or with
both, or the pairing of the latter—never with respect to the basic form of
the exoccipitals. Those parts of the exoccipitals which actually enclose
the foramen magnum are quite constant in their basic form (except in
Leptotyphlops humilis, where they are widely separated dorsad). The
second resemblance seems fundamental and has to do with the develop-
ment of the metapophyses of the vertebrae. McDowell and Bogert refer
to them in Leptotyphlops but not in Typhlops. They are even more
highly developed, however, in the latter genus and give the vertebrae in
dorsal view their very characteristic hourglass appearance. These proc-
esses are one of the more prominent features of the vertebrae of all the
blind snakes (Plate 13). Although they are somewhat reduced in size in
the vertebrae of boids, they are quite prominent in the higher snakes,
being especially long and slender in the racers (Masticophis). Metapo-
physes are not present in amphisbaenids, Ophisaurus, platynotans, nor in
any other lizard, to judge from the numerous figures of Camp (1923).
This would seem to be one of the more significant features linking all the
blind snakes with the higher forms.

There still remains, of course, a number of unsnakelike characters, the
more important of which are the rigid dentary symphysis, the closed

DISCUSSION 55

Meckelian groove, the long splenio-coronoid suture, and the unique form
and suspension of the maxilla. In spite of these peculiarities, the evidence
as a whole favors the inclusion of all the blind snakes in the Ophidia and
the third hypothesis mentioned above as the correct one—the typhlopids
and anomalepids on the one hand, the snakes and leptotyphlopids on the
other, have diverged from each other at an early date but are derived
from a common ancestor.

Underwood (1957) criticized various points of McDowell and Bogert’s
1954 work, including their suggestion that the Typhlopidae be removed
from the Serpentes. He has pointed out a number of ophidian features of
Typhlops, particularly in their soft anatomy: circulatory system, eye
structure, thymus bodies, liver and gall bladder relationships, even the
snakelike odor of cloacal gland secretions. “Typhlops combines a number
of distinctly ophidian features with a few which are clearly primitive
from an ophidian standpoint. To these it adds a number of divergent
features (a few of them shared with Leptotyphlops). In my opinion this
argues that the Typhlopidae are divergent descendants of ancestral snake
stock. . . . I strongly urge that the Typhlopidae should be retained in
the Serpentes.”

Robb (1960), on the other hand, has concluded that “the numerous
peculiarities of the internal organs of Typhlops support the hypothesis
that the group should indeed be removed from the Ophidia.” She
suggests that the typhlopids “should either be given subordinal rank,
equivalent to the Sauria and the Serpentes, or be made an infra-order of
the Sauria.” Her paper describes in detail for the first time the digestive,
circulatory, respiratory, and reproductive systems of Typhlops. She notes
“points of dissimilarity of structure between this genus and the snakes, in
every system examined,” with the respiratory and reproductive systems
having the most striking peculiarities. Specifically, there are two elongate
lungs, both apparently functional, lying one ahead of the other. On the
basis of blood supply, the anterior one appears to represent the left lung
and the posterior one the right. Although this is a unique arrangement, it
may well be viewed as just one more solution to the ophidian problem of
what to do with two lungs in a very slender body.

Robb reports a truly startling situation in the nature of the hemipenes,
which are slender, solid, protrusible structures. Each consists in large
part of apparently erectile tissue, bears a longitudinal external groove but
no spines, and when retracted is coiled within a sheath that lies in the tail
and opens into the cloaca. Robb notes: “Hence, in that it is solid, and
externally grooved, and is retracted into the resting position, each
hemipenis of Typhlops bears a greater superficial resemblance to the
single penis of the crocodiles and chelonians, than to the hemipenis of
other snakes.”

56 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

It seems to me that this statement holds only if the hemipenis is
considered in isolation. In that they are paired, and are contained in
definite sheaths, and lie in the tail (posterior to the anus, not in the
cloaca proper), these typhlopid copulatory structures still basically
represent the squamatan pattern. Further, I should like to suggest that
the hemipenes of Typhlops may merely represent a very primitive
condition, from which the hemipenes of modern snakes (and lizards)
could have been derived by the simple reduction and loss of the solid,
grooved, protrusible portions of the system, the sheaths themselves then
serving as copulatory organs when evaginated. In this view, the hemi-
penes of a modern snake are homologous to the typhlopid sheaths and
not at all homologous to the solid copulatory structure that each of the
latter contains. Robb mentions, incidentally, that “at its posterior end, the
sheath becomes fairly loosely attached to the hemipenis, and somewhat
inverted within its own cavity. This is, of course, especially the case when
the hemipenis is protruded into and beyond the cloaca” (italics mine).

In any case, in spite of the above (and other) unusual features of the
typhlopid soft anatomy, the basic nature of the animals seems to me to be
ophidian.

One final point may be noted. When this present work was begun it
was anticipated that there might appear enough skeletal variations to
suggest the establishment of subfamilies or new genera. This was
particularly expected in the large genera Typhlops and Leptotyphlops.
Although a number of interspecific variations were noted they showed no
correlation with each other, and none by itself seems important or
constant enough to serve as a sole generic criterion. Such a feature as the
paired or fused parietals would appear to be important, for example,
were it not for known intermediate conditions and even changes from the
paired to the fused state during postembryonic development. Possibly
some of the more bizarre species of Typhlops, those with quite flattened
snouts, for example, might be worthy of generic differentiation, but none
such was included in this study. On the present evidence, therefore, there
seems to be no basis for subdividing either Typhlops or Leptotyphlops.

SUMMARY

The skeletons of thirty-two species of blind snakes were studied in an
effort to clarify the taxonomy and phylogeny of the groups. As a whole,
these snakes show a peculiar combination of primitive, lizard-like
characters and highly specialized features. Some of the latter are

SUMMARY Si7/

obviously correlated with the burrowing mode of life and others are not.

A. Reinterpretations of a number of skeletal homologies or other
features have been suggested by this study, largely due to the utilization
of a greater variety of species compared to previous works. These
reinterpretations include the following:

1. The hyoid of the anomalepids consists of a reduced basihyal, a pair
of anteriorly directed hypohyals, and a pair of posteriorly directed and
recurved ceratohyals. All these elements are fused to form a threadlike
structure in the general form of an M with the legs bent back upon
themselves.

2. The hyoid apparatus of Typhlops may consist of either the
basihyal or the second ceratobranchials or both. The hyoid of Leptotyph-
lops consists of the basihyal alone, with elongate posterior extensions.
The hyoid of most higher snakes is most likely the basihyal alone, minus
the anterior glossohyal process.

3. The odontoid process of all the blind snakes is quite broad, about
as large as the pleurocentrum of the axis, and the small knob of calcified
cartilage on the anterior face of the axis represents the proatlas.

4. The ectopterygoid in Typhlops seems to have fused to the
pterygoid rather than to the palatine, as has been previously suggested.

5. The ventral vertebral foramina, whether paired or single, are
homologous to each other and to the similar foramina of other snakes and
lizards. They are passages for adult derivatives of the intersegmental
arteries of the embryo.

6. In the blind snakes the articular cup of the rib seems to represent
not a fusion of capitulum and tuberculum but a new formation between
them, since rudimentary capitula and tubercula are still present.

7. The small bone near the rear end of the quadrate in Liotyphlops is
the tabular, not the squamosal.

8. The bone below and behind the dentary in Liotyphlops is the
splenial, not the angular.

9. The zygantra and zygosphenes of the blind snakes, although
somewhat reduced, are basically the same as those of higher snakes.

10. The dorsal scales/vertebrae ratio is not 2:1 in the typhlopids
(Mahendra, 1936, and others) and leptotyphlopids (Schmidt, 1950).
Rather, in the typhlopids and anomalepids there is no definite ratio; it
ranges from 1.5:1 to 2.3:1. In Leptotyphlops the ratio is 1:1, as in higher
snakes.

B. Skeletal features noted for the first time in the blind snakes and
described above include:

1. The presence of a pelvic girdle in Liotyphlops.

2. The unusual “urostyle” at the tip of the tail in some species of
Typhlops.

58 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

3. Variations in the hyobranchium of Typhlops, including the pres-
ence of ceratobranchials.
4. The presence of three teeth (rather than one), including a
replacement tooth, on the dentary of Liotyphlops.
5. The unusually compressed maxillary teeth of Liotyphlops.
6. Evidence of a tabular in various species of Leptotyphlops.
7. Ossified or calcified ilia and pubes in some species of Typhlops.
8. Vestiges of postfrontals in a second species of Typhlops (reticu-
latus ).
9. Calcified palatal cartilages in Leptotyphlops.
10. The paired condition of the parietals and supraoccipitals in some
species of Leptotyphlops.
C. On the basis of the skeletal features outlined in the previous
sections of this work, two major conclusions are reached:

1. There is justification for the erection of a third family of blind
snakes, the Anomalepidae, composed of four genera: Anomalepis, Lio-
typhlops, Helminthophis, and Typhlophis.

2. The typhlopids and anomalepids are properly placed in the Ophidia.
Examination of a variety of species shows insufficient justification for
their removal from the snakes. Arguments for removing them, as set forth
in recent works, are considered inadequate in the light of the present
study of a series of species.

59

ABBREVIATIONS USED IN PLATES

Ad —arytenoid

An — angular

Ar —articular

At — atlas

Ax —axis

Bh — basihyal

Bo — basioccipital
Bs — basisphenoid
C —coronoid

CbI —ceratobranchial I
CbII — ceratobranchial II
Ch —ceratohyal

Cl —claw

Con — condyle

Cot — cotyle

Cp — composite bone
Cr —cricoid

Ct —capitulum

D —dentary

Ee —ectopterygoid
Eo — exoccipital

F — frontal

Fe — femur

Gh —glossohyal process
He — hypocentrum

Hh — hypohyal
Hp — hypapophysis

Hy — hyobranchium

IF W— intervertebral foramen
Il —ilium

Is —ischium

J — jugal

LF — lateral foramen

M — maxilla

Met — metapophysis
N —nasal

NA — neural arch
NC — neural canal

Od — odontoid process
P W—parietal

P — pubis

Pa — proatlas

Pe — pleurocentrum

Pf — prefrontal

Pal — palatine

Pl — palpebral

Pm — premaxilla

Po — prootic

Pof — postfrontal

Poz — postzygapophysis
Prz — prezygapophysis
Pt — pterygoid

Pu — pubis

Q — quadrate

Rb —rib

S —splenial

Sm — septomaxilla
So —supraoccipital

Sp — laterosphenoid (?)
Syn — synapophysis
T —tendon (?)

Tb — tabular

Tb — tuberculum

TC —tracheal cartilage
V —vomer

VF — ventral foramen
Zn — zygantrum

Zs — zygosphene

In all figures the scale line equals one millimeter.

60

PLATE 1

Skulls, minus lower jaw, dorsal view.

Fig. 1. Typhlops lineatus JCL 1013.

Fig. 2. Liotyphlops albirostris USNM_ 61989.
Fig. 3. Leptotyphlops bakewelli USNM 25242.

62

PLATE 2

Skulls, lateral view.

Fig. 1. Typhlops lineatus JCL 1013.

Fig. 2. Liotyphlops albirostris USNM_ 61989.
Fig. 3. Leptotyphlops bakewelli USNM 25242.

64

PLATE 3

Skulls, minus lower jaw, ventral view.

Fig. 1. Typhlops lineatus JCL 1013.

Fig. 2. Liotyphlops albirostris USNM_ 61989.
Fig. 8. Leptotyphlops bakewelli USNM 25242.

66

PLATE 4

Skulls, minus lower jaw, dorsal view.

Fig. 1. Typhlops vermicularis CNHM 28572.
Fig. 2. Typhlops reticulatus CNHM 35592.
Fig. 3. Typhlops platycephalus MCZ_ 38337.
Fig. 4. Typhlops rostellatus MCZ 38370.
Fig. 5. Typhlops polygrammicus JCL 1018.
Fig. 6. Typhlops lumbricalis MCZ 22279.

68

PLATE 5

Skulls, lateral view.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

ite
. Typhlops reticulatus CNHM 35592.

. Typhlops platycephalus MCZ_ 38337.
. Typhlops rostellatus MCZ 38370.

. Typhlops polygrammicus JCL 1018.

. Typhlops lumbricalis MCZ 22279.

Dok W WO

Typhlops vermicularis CNHM = 28572.

PLATE 6

Skulls, minus lower jaw, ventral view.

Fig.
Fig.
Fig.
Fig.
Fig.

O

Fig.

DI fk WwW

. Typhlops vermicularis CNHM 28572.
. Typhlops reticulatus CNHM _ 35592.

. Typhlops platycephalus MCZ_ 38337.
. Typhlops rostellatus MCZ 38370.

. Typhlops polygrammicus JCL 1018.
. Typhlops lumbricalis MCZ 22279.

SV
{
oe ota
7 "| N t) f \\ YW =
\ Zz
il IAA

72

PLATE 7

Skulls, minus lower jaw, dorsal view.
Typhlops braminus JCL 1022.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

Ie
2. Typhlops flaviventer JCL 1012.
3. Typhlops pusillus MCZ 8758.
4,
5
6

Typhlops blanfordi lestradei

. Typhlops schlegelii mucruso

MCZ_ 48077.

. Typhlops boettgeri JCL 1014.

MCZ_ 30058.

74

PLATE 8

Skulls, lateral view.
Typhlops braminus JCL 1022.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

i.
. Typhlops flaviventer JCL 1012.
. Typhlops pusillus MCZ 8758.

. Typhlops blanfordi lestradei
. Typhlops boettgeri JCL 1014.

aow1rk wo lh

. Typhlops schlegelii mucruso

MCZ 48077.

MCZ 30058.

76

Skulls, minus lower jaw, ventral view.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

IL.
. Typhlops flaviventer JCL 1012.
. Typhlops pusillus MCZ 8758.

Dork WO WD

PLATE 9

Typhlops braminus JCL 1022.

. Typhlops blanfordi lestradei
. Typhlops boettgeri JCL 1014.
. Typhlops schlegelii mucruso

MCZ 48077.

MCZ 30058.

<5 AY, _

~)
iA.

78

PLATE 10

Skulls, minus lower jaw, dorsal view.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

1,
. Leptotyphlops nigricans MCZ_ 21473.

. Leptotyphlops maximus UIMNH _ 34999.

. Leptotyphlops emini CNHM _ 56374.

. Leptotyphlops magnamaculata’ CNHM _ 87.
. Leptotyphlops humilis cahuilae JCL 1000.

De WwW WD

Leptotyphlops dulcis dissectus USNM 99821.

80

Skulls,

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

Our OD

PLATE, it

lateral view.

Leptotyphlops dulcis dissectus USNM 99821.

. Leptotyphlops nigricans MCZ 21473.

. Leptotyphlops maximus UIMNH 34999.

. Leptotyphlops emini CNHM 56374.

. Leptotyphlops magnamaculata) CNHM_ 87.
. Leptotyphlops humilis cahuilae JCL 1000.

82

PLATE 12

Skulls, minus lower jaw, ventral view.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

. Leptotyphlops dulcis dissectus USNM 99821.
. Leptotyphlops nigricans MCZ 21473.

. Leptotyphlops maximus UIMNH _ 34999.

. Leptotyphlops emini CNHM 56374.

. Leptotyphlops magnamaculata’ CNHM _ 87.

. Leptotyphlops humilis cahuilae JCL 1000.

84

PLATE 13

Thoracolumbar vertebrae, at mid-body.

Fig. 1. Liotyphlops albirostris USNM_ 61989.
Fig. 2. Typhlops lineatus JCL 1013.

Fig. 3. Leptotyphlops humilis humilis JCL 1020.
. Dorsal.

. Lateral.

. Ventral.

. Anterior.

HOOwW >

. Posterior.

86

Puate 14

Atlas (Fig. 1), axis (Fig. 2), and terminal caudal vertebrae with “urostyle”
(Figs. 3-7).

Fig. 1. Typhlops richardi MCZ 38350.

Fig. 2. Typhlops richardi MCZ_ 38350.

Fig. 3. Typhlops polygrammicus JCL_ 1018.
Fig. 4. Typhlops vermicularis CNHM 28572.
Fig. 5. Typhlops rostellatus MCZ 38370.
Fig. 6. Typhlops jamaicensis MCZ_ 7370.

Fig. 7. Typhlops lineatus JCL 1013.
A. Anterior.

B. Posterior.

C. Right side.

Or” GY sae

a 10.

88

PLATE 15

Hyobranchia and adjacent rib tips, ventral view.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

13
. Typhlops polygrammicus JCL_ 1018.

. Typhlops pusillus MCZ_ 8758.

. Typhlops vermicularis CNHM 28572.

. Typhlops boettgeri JCL 1014.

. Typhlops reticulatus CNHM 35592.

. Typhlops lumbricalis JCL 1007.

. Typhlops schlegelii schlegelii MCZ 29174.
. Typhlops blanfordi lestradei MCZ 48077.

OMAN ADA IK WW

Typhlops braminus JCL 1022.

90

PLATE 16
Hyobranchia and adjacent rib tips, ventral view.
Fig. 1. Leptotyphlops humilis humilis JCL 1025.

Fig. 2. Leptotyphlops nigricans MCZ 21473.

Fig. 3. Leptotyphlops dulcis dissectus USNM 99821.
Fig. 4. Leptotyphlops emini CNHM 56374.

Fig. 5. Leptotyphlops humilis cahuilae JCL 1000.
Fig. 6. Leptotyphlops magnamaculata) CNHM __ 87.
Fig. 7. Leptotyphlops phenops CNHM _ 36345.

Fig. 8. Leptotyphlops maximus UIMNH 34999.

Vl co OF ©
——

LAK LURK

So

92

PLATE 17
Laryngeal cartilages (Figs. 1-4); laryngeal and tracheal cartilages and
hyobranchium (Figs. 5-8); ventral views.
Figs. 1 and 5. Typhlops reticulatus CNHM _ 35592.
Figs. 2 and 6. Typhlops polygrammicus JCL_ 1017.
Figs. 3 and 7. Liotyphlops albirostris USNM_ 61989.
Figs. 4 and 8. Leptotyphlops humilis humilis JCL 1020.

a TTD WM
Su ee J
ee Ze = = 00

SMM IAP DIMOU OO ee
bm |
pl

O
re foneP es Wy ~
a

Bes. CUTAN DSU TA La dT J

eevor2= TTA AELLLLELPoe ee U
an (ag >

7 & re) ¥ ]
= E va

94

PLATE 18

Saurian and ophidian hyobranchia. Figs. 1-3 and 5-7 after Cope, 1900.
Fig. 1. Sawromalus ater.

Fig. 2. Ctenosaura teres.

Fig. 3. Xenosaurus grandis.

Fig. 4. Liotyphlops albirostris USNM_ 61989.
Fig. 5. Anguis fragilis.

Fig. 6. Rhineura floridana.

Fig. 7. Anniella pulchra.

Fig. 8. Typhlops platycephalus MCZ 38337.
Fig. 9. Typhlops lehneri MCZ 48929.

Fig. 10. Typhlops lumbricalis USNM_ 66887.
Fig. 11. Leptotyphlops bakewelli USNM 25242.
Fig. 12. Thamnophis radix.

96

PLATE 19

Pelvic girdles and adjacent ribs.

Fig. 1. Leptotyphlops dulcis dissectus MCZ 39681.
Fig. 2. Leptotyphlops bakewelli USNM 25242.
Fig. 3. Typhlops platycephalus MCZ 38337.

Fig. 4. Liotyphlops albirostris USNM_ 61989.

Fig. 5. Typhlops rostellatus MCZ 38370.

Fig. 6. Typhlops richardi MCZ_ 38350.

Fig. 7. Typhlops lumbricalis USNM_ 66887.

Fig. 8. Typhlops lineatus JCL 1013.

Fig. 9. Typhlops lehneri MCZ 48929.

A. Ventral.

B. Right side.

F am 17 oY
ae x Ae ore

98

PLATE 20

Pelvic girdles and adjacent ribs.

Fig. 1. Leptotyphlops humilis cahuilae |JCL 1000.
Fig. 2. Leptotyphlops magnamaculata’ CNHM __ 87.
Fig. 3. Leptotyphlops dulcis dissectus USNM 99821.
Fig. 4. Leptotyphlops emini CNHM 56374.

Fig. 5. Leptotyphlops nigricans MCZ 21473.

Fig. 6. Leptotyphlops maximus UIMNH 34999.

A. Right side.

B. Ventral.

100

PLATE 21

Pelvic girdles and adjacent ribs.

Fig. 1. Typhlops boettgeri JCL 1014.

Fig. 2. Typhlops pusillus MCZ _ 8758.

Fig. 3. Typhlops braminus JCL 1022.

Fig. 4. Typhlops polygrammicus JCL_ 1018.
Fig. 5. Typhlops vermicularis CNHM _ 28572.
A. Right side.

B. Ventral.

PLATE 22

Pelvic girdles and adjacent ribs.

Fig. 1. Typhlops blanfordi lestradei MCZ 48077.
Fig. 2. Typhlops schlegelii mucruso MCZ_ 30058.
Fig. 3. Typhlops schlegelii schlegelii MCZ 29174.
Fig. 4. Typhlops reticulatus CNHM 35592.

A. Right side.

B. Ventral.

Oe Ge Che | RASA

Neue SN

104

LITERATURE CITED

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snake, Typhlops braminus (Daudin), with special reference to the sense
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Boulenger, G. A. 1890. The Fauna of British India (Reptilia and Batrachia).
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. 1893. Catalogue of Snakes in the British Museum (Natural History),
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Brock, G. T. 1932. The skull of Leptotyphlops (Glauconia) nigricans. Anat.
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Brongersma, L. D. 1958. Upon some features of the respiratory and circulatory
systems in the Typhlopidae and some other snakes. Arch. néerl. Zool.
XIII, Suppl. I:120-127.

Camp, Charles L. 1923. Classification of the lizards. Bull. Amer. Mus. nat.
Hist. 48:289-480.

Cope, E. D. 1900. The Crocodilians, Lizards, and Snakes of North America.
Rep. U.S. nat. Mus., 1898.

Davis, D. D., and U. R. Gore. 1936. Clearing and Staining Skeletons of Small
Vertebrates. Publ. Chicago nat. Hist. Mus., Tech. Series, no. 4, 16 pp.

Duerden, J. E., and R. Essex. 1923. The pelvic girdle in the snake, Glauconia.
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Dumeril, A. M. C., and G. Bibron. 1834-54. Erpetologie generale ou histoire
naturelle des reptiles. 9 vols. and atlas. Paris.

Dunn, E. R. 1941. Notes on the snake genus Anomalepis. Bull. Mus. comp.
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, and J. A. Tihen. 1944. The skeletal anatomy of Liotyphlops albirostris.
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Essex, R. 1927. Studies in reptilian degeneration. Proc. zool. Soc. Lond.
Part IV:879-945.

Evans, Howard E. 1955. The osteology of a worm snake, Typhlops jamaicen-
sis (Shaw). Anat. Rec. 122 (3) :381-396.

Gadow, Hans. 1901. Amphibia and Reptiles. Cambridge Natural History,
Vol. VIII. London,

LITERATURE CITED 105

Goodrich, E. S. 1930. Studies on the Structure and Development of Verte-
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Grobman, A. B. 1943. The appearance during ontogeny of a suture between
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Haas, Georg. 1930. Uber das Kopfskelett und dis Kaumusculatur der Typh-
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Tiere 52:1-94.

Hayek, Heinrich. 1923. Uber den Proatlas und die Entwicklung der Kopf-
gelenke beim Menschen und bei Saugetieren. Akad. d. Wiss., Wien.

. 1924. Uber das Schicksal des Proatlas und itiber die Entwicklung der
Kopfgelenke bei Reptilien und Vogeln. Morph. Jb. 53:137—163.

Hoffstetter, Robert. 1946. Les typhlopidae fossiles. Bull. Mus. Hist. nat.,
Paris 18(3) :309-315.

Huxley, T. H. 1871. A Manual of Anatomy of Vertebrated Animals. London.

Jan, Georges, and Ferdinand Sordelli. 1860-66. Iconographie generale des
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Johnson, Ralph G. 1955. The adaptive and phylogenetic significance of verte-
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Kingsley, J. S. 1925. The Vertebrate Skeleton. Philadelphia.

List, J. C. 1955. External limb vestiges in Leptotyphlops. Herpetologica
11(1):15—16.

Mahendra, Beni C. 1935. The sub-central foramina of the Squamata. Curr.
Sci. 4(5) :320-322.

. 1936. Contributions to the osteology of the Ophidia. I. The endo-

skeleton of the so-called “Blind-Snake,” Typhlops braminus (Daudin).

Proc. Ind. Acad. Sci. (Sec. B) 3(2):128-142.

. 1938. Some remarks on the phylogeny of the Ophidia. Anat. Anz.
86:347-356.

McDowell, Samuel B., Jr., and Charles M. Bogert. 1954. The systematic
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Bull. Amer. Mus. nat. Hist. 105(Art. 1):1-142.

Mehely, L. von. 1907. Archaeo- und Neo-Lacerten. Am. Mus. nat. Hungarici
5:469-493.

Mookerjee, H. K., and G. M. Das. 1932. Occurrence of a paired parietal bone
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. 1933. On the peculiar apertures in the vertebral centra of Typhlops
braminus. Proc. zool. Soc. Lond. Part TV:283.

Mosauer, Walter. 1935. The myology of the trunk region of snakes and its
significance for ophidian taxonomy and phylogeny. Publ. Univ. Calif. Los
Angeles biol. Sci. 1:81—120.

Muller, August. 1831. Beitrage zur Anatomie und Naturgeschichte der Am-
phibien. Z. Physiol., Vol. 4.

Nakamura, K. 1941. Studies on the blind snake. Trans. nat. Hist. Soc. Formosa
31:299-305.

Owen, Richard. 1853. Descriptive Catalogue of the Osteological Series in the
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. 1866. Anatomy of Vertebrates. Vol. I, Fishes and Reptiles. London.

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Berlin.

106 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

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(Schlegel). S. Afr. J. Sci. 45:117-140.

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hyobranchium. Herpetologica 4(6) :189-193.

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Zangerl, Ranier. 1944. Contributions to the osteology of the skull of the
Amphisbaenidae. Amer. Midl. Nat. 31 (2):417—454.

. 1945. Contributions to the osteology of the post-cranial skeleton of the

Amphisbaenidae. Amer. Mid]. Nat. 33(3):764—780.

MATERIALS EXAMINED

Museums or collections are indicated by the following abbreviations: CNHM,
Chicago Natural History Museum; JCL, James C. List, private collection; MCZ,
Museum of Comparative Zoology, Harvard; UIMNH, University of Illinois Mu-
seum of Natural History, Urbana; USNM, United States National Museum, Wash-
ington, D.C.

MATERIALS EXAMINED

Leptotyphlops albifrons USNM 25243, Nicaragua.

bakewelli USNM 25242, Nicaragua.

conjuncta JCL 1015, Smithfield, Transvaal.
dulcis dissectus MCZ 39681, Tulsa, Oklahoma.

“

ce
“

tas

emini

i USNM 99821, Lake City, Kansas.

. USNM 99822, ‘“ os

e USNM 99823, “ ‘ iS
CNHM 56374, Belgian Congo.

humilis cahuilae JCL 1000, Imperial Co., Calif.
a3 as ce

ia

7 JCL 1026,
humilis JCL 1020, San Diego Co., “

“ AKGALE 1023, a9 ce cc a3

ins JCL 1024, ce ing ce iss

“ ANGIE; 1025, ce “ cc ia
segregus USNM 17017, Tucson, Arizona.

= USNM 17015, “ 33

: USNM 17016, “ cs

longicauda MCZ 40116, Ngatana, Kenya.
magnamaculata CNHM 87, Old Providence Island, West Indies.
maximus UIMNH 34999, Guerrero, Mexico.
nigricans MCZ 21473, Grahamstown, South Africa.
phenops CNHM 36345, Yucatan, Mexico.

ins

CNHM 20606, a

Liot yphlops albirostris USNM 61989, Panama.

as

Typhlops ater JCL

tag

blanfordi

boettgert

MCZ 31541, Chiriqui, Panama.
1006, Soa Konorra, Halmahera.
lestradei MCZ 48077, Mushungero, 8.W. Uganda.
JCL 1014, Majunga, W. Madagascar.

braminus USNM 72319, Bangkok, Thailand.

lehneri
lineatus

“

“ce

USNM 78164, Silay, Philippine Islands.
USNM 80575, Victorias, ‘“‘

USNM 80576, s oe
CNHM 53270, Mindanao, se cu
CNHM 53271, Z: ~

UIMNH 15920, Guerrero, Mexico.
UIMNH 15926, “3

MCZ 7580, Buitenzorg, Java.
JCL 1004,

JCL 1005, ce ve:

JCL 1003, Majunga, Madagascar.
JCL 1021, Miyanapalava, Ceylon.
JCL 1022, Dadanduwa, eS

are JCL 1012, Soa Konorra, Halmahera.
jamaicensis MCZ 7370, Kingston, Jamaica.

MCZ 48929, Acosta District, Venezuela.
JCL 1002, no data.

JCL 1013, Buitenzorg, Java.

USNM 43386, “

lumbricalis JCL 1007, Havana, Cuba.

“

as

MCZ 29979, Soledad, “
USNM 66887, Santo Domingo.

microstomus CNHM 36347, Yucatan, Mexico.

107

108 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

Typhlops platycephalus CNHM 38581, Rio Piedras, Puerto Rico.

MCZ 38337, Canovenas, ff
st USNM 27324, Bayanion: s Ke
a USNM 29364, Mayaguez, zi e
polygrammicus JCL 1016, no data.
oy JCL 1017, no data.
if JCL 1018, no data.
s JCL 1019, no data.
punctatus CNHM 58351, Katire, Anglo-Egyptian Sudan.
= CNHM 21082, Sangmelina, Cameroons.
os MCZ 7843, Kribi,
JCL 1009, Duala, a
os JCL 1010, i
pusillus MCZ 8758, Ennery, Haiti.
reticulatus CNHM 35592, Santo Cruz, Bolivia.
richardi MCZ 38350, Tortola Island.
rostellatus MCZ 38370, Canovanas, Puerto Rico.
schlegelit MUCTUSO CNHM 52900, Anglo-Egyptian Sudan.
A MCZ 30058, Mwaya, Tanganyika.
re JCL 1008, Cubal, Angola.
r schlegelii MCZ 29174, 8. Sihodlesin,
simonit JCL 1011, Haiffa, Israel.
vermicularis CNHM 28572, Benyamina, Israel.

INDEX

109

Abbreviations used in plates, 59

Amphisbaenidae: vertebrae, 25, 27,
28; mentioned, 45, 52, 54

Anguinidae, 49

Anguinomorpha, 49, 52

Anguis fragilis, 94

Angular, 21, 22, 23, 24, 25, 46, 47

Aniliidae, 43

Anniella pulchra: hyoid, 41; 95

Anniellidae, 49

Anomalepidae: genera, 4, 47; pro-
posed by Taylor, 46; skeletal
characteristics, 46-47; taxonomic
position, 47, 58; phylogeny, 55

Anomalepis: key characters, 2; distri-
bution, 2; skull, 7-18; lower jaw,
23; teeth, 23; vertebrae, 26, 30,

31; hyoid, 39-40; pelvic girdle,

45

aspinosus: earlier descriptions, 5,
Pe AS.35

dentatus: earlier descriptions, 11,
18

Archaeophis proavus, 25
Articular, 20, 24, 50
Arytenoid, 40

Atlas, 27-30, 46

Axis, 27-30

Bachia, 34
Basihyal, 39, 40, 41, 42, 54

Basioccipital, 6, 50

Basisphenoid, 9, 49, 52

Blind snakes: primitive features, 1,
46; earlier studies, 2, 3, 55; de-
fined, 4; burrowing modifications,
45

Boidae, 43

Celestus, 39

Ceratobranchial, 41, 42, 53, 54

Ceratohyal, 39, 40, 41, 42, 51

Chamaesaura, 34

Coleonyx, 22

Columella, 7, 21, 23, 51

Compound bone of mandible, 20, 22,
93, 24

Coronoid. 20) 22) 23. 240 95-51 538

Cranial nerves, 7

Cricoid, 39

Crocodilia, 27

Ctenosaura teres, 95

Cylindrophis, 40

Deéntary,” 20, 21,°22, 285 25:46, 50,
54

Dibamus, 39, 52

Diploglossa, 20, 49, 52, 53

Ectopterygoid, 14, 15, 46, 50
Epipterygoid, 18

110 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

Eryx, 40
Exoccipital, 6, 7, 50, 54

Femur, 43, 44
Fontanel bone, 7, 19
Frontal, 9, 10, 50, 52

Glossohyal process, 40, 41
Gyrinophilus porphyriticus, 9

Helminthophis: key characters, 2;
distribution, 2; lower jaw, 28;
vertebrae, 30, 31; pelvic girdle,
45; hyoid, 47

Hyoid, 38-43, 45, 46, 47, 53, 54

Hypapophyses, 27, 28, 29, 30, 32, 36,
45

Hypohyal, 39, 40, 41, 42, 51

Iguana, 13
Ilium, 43, 44
Ischium, 43, 44

Jugal, 12, 50, 51

Lanthanotus, 3, 49, 50
Laterosphenoid, 18, 46, 52
Leptotyphlopidae: key characters,
1; distribution, 2; skeletal char-
acters, 49, 50; taxonomic position,
49, 51, 58; phylogeny, 55
Leptotyphlops: key characters, 1;
distribution, 2; skull, 6-19; pala-
tal calcifications, 16; lower jaw,
23-25; vertebrae, 27-38; ribs, 35;
hyoid, 38-43; pelvic girdle, 43-
44
albifrons: earlier descriptions, 5;
pelvic girdle, 44
bakewelli: skull, 6; pelvic girdle,
43: 61, 63, 65, 95, 97
deux-raies: earlier descriptions, 5
dimidiata: earlier descriptions, 5,
1) Vo. 16
dulcis: vertebrae, 29; hyoid, 42;
external claw, 44; 79, 81, 83,
91, 97, 99
emini: skull, 6, 8, 16; vertebrae, 29,
31; 79, 81, 83, 91, 99
humilis: skull, 8; axis ribs, 29; ver-

tebrae, 29, 31, 32; exoccipitals,
54; 79, 81, 83, 85, 91, 93, 99
macrolepis: earlier descriptions, 5
magnamaculata: skull, 6, 25; verte-
brae, 29, 31; 79, 81, 83, 91, 99
maximus: skull, 9, 16; vertebrae,
29; 79, 81, 83, 91, 99
nigricans: earlier descriptions, 3, 5,
24, 44; skull, 6, 17, 24; verte-
brae, 29; 79, 81, 83, 91, 99
phenops, 91
Liotyphlops: key characters, 2; distri-
bution, 2; skull, 6-19; teeth, 13,
23; lower jaw, 21-23; vertebrae,
27-37; ribs, 35; hyoid, 39-40;
pelvic girdle, 45
albirostris: earlier descriptions, 5,
12, 26, 29, 35; skull, 18; scales/

vertebrae ratio, 35; pelvic
girdle, 45; 61, 63, 65, 85, 93,
95, 97

Lower jaw, 19-25, 47
Lymphapophysis, 36

Masticophis, 54

Maxilla, 12, 18, 14, 15, 16, 46, 47, 50,
5s 5a

Meckelian groove, 25, 49, 50, 55

Metapophysis, 32, 36, 54

Museum abbreviations, 106

Nasal, 18, 19, 45, 47, 50, 52

Odontoid, 27, 28

Ophidia: suborder characters, 48, 49,
BB, tBYS:

Ophisaurus, 54

Palatal calcifications, 16

Palatine, 14, 15, 16

Palpebral, 12

Parietal, 8, 9, 46, 48, 49, 52

Pelvic claw, 44

Pelvic girdle: earlier descriptions,
43; 43-45; mentioned, 46, 47

Platynota, 20, 49, 50, 52, 53, 54

Postfrontal, 10, 11, 12, 45, 50

Postorbital, 11, 12

Prearticular, 20, 24, 50

Prefrontal, 18, 50, 52

Premaxilla, 19, 45

Proatlas, 28, 46

Prootic, 7, 49

Pterygoid, 13, 14, 15, 16, 50
Pubis, 43, 44

Python, 33

Quadrate, 19, 22, 23, 24, 46, 50

Rhineura floridana, 95

Rhinophis, 40

Rib: cervical, 29; thoracolumbar, 35;
cloacal, 36

Sauria, 49, 55

Sauromalus ater, 95

Scales, 1

Scales/vertebrae ratio, 34, 35, 37-
38, 46, 47

Septomaxilla, 17, 18, 19, 53

Serpentes, 49, 55. See also Ophidia

Seymouria, 27

Skull, 4-19

Sphenodon, 28

Splenial, 20, 21, 22, 23, 25, 49, 50, 51

Squamosal, 21

Stenostome, 5

Supraoccipital, 6, 7, 47, 50, 54

Supraorbital, 11-12

Surangular, 20, 23, 24, 46, 50

Tabular, 21,.22, 24, 46, 50
Teeth, 18, 22—23, 25, 46, 47, 50, 52
Thamnophis, 31, 33, 35
radix, 29, 35, 95
Thyrohyal, 39
Typhlophis: key characters, 2; distri-
bution, 2; lower jaw, 23; verte-
brae, 30, 31; pelvic girdle, 45;
skull, 47
Typhlopidae: key characters, 2; taxo-
nomic position, 48, 49, 51, 55, 58;
skeletal characters, 52-54; phy-
logeny, 55
Typhlops: key characters, 2; distribu-
tion, 2; skull, 6-19; teeth, 13;
lower jaw, 19-21; vertebrae, 27—
38; ribs, 35; hyoid, 38-43; pelvic
girdle, 43-44; soft anatomy, 55;
hemipenial homologies, 55-56
bituberculatus: earlier descriptions,

8

INDEX itl

blandfordi: hyoid, 41, 42; 73, 75,
77, 89, 101

boettgeri: skull, 7; hyoid, 41; 73,
75, 77, 89, 101

braminus: earlier descriptions, 2,
3, 5, 7, 11, 26, 38, 34; distribu-
tion, 2; skull, 8, 11, 15, 21; ver-
tebrae, 29, 30, 31, 33; scales/
vertebrae ratio, 34; hyoid, 41;
Mas 1D.) 01, 00,101

cariei: fossil vertebrae, 26

delalandii: earlier descriptions, 5

diardi: earlier descriptions, 5

dinga, 5

flaviventer: vertebrae, 31; 73, 75,
77

grivensis: fossil vertebrae, 26

jamaicensis: axis ribs, 29; “uro-
style,” 37; 87

lehneri, 95, 97

lineatus: skull, 7, 8; axis ribs, 29;
vertebrae, 32; “urostyle,” 37;
61, 63, 65, 85, 87, 97

lumbricalis: earlier descriptions, 5;
skull, 15; axis ribs, 29; verte-
brae, 31; hyoid, 41; 67, 69, 71,
89, 95, 97

platycephalus: skull, 15; vertebrae,
31; 67, 69, 71, 95, 97

polygrammicus: vertebrae, 31;
“urostyle,” 37; hyoid, 40, 41;
67, 69, 71, 87, 89, 93, 101

punctatus: earlier descriptions, 5,
11, 48; skull, 20

pusillus: hyoid, 41; 73, 75, 77, 89,
101

reticulatus: earlier descriptions, 5;
vertebrae, 31; hyoid, 41; 67,
69, 71, 89, 93, 103

richardi: earlier descriptions, 5;
vertebrae, 31; 87, 97

rostellatus: vertebrae, 31; “uro-
style; 37: 67, 69, 71,87, 97

schlegelii: earlier descriptions, 5;
skull, 20; axis ribs, 29; verte-
brae, 31; hyoid, 41; 73, 75, 77,
89, 103

vermicularis: vertebrae, 31; “uro-
style,” 37; 67, 69, 71, 87, 89,
101

112 OSTEOLOGY OF TYPHLOPIDAE AND LEPTOTYPHLOPIDAE

“Urostyle,” 37

Vertebrae, 25-38; earlier descrip-
tions, 26; regions of the column,
26, 27; foramina, 26, 30, 31, 36;
atlas and axis, 27-30; thoracolum-
bar, 30-35; scales/vertebrae ratio,
34, 35; cloacal, 36; caudal, 36, 37;
mentioned, 49, 53

Vomer, 17, 52

Xenosauridae, 49
Xenosaurus grandis, 95

Zygantra, 3, 36, 48, 53
Zygapophyses, 32, 33, 36, 49
Zy gosphenes, 33, 36, 48, 53

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