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The Hyoid and Its Associated Muscles in Snakes

The Hyoid
and Its Associated Muscles

in Snakes

DAVID A. LANGEBARTEL

ILLINOIS BIOLOGICAL MONOGRAPHS 38

UNIVERSITY OF ILLINOIS PRESS URBANA, CHICAGO, AND LONDON 1968

Board of Editors: Robert S. Bader, James E. Heath, Richard B. Selander, Hobart M. Smith,
and Ralph S. Wolfe.

This monograph is a contribution from the Department of Zoology, University of Illinois.
Issued January, 1968.

© 1968 by the Board of Trustees of the University of Illinois. Manufactured in the United
States of America. Library of Congress Catalog Card No. 68-11026.

Acknowledgments

My thanks first go to Dr. Hobart M. Smith of the Department of
Zoology, University of Illinois. He has been a constant source of assis-
tance in every way possible during this study.

Dr. Robert F. Inger and Mr. Hymen Marx of the Chicago Natural
History Museum were very gracious in their loan of many specimens,
as were Dr. Doris M. Cochran and Dr. James Peters of the United
States National Museum, Dr. Ernest E. Williams of the Museum of
Comparative Zoology at Harvard University, the late Dr. F. A. Shan-
non of Wickenburg, Arizona, and Dr. D. F. Hoffmeister of the Univer-
sity of Illinois Museum of Natural History. All the individuals men-
tioned generously allowed the author to dissect as was required.

Mrs. Barbara Schwarz, of the Department of Anatomy, University
of Wisconsin Medical School, was very patient and careful in her
typing of the entire manuscript.

Davin A. LANGEBARTEL

Department of Anatomy
University of Wisconsin

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CONTENTS

INTRODUCTION 1
PARTI. THE HYOID APPARATUS 5
A. General Anatomy 5
B. Form and Composition 6
C. Descriptions of Examined Hyoids 18
D. Discussion 35
E. Summary 4]
PART II. THE ASSOCIATED MUSCLES OF THE HYOID 44
A. Preliminary Remarks 44
B. In Lizards 47
C. Accounts of Muscles in Snakes 49
D. Discussion
E. Summary 87
PART III. PHYLOGENETIC SIGNIFICANCE OF THE HYOID AND
ITS ASSOCIATED MUSCLES IN SNAKES 89
A. Discussion 89
B. Summary 99
LITERATURE CITED 101
EXPLANATION FOR FIGURES 107
FIGURES 108

INDEX 147

INTRODUCTION

This study has been made to further the knowledge of variation in
the hyoid apparatus in snakes, to make known the differences in the
musculature associated anatomically and functionally with the hyoid,
and to correlate these findings phylogenetically.

The form of the hyoid has been known in a few snakes since the first
third of the nineteenth century (Losana, 1832; and d’Alton, 1834). A
few other papers treated the subject in subsequent years, but it was
not until well over a century after Losana’s and d’Alton’s works, in
1948, that any extensive study on the variation of the structure was
published. In that year Smith and Warner published their findings to
establish at once both a remarkable constancy of general hyoid mor-
phology within apparently phyletically related familial groups, and a
variability of minor points of the morphology on the generic level.

This author undertook with Smith the project of augmenting the
number of snake genera examined for the hyoid. The work was then
put aside until some years later, when the author continued it, and also
added to it a study of the musculature of the hyoid; the entire work
was then offered as a thesis for the Ph.D. degree in zoology at the Uni-
versity of Illinois. Since the completion of the thesis, the entire work
has been rewritten, new data added, and the literature brought up
to date.

The word “hyoid” is used in this work to denote the total tongue

2 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

skeleton. Other words found in the literature referring to this struc-
ture are the “hyobranchium” and “hyoglossum.”

The hyoid is usually easy to find in most species, lying close to the
skin, and only partly covered by muscles. However, in the species of
the typhlopid and leptotyphlopid snakes, the structure is buried in
muscles and therefore not so easy to find without careful dissection.

Anatomists have more actively studied the associated musculature
of the hyoid in vertebrates than the structure itself. This is also true
for snakes, and the beginning of myological investigation again dates
back to the first third of the past century (Dugés, 1827; Duvernoy,
1832; and d’Alton, 1834). It is interesting to note that d’Alton’s 1834
essay on the python’s muscles is remarkably more accurate than a great
number of works which followed his — even of this century. The most
research on these muscles in snakes has been done by German
anatomists.

Difficulties in muscle dissection are caused by distorted specimens,
and by the length of time the specimens have been preserved. Long
preservation, particularly in alcohol, softens muscles and causes them
to fray and break easily upon dissection.

One reason the ventral head musculature of snakes has been so often
incompletely or incorrectly illustrated in the past is that the cutaneous
layer has not been recognized or shown. This muscle is very easily
destroyed or disarranged upon dissection or even in skinning the head.

The drawings of the muscles were executed by the author and are
somewhat diagrammatic.

The following family classification is used in this work:

Anomalepididae

Typhlopidae

Leptotyphlopidae

Uropeltidae

Aniliidae

Xenopeltidae

Boidae

Colubridae

Elapidae

Hydrophidae

Viperidae

Crotalidae

The families Boidae and Colubridae are taken in their broadest
sense.
Of this list nearly every genus in all families save the Colubridae

INTRODUCTION 5)

has been examined for the hyoid. Of the colubrids probably a fourth
of the genera have been examined. Fewer genera in most families have
been dissected for musculature. Several rare genera would have been
very desirable to investigate. The east Indian Anomalochilus, presum-
ably an aniliid, is one; two others, Casarea and Bolyeria, are puzzling
boidlike forms found on several islands in the Indian Ocean. Fortu-
nately, Anthony and Guibé of the Paris Museum have examined these
boids for the hyoid at least and have published their results (1952).

PART I. THE HYOID APPARATUS

A. General Anatomy

The hyoid apparatus in snakes is in several morphological patterns,
depending upon the family; it is, in all cases, simplified from the
largely more generalized lizard type, and always consists of only one
bar, simple or recurved, on each side. These bars are joined anteriorly
in most species, and in these species there may or may not be a promi-
nent lingual process. (See Figs. 1 and 2.)

The hyoid’s position is rather constant: on the under surface of the
head and neck, immediately deep to the muscles beneath the skin in
this area. However, in the anomalepidids, typhlopids, and leptotyphlo-
pids, the hyoid lies completely posterior to the head. It can generally
be said that except in those families just mentioned the anterior end of
the hyoid closely approximates the position of the first ventral scute.
There is a reason for this: the anterior fibers of the costocutaneus
superior muscle originate on the anterior fraction of the hyoid and
insert on the few first scutes.

In colubrids and all families of poisonous snakes, the anterior part
of the hyoid lies deep to the costocutaneus superior, and the posterior
part of the hyoid lies deep to the obliquus internus plus transversus
abdominis.

In boids, xenopeltids, aniliids, and uropeltids, the hyoid lies deep to

6 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

the costocutaneus superior, but peripheral to the obliquus internus plus
transversus abdominis.

In the genus Cylindrophis (Aniliidae), the hyoid cornua are very
reduced and the costocutaneus swperior muscle has no connection with
them. This is also true for uropeltids.

The typhlopids and leptotyphlopids are unique in having the hyoid
buried in the extrinsic tongue muscles, which, in turn, lie deep to the
obliquus internus plus transversus abdominis.

B. Form and Composition

The hyoid apparatus in snakes is derived from branchial (pharyn-
geal, visceral) arch cartilages, as in other vertebrates. Branchial arches
are here taken to mean the entire arch series, including the Jaw arches.
The exact contributions of the several arches to the hyoid in snakes are,
frankly, not altogether clear; this subject will be discussed later in
this section.

As a preliminary step, it seems wise to review the hyoid of lizards,
where the structure is much easier to deal with than in snakes.

LInzard Hyoids. The hyoid varies in form and obviously in derivation
among lizards, but the sources of the parts seem fairly straightforward.
In general, three branchial arches — 2, 3, and 4 — contribute cartilages
to the lizard hyoid, but many lizard species have hyoids derived from
only two arches.

In the most complete type, which is also common to adult amphibia,
and may be considered as the basic generalized lizard type, all three
arches contribute (Fig. 1, B). The development of this generalized type
can be followed quite easily in early embryonic stages. Kallius (1901)
and El-Toubi and Kamal (1959) have shown and illustrated this very
well. Derivatives of the three arches are identifiable in this way:
2nd arches — lingual process (processus entoglossus), basihyal (body
of hyoid), paired hypohyals and ceratohyals; 3rd arches — paired Ist
ceratobranchials; 4th arches — paired 2nd ceratobranchials. The three
paired cartilages form the three pairs of cornua, or bars, on each side.

Of the 2nd arch parts, the lingual process and basihyal are median
in position, although the basihyal is probably often forked posteriorly.
The hypohyals fuse with the basihyal and routinely are directed an-
teriorly to some degree; the ceratohyals are generally direct continua-
tions of the hypohyals but are always at an angle with the hypohyals,
being directed posteriorly. In some species the hypohyals are actually
physically separated from the ceratohyals. In many species the cerato-

THE HYOID APPARATUS ii

hyals have recurrent cornua directed anteriorly which often reach the
stapes. The 2nd arch parts are always cartilaginous in lizards.

Of the 3rd arch parts, the 1st ceratobranchials are usually sturdy in
form and commonly bony, entirely or in part. The cornua are typically
slightly bowed or curved, divergent from midline, and are directed
posteriorly. The 1st ceratobranchial cornua usually articulate with the
basihyal by a distinct joint, which at least in some cases appears to be
discontinuous. The hyoglossal muscles always attach to the 1st cerato-
branchials.

Of the 4th arch parts, the 2nd ceratobranchials are always cartilagi-
nous and are usually very long. These cornua are parallel to the mid-
line and often close together, sometimes touching for their entire length.
They are fused to the basihyal.

It is not known whether hypobranchial elements, derived from the
3rd and 4th arches, contribute to the basihyal median piece in lizards.

Many species of agamids, gekkonids, iguanids, lacertids, and scincids
have the complete generalized type. Few other families have species
which do.

Most lizards have a hyoid in which the 2nd ceratobranchials are
lacking, so that the structure consists of the lingual process, basihyal,
and two pairs of cornua—hypohyals plus certatohyals and the Ist
ceratobranchials. Examples are: Varanus (Fig. 1, A), Gerrhonotus
(Fig. 1, D), Gehyra (Fig. 1, E), Xenosaurus (Fig. 1, G), Lanthanotus
(Fig. 2, B), Anguis (Fig. 2, C), Heloderma (Fig. 2, D), and Rhineura
(Fig. 2, E). In some genera, e.g., Lanthanotus, Anguis, and Rhineura,
the 2nd arch cornua are reduced to anteriorly directed rods which
probably are the hypohyals alone; if so, then, of course, the ceratohyals
are missing.

The genus Anniella is the only lizard genus in which the author has
found by dissection a hyoid composed of a single pair of cornua plus
the lingual process and basihyal (Fig. 2, A). These cornua are consid-
ered Ist ceratobranchials because they are bony, diverge in a posterior
direction from the midline, and are the attachments for the hyoglos-
sal muscles; in general form they also closely resemble the 1st cerato-
branchials in hyoids of the complete generalized type. Versluys (1936)
stated that ‘“Dibanus” (should be Dibamus) is like Anniella and has a
reduced hyoid with only one pair of cornua — the 1st ceratobranchials.

It seems that in lizards retention of either the 2nd arch cornua or
the 4th arch cornua alone is never found. The lingual process is found
in all lizards, as far as is known.

Lizard hyoids are generally well developed, relatively large, and, as
just indicated, commonly with at least two pairs of cornua in some

8 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

form. However, in burrowing lizards, particularly, the hyoid tends to
be reduced in relative size; e.g., Amphisbaena (Fig. 1, C), Anguis,
Rhineura, and Anniella. In the first three genera, the 2nd and 3rd arch
cornua are present. The special case of Anniella has already been
given.

Among anguinomorphan lizards, which are perhaps the ancestral
group for snakes, probably a majority of the modern species have the
most common lizard type — composed of parts from the 2nd and 3rd
arches, and having two pairs of cornua. Examples are: Varanus (Fig.
1, A) Gerrhonotus (Fig. 1, D), and Xenosaurus (Fig. 1, G).

Snake Hyoids. The hyoids of snakes are more of a problem to under-
stand than those of lizards because identities of the cornua are not at
all certain. This is because snake hyoids are severely reduced in com-
position, and it is true that in matters of evolution where parts have
been lost, identity of what remains is apt to be very difficult to
establish.

Snake hyoids are cartilaginous with the exception of the genus
Typhlops, where the hyoid is entirely or partly bony in some specimens.
In a specimen of JT. schlegeli mucruso, for example, the entire hyoid
was bony, but in a specimen each of 7. schlegeli brevis, T. polygram-
micus, and T. bibroni, it was cartilaginous. Age may be the important
factor here. Anyway, only in typhlopids does the hyoid become bony.
Hyoids of many presumably old specimens of various species of snakes
are often found to be calcified, that is, quite hard and brittle. List
(1966) mentioned that he found calcification in the hyoids of many
leptotyphlopids.

There are four morphological groups of snake hyoids (Fig. 1, H, J-
M). These groups are remarkably constant, and are noticeably distinct
from each other. The families of snakes can be fit very neatly into
these morphological groups, with only several genera as exceptions.

The four groups are simply called: (1) “M” type, (2) “Y” type,
(3) “V” type, and (4) parallel type.

(1) “M” type (Fig. 1, H). This type is found exclusively in the
Anomalepididae, a neotropical family of four fossorial, closely allied
genera: Anomalepis, Liotyphlops, Helminthophis, and Typhlophis.
The first three genera have been examined for the hyoid, and it has
been found to be similar in all specimens. The apparatus is basically
M-shaped, with the posteriorly directed cornua having recurrent
parts as long or longer than the cornua themselves.

The transverse cartilage is depressed centrally to show a concave
surface anteriorly. The transverse piece then curves posteriorly on
each side, and is directed posteriorly and a little laterally. The re-

THE HYOID APPARATUS 9

current cornua are very thin and also tend to curve somewhat medi-
ally; in some specimens these recurrent cornua can be traced to the
skull. It should be noted that in this type the hyoid is a cartilaginous,
slender, continuous strand with no visible joints.

The described parts can be identified as follows: the central con-
cave part is provisionally called the basihyal; the adjacent convex
parts of the cornua are called the hypohyals; the posteriorly directed
cornua are the ceratohyals; the recurrent cornua are merely recurrent
parts of the ceratohyals. The hyoglossal muscles attach only to the
ceratohyals because these are the only parts of the hyoid available for
attachment. Therefore, in anomalepidids the hyoid is considered by
the author to be composed entirely of contributions from the 2nd
branchial arches.

No lingual process is present.

Identification of the parts is based on direct comparison with lizard
hyoids. For example, in Fig. 1, item G is the hyoid of the lizard
Xenosaurus grandis, and H is that of Liotyphlops, an anomalepidid.
Note the striking similarity of the 2nd arch cornua of Xenosaurus, or
of nearly any other lizard for that matter, to the anomalepidid hyoid.
In short, if the lingual process and the 1st ceratobranchials were re-
moved from the hyoid of Xenosaurus, the remaining parts would ap-
pear very much like the anomalepidid hyoid. Actually, whether or not
the medial concave segment represents the basihyal is problematical.

Smith and Warner (1948) made the same identities. List (1966)
has taken a similar stand. McDowell and Bogert (1954) assumed that
the hypohyals meet in a median symphysis; this could just as well be
true as not. McDowell and Bogert also were of the opinion that the
anterior element discovered by Dunn and Tihen (1944) lying between
the lower jaws in Liotyphlops represented part of the glossal skeleton.
It is true that this element in stained specimens does resemble an in-
verted “Y” hyoid as seen in Typhlops, but Warner (1948) conclusively
showed this to be the ventral cricoid arch of the larynx, and simul-
taneously showed that what Dunn and Tihen finally decided to be a
pectoral girdle was nothing more or less than the hyoid. Gross dis-
section easily substantiates Warner’s stand (Fig. 7). In this figure
the cricoid arch of the larynx is hidden from view by the tongue, but
the hyoid and its muscles are shown.

The fact that the recurrent cornua extend forward to the skull in at
least some specimens, as reported by Smith and Warner, is surely
more evidence for a 2nd arch derivation, since the 2nd arch hyoid
derivatives in vertebrates commonly retain such a connection.

(2) “Y” type (Fig. 1, J, K). The Typhlopidae and Leptotyphlopidae,

10 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

each family with a single recognized genus, have this hyoid type.
Basically it is similar in appearance to an inverted Y, with the single,
long, median lingual process directed anteriorly, and the two cornua
directed posteriorly and somewhat divergent from the midline.

List (1966), however, in his examination of the osteology of these
animals, showed by clearing and staining that a specimen each of
T. lumbricalis and T. pusillus did not have the lingual process, so
that the hyoid was reduced to a pair of subparallel cornua (Fig. 2, G).
The author has checked a second specimen of each species: the lingual
process was lacking in 7. pusillus; in T. lumbricalis there was a very
small process which was joined to the two cornua. List also found
that in several other species of Typhlops that he examined the cornua
were not fused with the lingual process — there being a distinct gap
between the median piece and each cornu (Fig. 2, F); 7. reticulatus,
T. platycephalus, and T. blanfordi lestradez showed this condition. The
author has dissected a second specimen of 7. reticulatus and found that
no lingual process was evident, so that the two cornua were separated
anteriorly. None of the other species of Typhlops examined by the
author either lacked a process or had the cornua separated from the
lingual process.

The species of Leptotyphlops, as far as known, invariably retain
the complete Y form.

Identification of the parts is as follows: the median piece is cer-
tainly the lingual process, which incorporates the basihyal; the cornua
are considered to be the 1st ceratobranchials. The hyoid may be
totally bony in many typhlopid specimens, or else the cornua alone
may be bony (Fig. 2, F and G). The hyoglossal muscle fibers attach
individually to the cornua.

The identification is based upon comparison with lizard hyoids.
In Anniella the hyoid consists of a lingual process plus basihyal and
one pair of cornua, the 1st ceratobranchials, which are bony and to
which the hyoglossal muscles attach as in all other lizards. The “Y”
type snake hyoid bears a great resemblance to that of Anniella or to
that of any lizard with the basihyal and 1st ceratobranchials taken
alone; the cornua are frequently bony in typhlopids, and they also
provide attachment for the hyoglossz.

List (1966) felt that there seemed to be three conditions present
in the typhlopids: (1) basihyal and lingual process with Ist cerato-
branchials; (2) lack of basihyal and lingual process, leaving only
the two Ist ceratobranchials; (3) basihyal and process only, with loss
of ceratobranchials. He indicated that a series can be arranged to
show the regressive change from the basic condition (1) to conditions

THE HYOID APPARATUS 11

(2) and (3). This series seems reasonable, but condition (3) cannot
be conclusively proven without embryological evidence. List showed
several Typhlops with an obvious basihyal cartilage separated from
the bony Ist ceratobranchials: TJ. reticulatus (Fig. 2, F), and T.
blanfordi lestradei. He illustrated condition (2), with the basihyal
lacking and only Ist ceratobranchials present, in 7. pusillus (confirmed
by the author) and 7. lumbricalis (a small process in a second speci-
men). He figured several more species which he interpreted as having
only the basihyal present as condition (3): T. braminus, T. polygram-
micus (Fig. 2, H), and 7. vermicularis; this basihyal element always
proved to be cartilaginous, with the prongs relatively short. The author
has checked a second specimen of 7’. polygrammicus and the hyoid is
also cartilaginous.

As mentioned, ossification in the hyoid of typhlopids is variable.
A large specimen of 7. schlegeli mucruso was found to have a com-
pletely ossified hyoid. List found the same condition in a specimen
each of T. boettgeri and T. s. schlegeli. However, the author found
the hyoid to be totally cartilaginous in a specimen of T.. schlegeli brevis.
Very possibly the matter of ossification may be directly correlated with
age.

Smith and Warner (1948) supposed that the hyoid of the “Y” type
is composed of a median basihyal and its process plus the cornua,
which are implied in previous paragraphs of their paper to be equal
to the hypohyals. Comparison with most lizard hyoids easily shows
this idea to be of little value, for in lizards the hypohyals lie in a
transverse or anterolateral plane and are never bony.

For the species of examined leptotyphlopids, the hyoid is very
constant: it is always cartilaginous, the lingual process is joined to
the cornua, and the cornua are usually relatively longer than in
Typhlops (Fig. 2, J).

The relationship of the typhlopid and leptotyphlopid snakes is not
clear, and the two families have often been considered by some workers,
e.g., McDowell and Bogert (1954), to be very distantly related, if
at all in any sort of recent sense. However, the hyoid, which is similar
for the two families and yet is distinct from all other snakes, tends
to indicate that these families have more of a relationship than might
otherwise be awarded them. This viewpoint is materially strengthened
by musculature patterns presented in the second part of this paper.
McDowell and Bogert combined typhlopids and the anomalepidids
into the Typhlopidae. They felt that “the hyoid of Typhlops differs
from that of ordinary snakes, leptotyphlopids, and the vast majority of
lizards” in having the hyoid confined to the tongue itself. Actually,

12 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Leptotyphlops has nearly the same muscle-hyoid relationships that
are found in Typhlops. They also regarded the hyoid of Typhlops
as being composed of the basihyal alone. Then they proposed that
the leptotyphlopid and other snakes’ hyoids are composed of a fused
basihyal plus Ist ceratobranchials, except where the basihyal has
been secondarily lost. The opinion of List on the possibility that the
basihyal alone may compose the hyoid in at least some typhlopids has
been given previously; the author does not disagree with it. However,
the author cannot agree that Leptotyphlops and “ordinary snakes”
all have the same components forming the hyoid; even so, McDowell
and Bogert did devise the correct combination of basihyal and 1st
ceratobranchials for the leptotyphlopids.

(3) “V” type (Fig. 1, L). This is found in the families Aniltidae,
Boidae (with the exception of several puzzling genera), Uropeltidae,
and Xenopeltidae. The hyoid is basically of an inverted V form, or is
reduced, by loss of the anterior connection and parts of the cornua, to
a pair of subparallel rods. The cornua diverge posteriorly from the
midline and may be slightly bowed. They are always cartilaginous
and the hyoglossal muscles attach to them as separate bundles. No
lingual process is present and the arch of the cornual union is very
slender when present.

Loss of the anterior connection may not perhaps have much mean-
ing phylogenetically; for example, in one specimen of Charina bottae,
the cornua were joined anteriorly, but in another, they were not.
A specimen of Epicrates angulifer had the cornua united, but a speci-
men of H. cenchris did not.

It seems evident to the author that the cornua of this type must be
1st ceratobranchials, and that the basihyal is either very small in those
hyoids that have united cornua, or else entirely absent, which it cer-
tainly is in the many cases where the cornua are distinctly separated
anteriorly. Again it is comparison with lizards that gives the answer.
The cornua of the “V” type are definitely very similar in general ap-
pearance and position to the 1st ceratobranchials in lizards. Remove
the entire basihyal, hypohyals, ceratohyals, and 2nd ceratobranchials
from a generalized lizard hyoid, such as Anolis (Fig. 1, B), or the
entire basihyal, hypohyals, and ceratohyals from the more common
lizard type, as seen in Varanus (Fig. 1, A), Gerrhonotus (Fig. 1, D),
or Gehyra (Fig. 1, E), and the 1st ceratobranchial cornua that are
left certainly resemble the cornua of the “V” type.

The author considers the basihyal to be missing, for all practical
purposes, but Edgeworth (1935) stated, with no further discussion,
that Boa and Python molurus have the anterior ends of the cornua

THE HYOID APPARATUS is

“eontinuous with a small basihyobranchiale.”’ To the contrary,
Gnanamuthu (1937) from Fiirbringer stated that in Python the “basi-
hyoid” is gone and the two “thyrohyals” (meaning the cornua) are
practically free of each other. “Thyrohyal” is a name reserved for an
element from the 3rd branchial arch. It is not customarily used in
lizards, and it seems improper to sanction the use of the word in
snakes. Smith and Warner (1948) have stated a similar view, but
proposed at the same time to call the cornua of the “V” type the
hypohyals. From comparison with lizards, it does not seem likely that
these could be equal to the hypohyals.

(4) Parallel type (Fig. 1, M). This type is found in colubrids,
hydrophids, elapids, viperids, and crotalids, and in a few genera of
what are usually considered to be boids: Bolyeria, Casarea, Trachy-
boa, and Tropidophis. The parallel type consists of a pair of very
long parallel cornua which are always joined anteriorly. The arch of
this union is sometimes smooth and sometimes has an anteriorly di-
rected lingual process. This hyoid type is always cartilaginous. The
cornua provide the attachment for the hyoglossal muscles.

Identification of the parts is as follows: the lingual process, if pres-
ent, is obvious; the arch at the union of the cornua is considered to be
the basihyal, although it perhaps is not really present when there is no
lingual process; the cornua are considered to be the 2nd cerato-
branchials. The cornua are always fused indistinguishably with the
basihyal arch, or at least to each other.

The little work that has been done on the development of the
snake hyoid has all centered on the parallel type. This evidence has
not been satisfactory overall; it has been conflicting in part and the
early blastemal stages of the hyoid components have not been identi-
fied. It can be pointed out that this problem, as well as a great many
others in the subject of snake ontogeny, presents a worthwhile and
fertile field for investigators. The author has studied fairly early
embryos of both Pituophis and Thamnophis but has not yet been
satisfied as to the origin of the parts of the parallel type hyoid. The
embryological evidence must at this time largely yield to the morpho-
logical comparison with lizard hyoids.

There has been no trouble with the identification of the basihyal and
its lingual process, if one is present. They are certainly 2nd arch
derivatives. It is the cornua which have given identity problems.
Most investigators have called the cornua ceratohyals, or at least
have meant that they are of 2nd arch derivation. A lesser number of
investigators have considered the cornua to be 1st ceratobranchials,
of 3rd arch derivation. And, as already noted above, the author

14 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

considers the cornua to be the 2nd ceratobranchials, of 4th arch
derivation.

Rathke (1839) claimed to have observed a connection between the
cornua and the columella auris in Tropidonotus; this observation was
offered to substantiate his view that the cornua are 2nd arch deriva-
tives.

Owen (1866) called the cornua ceratohyals, as did Walter (1887).
McKay (1889) varied the name somewhat by calling the cornua
“hyoid bones” or “hypobranchial bars.” Neither term is very ap-
propriate. Gaupp (1904) followed Rathke in deciding that the cornua
are 2nd arch derivatives and called them ‘“cornua hyalia.”

Peyer (1912) studied several stages of Vipera aspis. He could not
find a 8rd branchial arch in his embryos, and also did not observe
a connection between a cornu and the columella auris, as Rathke
claimed to have seen. At the 70-mm stage, Peyer said that the hyoid
consisted of two “hyal cornua” with a separate, anterior “processus
entoglossus.” In the 125-mm stage, the hyoid was complete. The
cornua were definitely shown to originate in a nearly parallel fashion
posterior to the basihyal element — the lingual process; the cornua then
grew anteriorly to meet the process.

Sewertzoff (1929) called the cornua the ceratohyals. Backstrom
(1931) did not positively name the cornua but implied that they are
of 2nd arch derivation.

In 1935 Edgeworth called the single element of the hyoid the
“basihyobranchiale” and-the cornua the “cornua branchiale i.” He
also stated that he believed the ceratohyals have been lost. No
reasons were given for any of his conclusions, however.

Versluys (1936) called the connecting piece the “corpus hyale”
but used Firbringer’s (1922) interpretation in naming each cornu
the “cornu branchiale I.” Versluys based his conclusion on the com-
parison with the reduced hyoids of the lizards Anniella and Dibamus,
where it is probable that the cornua are the 1st ceratobranchials.
DeBeer (1937) called the cornua the ceratohyals.

Kesteven (1944), from observations on Pseudechis, an elapid, re-
marked that “this single hyoid arch is probably the second; it appears
too far back to be the ceratohyal.” Apparently Kesteven called the
2nd arch of the series the 1st branchial arch, a common procedure
in comparative anatomy (the 1st arch of the series — mandibular plus
maxillary processes — would compose the jaw arch). If such is the
case, then the ‘“‘second” arch he referred to would be the 38rd branchial
arch of this paper. Kesteven therefore considered the hyoid cornua
to be the 1st ceratobranchials.

THE HYOID APPARATUS 15)

Smith and Warner (1948) used basihyoid plus hypohyals for the
components. It does not seem to the author that hypohyals are a
reasonable choice. In lizards they are always in a transverse or
anterior-directed plane and relatively short.

Cowan and Hick (1951) used ceratohyals for the cornua in
Thamnophis. These authors found two tendinous inscriptions in the
neurocostomandibularis muscle of Thamnophis, and they considered
these inscriptions to be traces of the 1st and 2nd ceratobranchials.
However, the possibility of the inscriptions being traces of the Ist and
2nd ceratobranchials would not correctly fit with their interpretation
of the cornua as ceratohyals, because the ceratohyals would be in the
wrong position relative to the ceratobranchials. If anything, their
suggestion as to the identity of the inscriptions would fit in better
with the author’s idea that the cornua are 2nd ceratobranchials.

In 1954 McDowell and Bogert stated that the parallel type of snake
hyoid consists of a basihyal fused to the 1st ceratobranchials. They
arrived at this solution by comparing the hyoids with those of lizards,
but the drawback is that they included Leptotyphlops with the group
represented by the parallel type. It is surely clear that Leptotyphlops
has a hyoid which is distinctly different from the parallel type, and
is really similar to that of Typhlops. The author does consider the
“Y” type of hyoid as seen in the leptotyphids and typhlophids as
being basically composed of a basihyal plus Ist ceratobranchials.

Pringle (1954) has done considerable work on the cranial develop-
ment in snakes, studying the colubrids Lamprophis ornatus and
Dasypeltis scaber, the viperid Causus rhombeatus, and the elapid
Hemachatus hemachatus. He named the cornua the ceratohyals.

In the 69-day stage of Lamprophis, he noted that the “two cerato-
hyals fuse below; basihyal present.” He also noted that during de-
velopment the basihyal moves forward.

In the 43-day stage of Dasypeltis, “the hyobranchial apparatus
consists of two ceratohyals which fuse anteriorly.” He found no
basihyal at this stage; later, however, the basihyal appeared.

As for the 54-day stage in Causus, the “ceratohyals” fused below
the basicranial fenestra. He saw no basihyal in this species, even
in the young adult.

In Hemachatus the 8-mm stage revealed that the “ceratohyals fuse
below the basicranial fenestra, and during development this point of
fusion moves forward. There is no basihyal in any of the stages ex-
amined as in Causus.”’

It is evident that at least in these genera the cornua fuse first, and
the basihyal element, if there is one, later fuses to this union. A

16 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

check of specimens by the author revealed that both Cauwsus and
Hemachatus lack a lingual process in the adult, as suggested by
Pringle; this seems to indicate that a rounded arch means absence of
all basihyal elements.

There were no particular reasons advanced by Pringle for calling
the cornua ceratohyals. And it might easily be construed that the
matter of the fusion of the cornua and their subsequent moving
forward would be evidence for their being derived from an arch other
than the 2nd. The later fusion of the obvious basihyal piece, where
it was present, would add support to this idea.

Srinivasachar (1954) called the cornua ceratohyals; he gave no
reasons.

List (1966) decided that since the basihyal may be the only piece
present in some typhlopids and is the only piece present in Lepto-
typhlops, it must also compose the entire hyoid in those snakes with
the parallel type. The long cornua, according to him, would merely
represent elongations of the posterior basihyal processes. In his
interpretation the processes would not strictly be hypohyals or cerato-
hyals, apparently. List’s idea is not an unattractive one, but there
are arguments against it. One is that Typhlops must be far removed
phyletically from the snakes with a parallel hyoid, so what is true
for the typhlopid and leptotyphlopid hyoid would not necessarily
apply to the parallel type. A second argument is that Pringle has
shown in several species that the cornua develop separately from
the basihyal element, if one is present at all.

Romer (1956) stated that “the ‘prongs’ are presumably the first
branchials; the small connecting piece, the corpus, with a short lingual
process.”

Sondhi (1958) called the basihyal the basihyoid, and used only
cornua for those bars. He also parenthetically referred to Versluys by
including the latter’s respective synonyms: corpus hyale and cornua
branchialia I. Apparently he followed Versluys in believing the cornua
to be 1st ceratobranchials.

Albright and Nelson (1959) considered that the hyoid in Elaphe
is composed of a “basihyoid with paired ceratohyals.” They gave no
explanation for their choice.

In 1961 El-Toubi and Magid considered that the cornua are de-
rived from the 2nd arch. The most recent paper, and probably the
best, to appear on the development of the snake skull is the one by
Kamal and Hammouda (1965) who studied very closely the ontogeny
of the skull of Psammophis sibilans, a colubrid. This paper is especially
interesting because it clearly seems to refute some of the evidence

THE HYOID APPARATUS 17

of Pringle, but also seems to substantiate List’s idea that the cornua
are extensions of the basihyal.

In their “stage I, age 15 days, 47 mm” of Psammophis embryos,
Kamal and Hammouda found, and clearly illustrated, a small inverted
v-shaped body which was chondrifying and lay between Meckel’s
cartilages. At stage II the piece had a distinct anterior projection on
it which the authors called the processus entoglossus. At stage III
both the process and the posterior-directed prongs had enlarged and
lengthened so that the piece was rather y-shaped. At stage IV the
prongs had lengthened noticeably and were called the ceratohyals.
Successive stages clearly demonstrated that the ceratohyals were
formed by the increase in length of the two rods. Kamal and Ham-
mouda have shown very well that in Psammophis the cornua have
grown from a common piece and have not formed independently of
the basihyal element as Pringle demonstrated. However, have they
really proved, as List thought, that the parallel type cornua are exten-
sions of the basihyal? List’s conclusion appears very convincing
at first glance, but the heart of the matter is understanding from what
the chondrifying blastema has been derived. Kamal and Hammouda,
for all their very good work, have not really demonstrated whether
the initial v-shaped piece has been derived of blastemal material from
the 2nd arches alone, or whether blastemal material from another set
of arches, particularly the 4th, has also contributed. Blastemal origin,
then, is the crux of the problem, and until this is solved, the exact
explanation of the derivation of the parallel type of hyoid’s cornua
must be based on morphological evidence.

At the conclusion of this review of the literature on the problem,
it might as well be mentioned that many authors have just regarded
the apparatus as the “hyoid” and let it go at that. A short summary
of the pertinent nomenclature of the parts of the parallel type hyoid
should prove helpful.

1839 Rathke: cornua hyalia (2nd arch)

1866 Owen: ceratohyals

1887 Walter: ceratohyals

1889 McKay: hyoid bones or hypobranchial bars

1904 Gaupp: cornua hyalia (2nd arch)

1912 Peyer: hyal cornua with processus entoglossus

1929 Sewertzoff: ceratohyals

1931 Backstrém: 2nd arch origin inferred

1935 Edgeworth: basihyobranchiale plus cornua branchialia i

1936 Versluys: corpus hyale plus cornua branchialia I

1937 DeBeer: ceratohyals

1944 Kesteven: not named directly, but apparently 1st ceratobranchials
1948 Smith and Warner: basihyoid plus hypohyals

18 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

1951 Cowan and Hick: ceratohyals

1954 McDowell and Bogert: basihyal plus Ist ceratobranchials

1954 Pringle: basihyal plus ceratohyals

1954 Srinivasachar: ceratohyals

1956 Romer: corpus, lingual process, and “presumably the first branchials”
1958 Sondhi: basihyoid plus posterior cornua

1959 Albright and Nelson: basihyal plus ceratohyals

1961 El-Toubi and Magid: derived from 2nd arch

1965 Kamal and Hammouda: processus entoglossus plus ceratohyals

1966 List: basihyal plus basihyal processes

The history shows that most investigators have regarded the cornua
as ceratohyals; few have shown any reasons for their actions. Only
Rathke, Peyer, Pringle, and Kamal and Hammouda have used em-
bryological evidence, and this seems to be somewhat contradictory
in a few respects. The author’s conclusion that the cornua are 2nd
ceratobranchials is only based upon direct comparison with the
complete generalized lizard hyoid type. A look at one of these
generalized lizard hyoids, e.g., Anolis (Fig. 1, B), will demonstrate
what is meant: by removing the hypohyals plus ceratohyals and the
1st ceratobranchials, the remaining continuous cartilage will be com-
posed of the lingual process, a basihyal arch, and the very long, parallel
cornua, the 2nd ceratobranchials. The similarity of this altered hyoid
of Anolis to that of any snake with a parallel type hyoid (including a
lingual process) is remarkable. It is true that in the lizard, the hyo-
glossi attach to the 1st ceratobranchials. However, if only the 2nd
ceratobranchials are present in certain snakes, these are obviously the
only cornua which are available for the hyoglossi. Note that in the
lizards Amphisbaena (Fig. 1, C) and Mabowa (Fig. 1, F), the hyoids
as a whole are somewhat reduced, and the 2nd ceratobranchials in par-
ticular are relatively very short. In these species the 2nd cerato-
branchials resemble very much the developing cornua of the parallel
type hyoid as shown by Kamal and Hammouda.

C. Descriptions of Examined Hyoids

The following measurements are given in millimeters (mm). Those
measurements concerning the hyoid are rounded to the nearest .6 mm.
Due to the natural difficulty of measuring cartilaginous strands in pre-
served specimens, the results have to be regarded chiefly as a means of
comparing relative sizes of various hyoids.

In the parallel type of hyoid, the width of the hyoid is that measure-
ment taken at the greatest width of the two cornua. Actually, the arch
of the basihyal is usually somewhat more narrow than the width. The

THE HYOID APPARATUS 19

length of the parallel type of hyoid is its entire length — from the tip
of the lingual process, if one is present, to the end of the cornua.

Museum abbreviations are: UI, University of Illinois Museum of
Natural History; CNHM, Chicago Natural History Museum; USNM,
United States National Museum; MCZ, Museum of Comparative
Zoology, Harvard University.

ANOMALEPIDIDAE (“M” type)

Helminthophis flavoterminatus (USNM 69333). Hyoid not measured
but with same essential shape and relationships as in the following
species.

Liotyphlops albirostris (MCZ 25232) (Fig. 1, H). Recurrent con-
tinuations extend craniad from the legs of the ‘“M”’; central depression
4 mm from mental; width of shoulders of transverse bar 1 mm; length
of one descending cornu 2 mm; length of one ascending (recurrent)
cornu 1.5mm. Body length 181 mm.

TYPHLOPIDAE (“Y” type)

Typhlops bibroni (CNHM 17718) (Fig. 8, B). Hyoid cartilaginous;
process 1.5 mm, 20 mm from mental; one cornu 2 mm; posterior sepa-
ration of cornua 2 mm; hyoid lies between ribs 9-11. Body length
375 mm.

Typhlops intermedius (CNHM 53636). Hyoid cartilaginous; process
1.5 mm, 24 mm behind mental; hyoid median length 2 mm; hyoid lies
between ribs 11-13. Body length 313 mm.

Typhlops schlegeli mucruso (CNHM 81018) (Fig. 1, J). Hyoid
bony; process 1.5 mm, 33 mm behind mental; hyoid median length 2.5
mm; posterior separation of cornua 1.5 mm. Body length 365 mm.

LEPTOTYPHLOPIDAE (“Y” type)

Leptotyphlops maximus (CNHM 38282) (Fig. 1, K). Process 2 mm,
16 mm behind mental at 9th rib; hyoid median length 6 mm. Body
length 326 mm.

Leptotyphlops septemstriatus (CNHM 26660). Process 1.5 mm, 12
mm behind mental; one cornu 2.5 mm; hyoid lies between ribs 6-13.
Body length 245 mm.

UROPELTIDAE (“V” type)
Platyplectrurus madurensis (CNHM 40458). Cornua separated

20 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

anteriorly by 3 mm, posteriorly by 6 mm; median length 7.5 mm;
hyoid ends 5th ventral. Body length 285 mm.

Rhinophis blythi. Three specimens examined, all with cornua sepa-
rated anteriorly; measurements of two specimens given. In CNHM
25930 (Fig. 11), cornua separated anteriorly by 2 mm, posteriorly by
4 mm; cornua 7.5 mm behind mental; median length of hyoid 3.5 mm;
cornua begin Ist ventral, end 4th. Body length 282 mm.

In another specimen, cornua separated anteriorly by 2 mm, posteri-
orly by 7.5 mm; cornua 6 mm behind glottis; cornua 5.5 mm, begin Ist
ventral, end 6th. Body length 255 mm.

Rhinophis planiceps. Cornua separated 1.5 mm anteriorly, 3 mm
posteriorly ; cornua 4.5 mm behind glottis; cornua 2.6 mm, begin 1 mm
anterior to lst ventral, end rear of 2nd; cornua nearly parallel for first
quarter, then flare laterally. Body length 167 mm.

Silybura beddomit (CNHM 16110). Cornua separated anteriorly by
2 mm, posteriorly by 4 mm; cornua 6.5 mm behind mental; hyoid
median length 3.6 mm. Body length 159 mm.

ANILIIDAE (“V” type)

Anilius scytale. Four specimens examined, all with cornua joined
anteriorly and with no process; measurements of two specimens are
given. In CNHM 16948 point of arch 8.5 mm anterior to 1st ventral;
cornua end 2nd ventral; arch .6 mm wide; right cornu 10 mm, left
cornu 12 mm; cornua separated anteriorly by 7 mm; anterior parts of
cornua very thin. Body length 537 mm.

In CNHM 35683 (Fig. 12, A), point of arch 20 mm from mental;
cornua separated posteriorly by 8 mm; hyoid median length 15 mm.
Body length 770 mm.

Cylindrophis maculatus. Hyoid much reduced. In MCZ 15795 (Fig.
12, C), cornua 14.5 mm behind mental, separated anteriorly by 6 mm.
Cornua 4 mm, begin 3 mm behind hyoglossal split; anterior half of
each cornu free from hyoglossal muscle. Body length 315 mm.

In CNHM 25928, cornua 12 mm behind mental; cornua separated
anteriorly by 2.5 mm, posteriorly by 4 mm; cornua end 7th ventral;
hyoid median length 2 mm. Body length 283 mm.

Cylindrophis rufus. Two specimens examined have separate cornua.
In CNHM 67269 (Fig. 12, B), cornua 15.5 mm behind mental; cornua
separated anteriorly by 2.56 mm; cornua begin 4th scale anterior to Ist
ventral, end 8rd ventral; hyoid median length 8.56 mm. Body length
490 mm.

In CNHM 30547, cornua 11.5 mm behind mental; cornua separated

THE HYOID APPARATUS Pall

anteriorly by 3 mm; posteriorly by 7.5 mm; hyoid median length 4.5
mm. Body length 401 mm.

XENOPELTIDAE (“V” type)

Xenopeltis unicolor. Three specimens examined, all have divergent
cornua joined anteriorly. In CNHM 15273 (Fig. 18), point of arch
14 mm behind glottis; hyoid begins 5 mm before Ist ventral, ends 9th
ventral; cornua 30 mm, separated posteriorly by 12 mm. Body length
698 mm.

In another, unnumbered specimen, arch 23 mm behind mental; arch
1 mm wide; hyoid begins 1st ventral, ends 11th; cornua separated
posteriorly by 10 mm; hyoid median length 26 mm. Body length
770 mm.

BOIDAE (sensu lato) (“V” type and parallel type)

Aspidites melanocephalus (USNM 11034). Cornua joined anteriorly
as rounded arch; hyoid begins 20 mm before Ist ventral, ends 6th
ventral; cornua separated posteriorly by 19 mm; cornua 35 mm. Body
length 987 mm.

Boa canina (CNHM 25537). Cornua separated anteriorly upon
dissection, but may have been joined naturally; cornua begin 12 mm
behind glottis, end 4th ventral; cornua 13.5 mm. Body length 610 mm.

Boa cookii (CNHM 41171). Cornua separated anteriorly; cornua
begin 17 mm behind glottis, end 4th ventral; hyoid median length
18 mm. Body length 1380 mm.

Calabaria reinhardti (USNM 24224). Cornua joined anteriorly by a
very thin arch; arch 6 mm behind glottis; arch 1.5 mm wide; cornua
separated anteriorly by 10.5 mm; cornua 21 mm and 20.5 mm long.
Body length 563 mm.

Charina bottae. In three specimens examined, cornua are close
anteriorly but do not join in two; cornua joined as a rounded arch in
the third. In one of the former specimens, cornua separated anteriorly
by .6 mm, posteriorly by 14 mm; cornua end at rear edge of 2nd
ventral; cornua 15.5 mm. Body length 494 mm.

In the specimen with cornua joined, arch lies 8.5 mm anterior to Ist
ventral; hyoid ends 3rd ventral; arch 2.6 mm wide; cornua separated
posteriorly by 8 mm; hyoid median length 11 mm. Body length
411 mm.

Chondropython viridis (CNHM 14075). Cornua rather flat and
joined anteriorly; arch 20 mm behind mental; cornua end 5th ventral;

22 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

cornua separated posteriorly by 6 mm; hyoid length 24.5 mm. Body
length 980 mm.

Constrictor constrictor ortont (CNHM 8360). Cornua separated
anteriorly, begin 16 mm behind glottis, end just anterior to 1st ventral;
cornua separated anteriorly by 3 mm, posteriorly by 15.5 mm; hyoid
median length 16 mm. Body length 1000 mm.

Enygrus bibronu (USNM 56211). Cornua joined at a narrow,
sharp-pointed arch 9 mm behind glottis; cornua 12 mm, end at rear
edge of 2nd ventral; cornua separated posteriorly by 8.5 mm. Body
length 505 mm.

Epicrates angulifer (USNM 84045). A blunt arch 8.5 mm behind
glottis; arch 6 mm wide; cornua 17.5 mm, separated posteriorly by 8
mm. Body length 592 mm.

Epicrates cenchris (CNHM 31148) (Fig. 14, C). Cornua separate,
begin 20 mm behind mental, end 5th ventral; cornua separated anteri-
orly by 1.5 mm; cornua 23 mm. Specimen is head only.

Eryx c. colubrinus (CNHM 81224) (Fig. 14, B). Cornua joined
anteriorly into irregular arch 12 mm behind mental; arch 2 mm wide;
cornua separated posteriorly by 11 mm; hyoid length 18 mm. Body
length 590 mm.

Eryx jaculus. In two specimens examined cornua are separate; one
set of measurements given. In USNM 56348, cornua begin 10 mm
behind glottis; cornua separated anteriorly by 3.5 mm, posteriorly by
12 mm; right cornu 13 mm, left cornu 16 mm. Body length 487 mm.

Eryx john (USNM 84034). Cornua separated anteriorly, begin 10
mm behind glottis; cornua separated anteriorly by 1.5 mm, posteriorly
by 14.5 mm; right cornu 16 mm, left cornu 17 mm. Body length
703 mm.

Eunectes gigas (CNHM 30954). Anterior ends separated, apparently
due to injury which makes specimen incomplete. Cornua begin 16 mm
behind glottis. Body length 900 mm.

Tnasis albertisii (CNHM 13874). Cornua joined anteriorly; arch
begins 8 mm anterior to 1st ventral, ends 6th ventral; arch 6 mm wide;
cornua separated posteriorly by 4 mm; right cornu 17 mm, left cornu
16.5 mm. Body length 392 mm.

Liasis childreni (CNHM 75120). Cornua joined by a rounded arch
11.5 mm behind mental; arch 1 mm wide; cornua separated posteri-
orly by 8 mm; hyoid median length 13 mm. Body length 520 mm.

Inchanura roseofusca (CNHM 21568). Cornua separate, begin 13
mm behind glottis, end 4th ventral; cornua separated anteriorly by
3 mm; hyoid median length 16 mm. Body length 880 mm.

bo
oO

THE HYOID APPARATUS

Loxocemus sumichrastt. Cornua joined as a pointed arch 18 mm
behind mental; cornua end 46.5 mm behind mental; right cornu 30
mm, left cornu 31 mm; cornua separted posteriorly by 20 mm. Body
length 794 mm.

Nardoana boa (CNHM 13834). Cornua joined by a rounded arch 13
mm behind glottis; cornua end 7th ventral; arch 1.5 mm wide; right
cornu 23 mm. Body length 785 mm.

Python regius (CNHM 20812). Cornua separate, begin 22 mm be-
hind mental, end 3rd ventral; cornua separated anteriorly by .6 mm,
posteriorly by 7.5 mm; cornua 23 mm long. Body length 742 mm.

Sanzinia madagascariensis (CNHM 18286) (Fig. 1, L). Cornua
separate (also in a second specimen); cornua begin 15 mm behind
mental, end 4th ventral; cornua separated anteriorly by 1 mm; hyoid
median length 15 mm. Body length 480 mm.

Trachyboa boulengert (CNHM 78106). Cornua joined anteriorly
and parallel with a process 2.6 mm long, 8 mm behind mental; hyoid
ends 6th ventral; hyoid .6 mm wide, 11 mm long. Body length 240 mm.

Tropidophis maculatus (USNM 56328) (Fig. 15, A). Cornua joined
and parallel with a process 1.5 mm long, 6.5 mm behind mental;
hyoid begins 3 scales before Ist ventral, ends 9th ventral; hyoid 1 mm
wide, 15 mm long. Body length 324 mm.

Ungaliophis continentalis (CNHM 19397). Cornua separate, begin
9.5 mm behind mental, end 6th ventral; cornua separated anteriorly

by 1.5 mm, posteriorly by 2.6 mm; cornua 9.5 mm long. Body length
441 mm.

COLUBRIDAE (parallel type)

Achalinus spinalis (CNHM 18775). No process; begins 8rd ventral,
ends 11th; hyoid 1 mm wide, 13 mm long. Body length 340 mm.

Achrochordus javanicus (USNM 20412) (Fig. 15, B). No process
(also true in another examined specimen) ; hyoid begins 15 mm behind
glottis; hyoid 3 mm wide anteriorly, cornua converge posteriorly;
hyoid 92.5 mm long. Body length 1185 mm.

Adelphicos veraepacis nigrilatus (UI 6254). No process; hyoid be-
gins 2nd ventral, ends 16th; hyoid 1 mm wide, 17 mm long. Body
length 210 mm.

Amblycephalus kuangtunensis (CNHM 24489). A long, heavy
process 1.5 mm; hyoid begins one scale before 1st ventral, ends 23rd;
hyoid 1 mm wide, 45 mm long. Body length 430 mm.

Amblycephalus stanleyi (CNHM 24990). A long, tapering process

24 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

2.5 mm, near level of glottis; hyoid 1 mm wide, 21.8 mm long. Body
length 183 mm.

Aparallactus capensis (CNHM 17710). Process 1 mm, begins 8 mm
behind mental; hyoid 1 mm wide, 18 mm long, ends 18th ventral.
Body length 207 mm.

Apostolepis quinquelineata (CNHM 26665). Process .6 mm, begins
8 mm behind mental; hyoid 1 mm wide, 16 mm long, ends 16th ventral.
Body length 277 mm.

Atretium schistosum (MCZ 1330) (Fig. 15, C). Process 1 mm; hyoid
begins Ist ventral, ends 20th; hyoid 1 mm wide, 35 mm long. Body
length 340 mm.

Boiga dendrophila latifasciata. No distinct process, but arch is
sharp; arch begins one ventral’s width before 1st ventral, ends 16th
ventral; hyoid 4.5 mm wide, 51.5 mm long. Body length 1120 mm.

Carphophis amoena vermis. No distinct process; arch lies 3 mm be-
hind glottis; hyoid ends 20th ventral; hyoid 1 mm wide, 18 mm long.
Body length 149 mm.

Cerberus rhynchops (Fig. 4, D). Two specimens examined with
very distinctive hyoids. In CNHM 41117, process is very long, 10.5
mm; process is 1 mm wide at arch then widens to 1.5 mm before
tapering to the apex; point of process 15 mm behind glottis, hyoid
ends 12th ventral; hyoid 2 mm wide, 37 mm long. Body length
644 mm.

In another specimen, process is also very long, 5 mm; base of process
formed of two convex rods which diverge 2 mm from basihyal to be
1 mm apart; then rods join and single process tapers to point; point
7 mm behind glottis; arch heavy, 1.6 mm wide; hyoid 1.5 mm wide,
23.5 mm long, ends 9th ventral. Body length 466 mm.

Chersodromus hebmanni. A small, sharp process, at 3rd ventral;
hyoid ends 26th; hyoid 1 mm wide, 29.5 mm long. Body length
168 mm.

Chersydrus granulatus (Fig. 4, H). No process in two specimens;
one set of measurements given. In CNHM 41118, rounded arch at
level of glottis; hyoid 1.65 mm wide, 17 mm long; ends of cornua
nearly touch. Body length 493 mm.

Chrysopelea ornata (CNHM 29165). Process rather triangular, .5
mm long, 19 mm behind mental; hyoid 1.2 mm wide, 29 mm long,
ends 16th ventral. Body length 626 mm.

Clelia clelia. Two specimens examined, process only indicated; one
set of measurements given. In CNHM 25414, point 13 mm behind
mental; hyoid 50 mm long, ends 23rd ventral. Body length 500 mm.

THE HYOID APPARATUS 29

Coluber c. constrictor. A very small process, begins 2nd ventral;
hyoid ends 16th ventral; hyoid 3 mm wide, 63 mm long. Body length
958 mm.

Coluber c. flaviventris. A very short process, 1.5 mm, begins 2nd
ventral; hyoid ends 16th ventral; hyoid 3.5 mm wide, 60 mm long.
Body length 940 mm.

Coluber c. priapus (Fig. 4, F). A short, thick process, 2 mm, at 2nd
ventral; hyoid 4 mm wide, 68 mm long, ends 21st ventral. Body length
740 mm.

Coniophanes imperialis copet. A sharp, triangular process, 1 mm, lies
11.5 mm behind mental at 2nd ventral; hyoid 1 mm wide, 30 mm long,
ends 20th ventral. Body length 259 mm.

Coniophanes i. proterops (CNHM 21890). A slender process, 2 mm,
hes 16 mm behind mental; hyoid 1.5 mm wide, 42 mm long, ends 19th
ventral. Body length 349 mm.

Conophis lineatus concolor (CNHM 49347). A long, tapering
process, 3 mm, at Ist ventral; hyoid 2 mm wide, 47 mm long, ends
16th ventral. Body length 684 mm.

Conopsis biserialis. No process, arch rounded; hyoid begins 2nd
ventral, ends 17th; hyoid 2 mm wide, 20 mm long. No body measure-
ment.

Crotaphopeltis h. hotamboeia (CNHM 4037). A tapering process,
1.5 mm, 8rd ventral; hyoid 2 mm wide, 36 mm long, ends 19th
ventral. No body measurement.

Cyclagras gigas. No process, arch rounded; hyoid begins two scales
before 1st ventral, ends 16th ventral; hyoid 2 mm wide, 36 mm long.
No body measurement.

Dasypeltis scaber. Two specimens examined with a long process;
in CNHM 12841, process 2.7 mm, 1 mm behind glottis; hyoid 2 mm
wide; hyoid cut 28 mm behind arch. Body length 439 mm.

In another specimen, process 2.56 mm; hyoid begins one scale before
Ist ventral, ends 17th; hyoid 1 mm wide, 34 mm long. No body
measurement.

Dendrophidion vinitor. A long, slender process enlarged at tip, 2
mm; hyoid begins Ist ventral, ends 13th; hyoid 2.56 mm wide, 55 mm
long. Body length 549 mm.

Diadophis punctatus arnyi. A tapering process, 1 mm; hyoid begins
Ist ventral, ends 18th; hyoid 1 mm wide, 15 mm long. Body length
119 mm.

Diadophis punctatus edwardsii (Fig. 4, C). Two specimens examined

26 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

with distinct process; one set of measurements given. Process 1 mm,
1.5 mm before 1st ventral; hyoid 1.5 mm wide, 29 mm long, ends 19th
ventral. Body length 340 mm.

Dipsadoboa unicolor (CNHM 19459). Distinct, pointed process,
1 mm, lies 13 mm behind mental; hyoid 1.5 mm wide, 39 mm long,
ends 17th ventral. Body length 607 mm.

Dispholidus typus (CNHM 48081). A blunt process, 2 mm, at Ist
ventral; hyoid 44 mm long, ends 16th ventral. Body length 1070 mm.

Dromophis lineatus. Long, slender process, 4.56 mm, 18 mm behind
mental; hyoid 2 mm wide, 51 mm long, ends 16th ventral. Body length
648 mm.

Drymarchon corais erebennus. Triangular process, 1 mm, at 3rd
ventral; hyoid 3 mm wide, 46.5 mm long, ends 20th ventral. Body
length 405 mm.

Drymobius bifossatus. Process 3 mm, at seale before 1st ventral;
hyoid 4 mm wide, 59 mm long, ends 13th ventral. Body length 1005
mm.

Drymobius m. margaritiferus. Long process, 1.8 mm, at Ist ventral;
hyoid 8 mm wide, 80.5 mm long, ends 29th ventral. Body length
500 mm.

Dryophis mycterizans. No process, although arch thick; arch lies
two scales before 1st ventral; hyoid 1.5 mm wide, 25 mm long, ends
6th ventral. Body length 1000 mm.

Elaphe guttata (Fig. 4, A). Long process, 3.5 mm, at Ist ventral;
hyoid 3.5 mm wide, 63 mm long, ends 15th ventral. Body length
1001 mm.

Elaphe laeta. Small process, 1 mm, at Ist ventral; hyoid 2 mm
wide, 23 mm long, ends 15th ventral. Body length 351 mm.

Elaphe o. obsoleta. Blunt process, 2 mm, at scale before 1st ventral;
hyoid 3 mm wide at arch, 7 mm wide at middle, 52 mm long, ends
13th ventral. Body length 1209 mm.

Elaphe vulpina. Short process, 1.5 mm, 5 mm before 1st ventral;
hyoid 2 mm wide, 38.5 mm long, ends 11th ventral. Body length
788 mim.

Elapomorphus nuchalis. Two specimens examined with very short
process; one set of measurements given. In CNHM 9028, process .1
mm, 9 mm behind mental; hyoid 1 mm wide, 14 mm long, ends 14th
ventral. Body length 214 mm.

Elapops modestus. Small, angular process, 1 mm, at 3rd ventral;
hyoid 2 mm wide, 38 mm long, ends 24th ventral. Body length 337 mm.

i)
“I

THE HYOID APPARATUS

Enhydris enhydris. Very long process, 9 mm, at nine scales before
1st ventral; hyoid 1 mm wide, 39.5 mm long, ends 13th ventral. Body
length 475 mm.

Enhydris plumbea. Three specimens examined have a long, thin
process; two measurements given. In CNHM 6686, process 1.5 mm,
12.5 mm behind mental; hyoid 1.5 mm wide, 21.5 mm long. Body
length 342 mm.

In CNHM 11552, process 5 mm, 8 mm behind glottis; hyoid 1 mm
wide, 48 mm long. Body length 374 mm.

Enulius wnicolor. Short, sturdy process, .6 mm, at 2nd ventral;
hyoid 1 mm wide, 19.5 mm long, ends 24th ventral. Body length
209 mm.

Farancia a. abacura. Sturdy, long process, 4 mm, at 2.5 mm before
Ist ventral; hyoid 2 mm wide, 34 mm long, ends 10th ventral; cornua
heavy. Body length 890 mm.

Farancia a. reinwardtu (Fig. 4, E). Strong process, 4 mm, at Ist
ventral; hyoid 3 mm wide, 41 mm long, ends 12th ventral. Body
length 745 mm.

Ficimia publia (UI 33650). Large process, 1 mm, at Ist ventral;
hyoid 3 mm wide, 48 mm long, ends 15th ventral. Body length 410 mm.

Fimbrios klossi (CNHM 71701). Small process, .6 mm, at 6th
ventral; hyoid 1 mm wide, 14.5 mm long, ends 15th ventral. Body
length 295 mm.

Geophis semidoliatus (UI 25952). No process, arch rounded, at 3rd
ventral; hyoid .6 mm wide, 27 mm long, ends 22nd ventral. No body
measurement.

Haldea striatula. No process, rounded arch, at 3rd ventral; hyoid
1 mm wide, 15 mm long, ends 17th ventral. Body length 147 mm.

Haldea valeriae elegans. No process, arch rounded, at 2nd ventral;
hyoid 1 mm wide, 22.5 mm long, ends 19th ventral. Body length
111 mm.

Haplopeltura boa (CNHM 63605). Long, heavy process, 3 mm, 11
mm behind mental; hyoid 1 mm wide, 33 mm long. Body length
460 mm.

Heterodon n. nasicus. No process, arch rounded, at 1st ventral;
hyoid 3.5 mm wide, 49.5 mm long, ends 18th ventral. Body length 450
mm.

Heterodon p. platyrhinos (Fig. 16, A). No process, but arch angular,
lies 15 mm behind glottis at 1st ventral; hyoid 4 mm wide, 58 mm long,
ends 15th ventral. Body length 596 mm.

28 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Homalopsis buccata (CNHM 11551). Long, slender process, 5.5 mm,
at 2nd ventral; hyoid 2 mm wide, 54.5 mm long, ends 18th ventral.
Body length 755 mm.

Lampropeltis calligaster. Small process, 1.5 mm, at 1st ventral;
hyoid 3 mm wide, 51.5 mm long, ends 14th ventral. Body length
979 mm.

Lampropeltis d. doliata (Fig. 4, B). No actual process, arch angular,
at Ist ventral; hyoid 4.6 mm wide, 49 mm long, ends 17th ventral.
Body length 825 mm.

Lampropeltis e. elapsoides. Small process, 1 mm, at 1st ventral;
hyoid 1.5 mm wide, 38.5 mm long, ends 22nd ventral. Body length
390 mm.

Lampropeltis getulus holbrooki. No process, arch rounded, lies 2 mm
before 1st ventral; hyoid 1.5 mm wide, 36 mm long, ends 17th ventral.
Body length 409 mm.

Lampropeltis getulus splendida. Two specimens examined. In one
specimen, a small process, .6 mm, at Ist ventral; hyoid 2 mm wide,
25.5 mm long, ends 19th ventral. Body length 310 mm.

In other specimen, no process, arch rounded, at 2nd ventral; hyoid
4.5 mm wide, 70.5 mm long, ends 21st ventral. Body length 957 mm.

Lampropeltis knoblocht. Small triangular process, .6 mm, at two
scales before 1st ventral; hyoid 1.5 mm wide, 39.5 mm long, ends 16th
ventral. Body length 630 mm.

Leptodeira maculata. Large, tapering process, 2 mm, at scale before
Ist ventral; hyoid 3 mm wide, 53.5 mm long, ends 25th ventral. Body
length 410 mm.

Leptodeira septentrionalis polysticta. Short, tapering process, 1.5
mm, at lst ventral; hyoid 1.5 mm wide, 53 mm long, ends 35th ventral.
Body length 660 mm.

Leptophis diplotropis. Large, sturdy process, 2 mm, at Ist ventral;
hyoid 2.56 mm wide, 37 mm long, ends 14th ventral. Body not measured.

Leptophis m. mexicanus. Process 1 mm, at 2nd ventral; hyoid 1.5
mm wide, 38 mm long. Body length 595 mm.

Manolepis putnam. Long, tapering process, 1 mm, at two scales
before Ist ventral; hyoid 2 mm wide, 32 mm long, ends 13th ventral.
Body not measured.

Masticophis f. flagellum. No process, rounded arch at 3rd ventral;
hyoid 8 mm wide, 52 mm long, ends 14th ventral. Body length 1142
mm.

Masticophis f. flavigularis. Small, pointed process, 2 mm, at 2nd

THE HYOID APPARATUS 29

ventral; hyoid 5 mm wide, 59 mm long, ends 14th ventral. Body
length 1246 mm.

Mehelya nyassae (CNHM 77612). Long process, 2.6 mm, at Ist
ventral; hyoid 3 mm wide, 55 mm long, ends 26th ventral. Body
length 510 mm.

Natrix cyclopion floridana. No process, rounded arch at 8.5 mm be-
fore Ist ventral; hyoid 4 mm wide, 57.5 mm long, ends 11th ventral.
Body length 768 mm.

Natrix e. erythrogaster. No process, rounded arch at 2nd ventral;
hyoid 2 mm wide, 58 mm long, ends 17th ventral. Body length 686 mm.

Natrix grahami. Short, distinct process, 1 mm, at Ist ventral; hyoid
1 mm wide, 42 mm long, ends 18th ventral. Body length 422 mm.

Natrix piscator. Short, pointed process, 1 mm, at 2nd ventral; hyoid
3.5 mm wide, 56 mm long, ends 19th ventral. Body not measured.

Natrix septemvittata (UI 16282). No process, rounded arch at 2nd
ventral; hyoid 2 mm wide, 39 mm long, ends 18th ventral. Body
length 525 mm.

Natrix sipedon confluens. No process, angular arch at 1st ventral;
hyoid 2 mm wide, 35 mm long, ends 18th ventral. Body length 443 mm.

Ninia d. diademata. No process, rounded arch at 3rd ventral; hyoid
1.5 mm wide, 25 mm long, ends 27th ventral. Body length 198 mm.

Ninia sebae morleyt. No process, rounded arch at 3rd ventral; hyoid
2 mm wide, 32 mm long, ends 24th ventral. Body not measured.

Nothopsis rugosus (CNHM 77604). Small process, 1 mm, at 3rd
scale before 1st ventral; hyoid 1 mm wide, 26 mm long, ends 19th
ventral. Body length 295 mm.

Opheodrys aestivus. No process, arch angular at 1st ventral; hyoid
1 mm wide, 32 mm long, ends 16th ventral. Body length 421 mm.

Opheodrys vernalis (Fig. 3, B). No process, angular arch at 2 mm
before Ist ventral; hyoid 2 mm wide, 35.5 mm long, ends 16th ventral.
Body length 390 mm.

Oxybelis acuminatus. In two specimens examined, process and arch
triangular; one set of measurements given. Process .6 mm, at scale
before 1st ventral; hyoid 1 mm wide, 18.5 mm long, ends 8th ventral.
Body length 745 mm.

Oxyrhabdinium leporinum. No process, rounded arch at 5th ventral;
hyoid 1.5 mm wide, 27.5 mm long, ends 16th ventral. Body length
472 mm.

Pituophis catenifer sayi. No process in two specimens; one set of

30 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

measurements given. In UI 39637, arch at Ist ventral; hyoid 4 mm
wide, 37 mm long, ends 13th ventral. Body length 870 mm.

Psammodynastes pulverulentus. No process, rounded arch at scale
before 1st ventral; hyoid 1.5 mm wide, 24.5 mm long, ends 17th
ventral. Body length 300 mm.

Rhadinaea flavilata (Fig. 4, J). Tapering process, 1 mm, 1 mm be-
fore Ist ventral; hyoid 1.5 mm wide, 32 mm long, ends 19th ventral.
Body length 238 mm.

Rhadinaea laureata. Process .6 mm, at scale before 1st ventral;
hyoid 2 mm wide, 39.5 mm long, ends 24th ventral. Body length
310 mm.

Rhadinella schistosa. Small process, at 1st ventral; hyoid .6 mm
wide, 15 mm long, ends 19th ventral. Body length 179 mm.

Rhinocheilus lecontei tessellatus. Small process, teatlike, 15 mm, at
two scales before 1st ventral; hyoid 2.6 mm wide, 50.5 mm long. Body
length 637 mm.

Salvadora grahamiae hexalepis (Fig. 3, H). Long, tapering process,
5 mm, at Ist ventral; hyoid 1.5 mm wide, 38.5 mm long, ends 17th
ventral. Body length 675 mm.

Salvadora intermedia richardi. Long, tapering process, 2.6 mm, at
scale before 1st ventral; hyoid 1.5 mm wide, 35 mm long, ends 17th
ventral. Body length 553 mm.

Salvadora mexicana. Long, sharply tapering process, 2 mm, at scale
before Ist ventral; hyoid 3 mm wide, 43 mm long, ends 14th ventral.
Body length 760 mm.

Sibynomorphus catesbyi (CNHM 35711). (Fig. 3, D). No process,
rounded arch 3 mm behind glottis; hyoid 1.6 mm wide, 49.5 mm long.
Body length 422 mm.

Sibynophis collaris (CNHM 71708). Sharply tapering process, 2
mm, at 2nd ventral; hyoid 1 mm wide, 31.5 mm long, ends 23rd
ventral. Body length 360 mm.

Sonora o. occipitalis (see Fig. 3, G). Process 1 mm, at Ist ventral;
hyoid 1 mm wide, 20 mm long, ends 18th ventral. Body length
230 mm.

Sonora taylorz. Small process, .6 mm, at two scales before 1st ventral;
hyoid .6 mm wide, 18 mm long, ends 18th ventral. Body length
194 mm.

Stilosoma extenuatum. Large, sharp process, .6 mm, at 1st ventral;

hyoid 1 mm wide, 15.5 mm long, ends 11th ventral. Body length
410 mm.

THE HYOID APPARATUS 31

Storeria dekayi (Fig. 3, C). Two specimens examined, without
process; one set of measurements given. Rounded arch at 2nd
ventral; hyoid 1 mm wide, 21 mm long, ends 22nd ventral. Body length
138 mm.

Tantilla gracilis (Fig. 3, F). Tapering process, .6 mm, at 1st ventral;
hyoid 1 mm wide, 15.5 mm long, ends 18th ventral. Body length
138 mm.

Thamnophis eques. No process, rounded arch at scale before Ist
ventral; hyoid 1.5 mm wide, 62 mm long, ends 20th ventral. Body
length 582 mm.

Thamnophis elegans vagrans (Fig. 16, C). No process, rounded
arch at 1st ventral; hyoid 3 mm wide, 50 mm long, ends 18th ventral.
Body length 600 mm.

Thamnophis melanogaster canescens (UI 18875). Process bluntly
triangular, 1 mm, at scale before 1st ventral; hyoid 1.5 mm wide, 30
mm long, ends 14th ventral. Body length 395 mm.

Thamnophis s. scalaris. Small, triangular process, .6 mm, at Ist
ventral; hyoid 2.5 mm wide, 33 mm long, ends 18th ventral. Body
length 326 mm.

Toluca l. lineata. No process, arch angular at 1st ventral; hyoid
1.5 mm wide, 26 mm long, ends 18th ventral. Body length 199 mm.

Trimorphodon b. biscutatus. Long, tapering process, 2 mm, at two
scales before Ist ventral; hyoid 2 mm wide, 36 mm long, ends 17th
ventral. Body length 713 mm.

Tropidoclonion lineatum. No process, arch angular, at 4th ventral;
hyoid 1.5 mm wide, 21.5 mm long, ends 24th ventral. Body length
159 mm.

Tropidonotus natrix (Fig. 3, E). No process, rounded arch at Ist
ventral; hyoid 2 mm wide, 46.5 mm long, ends 20th ventral. Body
length 452 mm.

Xenodermus javanicus (CNHM 67247). Short process, .6 mm, at
11 mm behind mental; hyoid 1 mm wide, 59 mm long; a relatively
long hyoid. Body length 500 mm.

ELAPIDAE (parallel type)

Acanthophis antarctica (CNHM 13871). Process and arch triangu-
lar, 14 mm behind mental; hyoid 3.5 mm wide, 31 mm long. Body
length 328 mm.

Aspidelaps scutatus. Small process, 11 mm behind mental; hyoid
3.5 mm wide, 40 mm long. Body length 392 mm.

THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

isu)
LS)

Bungarus multicinctus (CNHM 25166). Process 2 mm, 10 mm be-
hind mental; hyoid 2 mm wide, 33 mm long. Body length 642 mm.

Calliophis macclellandii (CNHM 6659). Long process, 1 mm, 7 mm
behind mental; hyoid 1 mm wide, 20 mm long. Body length 390 mm.

Demansia nuchalis (CNHM 15884). No process, angular arch 15.5
mm behind mental; hyoid 2 mm wide, 47 mm long. Body length
916 mm.

Dendraspis viridis (CNHM 44885). Process 2 mm, 18 mm behind
mental; hyoid 2 mm wide, 85 mm long. Body length 1210 mm.

Denisonia woodfordi (CNHM 138834). Long process, 2.6 mm, 17.5
mm behind mental; hyoid 2 mm wide, 33 mm long, ends 12 ventral.
Body length 618 mm.

Doliophis bilineatus (CNHM 53555). Angular process, 1 mm, 9 mm
behind mental; hyoid 21 mm long. Body length 479 mm.

Elaps lacteus (CNHM 17717). Process 1 mm, at 5th ventral; hyoid
17 mm long, ends 21st ventral. Body length 229 mm.

Elapsoidea sundervalli fitzsimonsi (CNHM 17667). Tapering pro-
cess, 1 mm, 12.5 mm behind mental; hyoid 2 mm wide, 54 mm long,
ends 19th ventral. Body not measured.

Furina annulata (CNHM 29114). Long, slender process, 2 mm,
9 mm behind mental; hyoid 1.5 mm wide, cornua 17 mm long but
incomplete. Body length 549 mm.

Hemachatus hemachates. No process, arch flat in two specimens;
one set of measurements given. In CNHM 17668, arch 11.5 mm behind
mental; hyoid 2 mm wide, 30 mm long, ends 15th ventral. Body length
285 mm.

Hemibungarus kelloggi (CNHM 24999). Long, slender process, 1.5
mm, 9 mm behind mental; hyoid 2 mm wide, 25.56 mm long, ends
13th ventral. Body length 485 mm.

Leptomicrurus narducci (CNHM 27081). Short process, .6 mm,
8 mm behind mental; hyoid 1 mm wide, 12 mm long, ends 11th ventral.
Body length 422 mm.

Maticora bivirgata (CNHM 30546). Short process, 1 mm, 14 mm
behind mental; hyoid 2 mm wide, 51 mm long, ends 20th ventral.
Body length 1030 mm.

Micropechis ikaheka (CNHM 13937). Process 3 mm, at 1st ventral;
hyoid 3 mm wide, 50 mm long, ends 14th ventral. Body not measured.

Micruroides euryxanthus (CNHM 48526). Short process, 1 mm, at
4th ventral; hyoid 1.5 mm, 22 mm long, ends 21st ventral. Body
length 349 mm.

(Se)
we)

THE HYOID APPARATUS

Micrurus a. affinis. Long, triangular process, 3 mm, at 2nd scale be-
fore Ist ventral; hyoid 1 mm wide, 27 mm long, ends 16th ventral. Body
length 430 mm.

Micrurus fulvius (Fig. 3, H). Two specimens examined, with short
process; one set of measurements given. Process 1 mm, at Ist ventral;
hyoid 2.5 mm wide, 35.5 mm long, ends 18th ventral. Body length
560 mm.

Naja naja samarensis (CNHM 53542). Process only indicated, 14
mm behind mental; hyoid 5.6 mm wide, 39 mm long. Body length
766 mm.

Notechis scutatus (CNHM 15800). Triangular process, 3.5 mm,
14.5 mm behind mental; hyoid 4 mm wide, 45 mm long. Body length
788 mm.

Ogmodon vitianus (CNHM 22999). Hyoid damaged anteriorly;
hyoid ends 11th ventral. Body length 128 mm.

Pseudelaps mulleri (CNHM 14200). Large process, 2.3 mm, 8 mm
behind mental; hyoid 1 mm wide, 16 mm long. Body length 344 mm.

Ultrocalamus prussi (CNHM 43030). Long process, 2 mm, 11 mm
behind mental; hyoid 1 mm wide, 10 mm long, ends 5th ventral. Body
length 630 mm.

HYDROPHIDAE (parallel type)

Aipysurus eydouxu. Two specimens examined, with long process;
one set of measurements given. In CNHM 11572 (Fig. 17, B), process
4 mm, at eight scales before 1st ventral; hyoid 1.5 mm wide, 28 mm
long, ends 7th ventral. Body length 460 mm.

Hydrophis cyanocinctus (CNHM 28311). Long, sharply tapering
process, 4.5 mm, 8 mm behind mental; hyoid 2 mm wide, 17.5 mm
long. Body length 522 mm.

Kerilia jerdonii. Long, slender process, 5 mm, 10 mm behind mental;
hyoid 2 mm wide, 17 mm long. Body length 763 mm.

Lapemis hardwicki (CNHM 11583). Long, slender process, 5 mm,
11 mm behind glottis; hyoid 2.6 mm wide, 34 mm long. Body length
650 mm.

Laticauda colubrina (CNHM 4047). Long, slender process, 4.5 mm,
3 mm behind glottis; hyoid 1.5 mm wide, 27 mm long. Body length
740 mm.

Pelamis platurus. Two specimens examined, process long and slender.
In CNHM 40468, process 2 mm plus (tip broken), about 18 mm behind

34 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

mental; hyoid 1.5 mm wide, 15 mm long, ends 6th ventral. Body
length 415 mm.

In CNHM 41591, process 3 mm, at scale before 1st ventral; hyoid
2.5 mm wide, 18.5 mm long, ends 8rd ventral. Body length 542 mm.
Cornua abnormal: do not attach to hyoglossal muscles, but bow out
on either side to end independent of muscles.

Thalassophina viperina (CNHM 11567). Process broken; hyoid 1
mm wide, ends 7th ventral. Body length 325 mm.

VIPERIDAE (parallel type)

Aspis cerastes (CNHM 41596). Long process, 4 mm, 22 mm behind
mental; hyoid 2 mm wide, 29 mm long. Body length 539 mm.

Atheris nitschei (CNHM 9901). No process, rounded arch at 19.5
mm behind mental; hyoid 2 mm wide, 25 mm long. Body length 535
mm.

Atractaspis microlepidota (CNHM 375). Very long process, 4.5 mm,
14 mm behind mental; hyoid 1.6 mm wide, 40 mm long, ends 21st
ventral. Body length 225 mm.

Bitis cornutus (CNHM 16039). Short process, .6 mm, 10 mm be-
hind mental; hyoid 2.5 mm wide, 35 mm long. Body length 326 mm.

Bitis nasicornis (CNHM 12820). No process, rounded arch 23 mm
behind mental; hyoid 6 mm wide, 57 mm long. Body length 703 mm.

Causus rhombeatus (CNHM 12969). No process, rounded arch 8.5
mm behind mental; hyoid 2 mm wide, 36 mm long. Body length
457 mm.

Cerastes vipera. Two specimens examined, with long process; one
set of measurements given. In CNHM 63115 (Fig. 17, C), process
3.5 mm, at two scales before Ist ventral; hyoid 1 mm wide, 28 mm
long, ends 13th ventral. Body length 460 mm.

Echis carinatus (CNHM 18215). Long process, 3.5 mm, 13.5 mm
behind mental; hyoid 2 mm wide, 30 mm long. Body length 404 mm.

Pseudocerastes fieldi (CNHM 11062). No process, rounded arch
16 mm behind mental; hyoid 1.5 mm wide, 33 mm long. Body length
550 mm.

Vipera berus. Long process, 2 mm, at 1st ventral; hyoid 1.5 mm
wide, 22 mm long, ends 15th ventral. Body length 271 mm.

CROTALIDAE (parallel type)

Agkistrodon contortriz. Very short process, 1 mm, at 2nd ventral;
hyoid 3 mm wide, 48 mm long, ends 18th ventral. Body length 592 mm.

THE HYOID APPARATUS 35

Agkistrodon p. piscivorus (UI 26861). Process 3 mm, at 4th ventral;
hyoid 6 mm wide, 49 mm long, ends 14th ventral. Body length 895 mm.

Bothrops atrox. Long process, 5 mm, at Ist ventral; hyoid 5 mm
wide, 65.5 mm long, ends 12th ventral. Body length 1515 mm.

Bothrops mexicanus (Fig. 1, M). Two specimens examined, with
long processes; one set of measurements given. In USNM 123712,
process 1.5 mm, at Ist ventral; hyoid 3 mm wide, 39 mm long, ends
13th ventral. Body length 589 mm.

Crotalus cerastes (UI 171). Long process, 3 mm, at scale before 1st
ventral; hyoid 2.5 mm wide, 32 mm long, ends 13th ventral. Body
length 495 mm.

Crotalus pricei pricei (CNHM 1459A). Large, triangular process,
2 mm, 16.5 mm behind mental; hyoid 3 mm wide, 34.5 mm long,
ends 19th ventral, beyond termination of hyoglossi. Body length
413 mm.

Crotalus tigris. Long, triangular process, 4 mm, 4 mm before Ist
ventral; hyoid 3.5 mm wide, 54.5 mm long, ends 18th ventral. Body
length 646 mm.

Lachesis muta (CNHM 22991). Process 4 mm, at 38rd ventral;
hyoid 6 mm wide, 53 mm long, ends 15th ventral. Body incomplete,
but very large.

Sistrurus miliarius. Long, tapering process, 3.5 mm, at Ist ventral;
hyoid 2 mm wide, 37 mm long, ends 17th ventral. Body length 421 mm.

Sistrurus ravus. Triangular process, 2 mm, at scale before Ist
ventral; hyoid 3.5 mm wide, 46.5 mm long, ends 15th ventral. Body
length 547 mm.

Trimeresurus waglert (CNHM 53564). Long process, 2.6 mm, 34

mm behind mental; hyoid 1.5 mm wide, 39 mm long. Body length
562 mm.

D. Discussion

Variations. The variations discovered within any one morphological
group were not remarkable, and in any case they merely represented
some reduction or variant of the basic form. None of the variations are
considered to have adaptive value.

In the anomalepidids, no particular variations were noted in the
few specimens examined. The median hyoid length/body length ratio
is about 1 per cent.

For the “Y” type hyoid in typhlopids a certain number of variations

36 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

have been described, chiefly by List (1966). He has illustrated three
forms of the hyoid: (1) a complete Y shape, (2) complete except that the
cornua are disconnected from the basihyal, and (3) hyoid composed
only of the two separated cornua. His preparations were stained speci-
mens. The author has examined specimens with forms (1) and (3). In
any case, the basic typhlopid type is one with a basihyal and attached
Ist ceratobranchial cornua. The straight length of the hyoid is less
than 1 per cent of the body length. The hyoid is all or partly bony in
some species.

No particular variations were found in the “Y” type hyoid of
leptotyphlopids. The basihyal and attached 1st ceratobranchials are
considered to be present, Just as in the basic typhlopid hyoid. The
leptotyphlopid hyoid is longer relatively, being about 2 per cent of
the body length.

Uropeltids have the “V” type hyoid, modified by the 1st cerato-
branchial cornua being separated at their anterior ends; no basihyal
is considered present. The hyoid is relatively small; the length of
the cornua tends to be about 2 per cent of the body length. The cornua
usually begin opposite the Ist ventral and the end around the 5th.
Among the examined species, Rhinophis planiceps has the most re-
duced hyoid.

Aniliids also have the “V” type hyoid. The new world genus
Anilius has a complete type, with the 1st ceratobranchial cornua
united anteriorly; no lingual process or other enlargement at the union
is present. The hyoid has a straight length of about 2 per cent of the
body length. In the old world genus Cylindrophis the cornua are
reduced and separate, and are about 1.5 per cent of the body length.
C. maculatus, in particular, his very slender and markedly reduced
cornua, lying on the lateral aspect of the posterior part of the hyoglossi.

The well-formed “V” type hyoid of Xenopeltis is about 3 per cent
of the body length, and extends from about the 1st ventral to the 11th.

In the Boidae (sensu stricto) the cornua are of the “V” type and may
or may not be joined anteriorly, and there does not seem to be any cor-
relation of this variation with the pythons and boas. In general the
cornua are always well developed among boids, even if not joined; and
in those cases where there is no union, the anterior separation is never
great. The median hyoid length is up to 4 per cent of the body length.

The parallel type hyoid is always well developed and always has the
cornua joined anteriorly. The boidlike genera Tropidophis, Trachyboa,
Casarea, and Bolyeria have a parallel type hyoid and always have a
distinet lingual process as well. In fact, this hyoid resembles closely the
hyoid of any number of colubrids and elapids, ete. In Tropidophis,
where the hyoid has been investigated in several species — maculatus,

(J)

THE HYOID APPARATUS

melanurus, and pardalis — the hyoid is at least 4.5 per cent of the body
length; the percentage is similar for Trachyboa. The significance of
the parallel type hyoid in these four genera is puzzling. About the only
point that can be made at this time is that these genera probably repre-
sent a group that early diverged from the main body of boids with their
hyoid form paralleling that of the rest of the snakes with the same kind
of hyoid.

For the families Colubridae, Elapidae, Hydrophidae, Viperidae, and
Crotalidae, there is noticeable variation in the lingual process. Usually
the process is tapered when long, and stubby when short, often with a
rounded, expanded tip. The process may also be triangular in form; in
this ease it is difficult to tell whether this really constitutes a true
process of the basihyal, the basihyal itself, or merely the shape of the
fusion of the cornua with the basihyal elements missing. The cornua
form a smooth continuous arch in front in many species. All basihyal
elements are probably missing in these cases.

The length of the process, and indeed, the presence of the process, is
lable to variation in some genera. Among the colubrids examined an
arbitrary inspection shows that there are approximately equal numbers
of genera without processes, with small ones (roughly 3-4 per cent of
the hyoid total length), and with well-developed ones (more than 4 per
cent). Genera in which two or more specimens of a species, or several
species, were examined, and which show two or more conditions, are
Coniophanes, Lampropeltis, and Elaphe (all small, large) ; and Masti-
cophis, Natrix, and Thamnophis (all none, small). It would seem from
this admittedly limited sample that if a genus has a species with a long
process, the genus does not have species with none at all. The sample
is not large enough to justify a flat statement, of course, but the trend
at least suggested.

The longest processes seen in the colubrids belong to Cerberus and
Enhydris. The former has the process 20-30 per cent of the hyoid
length, and the latter up to at least 22 per cent. In Salvadora gra-
hamiae and Farancia the process is at least 12 per cent. In Cerberus
the lingual process is the most ornate among snakes; it is long, heavy,
and in two cases, with a prominent swelling (Fig. 4, D). A third speci-
men lacks the swelling, although the process and the arch are heavy.

It is possible that the basihyal may either be reduced or else absent
in certain genera, e.g., Masticophis, Natriz, Thamnophis, as noted
above. These examples, together with other colubrid genera having
smooth, rounded arches, possibly show that there is a trend toward
loss of the basihyal thereby reducing the hyoid to the pair of 2nd
ceratobranchials.

—s
n

38 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

The elapids are much more consistent in the presence of a lingual
process than the colubrids. Nearly every elapid genus has been ex-
amined, and results show that the process is present in every genus
examined save Hemachatus, an African cobra. In this species Pringle
(1954) studied the embryonic development and noted that apparently
no basihyal formed. The arch is rounded and smooth in the adult,
which substantiates Pringle’s view. About one-half of the elapid
genera have a process that can be considered long. In Ultrocalamus the
process is about 19 per cent of the hyoid length; this seems to be the
relatively longest process among elapids.

In the six genera of hydrophids examined, there is a very long process
in every case, ranging from 14 to 28 per cent of the hyoid length. A
specimen of Kerilia jerdoni has the longest one, relatively speaking
(28 per cent). It is hard to see a particular, functional advantage in a
long process, since in snakes it provides no special support for the
tongue, despite the name.

Among the viperids there are four genera with species that have a
very small lingual process (Atheris, Bitis, Causus, and Pseudocerastes) ,
and five genera with species that have a noticeably large one (Aspis,
Atractaspis, Cerastes, Echis, and Vipera). The relatively longest pro-
cess is found in Aspis—14 per cent. Bitis nasicornis has a small
process, whereas B. cornutus has none.

Among crotalids the lingual process is apparently always present; it
is also generally well developed. Perhaps the longest one — 10 per cent
of the hyoid length — is found in the genus Sistrurus. In Agkistrodon
contortrix the process is small and triangular; in A. piscivorus the
process is long and prominent.

It might be concluded that, in general, the poisonous snake species
tend to have a prominent lingual process, whereas the colubrid species
show much more variation in size and presence of the process.

The cornua in the parallel type are generally longer relatively than
in the ‘“V” type. Whereas the hyoid is usually a little less than 4 per
cent of the body length in the Boidae, the hyoid is usually at least 8 per
cent of the body length, and often about 10 per cent in those families
with a parallel type hyoid. There are, of course, exceptions, such as
Boiga and Chersydrus, two colubrid genera which have a percentage of
about 4 per cent. The longest hyoids relative to body length were
found in: Drymobius, 16 per cent, Chersodromus, 17 per cent, Atracta-
spis, 18 per cent, Natrix sipedon (a juvenile), 19 per cent, and Haldea
valeriae, 20 per cent. These are all colubrids except Atractaspis, a
viperid.

Functions. The primary function of the hyoid is to provide a support

THE HYOID APPARATUS 39

for the tongue muscles, the hyoglosst, which attach posteriorly to the
cornua. Muscles from the mandibles also attach to the cornua in all
snakes; also, there are muscles, of a variable number and identity in
different species, which run from the skin, nape region, and the anterior
ribs to the cornua. When these muscles act they tend to act in opposing
sets and thereby hold the hyoid firm so that the hyoglossi may operate
efficiently.

Gnanamuthu (1937) claimed that the cornua flex in the boa con-
strictor upon tongue protraction, and upon retraction elasticity returns
the cartilage to normalcy and thus aids in withdrawing the tongue.
In view of muscle relationships this does not seem likely. Moreover, in
the parallel type it is difficult to believe that the cornual cartilages,
lying along the longitudinally placed hyoglosst, are flexed upon protrac-
tion of the tongue. The only directions available for flexing would be
dorsal or ventral, and this simply does not happen, as inspection and
experimentation have shown. Surely the hyoid is fixed in position when
the tongue is protracted and vibrated.

Phylogenetic Significance. It is not especially reasonable to derive a
phylogenetic pattern from the morphological types of one structure.
The hyoid in snakes is no exception. However, the hyoid types do have
a certain value, and they certainly seem to indicate some sort of
natural groupings.

The following discussion is based on the assumption that all modern
snakes are monophyletic.

The basic, complete lizard hyoid is a good place to start: three pairs
of cornua with a basihyal and its lingual process. It is altogether
reasonable that the early snakes also had such a complete hyoid, and
this idea is reinforced by the evidence already given — that all three
pairs of cornua are present in modern snakes, but only one pair is
present in any one family.

In looking over the modern lizards in hopes of finding traces of
ancestry for the snakes, it is easy to fall prey to a fallacious line of
reasoning: that modern lizards are necessarily lke those ancestors
which gave rise to snakes. After all, it is surely true that modern
snakes have changed from their earlier relatives; so it might be as
reasonably true that modern lizards have changed from theirs. Indeed,
there is no living lizard, or even group of them, that can unquestionably
be called related to the ancestors of snakes. Rather than select some
group of lizards and positively work with it as a source for the snakes,
the author prefers at this point merely to establish a likely basic
pattern for the hyoid. Such a pattern might well be called primitive,
and probably consisted of three pairs of cornua and the basihyal.

40 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

From early snakes with this pattern one event probably occurred
quite early in the evolutionary scale — one group lost both the 1st and
2nd ceratobranchials, leaving a hyoid composed solely of 2nd arch
components, the ceratohyals and hypohyals. This line of evolution has
given us the Anomalepididae, which lack also a lingual process and
perhaps any trace of the basihyal altogether.

The indication is that the remainder of the stock gave rise to forms
that sooner or later lost the 2nd arch cornua, although retaining the
basihyal and its lingual process. This hyoid would then be composed of
a basihyal and process plus the 1st and 2nd ceratobranchials. Probably a
fairly early diversion from this stock gave rise to a line which showed
a loss of the 2nd ceratobranchials. From this line came the present-day
Typhlopidae and Leptotyphlopidae. Their hyoids are very similar in
basic form and are considered, of course, to be composed of the basihyal
and process plus the Ist ceratobranchials.

The next event can well be considered to have been a loss of the 2nd
ceratobranchials, and eventually also a loss of the basihyal elements.
This group is represented by the present-day uropeltids, aniliids, xeno-
peltids, and boids (sensu stricto).

The remaining group of snakes eventually lost the 1st ceratobran-
chials entirely, and then had a hyoid composed of the 2nd cerato-
branchials plus basihyal elements. From this group of snakes, the
remaining modern families have descended — all of which have this
parallel type of hyoid composed of a basihyal, which is secondarily
lost in some species, plus what are considered to be 2nd ceratobran-
chials. Note that the boidlike genera Bolyeria, Casarea, Trachyboa,
and Tropidophis also seem to fit into this line of evolution.

This phylogenetic pattern is no doubt artificial in many respects.
However, in the overall sense, the four groups of the hyoid form in
modern snakes do outline such a pattern. Later, in the second part of
this work, the evidence of the musculature will modify this pattern,
and the end result can be seen in Figure 19.

There have been several obvious trends in the evolution of the snake
hyoid. (1) There has been a reduction in the number of cornua and a
resultant simplification of the hyoid form. The four main groups, all
with only one pair of coruna, which varies as to identity according to
the group, are evidences of this. (2) The hyoids within the respective
groups have also had a tendency to undergo further reduction or
simplification. This is illustrated in many cases by the absence of the
lingual process and by the apparent absence of the entire basihyal. In
some typhlopids there may also have been a loss of cornua, as sug-
vested by List (1966). (3) Ossification as a process has largely been

THE HYOID APPARATUS 4]

lost for the hyoids in snakes. Only in the Typhlopidae does ossification
ever take place in the hyoid, and here apparently this occurs only in
some species, and perhaps only in older specimens of these species.

It should be noted explicitly that none of the hyoids of modern
snakes are at all primitive, but rather the opposite, being very much
modified and altered by reduction into simple forms.

E. Summary

1. The basic complete lizard hyoid type is taken to be one composed
of the basihyal plus lingual process, hypohyals and ceratohyals, 1st
ceratobranchials, and 2nd ceratobranchials; these parts are derived
from branchial arches 2, 3, 4. The 1st ceratobranchials are character-
istically bony to some degree.

2. The hyoid in snakes is located on the ventral surface of the head
and neck, generally just deep to the cutaneous layer of muscles. In the
Typhlopidae, Leptotyphlopidae, and Anomalepididae the hyoid lies
completely posterior to the head.

3. The hyoid of snakes is cartilaginous in all cases except in some
examined species of typhlopids, where the hyoid may be partly or
totally bony.

4. According to the shape of the hyoid, there are four seemingly
natural major types definable: (1) “M” type; (2) “Y” type, or reduc-
tion thereof; (3) a “V” type, or reduction thereof; (4) parallel type.

5. The “M” type is found in the Anomalepididae only; it is pre-
sumed to consist of components derived solely from the 2nd branchial
arches — hypohyals, ceratohyals, and recurrent cornua. Presence of a
basihyal element is uncertain.

6. The “Y” type is found in the Typhlopidae and Leptotyphlopidae;
it les in an inverted position, with the median process forward; it is
presumed to consist of the basihyal with its lingual process (from 2nd
arch), and the Ist ceratobranchials (from the 3rd arch). Either of the
parts may be lacking in some species of Typhlops.

7. The “V” type is found in the Uropeltidae, Aniliidae, Xenopeltidae,
and Boidae (sensu stricto) ; it lies in an inverted position with the apex
of the “V” forward; it is considered to consist solely of the 1st cerato-
branchials, derived from the 3rd branchial arches. Union of the cornua
is absent in uropeltids, most aniliids, and in some boids; in this reduced
condition the cornua are separate, subparallel rods.

8. The parallel type is found in the Colubridae, Elapidae, Hydro-
phidae, Viperidae, Crotalidae, and in four puzzling boidlike genera

42 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

which are, for convenience, grouped into the Boidae (sensu lato) ; these
genera are: Bolyeria, Casarea, Trachyboa, and Tropidophis. The
hyoid is considered to consist of a basihyal and 2nd ceratobranchials;
the basihyal may perhaps be absent in some cases. A lingual process
is often present.

9. Identification of the parts of each hyoid type is essentially based
upon comparison with the basic lizard type. This is not absolutely
satisfactory, but at present the embryological evidence is very spotty
and inconclusive, and forces the reliance on simple comparison.

10. The hyoid form is quite constant within any given group. Vari-
ations are minor and usually represent reduction from the hyoid type.
Reduction or even loss of the lingual process and the rest of the
basihyal is not uncommon. These variations within any one group are
probably not phylogentically important.

11. The function of the hyoid is, when fixed, to provide a stable
attachment for the hyoglossal muscles of the tongue. In many cases it
also provides the origin for the retractor of the larynx.

12. Based on the concept of monophyly for the snakes, the earliest
stock is conceived of having the basic lizard type of hyoid — basihyal
with three pairs of cornua. This is the primitive snake hyoid. At least
four lines of evolution can be recognized.

13. One line of evolution produced snakes which lost the 1st and 2nd
ceratobranchials. This line produced the modern-day Anomalepididae,
with the “M” type hyoid.

14. The remaining stock lost the hypohyals and ceratohyals. Out
of this stock came a line which lost the 2nd ceratobranchials but main-
tained a prominent basihyal and its lingual process. This line produced
the modern families Typhlopidae and Leptotyphlopidae, with the “Y”
type of hyoid.

15. Another line, or perhaps several lines, diverged from the stock
which kept the 1st and 2nd ceratobranchials; these lines produced
snakes that lost the 2nd pair of ceratobranchials plus the basihyal —
the “V” type hyoid. These snakes are the Uropeltidae, Aniliidae, Xeno-
peltidae, and Boidae (sensu stricto).

16. The final line of evolution involved those snakes which came of
the stock that had the 1st and 2nd ceratobranchials plus basihyal, but
kept only the 2nd pair plus basihyal —the parallel type hyoid. This
line produced the Colubridae, Elapidae, Hydrophidae, Viperidae, Cro-
talidae, and the four genera Bolyeria, Casarea, Trachyboa, and
Tropidophis.

17. There have been several obvious trends in the overall evolution
of the hyoid in snakes. One has been a loss of two of the three pairs

THE HYOID APPARATUS 43

of cornua found in the basic hyoid form. Another has been a further
simplification of the hyoid by loss of the basihyal elements, or the
cornua, as apparently happened in some typhlopids. Another trend has
been the almost total loss of ossification in any part of the hyoid skele-
ton; only the typhlopids retain ossification to any degree.

PART II. THE ASSOCIATED MUSCLES
OF THE HYOID

A. Preliminary Remarks

The muscles studied closely are those that, with a few exceptions,
generally have attachment to the hyoid — in at least some genera if not
in all. The exceptions are the genioglossus, which does not actually
attach to the hyoid but lies very close to the hyoid, and a few others.

Hiibner in 1815 published his thesis on the muscular system (“De
organis motoris .. .”) of a boa. The author has not seen his work,
and apparently the only muscles therein that are of concern to this
paper are (a) the latissimus ingluvier s. platysma myoides, which, fide
Edgeworth (1935), must be equivalent, at least in part, to the cerato-
mandibularis (as named herein); and (b) the retrahens laryngis, or
hyotrachealis.

In 1827 Anton Dugés gave what seems to be the first fairly complete
account of the ventral muscles of the snake head. His plates are quite
accurate in what they show, although not complete. Duges was in error
as to the function of certain muscles, believing, for example, that the
laryngeal protractor and retractor worked together as a chain to assist
in protracting the tongue.

The year 1832 saw the publication of two works of great importance
to snake anatomy. Both were by Duvernoy, a careful observer with a
clear idea of most of the muscle relationships of the snake head. His

THE ASSOCIATED MUSCLES OF THE HYOID 45

plates are good, and Owen (1866) used them in the first volume of his
“On the Anatomy of Vertebrates.”

However, probably a more important work than any of the preceding
is the 1834 classic by Ernst d’Alton on the python musculature. His
plates are excellent and his depiction of the costocutaneus superior
muscles well done. He used descriptive, generally functional, names
for the muscles, but was not always consistent in using the same for
text and illustration. Hoffmann (1890), in Bronn’s Thierreich, em-
ployed d’Alton’s work almost en toto, although using many new names.

Other important papers have been by Walter (1887), McKay (1889),
Phisalix (1914), Adams (1925), and Lubosch (1933). Lubosch ex-
amined a great many species of snakes of various families, unlike most
previous investigators who generally studied one, or at most several,
species.

The confusing 1937 paper of Gnanamuthu is a lesson in how to com-
plicate the obvious. The papers of Anthony and Serra (1950 and 1955)
are incomplete in coverage of the head musculature, although they ap-
parently did not intend to be thorough. Cowan and Hick did a care-
ful piece of work for their 1951 paper, using an unusual approach by
comparing cranial musculature in many specimens of the same species,
and finding points of constant variation.

Dullemeijer (1956 and 1958) did careful work on vipers in his
studies on functional anatomy of the head. Also, Albright and Nelson
(1959) presented a clear picture of head muscles in the colubrid Elaphe.
Sondhi (1958) did a straight anatomical study of Natrix piscator, but
his paper is confusing and not wholly accurate.

Following a brief, generalized discussion of the associated hyoid
muscles in lizards, the snake muscles are treated in groups according
to derivation: hypobranchial-spinal muscles and branchial arch
muscles.

HYPOBRANCHIAL-SPINAL MUSCLES

This group embraces most muscles of this study. They are derived
from myotomic parts of occipital somites and of the anteriormost post-
cranial somites. Those from the occipital somites are innervated by the
hypoglossal nerve, and those from the postcranial somites by spinal
nerves. However, there is a very close, natural association between
these several somatic masses, and some of the resultant muscles may
perhaps be innervated by both the hypoglossal and spinal nerves. The
distinction is often not clear.

The tongue is principally a muscular organ and is derived from the
occipital somites. Reese (1932) and Sewertzoff (1929) have studied

46 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

the tongue development in snakes, the latter in considerable detail.
Intrinsic tongue muscles, which will not be considered in this work, are
apparently derived from the same mass as the genioglossi. The pre-
sumptive intrinsic muscles surround the embryonic hyoglossi, which
will form the bulk of the tongue. The genioglossi and hyoglossi are
both included in this study.

Other hypobranchial-spinal muscles studied are the geniohyoideus,
ceratomandibularis, neuromandibularis, costomandibularis, costocutan-
eus superior, sternohyoideus, omohyoideus, and transversus branchialis.

BRANCHIAL ARCH MUSCLES

The 1st branchial arches give rise to the Jaw muscles, including the
intermandibular series of muscles which lie on the ventral surface of
the head and interconnect the lower jaws. In many species these are
close to the hyoid, and for this reason they are included here.

The 2nd branchial arches give rise to the constrictor colli muscles,
which are found erratically among snakes, but where present, in most
species have some sort of attachment to the hyoid.

The 4th branchial arches give rise to the hyotrachealis muscles, the
retractors of the larynx. This muscle originates on the hyoid in most
snakes.

The synonymy of many of the muscles is extensive and rather varied.
The author has tried to select those names which most aptly fit the
muscle’s origin and insertion; the majority of those selected usually
have been traditional. Where a new name was deemed necessary, the
same qualifications were used —muscle attachments. It should be
noted that the synonymy is not straightforward in many cases, for some
muscles described in the literature have been incorrectly illustrated and
described. Some have even been divided in such a way that exact cor-
relation of the name in the literature with the one used in this study
is not possible.

Examination of specimens has been by gross dissection, usually with
the aid of a binocular microscope. The following list of snakes has
been examined. A number of other colubrid species were also examined
but were not recorded because their musculature showed no particular
variations from what was expected.

Anomalepididae: Helminthophis flavoterminatus, Liotyphlops albi-
rostris.

Typhlopidae: JT. bibroni, T. intermedius, T. punctatus, T. schlegeli
brevis, T. schlegeli mucruso.

Leptotyphlopidae: L. maximus, L. septemstriatus.

THE ASSOCIATED MUSCLES OF THE HYOID 47

Uropeltidae: Platyplectrurus madurensis, Rhinophis blythi, Uropeltis
ceylanicus.

Aniliidae: Anilius scytale, Cylindrophis maculatus, C. rufus.

Xenopeltidae: NXenopeltis unicolor.

Boidae (sensu lato): Calabaria reinhardti, Charina bottae, Constrictor
constrictor, Eunectes sp., Epicrates cenchris, Eryx c. colubrinus,
Tiasis childreni, Python sebae, Sanzinia madagascariensis, Trachy-
boa boulengert, Tropidophis maculatus, T. melanurus.

Colubridae: Achalinus spinalis, Achrochordus javanicus, Amblycepha-
lus kwangtunensis, Aparallactus lineatum, Atretium schistosum, Cer-
berus rhynchops, Chersydrus granulatus, Dasypeltis scaber, Elaphe
0. obsoleta, Enhydris enhydris, Fimbrios klossi, Haplopeltura boa,
Heterodon p. platyrhinos, Mehelya nyassae, Nothopsis rugosus,
Natrix piscator, Sibynomorphus catesbyii, Sibynophis collaris,
Thamnophis elegans vagrans, Xenodermus javanicus, Xenodon
suspectus.

Elapidae: Denisonia par, Doliophis bilineatus, Naja melanoleuca,
Notechis scutatus.

Hydrophidae: Aipysurus eydouai, Hydrophis cyanocinctus, Laticauda
laticauda, Pelamis platurus.

Viperidae: Aspis vipera, Atractaspis microlepidota, Causus resimus,
Cerastes vipera, Echis carinatus, Vipera russelli.

Crotalidae: Agkistrodon piscivorus leucostomus, Bothrops mexicanus,
Crotalus horridus.

B. In Lizards

This is merely a brief resume of the associated hyoid muscles found
in Varanus (Fig. 6), with a comparison of those found in Anniella
(Fig. 5). For a more complete survey of these muscles in lizards,
Richter (1933), Camp (1923), and Oelrich (1956) should be consulted.

Generally speaking, the associated hyoid muscles of lizards are more
numerous than in snakes because nearly all lizards have a hyoid with
at least two pairs of cornua and some sort of pectoral girdle; these ele-
ments provide for more muscles than in snakes where only one pair of
cornua and no pectoral girdle are the absolute rules.

In Figure 6 of Varanus, the drawings are incomplete: the costocu-
taneus superior and intermandibular muscles are omitted.

HYPOBRANCHIAL-SPINAL GROUP

All the muscles in this group are innervated by the XIIth cranial
nerve and/or spinal nerves.

48 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Costocutaneus superior. This muscle lies over the hyoid completely
and therefore none of its fibers attaches to the structure.

Ceratomandibularis. This muscle is in two slips. The broad, main
slip runs from the middle third of the mandible posteriorly to the an-
terior edge of the 1st ceratobranchial and also onto the basihyal and
its lingual process. A narrow, separate slip hes medial to the main
muscle and attaches anteriorly to the dentary a short distance posterior
to the tip; it attaches posteriorly to the lingual process. Both slips of
the ceratomandibularis lie superficial to the hypohyal and ceratohyal.

Neuromandibularis. It arises as a broad aponeurosis over the dorsum
of the neck, directly behind the attachment of the cervicomandibularis.
The neuromandibularis then runs anteriorly and ventrally to insert into
the mandible on a line with and directly behind the ceratomandibular
attachment.

Geniohyoideus. This muscle is in two slips. The larger one arises
from the posterior third of the mandible and inserts onto the middle
third of the ceratohyal. The smaller slip is slender and arises from the
mandible under the anterior portion of the larger slip of the cerato-
mandibularis; it inserts into the free, expanded terminus of the
hypohyal.

Ceratohyoideus. This muscle runs between the posterior border of
the medial two-thirds of the ceratohyal posteriorly to the anterior
border of the Ist ceratobranchial.

Sternohyoideus superficialis. This muscle runs from the sternum an-
teriorly to a midventral raphe which is continuous onto the basihyal.
The muscle overlaps a rear fraction of the ceratomandibularis, and has
a tendinous intersection.

Sternohyoideus profundus. This muscle runs from the sternum an-
teriorly to the posterior border of the middle third of the 1st cerato-
branchial. This muscle also has a tendinous intersection. The muscle,
of course, lies deep to the sternohyoideus superficralis.

Omohyoideus. This muscle attaches to the girdle and runs anteriorly
and medially to insert upon the rear border of the anterior third of the
1st ceratobranchial. The muscle runs between the two sternohyoiden.

Hyoglossus. This is the principal tongue muscle and arises as an en-
capsulated muscle from the rear half of the 1st ceratobranchial. The
two muscles, one on each side, unite at the level of the lingual process
to form the bulk of the tongue.

Genioglossus. The gentoglossus arises from the medial edge of the
dentary directly posterior to the tip, and runs as a slender muscle

THE ASSOCIATED MUSCLES OF THE HYOID 49

posteriorly to be attached to the lateral surface of the respective
hyoglossus.

Gemotrachealis. This muscle arises from the dentary directly behind
and partly under the attachment for the genioglossus. The geniotra-
chealis then runs posteriorly and medially to insert into the larynx.
From this attachment a better name for it might be geniolaryngeus,
but to be consistent with the name chosen for the homologous muscle in
snakes, geniotrachealis is the choice.

BRANCHIAL ARCH GROUP

Intermandibulars. These do not attach to the hyoid in lizards, but
they are always in the vicinity, and should be mentioned for that
reason. The intermandibulars, which are not shown in Figure 6, are
wide and their fibers are practically transverse. They are in two sets
—an anterior and a posterior. Both arise from the medioventral border
of the mandible and attach to the midventral raphe with their mates.
The posterior lies between the two slips of the ceratomandibularis.
These muscles are innervated by branches of the mandibular division of
nerve V.

Constrictor colli. This muscle does not attach to the hyoid in lizards;
it is always superficial to the rest of the muscles. It forms a broad,
aponeurotic band on the ventrum of the throat and is innervated by a
branch of nerve VII.

In Anniella there are some differences in the musculature from
Varanus, and these differences are correlated with the reduction in the
hyoid skeleton. There is only one pair of cornua—the Ist cerato-
branchials. The musculature consists of a costocutaneus superior,
ceratomandibularis, neuromandibularis, sternohyoideus (a_ single
layer), hyoglossus, genioglossus, intermandibularis anterior and pos-
terior, and a constrictor colli. Muscles associated in Varanus with the
hypohyal and ceratohyal—the geniohyoideus and ceratohyoideus —
are missing in Anniella.

C. Accounts of Muscles in Snakes
HYPOBRANCHIAL-SPINAL MUSCULATURE

GENIOGLOSSUS
Synonymy. 1827, Genio-glosse, Dugés. (Genio-vaginien, Duges.
Slip to lingual sheath.) 1832, Genio-vaginien, Duvernoy. 1834, Vor-

50 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

wartszieher des Zungenbeins, d’Alton. 1838, Genio-glosse, Meckel.
1839, Vortszieher des Zungenbeins, Vogt. 1848, Genioglossus, Bendz.
1866, Genioglossus, Owen. 1880, Genio-vaginiens, Minot. 1887, Genio-
glossus, Walter. 1889, Genioglossus, Ludwig Ferdinand v. Bayern.
1889, Genio-hyo-glossus, McKay. 1924, Genio-hyoideus, DeJong. 1925,
Genioglossus, Adams. 1929, Genioglossus profundus (or geniovagina-
lis), Sewertzoff. 1933, Geniovaginalis and geniohyoideus (in error?),
Lubosch. 1935, Genioglossus, Edgeworth. 1937, Genioglossus (ventral
division, bundle “‘a’”’— one slip; dorsal division), Gnanamuthu. 1938,
Genioglossus, Nishi. 1944, Genioglossus, Kesteven. 1951, Genioglossus,
Cowan and Hick. 1956, Genio-hyoideus, Dullemeijer. 1958, Genio-
hyoideus, Dullemeijer. 1958, Genioglossus, Sondhi. 1959, Genioglossus,
Albright and Nelson.

The pair of genioglossi act as protractors of the tongue and are con-
stant in snakes. They are also present in lizards, and the homology is
obvious. Each genioglossus is a long, slender muscle which may have
one or two heads at the origin depending on the species. It is closely
applied to the tongue for most of its length.

Origin. For a single head it is usually on the inter-ramal fibrous pad
immediately medial to the tip of the dentary bone. If two heads are
present the common origin site for the lateral (larger) head is the
ventral medial angle of the tip of the dentary. Arising directly lateral
to it and closely applied to the external head for part of its length is the
geniotrachealis. Only in one family, the Typhlopidae (and possibly
the Uropeltidae), did the author detect that the lateral head arose
from the inter-ramal pad rather than the bone itself, although the con-
nection was close. The medial head, where present, constantly originates
on the inter-ramal pad, directly dorsal to the first part of the inter-
mandibularis anterior (if it is present).

Course. From the origin the fibers proceed medially and posteriorly,
soon entering the lingual sheath which invests the intrinsic muscles of
the tongue. The medial head, where present, runs almost its complete
way along the tongue before uniting with the lateral head.

Insertion. The muscles are bound to the tongue by the sheath, and
the fibers do not mingle with the other tongue muscles. The genioglossi
are now rather lunate or crescentic in transverse section, fitting exactly
over the curved lateral faces of the tongue. They extend with the
sheath at least as far as the hyoglossal split, but in a few cases they
continue past this point, each one, however, still bound to its respec-
tive hyoglossus; examples of this are found in Liasis, Eryx, and Xeno-
peltis.

THE ASSOCIATED MUSCLES OF THE HYOID 51

Innervation. The gentoglossus is served by an anterior branch of the
XIIth, or hypoglossal, cranial nerve. The cranial nerves vary in their
patterns in snakes; a frequent pattern consists of the IXth plus Xth
bound with the XIIth. After IX plus X is given off to the larynx and
vicinity, an anterior branch of XII goes on, soon uniting with sensory
fibers from V; fibers of XII continue past this point to innervate the
genioglossus and the geniotrachealis.

Action. Simply to protract the tongue. Note that protraction is con-
fined to the part of the tongue anterior to the hyoglossal split — pos-
terior to which the hyoglossi usually affix to the hyoid.

Variation. This is slight. Outside of the variation in the number of
heads, few differences exist in snakes. In the anomalepidid Liotyph-
lops, the genioglossus has two heads and ends at the level of the divi-
sion of the hyogloss: (Fig. 7). In the Typhlopidae the genioglossi
originate completely from the inter-ramal connective tissue, arising
from approximately the same point on the midline just posterior to the
tips of the dentary bones. It is probable that these slips represent the
medial ones, with the lateral heads not present. The genioglossi are
fairly wide, each being about one-fifth the width of the tongue, and
they end at the level of the hyoglossal division, this being well anterior
to the hyoid (Figs. 8 and 9).

In the Leptotyphlopidae each genioglossus has a single head, which
originates by way of a tendon on the genial surface of the dentary.
Muscle fibers arise from this tendon to make up an especially wide and
semi-circumferential genioglossus (Fig. 10). Together the genioglossi
completely ensheathe the tongue for part of its length. The genroglossi,
which taper posteriorly, extend to the posterior end of the hyoglossi
(which attach to the cornua of the hyoid) ; this condition is found in no
other snake.

Rhinophis, a uropeltid, has only the medial head, originating on the
inter-ramal pad (Fig. 11). The genioglossus ends with the sheath at
the hyglossal split. Another uropeltid, Platyplectrurus, on the other
hand, lacks the medial head, having only the lateral head.

Other snakes with only a single (lateral) head are the aniliid Cylin-
drophis rufus (Fig. 12, B), the boid Sanzinia, the colubrid Enhydris,
the hydrophid Aipysurus (Fig. 17, B), and the crotalid Bothrops (Fig.
18, A).

Outside of the Leptotyphlopidae, the presence of the lateral heads
alone seems to be of erratic appearance in snakes. That the genioglossi
have two heads is definitely more common in snakes, and where two
heads are present, the medial is always the thinner.

52 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

HyoGLossus

Synonymy. 1827, Hyoglosse, Dugés. 1832, Hyo-vaginien, Duvernoy.
1832, Cerato-vaginiens, Duvernoy. 1834, Zungenbeinzungenmuskel,
d’Alton. 1848, Ceratoglossus, Bendz. 1866, Hyoglossus, Owen. 1880,
Ceratoglossus, Minot. 1884, Hyoglossus, Ludwig Ferdinand v. Bayern.
1887, Hyoglossus, Walter. 1889, Hyo-glossus, McKay. 1890, Hyoglos-
sus, Hoffmann. 1924, Hyoglossus, DeJong. 1925, Hyoglossus, Adams.
1929, Hyoglossus, Sewertzoff. 1932, Ceratoglossus, Reese. 1933, Hyo-
trachealis (probably in error), Lubosch. 1935, Hyo-glossus, Edgeworth.
1937, Hyoglossus, Gnanamuthu. 1938, Hyoglossus, Nishi. 1941, Cerato-
glossus, Hershkowitz. 1944, Thyro-hyoideus of lacertilians, Kesteven.
1951, Hyoglossus, Cowan and Hick. 1956, Hyoglossus, Dullemeijer.
1958, Hyoglossus, Dullemeijer. 1958, Hyoglossus, Sondhi. 1959, Hyo-
glossus, Albright and Nelson.

This muscle is the retractor of the tongue; it also makes up the bulk
of this organ. All snakes and lizards have the hyoglossus.

Each hyoglossus is long, in fact extending the length of what is
considered the tongue, and projecting posteriorly from the tongue for
a considerable distance as well. Within the tongue itself, the hyo-
glossal fibers combine with intrinsic muscles; however, the hyoglossi
tend to keep their identity throughout the actual tongue. The intrinsic
muscles, not discussed in this paper, are usually in four sets. They
have been described by Minot (1880), Ludwig Ferdinand (1884),
and in greater detail by Sewertzoff (1929).

Origin. Without exception the hyoglossus originates on some part
of the cornu. In the Anomalepididae the muscle originates on the
ceratohyal — the exact point of origin being at the ceratohyal-recurrent
cartilage junction. Each hyoglossus is bound to the cartilage as a unit,
and not by individual fibers (Fig. 7).

In the Typhlopidae the fibers attach by small tendons directly to
the cornua. This is unique in snakes. The hyoglossi utilize the entire
anterior surface of the cornua, and there may even be slight encroach-
ment upon the lingual process (Figs. 8 and 9).

In leptotyphlopids, the hyoglossal origin is similar to that found
in the remainder of snakes. That is, the posterior end of the muscle
is smooth and contained within a connective tissue capsule; no fibers
actually attach to the cartilage — instead the encapsulated muscle is
bound to it. As a point of difference, however, in leptotyphlopids each
hyoglossus is bound in its capsule to the entire length of the cornu,
the muscle fibers being grossly parallel to the direction of the respec-
tive cornu (Fig. 10). In most other snakes the hyoglossi are bound to
a mere fraction of the cornua.

or
(Je)

THE ASSOCIATED MUSCLES OF THE HYOID

In these other snakes, where the hyoglossi are attached only to a
rear fraction of the cornua, the cartilage has a tendency to be some-
what buried in the muscle throughout its length of strong attachment
— which is frequently little more than about one-tenth or one-twelfth
of the cornual length. Actually, each hyoglossus is usually also bound
to its cornu for perhaps half the cartilage’s length, but this attachment
is not strong.

Course. The hyoglossi are found in more or less three forms: (1)
separate, parallel fibers directly attaching to divergent cornua —
Typhlopidae; (2) encapsulated parallel fibers attaching to parallel
cornua — families with parallel hyoid type; (3) encapsulated divergent
fibers attaching to divergent cornua— “V” hyoid type families and
Leptotyphlopidae — and to the ceratohyals in the Anomalepididae.

The hyoglossi of group (3) converge anteriorly; this point ordinarily
corresponds to the posterior end of the tongue’s heavy encapsulating
sheath, and therefore to the beginning of the actual tongue itself. In
groups (1) and (2), with parallel fibers, the hyoglossal muscles also
seem to end at the sheath. In reality the hyoglossi in all snakes enter
the tongue to make up a considerable part of its musculature, and in
all cases the line between the independent part of the hyoglossi and the
tongue is well demarcated.

Also, in all cases the hyoglossi proceed straight anteriorly, keeping
their separate identity rather well throughout the tongue. In general
the muscles reach the tips.

Insertion. There is no firm insertion, of course. The intrinsic
tongue musculature and the surrounding sheath provide a certain
amount of attachment.

Innervation. Motor nerves to the hyoglossi are from the hypoglossal.
At least two branches usually serve each muscle, and occasionally
three. The principal branch generally comes off the commonly joined
IX + X + XII trunk a short distance anterior to the angle of the
jaw, and after several convolutions it penetrates both the sheath and
the genioglossus immediately anterior to the simultaneous termination
of these; then the nerve enters the substance of the hyoglossus; the
nerve turns and proceeds anteriorly, giving off twigs to the hyoglossus
and intrinsic muscles. There may also be a branch given off anterior to
the main one; if present, it lies anterior to the level of entrance to the
tongue of the sensory fibers of the Vth and VIIth. A posterior branch is
more common; it is a small twig usually given off the major branch and
running to the separate hyoglossus. Where the posterior branch is
absent, obviously the separate part of the hyoglossus must be served
by a twig from the principal branch.

54 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Action. The hyoid is stabilized by various muscles acting chiefly
in opposition to each other. With their attachment therefore firmly
fixed, the hyoglosst can contract and thereby shorten the protracted
tongue, causing it to retract into its sheath. Also, contraction of some
or parts of the hyoglossal fibers included within the tongue must
obviously assist various intrinsic muscle actions in causing vibration
of the tongue.

Variation. There is little of note. There are length differences which
coincide with differences in length of the hyoid (parallel type in par-
ticular). The variation in the way the muscles attach to the hyoid,
and their divergent or parallel attitude, has already been treated
sufficiently.

In hydrophids the tongue, and hence the hyoglossi, is relatively
short in Pelamis, but in several others, at least Laticauda and Aipy-
surus, it is relatively long. Fossorial species might be thought of as
having weak tongue and hyoglossal development, but such is not neces-
sarily the case. In the typhlopids and leptotyphlopids the hyoglossi
are very broad and thick, in fact they are relatively by far the bulkiest
among snakes (Figs. 8, 9, and 10). A functional correlation with the
relatively great bulk is a mystery. The protractors of these tongues, it
might be noted, are poorly developed in comparison.

GENIOHYOIDEUS

Synonymy. 1946, Geniohyoideus, Warner.

The name is restricted to the muscle found only in the Anoma-
lepididae (Fig. 7).

Presumably the muscle can be homologized with what Richter
(1933) named the geniohyoideus in lizards, where, in general, this
muscle runs between the ceratohyal and the lower jaw and was con-
sidered, along with the cerahyoideus (sic) (also of Richter), as the
forward continuation of the episterno-hyoideus-profundus (Fig. 6, B).

Origin. In the anomalepidids it originates on the rear half of the
lower jaw.

Course. The geniohyoideus sweeps posteriorly in a broad sheet that
does not meet its opposite anywhere along the midline. It is a thin
muscle and almost tendinous medially.

Insertion. It attaches continuously to the hypohyal (transverse
bar) and the ceratohyal (descending cornu).

Innervation. Although not demonstrated clearly in the specimens
examined, the innervation would surely be by the XIIth.

Action. By counteracting the pull of posthyoid muscles, the genio-
hyoideus would help stabilize the hyoid for the benefit of the hyo-

THE ASSOCIATED MUSCLES OF THE HYOID 55

glossal muscles. It seems unlikely that it would actually pull the
hyoid anteriorly, and thereby assist in protracting the tongue.

Remarks. By homologizing this muscle with the one commonly
found in the same relative position and with the same general attach-
ments in lizards, there seems to be no problem as to its identity. How-
ever, there is also in the anomalepidids examined a slender muscle
which anteriorly attaches to the tip of the dentary by a thin tendon
and posteriorly attaches to the discernible terminal fraction of the
recurrent cornu (Fig. 7). The geniohyoideus is in several separate parts
in many lizards, and so it seems likely that this slender, independent
muscle may well represent another portion of the geniohyoideus in
anomalepidids. During its course the independent slip lies deep to
the principal muscle and therefore is on a different plane; for this
reason this slender muscle may be the ceratomandibularis, which, be-
cause of the loss of the 1st ceratobranchials in the anomalepidids,
found a new attachment to the ceratohyal.

In Typhlops and Leptotyphlops there is a slender muscle attach-
ing anteriorly on the dentary and posteriorly on the lingual process
of the basihyal (Figs. 8, 9, and 10). Because the ceratohyals are pre-
sumed to be lost in these snakes, this muscle is taken as a cerato-
mandibularis, discussed in a following section. There is always the
possibility, though, that this also could be considered a geniohyordeus.

The foregoing discussion is, In a way, taking an easy way out
by definitely naming the muscle found in anomalepidids. Actually, one
must consider the fact that the geniohyoideus and ceratomandibularis
must come from the same premuscular mass, and in relation to the
single pair of cornua found in anomalepidids only one ramus-hyoid
muscle would be expected to develop from the mass, and this is nearly
so. Therefore, it might really be just a convenience to consider the
geniohyoideus in anomalepidids as a name for the muscular sheet de-
rived from the single premuscular mass. It is always difficult in myol-
ogy to identify muscles in animals whose ancestors certainly possessed
more muscles in the same general area and of the same derivation.

CERATOMANDIBULARIS

Synonymy. 1815, M. latissimus ingluvier s. platysma myoides,
Hiibner. 1827, Mylo-hyoidien, Dugeés. 1832, Costomandibulaire (part),
Duvernoy. 1834, Kieferzungenbeinmuskel, d’Alton. 1839, Kieferzwng-
enbeinmuskel, Henle. 1839, Kieferzungenbeinmuskel, Vogt. 1865,
Mylo-hyoidien (part), Duméril and Jacquart. 1866, Costomandibularis
(part), Owen. 1887, Geniohyoideus, Walter. 1889, Mylohyoideus,
Ludwig Ferdinand v. Bayern. 1889, Mylo-hyoideus, McKay. 1890,

56 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Mazxillo-hyoideus and mylo-hyoideus, Hoffmann. 1900, Genio-hyoidien
(?), Chaine (after Rouvieré). 1906, Vortwartszieher des Zungenbeins,
Hager. 1906, Hyo-mazillaire superficiel, plus part of cervico-mazillaire,
Rouvieré. 1914, Mylo-hyoidien, Phisalix. 1924, Mylo-hyoidiens (?),
DeJong. 1925, Mylohyoideus, Adams. 1929, Geniohyoideus plus mylo-
hyoideus, Sewertzoff. 1931, Neuro-costo-mandibularis (part), Haas.
1933, Branchiomandibularis spinalis, Lubosch. 1935, Geniohyoideus,
Edgeworth. 1937, Geniohyoideus, Gnanamuthu. 1938, Branchioman-
dibularis spinalis, Lubosch. 1944, Hyomandibular (?), Kesteven. 1950,
Mylo-hyoidien, Anthony and Serra. 1951, Geniohyoideus, Cowan and
Hick. 1955, Mylo-hyoidien, Anthony and Serra. 1955, Geniohyoideus,
Evans. 1956, Mylohyoideus, plus parts of branchiomandibularis and
neuro-mandibularis, Dullemeijer. 1958, Ditto, Dullemeijer. 1958,
Geniohyoideus (including possibly part of genio-lateralis), Sondhi.
1959, Neuro-costo-mandibularis, pars hyotdea, Albright and Nelson.
1962, Neuro-costo-mandibularis (part), Kochva.

This muscle is considered to be present, with considerable variation,
in all snakes except possibly the anomalepidids. In most snakes it is
broad, sheetlike, contributing to the complex known as the neurocosto-
mandibularis; in a few it is separate and narrow. At a ventral view
the broad ceratomandibularis in most species covers a considerable por-
tion of the snake head, although the muscle may itself be partially
overlain by fibers of the constrictor colli, if present, and the costo-
cutaneus superior.

Innervation is by the XIIth cranial nerve, but since the muscle is
so generally integrated in the majority of species with newromandibu-
laris and the costomandibularis, which are both served by spinal
nerves, it seems appropriate to place the discussion of the ceratoman-
dibularis here, followed by the other two.

As can be seen from the synonymy, the name ceratomandibularis
has not been used in snakes before, so the author has followed Richter
(1933) in his work on lizards. Richter called ceratomandibularis the
muscle which runs from the lower jaw to the Ist ceratobranchial;
he considered it an anterior continuation of the superficial layer of
the episterno-hyoid complex. In snakes with the parallel type hyoids,
the cornua are considered 2nd ceratobranchials and the muscles only
have these cornua for attachment. It seems reasonable to homologize
this muscle in lizards with the similar one in snakes. Use of the new
name for snakes is also strengthened by the fact that a mixed, con-
fusing group of names has been applied to the muscle by previous
investigators.

There is a problem as to the proper identity of the muscle in the

THE ASSOCIATED MUSCLES OF THE HYOID or

typhlopids, leptotyphlopids, and anomalepidids. Possibly the slender
muscle either represents the medial slip of the ceratomandibularis (as
found in lizards), or else it may represent a slip of the deep ramus-
hyoid layer, the geniohyoideus (also as in lizards). The first possibility
is accepted for the typhlopids and leptotyphlopids by reason of at-
tachment to the Ist ceratobranchial, and its similarity to the internal
slip in lizards. The first possibility is also suggested, with reservations,
for the anomalepidids and has been discussed earlier in the section
on the geniohyoideus.

Origin. With the exception of the Typhlopidae and Uropeltidae,
the origin of the ceratomandibularis seems to be largely confined to
the dentary in snakes. Usually, then, the line of origin is on the ventral,
or at times, slightly lateroventral, surface of the dentary. It extends
a variable distance, but most often begins well behind the angle of the
dentary, often opposite the middle of the intermandibularis anterior
muscle or the anterior end of the lingual capsule. The line of origin
usually extends posteriorly quite near the end of the dentary, and
sometimes onto the compound bone, e.g., Atretiwm and Epicrates. The
muscle arises from a strong tendinous sheet, often reduced, but in
some cases it is large and is closely applied to much of the ventral
surface of the dentary. In the Aniliidae the posterior half of the origin
of the ceratomandibularis is overlain by the tendon of the newro-
mandibularis.

The leptotyphlopids have a narrow ceratomandibularis arising from
a narrow tendon that is attached to the posterior ventral prominence
of the dentary. The tendon lies immediately ventral to the tendon
of the newromandibularis.

In the Typhlopidae the very slender tendon, which is very long and
extends to the side of the genioglossus before giving rise to fibers,
attaches to the splenial, although perhaps in some typhlopids where
the splenial is much reduced, as 7. braminus, the attachment must
probably be on the angular. The ceratomandibular tendon is separate
from the neuromandibular tendon.

In Rhinophis the origin of the ceratomandibularis is on the com-
pound bone. The narrow tendon is overlaid ventrally by similar
tendons of the newromandibularis and cervicomandibularis.

Course. From its origin on the lower jaw, the ceratomandibularis
proceeds posteriorly and somewhat medially. In the typhlopids the
muscle is very slender and lies closely applied to the genioglossus up
to the point where the ceratomandibularis angles toward its insertion
on the hyoid (Fig. 8). In leptotyphlopids the muscle expands and has

58 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

a more or less tripartite form (Fig. 10) discussed more fully under
Insertions.

The muscle in the uropeltids is narrow and its course is directly
toward the hyoid (Fig. 11). In the aniliids the muscle is a sheet and
heads for the midline and the hyoid (Fig. 12, B).

The muscle is a broad sheet in the remainder of the serpents and
generally runs from the lower jaw toward the midline, the hyoid, and
the more or less transverse raphe which is usually shared by the
neuromandibularis and costomandibularis.

Insertion. Some typhlopids have the ceratomandibularts inserting
on the lingual process. In T. schlegeli mucruso the process curves
ventrally at its tip and it is upon this curve that the muscle inserts.
However, in 7. bibroni the insertion is along the whole process, and
in 7’. punctatus there is a common raphe directly anterior to its inser-
tion upon the process. Also in 7’. punctatus, a slip from the main part
of the muscle proceeds posteriorly along the hyoglossus to insert by
means of a fine tendon to the posterior end of the cornu. In T. inter-
medius the entire muscle inserts upon the cornu by way of a tendon.

Leptotyphlops maximus shows a tripartite division of the cerato-
mandibularis in which the broad first slip inserts upon the midline in
a common raphe with its fellow. A second, or middle, slip is more
slender and inserts on the lingual process; the third slip inserts over
the first several ribs. L. septemstriatus is similar.

Rhinophis has a narrow ceratomandibularis inserting upon the hyoid.
The exact insertion is the lateral edge of about the first eighth of the
cornu (there is no basihyal).

Concerning aniliids, in Cylindrophis maculatus the ceratomandibu-
laris is composed of three distinct slips which attach in different places:
a broad medial slip has a long insertion on the median raphe; a lateral
one attaches to the anterior fourth of the hyoid cornu; and the middle
slip lies over the hyoid on its way to the first several rib ends. C.
rufus also has a long median insertion on a common raphe. This is
followed by fibers attaching to the anterior sixth or so of the cornu.
Also, some of the fibers proceed into the area between the cornua
to insert commonly on a raphe that also receives fibers of the costo-
cutaneus superior. In Anilius the insertion is continuous on the median
raphe and onto the hyoid, where it involves the lateral edge of nearly
half the cornu (Fig. 12, A).

The other snake families possess a type of insertion that is generally
common to all —this being an insertion upon an anterior fraction of
the hyoid and upon the tendinous inscription in the neurocostoman-
dibular complex, which serves as a common raphe for the three com-

THE ASSOCIATED MUSCLES OF THE HYOID 59

ponents (Fig. 16). One frequent variation is the added presence of
the midline insertion upon a raphe common to both ceratomandibulars;
this is a sporadic variation, however. For example, it is found in
Xenopeltis, many colubrids, some hydrophids (Aipysurus), some
viperids (Cerastes), and some crotalids (Agkistrodon, Bothrops). The
boids (sensu stricto) seem to lack this raphe; a reason might be that
the basihyal is absent in this family.

Insertion upon the hyoid is never more than half the length of the
cornu in the xenopeltids and boids (sensu stricto), where the cornua
are divergent and not proportionately as long as in the parallel type.
The length of insertion is seldom more than an eighth of the cornual
length in the parallel type.

Fibers of the ceratomandibularis usually insert upon the lingual
process where one is present. Length of the process does not mean
much, however, for Atpysuwrus and Laticauda both have a very long
process yet the ceratomandibularis does not attach to it. Hnhydris,
on the other hand, also has a very long process, and fibers insert upon
it as well as the midventral raphe anterior to it. An extreme example
is shown by Atractaspis where the fibers insert on the median raphe
and on the long process alone.

The insertion at the inscription shared with the newromandibularis
and costomandibularis is extensive. The inscription lies in a more or
less transverse plane somewhere near the angle of the jaw, and seems
to be composed both of fibrous intermuscular connections and of a
thin independent tendon. The inscription in long-preserved specimens
may be difficult to find. Cowan and Hick (1951) described two
tendinous inscriptions in the garter snake, Thamnophis, and maintained
that these represent the Ist and 2nd ceratobranchials. It is difficult
to differentiate two inscriptions in most snakes, although one is almost
always definable. The exact derivation of the inscriptions is, for the
moment, obscure.

Achrochordus has a unique ceratomandibularis among those snakes
with a parallel type hyoid. In this snake the insertion is entirely upon
the hyoid, there being no costomandibularis, and the neuromandibularis
is apparently either incorporated into the costocutaneus superior or is
missing. Of the two parts of the ceratomandibularis in Avpysurus, the
anterior inserts wholly on the lingual process, and the posterior on the
cornu. In Thamnophis and Heterodon, examples among many, pos-
terior fibers of those which are directed for the hyoid may pass ven-
trally or dorsally to the cornu to insert in a midventral raphe (Fig. 16).

Innervation. The XIIth cranial nerve serves this muscle. Numerous
twigs come from the IX + X + XII trunk as well as from the hypo-

60 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

glossal branches to the tongue. No twig of the XIIth proceeds posterior
to the tendinous inscription where one is found.

Action. The main function is surely to oppose certain other muscles,
namely, the costomandibularis, neuromandibularis, and costocutaneus
superior (and omohyoideus, where present). The opposition must
serve to hold the hyoid in a stable position. It has been a common
idea that the ceratomandibularis muscles must help in protracting
the tongue, but observation of snakes during normal tongue protraction,
as well as artificial stimulation of the ceratomandibularis by electrical
means, showed that the hyoid remains relatively stationary during
protrusion.

Various secondary functions can be: to assist in elevating the
floor of the mouth and to help bring the lower jaws back to a normal
position following swallowing of prey.

Variation. The noteworthy variations in the muscle have largely
been already given; a brief summary and commentary on them are
now made for the sake of convenience.

Presence of the muscle is debatable in anomalepidids. Width of
the muscle where it is definitely found ranges from very slender to
broad. Slender ones are found in the Typhlopidae, with somewhat
broader examples found in the Uropeltidae and Leptotyphlopidae. The
other snakes have a generally wide ceratomandibularis.

Insertions are always at least partly on the hyoid. Typhlopids,
uropeltids, and the strange colubrid, Achrochordus, have no other site
of insertion. In leptotyphlopids, one slip meets its fellow at a median
raphe, another attaches over the rib cage, and the other attaches to
the hyoid. Cylindrophis maculatus has what appears to be a costo-
mandibularis joining the ceratomandibularis; neither C. rufus nor
Anilius, however, shows this condition. In the xenopeltids, boids, and
remaining families, the newromandibularis and the costomandibularis
generally effect a union with the ceratomandibularis; this broad, ex-
tensive complex muscle is termed the newrocostomandibularis. The
line of junction is marked by a tendinous inscription.

In anomalepidids, typhlopids, leptotyphlopids, uropeltids, and ani-
liids, the newromandibularis is generally present but does not make
connection with the ceratomandibularis.

NEUROMANDIBULARIS

Synonymy. 1827, Cervico-maxillaire, Dugés. 1832, Vertebro-man-
dibulaire, Duvernoy. 1834, Nackenzungenbeinmuskel (part), d’Alton.
1836, Cervico-mandibulaire (?), Cuvier. 1839, Nackenzungenbein-
muskel (part), Vogt. 1865, Not named but numbered “6,” Dumeéril

THE ASSOCIATED MUSCLES OF THE HYOID 61

and Jacquart. 1866, Neuromandibularis, Owen. 1872, Depressor man-
dibulae, Humphry. 1874, Temporalis (part), Teutleben. 1889, Depres-
sor mandibulae, McKay. 1890, Cervico-hyoideus, Hoffmann. 1898,
Neuro-mandibularis, Kellicott. 1900, Digastrique (?), Chaine. 1906,
Neuromandibularis, Hager. 1906, Cervico-mazillaris (part), Rouviere.
1914, Newro-mandibulaire, Phisalix. 1925, Newro-mandibularis, Adams.
1929, Vertebro-mandibular (?), Fairley. 1929, Vertebrohyoideus,
Sewertzoff. 1933, Neuromandibularis, Lubosch. 1935, Newro-costo-
mandibularis (vertebral head), Edgeworth. 1935, Newro-mandibularis,
Radovanovic. 1938, Neuromandibularis, Lubosch. 1944, Sterno-hyoid
(?), Kesteven. 1950, Vertebro-mandibulaire, Anthony and Serra. 1951,
Neuro-costo-mandibularis (neural head), Cowan and Hick. 1955,
Vertebro-mandibulaire, Anthony and Serra. 1956, Newro-mandibularis
(part), Dullemeijer. 1958, Newro-mandibularis (part), Dullemeijer.
1958, Genio-lateralis, Sondhi. 1959, Newro-costo-mandibularis, pars
vertebralis, Albright and Nelson. 1962, Neuwro-costo-mandibularvs
(part), Kochva.

This muscle is present— with some variation and one exception
(Achrochordus) —in all snakes. Directly cranial to it, and present
in most snakes, is the cervicomandibularis. Despite the usual close
association of these two muscles, the latter is apparently innervated
by the VIIth cranial nerve, whereas the former is innervated by
spinal nerves. In the lizards the newromandibularis — or what has
been called it anyway —is not universally found. However there is
confusion in the literature attending the differentiation of this muscle
from the cervicomandibularis, and the exact status in lizards is there-
fore not at all clear. Where the muscle does seem to be clearly repre-
sented, for example in Anniella (Fig. 5) and Varanus (Fig. 6), it is
very smiliar to the muscle in those snakes where the newromandibularis
is separate and does not unite, or unites slightly, with the ceratoman-
dibularis. But it should be mentioned that in Anniella there is at least
a partial insertion of the neuwromandibularis into the ceratomandibu-
laris, showing a likely case of parallelism rather than direct homology
with the condition in snakes.

Origin. Invariably the muscle arises from an aponeurosis which is
attached to the dorsal midline in the nuchal area. The cervicomandibu-
laris, where present, always originates in the anterior nuchal region,
directly cranial to the newromandibularis.

Course. From the origin the neuromandibular sheet sweeps down-
ward and anteriorly, curving onto the ventral surface. The insertion
is a point of variation. The muscle is partially overlaid superficially
by the constrictor colli, where present, and the costocutaneus superior.

62 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Insertion. There are two patterns of insertion. The first is found
in the anomalepidids, typhlopids, leptotyphlopids, uropeltids, and
anilids, where the newromandibularis inserts by way of a tendon
onto the lower jaw, having no union with the ceratomandibularis.

Anomalepidids have a single muscle which seems to be a newroman-
dibularis. It inserts on the dentary.

As an example of the typhlopid condition, in Typhlops bibrom (Fig.
8) the fibers attach directly to the articular bone. The muscle les
superficial to the intermandibularis posterior and inserts on the bone
at the posterior edge of the intermandibularis anterior. In Lepto-
typhlops there is a single muscle which is probably the newromandibu-
laris. The insertion is by a long tendon, which lies deep to the colli
and superficial to the intermandibularis posterior and attaches to the
same process on the dentary as the ceratomandibularis. The tendon
of the latter muscle is superficial.

The uropeltid Rhinophis has a short tendon which inserts on the
compound bone between the tendons of the ceratomandibularis and
cervicomandibularis; the three muscles partially overlap near their
insertion. Platyplectrurus shows a similar condition. The aniliids all
have a more or less separate newromandibularis, with a strong tendon
inserting onto the compound bone. The insertion is external to the
ceratomandibularis; the tendon overlies a small part of the lateral
posterior section of the ceratomandibularis. The cervicomandibular
tendon attaches immediately behind the neuromandibular tendon. It
is noteworthy that in C. maculatus the newromandibularis is separate,
but in C. rufus and Anilius fibers from the ribs join the muscle, and
these mimic but probably do not represent a costomandibularis.

A second kind of insertion pattern is found in the Xenopeltidae,
Boidae, and the remaining families: the newromandibularis inserts
on the raphe, which is also shared by the ceratomandibularis and
costomandibularis, and in this way the neurocostomandibular complex
is formed (Fig. 13). No fibers of the newromandibularis apparently
insert on the hyoid itself, although the mixture of fibers sometimes
makes this difficult to determine for certain. The raphe is a tendinous
inscription that les roughly transversely about opposite to the end
of the lower jaw. In some cases the tendinous inscription is weak
and apparently neuromandibular fibers then reach the lower jaw for
attachment. This concept is commonly met in the literature, e.g.,
Sondhi (1958) and Dullemeijer (1956).

Innervation. By twigs of the ventral divisions of several, more
anterior spinal nerves.

Action. When the muscle is separate and has no connection with

THE ASSOCIATED MUSCLES OF THE HYOID 63

the ceratomandibularis it must have a role in depressing the lower
jaw. When the muscle is part of the neurocostomandibular muscle
complex the primary action would seem to be in concert with the
costomandibularis in opposing the action of the ceratomandibular part
of the complex muscle and thereby stabilizing the hyoid apparatus.
No doubt the neuromandibular part of the complex muscle can also
assist the cervicomandibularis (and the depressor mandibulae) in help-
ing to depress the mandible. Albright and Nelson (1959), with the
help of various experimental methods, showed that the newromandibu-
laris is only of value in helping to depress the lower jaw when the Jaw
has already begun to be depressed; that is, the muscle helps to enlarge
the gape.

Variation. A summary can be presented this way: (1) A separate
neuromandibularis without an accompanying cervicomandibularis
(Anomalepididae, Leptotyphlopidae) ; (2) A separate newromandibu-
laris with an accompanying cervicomandibularis, but no connection
with the ceratomandibularis (Typhlopidae, Uropeltidae, Anilidae) ;
(3) A fairly broad sheet that inserts largely into a tendinous inscrip-
tion that is also common to the ceratomandibularis and to the costo-
mandibularis, forming the so-called neurocostomandibular muscle
complex (the other families).

Patterns (1) and (2) do not form phylogenetic groups.

With the evolutionary trend toward the incorporation of the three
muscles to form the neurocostomandibularis, there is a correlated in-
crease in relative width of the newromandibularis. It is slender in the
anomalepidids, typhlopids, and leptotyphlopids. In uropeltids and
aniliids there is a distinct increase in relative width, particularly
anteriorly. In the remaining families the neuromandibular part of the
complex is a strong, wide muscle, although still tapering somewhat
from the dorsal aponeurosis.

The genus Achrochordus, referred to as a colubrid, apparently lacks
this muscle, unless its fibers are hopelessly meshed with and indis-
tinguishable from the very extensive costocutaneus superior.

CosTOMANDIBULARIS

Synonymy. 1827, Costo-mazillaire (part), Dugeés. 1832, Costo-
mazillien (part), Duvernoy. 1832, Costo-mandibulaire (part), Du-
vernoy. 1834, Nackenzungenbeinmuskel (part), d’Alton. 1865, Petit
oblique de abdomen (part) (?), Duméril and Jacquart. 1866, Costo-
mandibularis, Owen. 1887, Genio-costalis, Walter. 1889, Costo-man-
dibularis, McKay. 1890, Cervico-hyoideus (part), Hoffmann. 1898,
Submazillaris (part), Kellicott. 1906, Costomandibularis, Hager. 1914,

64 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Costo-mandibulaire, Phisalix. 1925, Costo-mandibularis, Adams. 1929,
Costo-mandibular, Fairley. 1929, Costohyoideus, Sewertzoff. 1933,
Costomandibularis, Lubosch. 1935, Neuro-costo-mandibularis (costal
head), Edgeworth. 1935, Costo-mandibularis, Radovanovic. 1950,
Costo-mandibulaire, Anthony and Serra. 1951, Newro-costo-mandibu-
laris (costal head), Cowan and Hick. 1955, Costo-mandibulaire, An-
thony and Serra. 1956, Branchio-mandibularis (part), Dullemeijer.
1958, Branchio-mandibularis (part), Dullemeijer. 1959, Newro-costo-
mandibularis, pars costalis, Albright and Nelson. 1962, Newro-costo-
mandibularis (part), Kochva.

The costomandibularis muscle is not universal in snakes, although
it appears to be restricted to them.

In the Anomalepididae, Typhlopidae, and probably in the Lepto-
typhlopidae, the costomandibularis is lacking. A band of fibers in
Leptotyphlops which is bound to the rib cage and merges with the
ceratomandibularis probably is only a slip of the latter muscle (Fig.
10). The muscle is present in some form in the remaining families.

This interesting muscle seems to represent specialization of fibers of
another muscle and subsequent capture of them by one new site of at-
tachment. From innervation and general relationship it is probable
that the costomandibularis is composed of a variable number of the
altered anterior slips of the costocutaneus inferior muscle, whose fibers
run from the ventral scales posteriorly to the cartilaginous ends of the
ribs (Mosauer, 1937).

In the xenopeltids, boids, colubrids, and poisonous snakes, the costo-
mandibularis is a part of the neuwrocostomandibularis complex.

Edgeworth (1935) placed this as true hyoid muscle, that is, one
derived from the 2nd branchial arch and thus served by the VIIth
cranial nerve. The author could not find any evidence for this position
and therefore adheres to the stand that the costomandibularis is a
derivative of the rectus series of the hypaxial trunk musculature, repre-
senting specialized anterior slips of the costocutaneus inferior.

Origin. The origin is either directly from a variable number of carti-
lage ribs (or directly above them on the true ribs), or else upon the
rib cage, where the fibers are bound by fascia to the trunk muscles
overlying the ribs. The first pattern is the more common. The exact
number of ribs providing attachment for slips is often impossible to
ascertain, because posteriorly the slips tend to taper off into the costo-
cutaneus inferior. Some examples of the ribs involved are: 2-3 in
Tropidophis, 2-5 in Thamnophis elegans, 4-6 in Atretium, 6-7 in
Cerastes. It seems that the 1st rib, which is short, is seldom a site
of origin.

or)
ou

THE ASSOCIATED MUSCLES OF THE HYOID

In Thamnophis there is also a medial slip which arises from the
peripheral surface of the lining of the pharyngeal floor.

Course. In the snakes with the parallel type of hyoid, the fibers
proceed anteriorly and more or less parallel to and usually lateral to
the adjacent cornu. In the snakes with the “V” type of hyoid, the
cornua are divergent and the end of each hyoglossus and its cornu
usually lie superficial to the rib cage so that the costomandibularis lies
deep to the hyoglossus and cornu; in this case the muscle also lies
medial to the posterior part of the cornu. In Cylindrophis maculatus
the costomandibularis, as an exception, lies external to the hyoglossus,
running forward to insert into the ceratomandibularis.

Where the origin of the muscle is upon the rib cage itself, the course
of the fibers is lateral to the hyoid, regardless of its type.

Insertion. The principal and usual insertion is upon the common
tendinous inscription of the neurocostomandibularis. A small medial
portion of the costomandibularis frequently inserts upon the lateral
edge of a cornu as well, directly posterior to the insertion of the
ceratomandibularis.

The insertion end of the muscle is often covered superficially by part
of the neuromandibularis; this condition is found in Xenopeltis; it is
also well marked in Thamnophis and to a lesser degree in other species.
In Cerastes there is no insertion to the hyoid itself, only to the in-
scription.

In the uropeltids Rhinophis and Uropeltis, the muscle attaches to
the cornu. In Anilius the costomandibularis does not insert upon the
hyoid, but runs deep to the newromandibularis to insert on the com-
pound bone of the lower jaw by a strong tendon shared with the neuro-
mandibularis. Cylindrophis rufus has slips going to the hyoid and
inserting upon the medial edge of the cornu, and may also have a slip
inserting on the mandible.

Innervation. By twigs from the ventral division of the spinal nerves,
in repetition of those serving the costocutaneus inferior.

Action. Primarily to serve as an antagonist to the ceratomandibu-
laris; therefore it has a role in the stabilization of the hyoid. Possibly,
and certainly in the case of Anilius and Cylindrophis rufus, the muscle
also assists the newromandibularis in depressing the lower Jaw.

Variation. A brief summary of the chief variations may be helpful:
The muscle is lacking in the Anomalepididae, Typhlopidae, and Lepto-
typhlopidae — as far as known. In the Uropeltidae the muscle is
small and runs from the ribs to the cornu. In the Aniliidae, Cylin-
drophis maculatus has a single muscle, running from the ribs to the

66 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

ceratomandibularis; in C. rufus, on the other hand, there are presum-
ably two bellies to the muscle, one from the rib ends to the hyoid, and
the other from the rib ends to the lower jaw. Anilius has only the latter
variation.

Most snakes have the origin upon the ends of certain of the anterior
ribs and the insertion largely upon the inscription in the newrocosto-
mandibularis plus a small bit on the hyoid. In a few there is the condi-
tion in which the muscle originates entirely upon the rib cage, bound
to the lateral wall muscles; examples are XYenopeltis and Liasis.

Epicrates has the muscle in two parts: the cranial slip from rib ends
6-8 proceeds lateral to the hyoid to insert in the inscription and on the
cornu; the caudal slip, from ribs 8 to at least 10, lies medial to the
cornu, inserting on the medial edge of the cartilage, but immediately
posterior to the transversus branchialis. Thamnophis elegans has the
interesting condition of a slip originating from the buccal floor between
the cornu and the main slip from the ribs.

The genus Achrochordus lacks the costomandibularis; it also lacks
the newrocostomandibularis.

CosSTOCUTANEUS SUPERIOR

Synonymy. 1827, Vertebro-hyoidien (?), Dugés. 1834, Der grosse,
aussere oder Seitenhautmuskel, d’Alton. 1865, Peaussier (continuous
with grand oblique), Duméril and Jacquart. 1866, Sqwamo-costales,
Owen. 1889, Obliquus externus, McKay. 1890, Cutaneus externus,
Hoffmann. 1904, Costocutaneus superior, Buffa. 1916, Obliquus ab-
dominis superficialis, Nishi. 1929, Sternohyoideus (?), Sewertzoff.
1931, Hautmuskel (H. 2) (part), Haas. 1932, Costocutaneus superior,
Wiedemann. 1933, Cutaneus externus, Lubosch. 1935, Cervico-hyoideus
(?), Edgeworth. 1935, Costocutaneus superior, Mosauer. 1937, Sterno-
hyoideus plus omohyoideus, Gnanamuthu. 1938, Cutaneus externus,
Lubosch. 1946, Sternohyoideus, Warner. 1951, Cervico-hyoideus,
Cowan and Hick. 1956, Neuro-mandibularis (part, apparently), Dul-
lemeijer. 1958, Neuro-mandibularis (part, apparently), Dullemeijer.
1958, Omohyoideus plus sternohyoideus plus sternothyroideus, Sondhi.
1959, Costocutaneus superior, Albright and Nelson.

This is a hypaxial trunk muscle, and also of a repetitious nature,
the slips coalescing in a way to form a continuous layer. It is included
in this paper because, even though it is a trunk muscle, in the majority
of snakes the most anterior slips attach upon part of the hyoid cornua.

The costocutaneus superior has been well described for the trunk
region (Buffa, 1904; Mosauer, 1935), but due to the difficulty in clearly
defining it in relation to the hyoid and “throat” region, its connection

THE ASSOCIATED MUSCLES OF THE HYOID 67

with the hyoid has usually not been shown. However, d’Alton (1834)
depicted the muscle in accurate fashion, but after him came a deluge
of incomplete illustrations and erroneous ideas as to the nature of the
muscles in this region. Dissection, even very careful dissection, on
many preserved specimens still leaves the costocutaneus superior
rather shredded and disarranged in the throat area, and this has ap-
parently been the reason why various authors refer to the costocu-
taneus in the hyoid area as the sternohyoideus, or omohyoideus, or
even sternothyroideus (see Synonymy). Cowan and Hick (1951)
used cervico-hyoideus, obviously in following Edgeworth (1935). The
author could not decide from the latter’s description exactly what
muscle is meant, but presumably it must be the hyoid part of the
costocutaneus superior.

To be sure, the anterior part of the costocutaneus superior muscle
does lie in a logical place for the sternohyoideus, but except in Typh-
lops and Leptotyphlops the sternohyoideus is probably not present as
a recognizable, discrete muscle in snakes. If traces of it do remain in
other snakes, they have become so involved in the cutaneous muscula-
ture that separation and definition are impossible.

Origin. Because of the presumed function of the anterior group of
fibers, their origin can most practically be considered as the anterior
ventrals (of varying number according to species) and adjacent rows
of lower dorsal scales. For the remainder of the costocutaneus superior
muscle, the origins are on the ribs, as the name suggests. It should be
noted that due to the mixing of the fibers of the anterior group with the
muscle as a whole, it is generally impossible to set the limits of the
fibers attaching to the hyoid and therefore no exact site of origin can
usually be made.

Course. The course of the anterior fibers runs from the origin on the
ventral and dorsal scales anteriorly in a slightly curved are to the
hyoid and adjacent tissues; this is true for most snakes. In all snakes
the main part of the muscle runs posteroventrally from the ribs toward
the lower dorsal scales and the ventrals.

Insertion. It must be mentioned first that in examined Typhlops and
Leptotyphlops, and in Rhinophis, Cylindrophis maculatus, and Achro-
chordus, the anterior fibers attach to the lower mandibles, thereby
completely overlying the hyoid and having no connection to it; in
these cases the attachment to the mandibles would likely represent an
origin. In Cylindrophis rufus, the fibers do not extend to the lower
jaws but attach to the posterior edge of the constrictor colli muscle;
therefore, the costocutaneus superior also overlies the hyoid in this
species (Fig. 12, B).

68 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

In the other examined species, the costocutaneus superior inserts
upon some part of the hyoid. In the anomalepidids the insertion is
upon the posterior or medial edge of the hypohyals and ceratohyals;
the recurrent cornua therefore lie deep to the geniohyoideus muscle
rather than to the costocutaneus superior (Fig. 7).

In most cases the fibers inserting on the hyoid do so beginning di-
rectly at the anterior end of the cornu (base of the lingual process).
Some fibers may begin attaching more posteriorly, as in Epicrates
(Fig. 14, C), but this is of rare occurrence. The length of insertion on
the cornu is seldom but a fraction of the cornual length — ordinarily
less than half with the “V” type hyoid, and much less with the parallel
type apparatus.

The fibers rarely encroach upon the lingual process, although the
crotalids show this tendency, as seen in Agkistrodon and Bothrops
(Fig. 18, A). The latter even has fibers anterior to the process affixing
to the midventral raphe.

Posterior to the short length of the insertion on the cornua, the re-
mainder of the hyoid lies deep to the costocutaneus superior fibers, so
that in the majority of snakes the hyoid is largely covered ventrally by
these fibers.

In addition to inserting on some part of the hyoid, the anterior fibers
also insert on surrounding tissues, there usually being the neurocosto-
mandibularis muscle complex, and the constrictor colli.

Innervation. Costocutaneus superior fibers are served by twigs from
the ventral divisions of anterior spinal nerves. Excepting the first
several spinal nerves, each ventral division nerve emerges ventral to
the body wall highly convoluted and comes to lie upon the ventral
surface of the obliquus abdominis internus. Twigs then go to the over-
lying costocutaneus.

Action. A majority of the fibers of the costocutaneus superior serve
only the trunk and have origins on the ribs and insertions on the scutes
and dorsal scales; these fibers draw anteriorly the scales and scutes,
which are then secured by the terrain. The costocwtanei inferiores,
which run from the scutes posteriorly to the ribs, act to draw forward
the ribs and therefore the snake’s body.

The hyoid portion of the costocutaneus superior has acquired a dif-
ferent function: assisting in stabilizing the hyoid apparatus so it will
be a firm foundation for the hyoglossit. When the hyoid part of the
muscle contracts, and the scales or scutes which serve as origins are
held fast, the hyoid will tend to be drawn posteriorly. This counteracts
the anteriorly directed movement initiated by the ceratomandibularis
muscles and the hyoid is thereupon fixed. The neuromandibularis and

THE ASSOCIATED MUSCLES OF THE HYOID 69

costomandibularis, when these are present and inserting on the hyoid
plus the neurocostomandibular raphe, have a synergistic action with
that of the costocutaneus superior.

Naturally in those snakes where the costocutaneus superior does not
attach to the hyoid and instead merely overlies it, e.g., Typhlops et al.,
the function of counteracting the ceratomandibularis would not occur;
the costocutaneus superior would then have only an effect on the skin.
Its role is taken over by the sternohyoideus in the typhlopids and
leptotyphlopids, and by the omohyoideus in Rhinophis and Cylindro-
phis maculatus.

Variation. The major variation involves attachment or nonattach-
ment to the hyoid; this has been discussed previously. There is, how-
ever, the case of the colubrid Achrochordus, which is given a separate
family by some investigators. In Achrochordus the costocutaneus su-
perior attaches to the lower jaw and is mixed with fibers of the cervi-
comandibularis in a confusing way; the hyoid is quite free from
connection with these fibers (Fig. 15, B).

The substantial insertion on the hyoid in Liotyphlops is noteworthy ;
in the other two families of blind snakes the hyoid is missed by the
muscle. Warner (1946) designated the fibers sternohyoideus in her
drawing of Anomalepis, but there seems to be no good evidence for
giving these fibers that name.

Commonly the transversus branchialis sends many of its fibers into
the costocutaneus superior, and in such cases a clear distinction be-
tween the two muscles is impossible.

STERNOHYOIDEUS

Synonymy. 1955, Sternothyroideus, Evans.

As a distinct, discrete muscle mass, the sternohyoideus can only be
indicated as likely in two families: the Typhlopidae (Fig. 8), and the
Leptotyphlopidae (Fig. 10). Various applications of the name sterno-
hyoideus in other snakes such as by Gnanamuthu (1937), Warner
(1946), and Sondhi (1958), are not recognized here. The muscle por-
tions so named by these authors are here considered to represent parts
of the costocutaneus superior muscle.

The author sees no reason to follow Evans in using the name sterno-
thyroideus. There is no true thyroid plate in the larynx of the snake
for one thing, and for another the muscle comes nowhere near the
larynx.

It would be most reasonable to regard this muscle as the sternohyo-
ideus, homologous in lizards to part of the episternohyoideus of Richter
(1933), and to the sternohyoid of Camp (1923) and Oelrich (1956). In

70 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

lizards the sternohyoid muscles have a rather medial placement, with
the origin upon the sternum and perhaps part of the clavicle. The
muscle in the two snake families where it is considered to be found
also has a medial placement, and, because of loss of the girdle, has
found a new origin.

Origin. The raphe of the anterior fourth or so of the ventral midline
(linea alba). The origin is deep to the abdominal muscles, and the
length of attachment is nearly as long as the muscle itself. The fibers
arise fanlike before forming the mass of the muscle.

Course. The fibers are directed anteriorly and somewhat deeply.
They unite to make up the bulk of the muscle, which gradually expands
anteriorly toward the insertion.

Insertion. Upon some part of the hyoid. Most of the insertion is on
the entire posterior edge of each cornu; this is true in Leptotyphlops
maximus and Typhlops bibront. In T. schlegelt mucruso there is addi-
tional insertion upon the lingual process, and the sternohyoideus actu-
ally divides closely into three slips on each side; one inserts on the pos-
terior edge of the cornu, one passes ventrally over the cornu to insert
along the length of the lingual process, and the third passes deep to the
cornu to attach along the lingual process (Fig. 9).

Innervation. A branch of the hypoglossal nerve descends in the mass
of the hyoglossus to serve the sternohyoid muscle. Very likely, at least
the first several spinal nerves also serve it.

Action. Obviously the major function is to stabilize the hyoid appa-
ratus by chiefly counteracting the pull of the ceratomandibularis.

Variation. The few variations have been discussed in the several
preceding sections. The muscle is very similar in Typhlops and
Leptotyphlops.

OMOHYOIDEUS

Synonymy. 1946, Omohyoideus, Warner.

The name is given to a small muscle which runs either from the end
of the hyoid or the hyoglossus to attach upon the rib cage. It has been
found in the Anomalepididae, the genus Cylindrophis, the genus Rhino-
phis, and in one examined species of the Boidae, Eryx c. colubrinus.
The distribution is certainly erratic.

The use of this name for certain muscle fibers in other snakes, as
Sondhi (1958) has done for Natrix piscator, for example, is ill-advised;
these fibers represent costocutaneus superior fibers.

In lizards, according to Richter (1933), the omohyoideus is part of
the episternohyoideus complex that unites the first branchial cornua

THE ASSOCIATED MUSCLES OF THE HYOID ral

with the pectoral girdle, and in lizards has, typically, a lateral site of
origin on the clavicles and scapula. These bony elements are lost in
snakes and if the muscle remains it must seek a new origin. Attach-
ment upon the rib cage has been the solution; this would be somewhat
similar in position to the typical lizard origin. Note the posthyoid
muscle in Anniella (Fig. 5), a limbless lizard, where the reduced
pectoral girdle is probably a remnant of the scapula-procoracoid
(Stokely, 1947). These muscles in snakes and Anniella compare closely
in many respects. There are differences, too: in Anniella the muscle
is relatively much larger, and inserts on the medial edge of the cornu,
whereas it always inserts on the lateral edge in snakes.

From its innervation (spinals) and position it is logical to assume
that the muscle in snakes, where it is found, is the partial homologue of
the episternohyoideus complex of lizards and could appropriately be
called the omohyoideus.

An apparent discrepancy in the Anomalepididae, where the muscle
attaches to the ceratohyal rather than to the first ceratobranchial as in
lizards and in the few other snakes involved, must be reckoned as the
result of the capture of the muscle by the 2nd arch derivative con-
comitant with the loss of the 3rd.

Origin. The muscle is bound by connective tissue to the lateral body
muscles shortly posterior to the end of the cornu. The extent of the
origin is variable according to the species.

Course and Insertion. From the origin the muscle runs for a brief
distance anteriorly and medially to insert on or about the posterior
fraction of the cornu in one of the several following ways: upon the
curve formed by the junction of the descending and ascending cornua
(Anomalepididae) ; upon the posterior tip of the hyoglossus (Cylindro-
phis) ; upon the lateral edge of the final third of the cornu (Rhinophis) ;
or upon the terminus of the cornu (Hryz).

Innervation. By several twigs from the ventral divisions of each of
several spinal nerves determined by where the muscle lies in relation
to the ribs. The first and second spinals, however, do not seem to be
involved.

Action. This is not a large muscle, either in bulk or length. Its pur-
pose is apparently to counteract protraction of the hyoid by the cerato-
mandibularis (or geniohyoideus in anomalepidids) and thereby to assist
in stabilizing the apparatus. Excepting Hryz, it should noted that, in
those snakes having the omohyoideus, the costocutaneus swperior
muscle overlies the hyoid and does not consequently attach to it;
therefore, in these snakes the omohyoideus plays the chief part as an
antagonist to the ceratomandibularis.

~I
bo

THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

TRANSVERSUS BRANCHIALIS

Synonymy. 1834, Quermuskel des Zungenbeins, d’Alton. 1890, Trans-
versus hyoideus, Hoffmann. 1910, Transverse, Chaine. 1935, Trans-
versus branchialis, Edgeworth.

This muscle is of varying occurrence, and perhaps may not really
be the same muscle for all snakes. Many of the supposed omissions of
the muscle are possibly due to the difficulty in separating the costo-
cutaneus superior fibers correctly so as to reveal the presence of a
distinet layer — the muscle described here. The transversus branchialis
should be considered unique to snakes.

Albright and Nelson (1959), in their study of Elaphe obsoleta quad-
rivittata, used the name transversus branchialis for another muscle,
which has a medial attachment to the midline raphe and then splits to
have one head attach to the submandibular gland and the other to the
oral mucosa.

Origin and Insertion. The two transversi arise from a varying length
of the medial edges of the cornua, and proceed posteromedially to
insert in a midventral raphe, and sometimes also into the costocutaneus
superior fibers. The transversus branchialis fibers always lie at a
posteriorly directed angle.

Innervation. The muscle is served by twigs from the ventral divi-
sions of several spinals. This suggests that the muscle is derived from
the rectus cervicis group.

Edgeworth (1935) thought that the transversus is served by the Vth,
which places it as a muscle of the first branchial arch. His evidence is
wanting, and the author could see no nerve from the mandibular divi-
sion of the Vth going to the transversus branchialis muscle.

Action. Apparently to help retain the form and position of the
cartilaginous cornua.

Variation. The families Anomalepididae, Typhlopidae, and Lepto-
typhlopidae lack the muscle. There is no place for it in these groups
because of the relation of the cornua to other muscles.

Rhinophis has a distinct transversus, originating on the medial edge
of the anterior fourth of the cornu and inserting on the linea alba
(Hie. )e

In the aniliids, Aniliuws has a well-developed transversus muscle,
attaching to the entire length of the cartilage (Fig. 12, A); in Cylin-
drophis rufus, it attaches to the anterior two-thirds (Fig. 12, B) ; but in
C. maculatus, where the hyoid is severely reduced, there is no muscle
at all.

Xenopeltis has the fibers originating on approximately the anterior

THE ASSOCIATED MUSCLES OF THE HYOID (6)

sixth of each cornu (Fig. 13). Every true boid examined, except Ep-
crates and Python, possessed the muscle. Tropidophis lacks the muscle.

The situation is varied in the remainder of the snakes. Many ex-
amined colubrids definitely have it, as Achrochordus, Amblycephalus,
Thamnophis, Nothopsis, Fimbrios, and Heterodon. Others do not:
Atretium, Haplopeltura, Enhydris, Cerberus, and Sibynophis. The sea
snakes Aipysurus, Laticauda, and Hydrophis, have it, and the elapid
Doliophis also does. Most other hydrophids and elapids lack it. The
viperids Cerastes and Causus lack the transversus. Among crotalids,
Agkistrodon has the muscle, whereas Bothrops does not.

Altogether it appears that except in the anomalepidids, typhlopids,
and leptotyphlopids, where it is apparently invariably not developed,
the muscle is of erratic appearance within families.

BRANCHIAL ARCH MUSCULATURE
CONSTRICTOR COLLI

Synonymy. 1832, Peaucier du cou, Duvernoy. 1834, Rickswarts-
zieher des Zungenbeins, d’Alton. 1839, Riickswartszieher des Zungen-
beins, Vogt. 1889, Platysma, McKay. 1890, Atlanto-epistropheo-hyo-
ideus, Hoffmann. 1923, Constrictor colli, Camp. 1931, Hautmuskel (H.
1) (?), Haas. 1933, Sphincter colli (facialis constrictor), Lubosch. 1935,
Constrictor colli, Edgeworth. 1937, Constrictor colli plus mylohyoideus
posterior, Gnanamuthu. 1938, Constrictor colli oralis and aboralis,
Lubosch. 1944, Superficial ventral constrictor (Csv. 2), or sphincter
colli facialis, Kesteven. 1951, Constrictor colli, Cowan and Hick.
1958, Mylohyoideus posterior, Sondhi. 1959, Constrictor colli, Albright
and Nelson. 1962, Constrictor colli, Kochva.

This muscle is of erratic appearance in snakes. The irregularity of
its presence is a condition which can even be found within a single
genus, e.g., Python. The author could find no trace of the muscle in
a young P. sebae (Fig. 14, A), while Lubosch (1933) plainly illus-
trated the facial constrictor for P. molurus, and even differentiated it
into two parts, oralis and aboralis. Lubosch noted that the muscle is
found in an asiatic species of Tropidonotus (Natrix), whereas it is
lacking in a European form of the same genus; the two species are
presumed to be close relatives. Sondhi (1958) described and illus-
trated the muscle for the asiatic Natrix piscator, naming it the mylo-
hyoideus posterior. The author has confirmed the presence of the
constrictor colli in this species. Lubosch stated that in snakes the
constrictor colli seems to be in a regressive stage — an observation with
which the author concurs.

74 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Dissection has shown that the muscle is often difficult to separate
clearly and even to identify. This is particularly true in specimens
which have been long or poorly preserved. Because the constrictor
hes almost entirely next to the skin and is bound to it rather firmly,
skinning of the head and neck can easily disarrange or destroy the
muscle so as to make its limits, and even its existence, doubtful.
Furthermore, the thinness of the layer contributes to the difficulty in
recognizing it.

Origin. Generally by means of a thin aponeurosis from the dorsal
area of the posterior part of the head, the nape, or both in combination.
Presumably the line of origin should be the dorsal midline, but since
the aponeurosis is usually tightly bound to the underlying muscles,
this is many times difficult to show.

Usually where the constrictor colli is distinctly present, it is broad
and covers the angle of the jaw. However, in many boids, e.g.,
Epicrates (Fig. 14, C), Liasis, and Sanzinia, the muscle is narrow,
originating in the area of the nape. The typhlopids have a distinct
condition in which the constrictor arises on the lateral aspect of the
neck region; the aponeurosis does not reach the dorsal midline.

Course. The constrictor colli is either transverse in position from
origin to insertion, as in Typhlops and Leptotyphlops, or else takes
on an anteroventral course. In all individuals where it is found, the
constrictor forms a sort of half ring about the throat region.

Insertion. Upon part of the hyoid in all but two families — the
Typhlopidae and Leptotyphlopidae, were the hyoid apparatus is far
posterior to the head, and the constrictor colli muscle of each side in-
serts upon the ventral median raphe. In other snakes the portion of
the muscle not inserting on the hyoid either ends in connective tissue
over the ceratomandibularis, as seen in Haplopeltura, or else mn a
common median raphe. The insertion on the cartilage may be by way
of fibers or by an aponeurosis.

Innervation. The VIIth, or facial, nerve serves the constrictor colli;
the twig comes from the hyomandibular branch which passes over
the stapes to innervate the depressor of the lower Jaw. The twig to the
constrictor colli then passes internally to the quadrate, emerges pos-
teriorly, and sends branches to the cervicomandibularis as well as to
the constrictor.

Action. The contraction of the muscle must, in those where fibers
insert into the hyoid, tend to pull back the hyoid in some measure.
In this way it could help to counteract the pull of the ceratomandibu-
laris. Indeed, d’Alton (1834) called the constrictor “Rickwartszieher

THE ASSOCIATED MUSCLES OF THE HYOID Figo)

des Zungenbeins” (retractor of the hyoid). Still, the main function
must be to constrict the pharynx. Of course it cannot be necessary
to snakes, for many live without it with obvious success.

Variation. The muscle was found in every family examined except
the Uropeltidae. The genera Rhinophis and Platyplectrurus did not
have it, but since the vagaries of the muscle are known it is possible
that the muscle is present in some other genus of the family which
was not examined.

Typhlopids and leptotyphlopids excepted, the constrictor colli has
been found wanting in some members of every family. As mentioned
previously the absence of it does not seem to be phylogenetically im-
portant since close relatives may vary in this respect. Perhaps in the
typhlopids and leptotyphlopids, where it seems to be uniformly present,
the muscle may represent the primitive condition, for the constrictor
colli is of constant occurrence in lizards.

Duvernoy (1832a) illustrated the muscle (equals peaucier du cou)
in the couleuvre collier (Tropidonotus) as being very broad with the
entire insertion upon a common midventral raphe. Inasmuch as in all
other examined colubrids, where the muscle is present, the insertion is
at least half upon the hyoid, this illustration of Duvernoy’s is prob-
ably in error. Edgeworth (1933) has used the same drawing.

In the boid genera Epicrates, Liasis, Sanzinia, and Loxocemus, the
constrictor colli is very narrow, and passes in its course behind the
angle of the jaw to insert upon the cornu. In these genera it is a dis-
tinctive muscle, much narrower than found elsewhere in the snakes.

INTERMANDIBULARS

These muscles lie between the mandibles and are not strictly as-
sociated with the hyoid in any species, with one exception. However,
they do lie in the immediate vicinity and are readily seen upon any
dissection of the hyoid and its musculature. The muscles are not
treated here as thoroughly as the others because of their rather inci-
dental importance to the subject. The synonymy is not complete.

The intermandibular muscles are innervated by the mandibular
division of the trigeminal nerve. Their general action is to adduct
the lower jaws.

There appear to be two sets of intermandibular muscles, but these
are divisible in many snakes into several parts or even into several
separate muscles. The two basic sets are the: intermandibularis
anterior and intermandibularis posterior. The intermandibularis pos-
terior in many species is further separated into the intermandibularis
posterior profundus and superficialis.

76 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

The same basic two sets of intermandibulars are recognized in
lizards, where the muscles are generally transverse in position and
usually very wide (Fig. 5). The intermandibularis posterior of lizards
is commonly in several slips that interleave with slips of the cerato-
mandibularis.

INTERMANDIBULARIS ANTERIOR

Synonymy. 1832, Adductor antérieur, Duvernoy. 1889, Interman-
dibularis, McKay. 1914, Intermandibulare antérieur, Phisalix. 1925,
Intermandibularis, 1 and 2, Adams. 1933, Intermandibularis, sym-
physial portion, Lubosch. 1935, Intermandibularis anterior, Edgeworth.
1951, Intermandibularis anterior, Cowan and Hick. 1956, Inter-
mandibularis anterior (parts 3 and 4), Dullemeijer. 1959, Interman-
dibularis anterior, pars cutaneo-mandibularis, Albright and Nelson.

This muscle is present in most snakes, but is distinctly missing in
Anilius and Nenopeltis, and is represented only by a tendon in the
uropeltid Rhinophis. The muscle is generally weakly developed in
boids (sensu lato), although in Eryx, as an exception, the muscle is
large; Trachyboa and Tropidophis the muscle is very slender. In boids
and the genus Cylindrophis, the lateral attachment is to the medial
surface of the tip of the dentary bone. The muscle runs posteriorly
and medially to a midline attachment with its mate on the midventral
raphe.

The intermandibularis anterior is a broad muscle in anomalepidids,
typhlopids, and leptotyphlopids; it is particularly transverse in anoma-
lepidids and typhlopids. The muscle may also exist as several distinct
masses in typhlopids and leptotyphlopids, and these masses are often
at angles to each other (Fig. 10). In anomalepidids, typhlopids, and
leptotyphlopids, the anterior muscle, or muscles, usually attach later-
ally to the medial surface of the dentary but at an appreciable distance
posterior to the tip.

The intermandibularis anterior is well developed and prominent in
the colubrids and poisonous snakes; it is usually in two recognizable
but continuous parts (Fig. 17, C). The anteriormost part (“1” of
Adams, “part 4” of Dullemeijer) is the larger and thicker one. Its
lateral attachment is to the medial surface of the tip of the dentary
and its medial attachment is to the fibrous inter-ramal pad. The
caudal part (“2” of Adams, “part 3” of Dullemeijer) lies more
obliquely and its medial attachment is to its mate at the midventral
raphe.

It is obvious that there has been a distinct trend in certain families
for a reduction in the intermandibularis anterior — Uropeltidae,

THE ASSOCIATED MUSCLES OF THE HYOID 77

Aniliidae, Xenopeltidae, and Boidae (sensu lato). For the Colubridae,
ete., the trends have been toward a more angular position and sub-
division into two continuous but recognizable parts. Particularly in
the Anomalepididae and Typhlopidae the basic lizard condition of
broad, transverse muscles is still pretty much intact.

INTERMANDIBULARIS POSTERIOR PROFUNDUS

Synonymy. 1890, Intermavillaris (part), Hoffmann. 1914, Inter-
mandibularis postérieur, Phisalix. 1925, Adductor medius, Adams.
1933, Intermandibularis, longitudinal portion, Lubosch. 1935, Inter-
mandibularis posterior, Edgeworth. 1951, Intermandibularis posterior,
pars anterior, Cowan and Hick. 1956, Intermandibularis posterior,
Dullemeijer. 1959, Intermandibularis posterior, pars anterior, Albright
and Nelson.

This muscle is found in all snakes examined except the colubrid
Amblycephalus kuangtunensis. It is usually deep to the ceratoman-
dibularis and/or neuromandibularis, or geniohyoideus in anoma-
lepidids. The muscle lies under the neuromandibular tendon and
over the ceratomandibular tendon in typhlopids and leptotyphlopids;
it lies between the geniohyoideus and the slender medial slip of the
geniohyoideus (ceratomandibularis?) in Liotyphlops. As an exception
to the above rule, in the colubrid Haplopeltura boa the intermandibu-
laris posterior profundus, if that is indeed the muscle, lies completely
superficial to the ceratomandibularis (in addition there is another more
posteriorly placed superficial intermandibular muscle).

In anomalepidids, typhlopids, and leptotyphlopids, the lateral at-
tachment is to the ventromedial edge of the mandible. This attach-
ment is directly behind or even sometimes overlapping that of the
intermandibularis anterior. The fibers then run nearly transversely
and between the ceratomandibularis and neuromandibularis (or genio-
hyoideus and slip in anomalepidids) to attach with those of the
muscle’s mate to the midventral raphe.

In uropeltids, aniliids, boids (sensu lato), and xenopeltids, the inter-
mandibularis posterior profundus arises from the mandible at a dis-
tance from the attachment of the intermandibularis anterior. The
direction of fibers is anterior and medial and the muscle always lies
deep to the ceratomandibularis. The medial attachment is to the
midventral raphe with its mate; there is at least a slight overlap with
the fibers of the anterior muscle, where one is present.

In colubrids and the poisonous snakes, the intermandibularis pos-
terior profundus is a stout muscle that attaches to the ventromedial
surface of the mandible at about its middle segment. The muscle is

78 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

missing in the specimen of Amblycephalus kwangtunensis examined.
It is very broad in the colubrid Achrochordus and attaches to the entire
middle third of the mandible. In Haplopeltura boa the lateral attach-
ment is over the external adductor muscle of the lower jaw; the fibers
are bound to the adductor mass and do not affix to bone. In all species
the muscle runs anteriorly and medially to attach to the midventral
raphe with its mate. In the hydrophid Aipysurus the muscle lies be-
tween two slips of the ceratomandibularis; this is the only case found
of such interleaving among colubrids and poisonous snakes. The
intermandibularis posterior is either overlapped by or else overlaps the
ntermandibularis anterior at the midventral line in most species. In
Enhydris, however, there is a gap between the muscles. In Haplopeltura
the situation is unique in having both muscles cross at the midline,
instead of meeting in a raphe, then interweaving, and continuing on to
attach to the opposite mandible just posterior to the attachment of the
intermandibularis anterior.

In the hydrophid Aipysurus a good deal of the medial attachment
of the profundus is to the very long lingual process of this species. This
is the only discovered case among snakes where an intermandibular
affixes to the hyoid.

INTERMANDIBULARIS POSTERIOR SUPERFICIALIS

Synonymy. 1889, Ceratomandibularis, McKay. 1925, Adductor pos-
terior, Adams. 1950, Intermandibulaire superficial, Anthony and Serra.
1951, Intermandibularis posterior, pars posterior, Cowan and Hick.
1959, Intermandibularis posterior, pars posterior, Albright and Nelson.

This muscle is found only in those snakes with a parallel type hyoid,
but it is not universally present in them. The muscle, where present,
always lies superficial to the ceratomandibularis, and it is generally a
thin, strongly aponeurotic structure.

Its lateral attachment is to the posterior end of the ventral surface
of the compound bone. The muscle is rather slender in most species
that have it, although in Thamnophis elegans vagrans (Fig. 16, C) it
is broad; in Thamnophis s. sirtalis (Fig. 16, B) it is narrower. The
muscle runs anteriorly and medially and usually steadily expands in
width anteriorly. The muscle is deep to the constrictor colli if one is
present. Those costocutaneous superior fibers that attach to the hyoid
lie posterior to the swperficialis and so do not cover it.

The anterior third or so of the superficialis is a thin tendon in many
species. The medial attachment is always to the midventral raphe with
its mate, where there is usually some overlap with the intermandibu-
laris anterior; the muscle always is superficial, of course, to the pro-
fundus.

THE ASSOCIATED MUSCLES OF THE HYOID 79

The muscle has been found in the colubrids Amblycephalus, Atre-
tium, Drymobius, Elaphe, Haplopeltura, Heterodon, Natrix, Pliocercus,
Thamnophis, and Xenodon, among others; it has been found in the
erotalid Bothrops and in the viperid Cerastes. Examined specimens
of Achrochordus and Enhydris, of the hydrophids Lapemis and Aipy-
surus, of the elapids Denisonia and Micrurus latifasciata, and of the
erotalids Agkistrodon, Crotalus, and Sistrurus did not seem to have
the muscle. Dullemeijer (1956) did not find one in Vipera berus, but
McKay (1889) did show one in Acanthophis, an elapid. The thinness
plus the subcutaneous position of the muscle made dissection and
identification of it difficult in many specimens, and this may account
for some of the supposed absences of this muscle.

At any rate, there is evidence to show that the swperficialis is of
an inconstant presence in the colubrids; it is mostly absent in the
poisonous snakes, and perhaps altogether in the hydrophids.

HYoOTRACHEALIS

Synonymy. 1815, Retrahens laryngis, Hibner. 1827, Laryngo-
hyoidien, Dugés. 1834, Riickwartszieher des Kehlkopfes, d’Alton. 1839,
Herabzieher des Kehlkopfes, Henle. 1880, Retractor trachea, Minot.
1886, Retractor laryngis, DuBois. 1889, Hyo-trachealis, McKay. 1890,
Hyoideo-laryngeus, Hoffmann. 1898, Hyo-trachealis, Kellicott. 1900,
Retractor laryngis, Goppert. 1929, Laringohyoideus, or retractor tra-
chea, Sewertzoff. 1933, Oesophageotrachealis (probably labeled incor-
rectly), Lubosch. 1935, Hyo-laryngeus, or hyo-trachealis, Edgeworth.
1938, Hyotrachealis, Nishi. 1944, Hyo-glossus (probably in error),
or retractor laryngis, Kesteven. 1956, Tracheo-hyoideus, Dullemeijer.
1958, Tracheo-hyoideus, Dullemeijer. 1959, Hyotrachealis, Albright
and Nelson.

The name hyotrachealis is used instead of hyolaryngeus because the
insertion of the muscle is usually upon what is more properly called
the trachea, rather than upon the specialized part of the air tube
called the larynx. The distinction, however, is not great.

The muscle is found in all snakes; there were no exceptions un-
covered by examination. There are few variations in the position of
the insertion and origin. This muscle is apparently unique to snakes.

Origin. In most snakes the site of attachment is upon the respective
cornu, but there are exceptions.

The anomalepidids, as shown by Lnotyphlops, are an exception:
fibers of the muscle are bound by connective tissue to the ventral
outer surface of the buccal floor lining at a level just anterior to the
hypohyals.

80 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

The typhlopids are another exception: the origin is upon hypaxial
trunk muscles lying over the ends of the rib cage, approximately from
ribs 2 to about 4 or 5. The hyotrachealis is bound by connective
tissue to the muscles.

Leptotyphlopids also are an exception: the origin is again upon the
external aspect of the lining of the ventral buccal floor. The level
in L. maximus is opposite the 1st rib; the site is slightly lateral to the
outer edge of the trachea.

Nearly all of the remainder of snakes have the origin upon the
cornu, generally upon the lateral edge. In the uropeltid Rhinophis
the muscle arises at about the anterior fourth of the cornu, but on
the medial edge.

As for aniliids, Cylindrophis maculatus and rufus both have the
origin on the lateral edge at about the second fourth of the cornu. In
Anilius the origin is more posterior.

Xenopeltis has the origin at about one-third the length of the cornu.
It usually lies farther posterior in boids, at least to the halfway point
or slightly beyond. Tropidophis is unusual in having the origin upon
the deep face of the raphe of the newrocostomandibularis.

In the colubrids and the poisonous snakes, there are a few exceptions
to the otherwise straightforward situation. Heterodon has the origin
upon the muscles of the rib cage; the situation is similar in Pseudaspis.
Agkistrodon is variable: the origin may be either on the rib cage
alone or else also the hyoid. Edgeworth (1935) noted that in Vipera
there is a split origin —one head lies over the rib cage and one at-
taches to the hyoid. In Cerastes the origin is upon the external surface
of the ventral buccal floor lining at the level of the end of the
gemoglossi. Thamnophis may also show a spht origin, one head at-
taching to the hyoid and the other to the deep face of the neuro-
costomandibular inscription (Fig. 16, C).

Course. The muscle runs from the origin anteriorly to the place
of insertion upon the side of the trachea or larynx. In those snakes
where the origin is upon the rib cage, or on the buccal floor, and in
those with the origin on the hyoid of the “V” type, the course is also
somewhat medial. In the parallel type of hyoid, the anterior course
of the muscle, when the origin is on the hyoid, is rather straight
because the lateral edges of the cornua are about on the same line
as the lateral faces of the larynx and trachea.

Insertion. Onto the trachea, or the laryngeal-tracheal region. It is
impossible to set a rigid boundary. Variations are minor.
The insertion of the hyotrachealis is generally dorsal and anterior

THE ASSOCIATED MUSCLES OF THE HYOID $1

to that of geniotrachealis but some genera do have the insertion ventral
to the geniotrachealis instead, e.g., Typhlops, Amblycephalus, Xeno-
peltis, and Agkistrodon piscivorus. A few snakes show a split insertion,
where the hyotracheal fibers attach both dorsal and ventral to the
geniotrachealis; Boa cookvi and Notechis are examples.

Usually the line of insertion is rather perpendicular, or at most
slightly angular, to the tracheal axis. On the other hand, the genio-
trachealis usually has its insertion along a more or less longitudinal
line. Where the hyotracheal insertion is markedly perpendicular, the
fibers attach usually to one tracheal ring alone, and sometimes in
addition upon the ericoid plate of the larynx.

Action. To withdraw the protracted larynx, plus trachea, into the
normal position within the mouth. The geniotrachealis, the protractor,
is a sturdy, strong muscle, with more bulk than the longer, thinner
hyotrachealis. Apparently the natural elasticity of the trachea as-
sists the retractor in pulling the protruded larynx back into the mouth.

Innervation. Contrary to Edgeworth (1935), who had the hyo-
trachealis splitting from the hyoglossus and thus acquiring innervation
from the XIIth, the cranial nerve involved apparently is the Xth. The
vagus nerve basically serves the fourth through sixth arches, from
which the laryngeal cartilages and all the intrinsic laryngeal muscles
are derived. The hyotrachealis would seem to be derived from a
mass splitting from the laryngeal intrinsic muscle primordium and
growing posteriorly to the site of origin. The geniotrachealis develops
with the genioglossus and thus has hypoglossal innervation.

Vogt (1839) had the XIIth serving the muscle. Cowan and Hick
(1951) also considered the muscle as a hypobranchial muscle, served
by the XIIth; they followed Edgeworth. Goppert, however, in 1910
stated that the IXth serves the muscle; since IX and X at least
partially fuse in snakes, his interpretation is understandable.

Actually, in many specimens the dissection does not clearly indicate
the nerve. This is because of the plexus-like arrangement of several
cranial nerves, to wit, IX, X, and XII. The trunks of these nerves
fuse variously, and the branches to various muscles are ascertained
with difficulty. Commonly IX plus the superior laryngeal branch of
X fuse and run forward together with the fibers of XII (anterior
branch); the Xth and the IXth leave to go to the larynx; nerve XII
continues forward to the tongue; the XIIth also serves the genioglossus
and geniotrachealis.

Variation. The variations are in the position of the origin or the
insertion. The muscle itself is of a rather constant form in snakes.

82 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

MISCELLANEOUS MUSCLES

During the course of the dissections, a few other muscles were met
with that were not considered germane to the study. Examples of
these are the: submandibular gland muscles, geniotrachealis, obliquus
abdominis internus, and transversus abdominis. A very short summary
of these muscles follows.

There were also a few muscles that were not identifiable. In the
anomalepidid Liotyphlops there is a muscular sheet between the
descending cornu of the ceratohyal and the recurrent cornu. This
muscle is not named and it is not shown on Figure 7. The direction of
the fibers is anteriorly and medially, and the fibers do not extend the
length of either cornu. There are some small muscles in the anterior
intermandibular region of typhlopids which are presumably part of the
intermandibular series but are not otherwise identified.

Submandibular gland muscles. Along each side of the tongue sheath
at the front of the mouth lies a prominent submandibular gland. There
are muscles associated with this gland in snakes, and there are at least
a pair of them in all species—a “constrictor” of the gland, and
presumably a “dilator.” Some typhlopids, at least, have another muscle
or two attaching to the gland. The muscles are innervated by nerve V.

In most snakes the constrictor attaches to the posterior border or
the posterodorsal border of the gland; the fibers in their course le
against the ventral surface of the gland and attach medially to the
fibrous inter-ramal pad.

The dilator of the gland in most snakes attaches to the posterior
apex of the gland; the fibers then run posteriorly and medially, but
laterally to the genioglossus and geniotrachealis, to attach to the
midventral raphe. This muscle is called the transversus branchialis
by Albright and Nelson (1959) after Cowan and Hick (1951); the
name does not really seem apt. In typhlopids the muscle is not present,
at least recognizably. Instead there is a muscle which runs from the
gland laterally to the dentary; it may have the same function.

Geniotrachealis. This is a constant muscle in snakes. It receives
a hypoglossal nerve supply. The muscle attaches anteriorly to the apex
of the dentary, or to the inter-ramal fibrous pad in some species. In its
course it lies on the lateral surface of the genroglossus. The posterior
attachment is to the trachea, immediately posterior to the larynx. Its
action is to protract the larynx and the following part of the trachea.

Obliquus abdominis internus. This muscle is in all snakes and forms
a sheet across the ventral aspect of the trunk. Fibers arise on the
medial face of the ribs and run anteriorly and medially to attach to
the linea alba.

THE ASSOCIATED MUSCLES OF THE HYOID 83

Transversus abdominis. This muscle also arises from the medial
face of the ribs, but its fibers run posteriorly and medially to attach
to the linea alba. The muscle lies on the deep surface of the obliquus
abdominis internus.

These two abdominal muscles form a double-layered sheet across
the ventral aspect of the trunk. In the Typhlopidae, Leptotyphlopidae,
and those snakes with a parallel type hyoid, the muscular sheets lie
superficial to the rear fraction of the cornua and its attached hyoglossi,
etc. In the snakes with a “V” type hyoid, the sheets he deep to the
cornua and attached hyoglossi.

D. Discussion

Ventral head muscles considered unique to snakes are the hyo-
trachealis, transversus branchialis, costomandibularis, and the neuro-
costomandibularis. Only the hyotrachealis is universal among serpents.

The hyotrachealis muscle, the laryngeal retractor, is of fairly con-
stant form, generally attaching to the hyoid at its posterior end, and
always attaching to the side of the trachea, near the larynx; the
posterior attachment in some species is to the rib cage or pharyngeal
floor. The author could not find a homolog in lizards, either by dis-
section or noted in the literature. Varanus does have a laryngeal pro-
tractor, although most lizards do not, but no retractor was revealed
in spite of careful search in several species. Watkinson (1916) also
recorded no retractor. Apparently the natural elasticity of the tra-
chea is enough to retract it, if the larynx is protracted to any degree
in varanids.

The transversus branchialis seems to have no homolog in lizards.
The muscle unites the two cornua but is of irregular occurrence among
serpents. No importance is attached to the variations.

As a muscle considered to be specially formed from slips of the
costocutaneus inferior, the costomandibularis perhaps deserves no sep-
arate name, but since this muscle has become well developed and
individual, the author feels that it deserves designation. The muscle
is not found in all snakes, being absent in anomalepidids, typhlopids,
and leptotyphlopids. In the uropeltids the muscle is distinct, although
small, and appears to be at its simplest form. The remaining snakes
all have the muscle in one form or another; the muscle arises from
a variable number of ribs and inserts either (1) to the respective cornu
(uropeltids and Cylindrophis rufus), (2) to the mandible (Anilius),
or (3) into the ceratomandibularis (Cylindrophis maculatus); (4)

84 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

most commonly the muscle is a contributor to the newrocostomandibu-
laris complex (the remaining snakes with the muscle).

The neurocostomandibularis formed by the costomandibularis,
ceratomandibularis, and newromandibularis is unique to snakes, al-
though it is by no means universal, being restricted to the xenopeltids,
boids, colubrids, and the poisonous families. Although lizards do not
have this muscle, as far as the author is aware, in Varanus and An-
nella, at least, the newromandibularis partially inserts into the cerato-
mandibularis; it might be noted that this combination of the neuro-
mandibularis plus ceratomandibularis does not exist in snakes. In
uropeltids and aniliids, the neuromandibular tendon overlies the origin
on the mandible of the ceratomandibularis, but no union of the fibers
occurs. Lubosch (1933) reported a union for Cylindrophis rufus, but
in a specimen dissected by the author this was not the case. The
neurocostomandibularis often has one or more distinct tendinous in-
scriptions. Ideally all three contributing muscles attach to the in-
scription, but this is frequently not entirely the case. Many fibers
of one of the muscles often proceed past the inscription to attach to
the mandible or to the cornu, as the case may be.

The ceratomandibularis in lizards is well developed in all species.
It is the superficial layer of the ramus-hyoid group (the deep layer
is the gentohyoideus), and runs from the mandible to the Ist cerato-
branchial; occasionally this main, broad sheet is accompanied by a
medial, slender one. Among snakes the ceratomandibularis is con-
sidered absent in the anomalepidids, where the 1st ceratobranchials
are lacking; however there is a slender, separate muscle in this family
which might possibly be interpreted as being a ceratomandibularis.
The remaining snakes are considered to have the muscle. In the
typhlopids and leptotyphlopids the muscle is very slender and re-
sembles the medial slip of many lizards. In the uropeltids and anilids,
the muscle is relatively broader. In the remainder of the families the
ceratomandibularis is a broad muscle. Lizards all have a generally
broad muscle, and it seems reasonable to suspect that the progenitors
of snakes also did. Following this line of thought, the narrow muscles
of typhlopids and leptotyphlopids and the moderately broad muscles of
uropeltids and aniliids therefore either show reduction in width,
or else merely represent the medial slip as seen commonly in lizards.
Of course, the ceratomandibularis also contributes to the newrocosto-
mandibularis complex where it is present. Dullemeijer (1956) felt
that the rostral part of the ceratomandibularis, as seen in Vipera, is
really a ‘““mylo-hyoid” muscle, belonging to the intermandibular series.

The newromandibularis, another component of the complex, is pres-

(94)
ou

THE ASSOCIATED MUSCLES OF THE HYOID

ent in all snakes save Achrochordus. It is separate in the anoma-
lepidids, typhlopids, leptotyphlopids, uropeltids, and aniliids; in other
snakes the muscle is a major contributor to the newrocostomandibularis.
In lizards the neuwromandibularis is commonly present and separate,
although some union with the ceratomandibularis does take place in
Varanus and Anniella.

The genioglossus is generally similar in lizards and snakes. It par-
tially ensheathes the respective hyoglossus and affords considerable
protractive ability for the tongue. Among snakes, the genioglossus
is relatively the largest in Leptotyphlops. The genioglossus in snakes
originates on the apex of the dentary bone and/or on the inter-ramal
fibrous pad. Genioglossal fibers do not mingle with the intrinsic tongue
muscles but are bound to the tongue by a tough sheath. There are no
special variations worth noting here.

The hyoglossus is similar in both snakes and lizards in several
respects: it is long, it is covered anteriorly by a strong membranous
sheath, it provides much of the tongue musculature, and it attaches
in some way to the hyoid. In lizards the muscles are divergent and
encapsulated, affixing to the divergent Ist ceratobranchials. Among
snakes the muscles are divergent and encapsulated in the anoma-
lepidids, leptotyphlopids, uropeltids, aniliids, xenopeltids, and boids
(sensu stricto), and attach to the divergent 1st ceratobranchials, ex-
cept in the anomalepidids where the divergent muscles attach to the
ceratohyals instead. In the colubrids and poisonous families, the 2nd
ceratobranchials are parallel, and the attaching hyoglossi are encapsu-
lated and juxtaposed. In the typhlopids, the hyoglossal fibers are
parallel, but individually affix to the cornua.

The greatest relative development in the bulk of the hyoglossi is
found in the fossorial typhlopids and leptotyphlopids. In other
snakes, the hyoglossi are routinely relatively long and slender. The
hyoglossi of typhlopids and leptotyphlopids do have a great similarity
in general appearance and form, but vary, as mentioned previously,
in several probably minor ways.

The geniohyoideus is commonly found in lizards, where it exists as
the deep layer of the ramus-hyoid series, running from the mandible
to the ceratohyal. The geniohyoideus is considered absent in all snakes
except the anomalepidids, where it is a broad muscle extending from
the ramus to the hypohyal plus ceratohyal. There is also a slender,
separate muscle in anomalepidids which runs from the ramus to the
end of the recurrent cornu; this is considered a slip of the genio-
hyoideus, but perhaps it is a slip of the ceratomandibularis, otherwise
considered lost in anomalepidids. Since the geniohyoideus and cerato-

86 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

mandibularis are derivatives of the same muscle primordium, the at-
tempt at trying to name certain slips is probably not important.

Also commonly found in lizards is the sternohyoideus; it frequently
is present in several layers. It runs from the sternum to the 1st
ceratobranchial. Only in the typhlopids and leptotyphlopids is there
anything which can be fairly designated the sternohyordeus. In these
snakes it is a very well-developed mass, and since there are no sternal
elements for posterior attachment the fibers attach posteriorly to the
linea alba. The anomalepidids and all other snakes, having lost the
1st ceratobranchials, also have lost the sternohyoideus.

The omohyoideus is generally a large muscle in lizards, running
between the 1st ceratobranchial and the shoulder girdle. The muscle
is considered to be present in a few snakes, but this identity is frankly
not definite: Rhinophis, Cylindrophis rufus and maculatus, Eryx, and
possibly Liotyphlops. In all cases the origin is over the rib cage and
the insertion is on some part of the respective cornu.

A muscle found in all snakes is the costocutaneus superior. This
muscle is for the most part restricted to the trunk, but the anteriormost
fibers do lie on the ventral surface of the head, where they attach
in most snakes to the hyoid, although in some species the fibers le
completely over the hyoid to attach to the mandibles. Examples
of the latter case are leptotyphlopids, typhlopids, uropeltids, Cy-
lindrophis, and the strange colubrid Achrochordus. All lizards, ap-
parently, also have these cutaneous muscles, which are derived from
the rectus superficialis system according to Camp (1923); the fibers,
however, never have attachments on the hyoid in lizards.

The constrictor colli, where present, partly inserts upon the hyoid
in snakes. Indeed, the constrictor may be present or absent in the same
species, apparently. With the lizards, the muscle is probably always
present and always well developed; it also never seems to attach to
the hyoid. The constrictor colli is never a sturdy muscle in snakes
where it is found, and there has been an obvious trend in evolution
for a reduction in the muscle — either entirely or in part.

Intermandibular muscles are present in both snakes and lizards.
In lizards, the intermandibulars are generally broad, straplike muscles
which often interleave with slips of the ceratomandibularis. In
typhlopids, leptotyphlopids, and anomalepidids, the intermandibular
muscles are broad and rather transverse, reminiscent of lizards. In the
other snakes, however, the muscles tend to be more angular in position
and relatively more slender. The intermandibularis anterior is gener-
ally weak or absent in the aniliids, uropeltids, xenopeltids, and boids
(sensu lato). The colubrids and poisonous snakes have both the inter-

THE ASSOCIATED MUSCLES OF THE HYOID S7

mandibularis anterior and intermandibularis posterior profundus well
developed. The intermandibularis posterior superficialis has been
found in many colubrids and has also been found in a viperid and
a crotalid; many colubrids and most poisonous snakes seem to lack
the superficialis.

E. Summary

1. Associated hyoid muscles of the lizard Varanus are the: costo-
cutaneus superior, hyoglossus, genioglossus, ceratomandibularis, neuro-
mandibularis, geniohyoideus, sternohyoideus, omohyoideus, cerato-
hyoideus, intermandibularis anterior and posterior, and constrictor
colli.

2. Associated hyoid muscles of the snakes are the: costocutaneus
superior, hyoglossus, genioglossus, ceratomandibularis, costomandibu-
laris, neuromandibularis, neurocostomandibularis, geniohyoideus, ster-
nohyoideus, omohyoideus, transversus branchialis, hyotrachealis, inter-
mandibularis anterior, intermandibularis posterior, and constrictor
colli. No one species has them all.

3. Muscles unique to snakes, but not found in all species, are the:
costomandibularis, neurocostomandibularis complex, transversus bran-
chialis, and hyotrachealis. The hyotrachealis is the single unique
muscle common to all snakes.

4. The hypobranchial-spinal group of muscles are innervated by the
hypoglossal nerve and spinal nerves and include all the muscles of
No. 2 except the hyotrachealis, intermandibulars, and constrictor colli.

5. Anterior fibers of the costocutaneus superior attach to the hyoid
in most snakes. However, these fibers attach only to the lower jaws
in typhlopids, leptotyphlopids, uropeltids, and the aniliid Cylindrophis.

6. Hyoglossal fibers are parallel in typhlopids, and attach directly
to the cornua. The hyoglossi are divergent and encapsulated in anoma-
lepidids, leptotyphlopids, uropeltids, aniliids, xenopeltids, boids (sensu
stricto), and lizards. The remaining snakes have the hyoglossi parallel
and encapsulated.

7. The genioglossi are similar for all snakes; they actually insert
into the tongue, having no attachment to the hyoid.

8. The ceratomandibularis is found in all snakes save the anoma-
lepidids, perhaps. It runs between the mandible and the cornu, and is
also a part of the neurocostomandibularis where present. The cerato-
mandibularis is narrow in typhlopids, leptotyphlopids, uropeltids, and
aniliids.

88 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

9. The costomandibularis is considered to be formed of modified slips
of the costocutaneus inferior. It is not found in typhlopids, leptotyph-
lopids, and anomalepidids.

10. The neuwromandibularis is found in all snakes, with a possible
exception of Achrochordus. It runs between the dorsum of the neck and
the mandible or the neurocostomandibular inscription.

11. The neurocostomandibularis is a large muscle complex which is
composed of the ceratomandibularis, costomandibularis, and neuro-
mandibularis, in xenopeltids, boids, colubrids, and poisonous snakes.
There is usually a common tendinous inscription.

12. The geniohyoideus is found only in the anomalepidids; it runs
from the mandible to the hypohyal and ceratohyal.

13. The sternohyoideus is found only in the typhlopids and lepto-
typhlopids, where it is very large; it runs from the hyoid posteriorly
to the linea alba.

14. A small muscle reservedly called the omohyoideus is found in a
few snakes of several families. It runs from the rib cage to the cornu.

15. The transversus branchialis connects the two cornua; it is of
erratic distribution in snakes.

16. The hyotrachealis attaches to the trachea and to the cornu in
most snakes; in a few it attaches posteriorly to other neighboring tis-
sues. It is innervated by X.

17. The intermandibulars are innervated by V. The anterior set is
absent or weak in many families; the posterior profundus is always
present and strong; the posterior superficialis is found in many colu-
brids and some poisonous snakes.

18. The constrictor colli is innervated by VII. It is of erratic appear-
ance in snakes; where present it partly attaches to the hyoid in many
snakes.

19. Miscellaneous muscles in the vicinity are the submandibular
gland muscles, geniotrachealis, obliquus abdominis internus, and ab-
dominis transversus.

PART III. PHYLOGENETIC SIGNIFICANCE
OF THE HYOID AND ITS ASSOCIATED MUSCLES
IN SNAKES

A. Discussion

Brief summaries of the hyoid structure and associated muscles of
the lizard Varanus and the families of snakes follow.

1. Varanus: WHyoid—complete basihyal, hypohyals, ceratohyals,
plus 1st ceratobranchials (bony). Costocutaneus swperior does not
attach to hyoid. Hyoglossi divergent, attach to ceratobranchials. Cerat-
omandibularis large, in two slips. Newromandibularis. Geniohyoideus
in two slips. Ceratohyoideus. Sternohyoideus in two layers, super-
ficialis and profundus. Omohyoideus. Intermandibularis anterior and
posterior; broad and transverse.

2. Anomalepididae: Hyoid —basihyal?, hypohyals, ceratohyals
with recurrent cornua; no lingual process; ‘““M” type. Costocutaneus
superior attaches to hyoid. Hyoglossi divergent, encapsulated, attach
to ceratohyals. Ceratomandibularis probably not present. Genio-
hyoideus present, between mandible and hyoid. Sternohyoideus miss-
ing. Omohyoideus? small. Intermandibularis anterior and posterior;
broad and transverse.

3. Typhlopidae: Hyoid — complete basihyal plus 1st ceratobranchi-
als; some parts may be missing in some species; ‘“Y” type; may be
bony. Costocutaneus superior does not attach to hyoid, only to jaws.
Hyoglossi large; parallel fibers attach to hyoid directly. Ceratomandib-

90 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

ularis very slender. Neuromandibularis separate. Sternohyoideus
large, attaches to linea alba. Intermandibularis anterior and posterior ;
broad and transverse.

4. Leptotyphlopidae: Hyoid — like in Typhlopidae, but never re-
duced and never bony. Costocutaneus superior does not attach to
hyoid, only to jaws. Hyoglossi large; divergent muscles encapsulated.
Genioglossi greatly expanded to cover tongue sheath. Ceratomandi-
bularis very slender. Neuromandibularis separate. Sternohyoideus
large, attaches to linea alba. Intermandibularis anterior and posterior;
broad and transverse.

5. Uropeltidae: Hyoid — 1st ceratobranchials only; cornua sepa-
rate; “V” type. Costocutaneus superior does not attach to hyoid.
Hyoglossi divergent. Ceratomandibularis narrow and separate. Neuro-
mandibularis separate. Costomandibularis present and separate, at-
taches to hyoid. Omohyoideus? Intermandibularis posterior profundus
only.

6. Aniliidae: Hyoid — 1st ceratobranchials only; cornua joined or
separate; “V” type. Hyoglossi divergent. Ceratomandibularis rather
broad, separate. Neuromandibularis separate. ANriLIuS — Cornua
united anteriorly. Costocutaneus superior attaches to hyoid. Costo-
mandibularis attaches to mandible. Intermandibularis posterior pro-
fundus only. CyLInpropHis— Hyoid reduced; cornua not joimed
anteriorly. Costocutaneus superior does not attach to hyoid. Costo-
mandibularis attaches to hyoid (rufus), or to ceratomandibularis
(maculatus). Omohyoideus? Intermandibularis anterior weak; inter-
mandibularis posterior profundus well developed.

7. Xenopeltidae: Hyoid — 1st ceratobranchials only; Joined anteri-
orly; “V” type. Costocutaneus superior attaches to hyoid. Hyoglossi
divergent. Neuwrocostomandibularis. Intermandibularis posterior pro-
fundus only.

8. Boidae (sensu stricto): Hyoid—1st ceratobranchials; cornua
joined or separated; “V” type. Costocutaneus superior attaches to
hyoid. Hyoglossi divergent. Neurocostomandibularis. Intermandib-
ularis anterior usually weak; intermandibularis posterior profundus
well developed.

9. Colubridae, Elapidae, Hydrophidae, Viperidae, and Crotalidae:
Hyoid — basihyal plus 2nd ceratobranchials; lmgual process and pos-
sibly complete basihyal sometimes missing; parallel type. Costocu-
taneus superior attaches to hyoid. Hyoglossi parallel and juxtaposed.
Neurocostomandibularis. Intermandibularis anterior and intermandi-
bularis posterior profundus both well developed; an intermandibularis
posterior swperficialis in addition in some species, particularly in the
Colubridae.

PHYLOGENETIC SIGNIFICANCE 91

10. Trachyboa, Tropidophis, and possibly Bolyeria and Casarea:
Same as No. 9, except they have a very weak intermandibularis an-
terior, and the intermandibularis posterior profundus only.

11. Achrochordus (a colubrid genus with many strange features) :
Costocutaneus superior does not attach to hyoid. Newrocostomandib-
ularis absent; ceratomandibularis is separate; apparently no neuro-
mandibularis or costomandibularis.

At this point it is a temptation to suggest a set of superfamilies.
Smith and Warner (1948) prepared such a provisional classification
based on the four types of hyoid form: Anomalepoidea, Typhlopoidea,
Boidoidea, and Colubroidea. At first glance this seems like a very effi-
cient and reasonable classification, but when the associated hyoid
musculature is taken into account, it is not entirely satisfactory.
Rather than prepare another provisional set of superfamilies, the au-
thor chooses to discuss the possible lines of evolution of snakes as
suggested by the hyoids plus their associated muscles. No special
names are proposed for these lines.

First, it seems worthwhile to try to interpolate the hyoid anatomy
of both snakes and lizards, in order to come up with some sort of likely
primitive snake condition. Once having that, the evolutionary lines
can be followed more easily.

From such interpolation, a possible ancestral stock of the snakes
might have had the following anatomy: (a) Hyoid —derived from
arches 2, 3, and 4; complete basihyal, hypohyals, ceratohyals, 1st
ceratobranchials (bony), and 2nd ceratobranchials. (b) Costocutaneus
superior fibers attach to jaws, not to hyoid. (ec) Hyoglossi divergent,
attaching to Ist ceratobranchials. (d) Genioglossus attaches to tip of
dentary. (e) Two ramus-hyoid muscles: a deep geniohyoideus, at-
taching to hypohyal and ceratohyal; a superficial ceratomandibularis,
attaching to Ist ceratobranchial. (f) Two hyoid-pectoral girdle mus-
cles: sternohyoideus and omohyoideus. (g) Neuromandibularis sepa-
rate, attaching to mandible. (h) Geniotrachealis present. (1) Hyotra-
chealis attaches to buccal lining posteriorly. (j) Intermandibularis
anterior and posterior; broad and transverse. (k) Constrictor colli
present, probably not attaching to hyoid.

From this stock, possible evolutionary lines can be worked out with
the evidence offered by the hyoid and its musculature (Fig. 19).

(1) The first line gave rise to the modern anomalepidids; these
changes were made from the primitive stock: (a) Loss of Ist and 2nd
ceratobranchials, and probably the entire basihyal. (b) Costocutaneus
superior fibers affixed to hyoid. (ce) Hyoglosst made new attachments
to the ceratohyals. (d) Sternohyoideus lost. (e) Ceratomandibularis

92 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

apparently lost; there is a slip, separate from the geniohyoideus, which
might represent the ceratomandibularis.

The significant loss in the number of muscles and parts of the hyoid
from the primitive stock seems to indicate that much time passed in
the evolution of the anomalepidid snakes as we see them today. The
unique presence of the presumed geniohyoideus and of a hyoid com-
posed only of 2nd arch derivatives surely indicates that this group is far
removed from other snakes, and that its evolution has been along a
line that diverged early from the primitive snakes.

It is probable that among the forms evolving in the main group of
the primitive stock were those which lost the hypohyals and cerato-
hyals, and the geniohyoideus. It was these snakes which seemed to
have become the main stock. From this stock emerged a second line.

(2) This line later split to give rise to the modern typhlopids and
leptotyphlopids; to give rise to the line, these changes were made from
the primitive stock: (a) Loss of 2nd ceratobranchials. (b) Hyoglosst,
and tongue in general, relatively enlarged. (ce) Ceratomandibularis re-
duced to a slender muscle. (d) Omohyoideus lost.

The typhlopids and leptotyphlopids have not often been considered
closely related, principally because of differences in the skulls. In fact
they have not usually been considered as even having a common
ancestral line. However, evidence presented here is contrary to at least
the latter view. The hyoid of the two families is similar in composi-
tion, and it is morphologically unlike those of other snakes. It is true
that the “V” type cornua are also ist ceratobranchials, but the lingual
process, which is so distinct and usual in the ““Y” type, 1s missing in
the “V” type.

Typhlopids and leptotyphlopids have relatively large hyoglossal
muscles, totally different in general form from other snakes. The two
families both have a very slender, independent ceratomandibularis,
which is unlike that of other snakes. The relatively large, almost mas-
sive, sternohyoideus is unknown for other snakes. These are surely
enough pieces of evidence from the ventral head region to give rise to
a distinct suspicion that these snakes have had a similar ancestry,
which was, itself, on a line removed from the other snakes.

After the emergence of the second line, the main stock had forms
with this anatomy: the sternohyoideus is lost, the intermandibulars
become angular in position, and the hyotrachealis takes attachment to
a cornu; then a new muscle, the costomandibularis, forms from the
costocutaneus inferior. These snakes made up a new or continuing
stock from which emerged a third line.

(3) This line evolved into the modern uropeltids; these changes were

PHYLOGENETIC SIGNIFICANCE 93

made from the stock: (a) Loss of 2nd ceratobranchials and basihyal.
(b) Intermandibularis anterior reduced appreciably. The status of the
uropeltids as a family is by no means clear. There are about six genera
usually recognized as belonging in this family. It may well be that at
least some of these will be found to be more naturally allied with the
aniliids.

Another small line, the fourth, also diverged from this stock.

(4) This line gave rise to the aniliids; these changes were made from
the stock: (a) Loss of 2nd ceratobranchials and basihyal. (b) Cerat-
omandibularis broadened. (c) Intermandibularis anterior reduced.

The relationships of this group as a natural family are also ques-
tioned. The aniliidae is usually formed of three genera. Two are
South Asiatic — Anomalochilus (not seen) and Cylindrophis — and
one is South American — Anilius. Cylindrophis differs from Anilius in
several outstanding ways, indicating at least a subfamily division.
Cylindrophis has an edentate premaxilla, a coronoid bone, a divided
anal, and scale pits. Anilius shows the opposite condition for each of
these traits.

In any case the aniliids probably have a close alliance with the
uropeltids, and this seems borne out by comparing the generally similar
hyoid anatomy of the two families.

A major anatomical and evolutionary event then occurred in the
stock by the formation of the newrocostomandibularis, a composite
muscle which was made up of the ceratomandibularis, costomandib-
ularis, and neuromandibularis. The remainder of the snakes, with the
exception of Achrochordus, all have this distinct composite muscle.

The stock is now considered to have consisted of snakes with a
hyoid composed of a basihyal, Ist and 2nd ceratobranchials, and with
a neurocostomandibularis, as well as costocutaneus superior, constrictor
colli, intermandibulars, ete. This stock is also considered to have been
the fifth line of evolution.

(5) This line, or stock, gave rise to the xenopeltids and the boids
(sensu lato); there was a general reduction in the intermandibularis
anterior.

Then, one line came off this stock which retained the 2nd cerato-
branchials but lost the Ist pair; these snakes became the genera
Trachyboa, Tropidophis, Bolyeria, and Casarea. The hyoglossi became
juxtaposed and attached to the cornua.

The rest of the stock lost the 2nd ceratobranchials and the basihyal;
this line further split to give rise to the boids (sensu stricto) and the
xenopeltids. In the xenopeltids the intermandibularis anterior was
totally lost.

94 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Frankly, the position of the four genera named above is once again
noted as uncertain and puzzling. These snakes seem boidlike in most
characteristics, and certainly have the general habitus of boas. Yet
their remarkable possession of a parallel type hyoid cannot be easily
discounted. Trachyboa and Tropidophis lack a coronoid bone in the
mandible, whereas Anthony and Guibé (1952) reported that Bolyeria
and Casarea have a coronoid, as the greater number of the true boids
do. Anthony and Guibé proposed the subfamily Bolyerinae, under
Boidae, for these two genera. This brief discussion of these four genera
merely points up the fact that the anatomical information about them
is incomplete.

The genus Xenopeltis has long been assigned its own monogeneric
family, chiefly for the reason of its having a peculiar lower jaw —
there being an intercalated coronoid bone and a movable dentary.
There has been a view toward grouping this species with Loxocemus, a
neotroprical genus sometimes recognized as the only new world python
(Haas, 1955). The two snakes differ in lower jaws — Loxocemus being
boidlike — but have certain other things in common: premaxillary
teeth present, two functional lungs, free projecting tabular bones. Haas
disclosed that the two also have similarities in cranial musculature in-
volving the adductor externus, and a double depressor mandibulae.
He decided that Loxocemus should be regarded as having split off from
the stock where the Xenopeltidae and the Boidae have diverged. The
anatomy of the hyoid may not be particularly significant as regards
the NXenopeltis-Loxocemus relationship. Nenopeltis lacks the inter-
mandibularis anterior, but otherwise, like Loxocemus, has a true boid
type of musculature associated with the hyoid.

It appears to the author that the snakes with the “V” type hyoid,
plus Trachyboa, etc., are the ones which present the greatest number
of problems in defining families and familial relationships.

From the stock of the fifth line, another line diverged which became
very important and produced the majority of snakes; this was the
sixth line.

(6) This line gave rise to the colubrids, elapids, hydrophids, viperids,
and crotalids; these changes were made from the stock: (a) Loss of
Ist ceratobranchials. (b) Hyoglossi became juxtaposed and attached
to 2nd ceratobranchials. (c) Intermandibularis posterior superficialis
added for some species. (d) Intermandibularis anterior enlarged.

The apparently aberrant genus Achrochordus has a strange and
unique set of muscles: the newromandibularis and costomandibularis
have been lost, the intermandibularis posterior profundus is extremely
broad, and the costocutaneus superior fibers attach to the mandibles

PHYLOGENETIC SIGNIFICANCE 95

and therefore overlay the hyoid. This genus surely represents a case of
losses and modifications of muscles.

The five families included as being derived from the sixth line have
a great deal in common, and obviously stand independently of the rest
of the snakes — with the possible exception of the genera T'rachyboa,
ete. The five families have been variously interpreted by many
authors, so that it is easy to find in the literature different familial
classifications. For example, a number of genera lumped together into
the Colubridae here have often been separated into their own families,
such as the Achrochordidae, Amblycephalidae, Dasypeltidae, ete. The
Elapidae, Hydrophidae, Viperidae, and Crotalidae also have been con-
sidered conservatively herein.

Some authors, e.g., Dowling (1959), have made the hydrophids a
subfamily, Hydrophinae, in the Elapidae, and the pit vipers a sub-
family, Crotalinae, in the Viperidae.

In examining the preceding phylogenetic patterns it becomes obvious
that reductions and losses have largely characterized the evolutionary
history of the hyoid and its associated muscles in snakes. Furthermore,
it is herein considered that some of the reductions and losses of the
same muscles or parts of the hyoid occurred in different lines, and
therefore more than once in the phylogenetic scheme (parallelism or
convergence). For example, it seems likely that loss of the 4th branchial
arch components — 2nd ceratobranchials — occurred in the line that
gave rise to the typhlopids and leptotyphlopids, also in the small lines
that gave rise, respectively, to the uropeltids and aniliids, and in the
line of the stock which gave rise to the true boids and xenopeltids.
There are other examples among the musculature.

The costomandibularis is the single new muscle that appeared, and
it really is a modification of another muscle — the costocutaneus in-
ferior —that was already present. The neurocostomandibularis was
formed as an amalgamation of three muscles already there but sepa-
rate. Another noteworthy modification was the shift in the posterior
attachment of the hyotrachealis from the buccal mucosa to the avail-
able cornu.

The phylogenetic tree proposed, and shown diagrammatically in
Figure 19, is of course based on the hyoid and its musculature. By
altering the emphasis on hyoid form and the muscles, it would be easy
to come up with another diagram that differed in some parts if
probably not in all. For example, it might be considered that the di-
vergence of the lines of snakes with the parallel type hyoid occurred
much earlier from the stock than is shown on the plate. The formation
of the neurocostomandibularis, which occurs in the parallel type as

96 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

well as in many of the snakes with the “V” type hyoid, would then
be considered a matter of convergence.

Comparison of the diagrammatic tree illustrated in Figure 19 with
several in the literature does not show many differences. Mahendra
(1938) based his diagram mainly on osteological characters, and his
diagram is not remarkably different from the author’s. He did not
recognize the Anomalepididae, and he considered Leptotyphlopidae
and Typhlopidae as unrelated families coming off a stock in quite
separate directions; these are the outstanding exceptions to the author’s
diagram. Schmidt’s (1950) diagram is much like Mahendra’s, although
he recognized the Achrochordidae as a separate family.

Bellairs and Underwood (1951) summarized the anatomy of snakes
and its phylogenetic importance. They also prepared a phylogenetic
diagram, which differs in some respects from the one shown in Figure
19. For one thing, they included the anomalepidids with the typhlopids.
Dowling (1959) in his review of the studies on the relationships of
snakes prepared a diagram on the bases of adaptiveness to habitat
and of morphological characters. His diagram differs in some ways
from the author’s: he did not recognize the anomalepidids, and he sup-
ported the view that the boids are the primitive and generalized snakes,
with the other snakes having radiated away from them.

Because so much, if not all, of the phylogenetic study of snakes must
depend upon interpreting the modern species alone, the past history
will always be one of debate and conjecture. For example, in Dowling’s
work he uses the boids as primitive snakes, but there seems to be no
good reason why modern boids should be a great deal like the actual
primitive stock. The modern species must surely be thought of as
having changed from earlier forms, and in this way are not the truly
primitive animals that he, and others, have made them out to be.
Indeed, as far as the hyoid and its musculature are concerned, the
modern-day boids, either in the restricted or in the broad sense, show
no more proof of being what the primitive snakes must have been like
than other snakes.

As far as the phylogeny of snakes goes, the truth is that the number
of snake families, or natural groups, is obviously rather small, no
matter how one interprets the classification. About twelve families
conservatively, and perhaps fifteen liberally, are about all that one has
to work with. Certainly the reasonable ways in which the phylogenetic
relationships can be figured out are limited. No wonder that all the
phylogenetic diagrams are liable to have many resemblances.

Perhaps the most interesting families of snakes, phylogenetically,
are the so-called blind snakes — Anomalepididae, Typhlopidae, and

PHYLOGENETIC SIGNIFICANCE 97

Leptotyphlopidae. They are small, highly adapted to a burrowing
existence, and superficially resemble each other as well as many limb-
less lizards. Up to 1939 the anomalepidids had been included with the
typhlopids, but Taylor in that year proposed the new family Anomale-
pididae by reasons of the cephalic squamation and the presence of
teeth on both jaws. In comparison, Typhlops has an edentate lower jaw
and Leptotyphlops has an edentate upper jaw.

McDowell and Bogert (1954) included the anomalepidids under the
Typhlopidae (as Dowling also did later). Partly because of this surely
erroneous inclusion certain of their conclusions are without good foun-
dation. Their inadequate handling of the hyoid apparatus, treated in
the first part of this paper, is a case in point. Underwood (1957) in
his critique of the former’s paper added a number of personal, and
new, observations on the anatomy of blind snakes which serve to point
up the need for a more thorough anatomical study of these animals.

McDowell and Bogert (1954) concluded that “typhlopids” are really
not snakes; leptotyphlopids were included in the snakes, however.
Moreover they believed that the typhlopids “are even more distinct
from leptotyphlopids than from the typical snakes.” However, at
least four (Nos. 5, 6, 7, 10) of the ten features that they listed on p. 86
as being unique to “typhlopids” are actually based on anomalepidids.
List (1966), after a thorough, comprehensive study of the skeleton of
the blind snakes, was convinced that the anomalepidids deserve family
rank. The work presented herein supports that view and furthermore
tends to show that the anomalepidids are snakes, but have evolved
along an entirely different line than the rest of the snakes.

The similarity in hyoids and associated muscles of Leptotyphlops
and Typhlops has been shown; a common derivation is indicated.
Underwood (1957) discussed similarities of the two families and de-
cided that the two might well have diverged from a common ancestor.

List and Underwood, in their respective papers, both discounted
most of McDowell and Bogert’s differences of Typhlopidae from
snakes in a broad sense. Again, the confusion caused by inclusion of
the anomalepidids discounts some of McDowell and Bogert’s points.
Underwood presented a list of features in which Typhlops is definitely
snakelike; e.g., the eye structure, thymus bodies, anal glands, platytra-
bie skull, and the facial artery’s course. With such characters as these,
plus presence of several snakelike characteristics of the ventral head
musculature, viz. hyotrachealis, strong development of the costocuta-
neus superior fibers, and reduced constrictor colli, a case for including
Typhlops with the snakes is definitely strong. This also holds for
Leptotyphlops.

98 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

In looking among the lizards for some clues as to the ancestry of
snakes, several problems are immediately evident. One is that since
modern snakes have evolved, or changed, from their ancestors, then it
is only fair to suggest that the lizards which gave rise to these an-
cestors also have changed to some degree. Therefore, it is hard to
believe that we can discover the ancestors to the serpents among the
modern species of lizards. But, of course, we may find evidence that
certain living species of lizards are the probable descendants of the
ancestors of snakes. In effect, by studying the modern species one is
only observing the current end points of evolution in snakes and
lizards.

Another problem which obscures the attempt to unravel the origin
of snakes is that of convergence. There are many examples of this
between lizards and snakes: loss of limbs and girdles, skull modifica-
tions of various sorts, ete.

No lizard is particularly like snakes in both the hyoid and the ven-
tral head muscles. However, Anniella, of the anguinomorphan family
Anniellidae, has a simple, inverted Y-shaped hyoid, obviously composed
of a basihyal with lingual process, and two attached 1st ceratobranchi-
als, which is very similar to that of Leptotyphlops and Typhlops. The
musculature includes the genioglossus, divergent hyoglossi, a well-
developed sternohyoideus (which possibly might be an omohyoideus),
a broad ceratomandibularis with a neuromandibularis partially at-
tached, constrictor colli not attached to hyoid, and broad transverse
intermandibulars; there is no laryngeal protractor or retractor.

The musculature does not precisely recall the condition in any snake,
including T’yphlops and Leptotyphlops. Naturally the main difference
is that Anniella lacks the hyotrachealis, as well as the geniotrachealis
— both present in the snakes. Excluding these important differences,
there is at least some resemblance to the typhlopids in muscles present.
There is also a certain similarity to Cylindrophis, which lacks, though,
the sternohyoideus (omohyoideus?) found in Anniella. Loss of the
basihyal of the aniellid hyoid would certainly leave a hyoid structure
very much like that in Cylindrophis (and others), of course.

But although Anniella shows other snakelike tendencies, such as the
eye covered by a scale, loss of temporal arches, and near limblessness,
it still retains enough lizard ones to suggest only convergence with
snakes rather than close relationship.

McDowell and Bogert (1954) suggested that ‘‘snakes are derived
from platynotan (Varanus-like) lizards.” In particular they found that
Lanthanotus is very similar to Leptotyphlops in many ways. With
respect to varanid-lke lizards as snake ancestors, Underwood (1957)

PHYLOGENETIC SIGNIFICANCE 99

found fault in many points, and finally decided that it was, in 1957,
too early in the course of phylogenetic studies to decide upon the
ancestry of snakes. It is probably still too early.

The hyoid and associated muscles in Varanus, as well as in most
lizards, are much more elaborated than in snakes. Comparison of
Varanus with snakes reveals that if a series of losses and reductions
in the hyoid anatomy of Varanus were made, a possible snakelike type
could be produced. The trouble with this view is that the same could
be said about a great many lizards! A point, though, that may indi-
cate modern varanids have evolved from types close to the ancestry of
snakes is the presence of a laryngeal protractor, which has not yet been
found in other lizards.

There is a considerable amount of literature concerning the an-
cestry of snakes. Much of this literature has centered on trying to
derive the snakes from platynotan lizards. The subject of the origin
of snakes has only been touched upon in this paper. The most compre-
hensive review of the literature on the subject is by Bellairs and Under-
wood (1951), who, themselves, were not at all convinced that snakes
were derived from platynotan lizards; Underwood (1957) later re-
emphasized that stand.

B. Summary

1. Characteristics of the hyoid and its associated musculature are
listed for the recognized families of snakes, and for the lizard Varanus.

2. Primitive snake stock might have had this anatomy: hyoid of
basihyal, hypohyals and ceratohyals, Ist and 2nd ceratobranchials;
two ramus-hyoid muscles, at least two girdle-hyoid muscles, hyotra-
chealis, geniotrachealis, costocutaneus superior attaching to mandi-
bles, constrictor colli, transverse intermandibulars.

3. A phylogenetic tree for snakes has been worked out on the basis
of their hyoid anatomy. This tree consists of a more or less main
stem or stock from which six lines of snakes have evolved.

4. The first line gave rise to the anomalepidids with their distinctive
“M” type hyoid and geniohyoideus, etc.

5. The stock lost the 2nd arch cornua. From this new stock evolved
the line which gave rise to the typhlopids and leptotyphlopids, with
their distinctive “Y” type hyoid and sternohyoideus, ete.

6. The stock lost the sternohyoideus and gained the costomandib-
ularis. A third, small line gave rise to the uropeltids, with their

reduced “V” type hyoid and intermandibularis anterior.

100 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

7. A fourth line emerged from the stock to give rise to the aniliids,
also with a reduced “V” hyoid, and with a broad ceratomandibularis.

8. A major event in the phylogeny was the formation of the newro-
costomandibularis. The stock itself had a reduction in the intermandib-
ularis anterior and formed the fifth line, which gave rise in one
direction to the true boids and xenopeltids, with a “V” hyoid type,
and in another direction to the genera Bolyeria, Casarea, Trachyboa,
and Tropidophis, with their parallel hyoid.

9. The sixth line, given off from the stock with the neurocostoman-
dibularis, lost the 1st ceratobranchials; this line gave rise to the
colubrids, elapids, hydrophids, viperids, and crotalids, with their paral-
lel hyoid and large, angular intermandibulars.

10. Reductions and losses have largely characterized the above
phylogenetic tree. Only the costomandibularis is a “new” muscle and
it is only a modification of one already present.

11. A brief discussion is given of other recent efforts in phylogenetic
studies of snakes.

12. The thesis that anomalepidids are distinct from typhlopids, and
the thesis that these two families are snakes, are substantiated.

13. The past, generally unsatisfactory search among modern lizards
for the ancestors of snakes is not helped much by the study of the
hyoid anatomy. It seems obvious that both modern snakes and lizards
have changed to some degree from their antecedents, making the
search very difficult.

LITERATURE CITED

Adams, L. A. 1925. Correlations of the musculature and the movements of
the skull in Natriz, with some suggestions of homology in the lacertilians.
Jour. Morph., 41: 159-181.

Albright, R. G., and E. M. Nelson. 1959. Cranial kinetics of the generalized
colubrid snake Elaphe obsoleta quadrivittata, I and Il. Jour. Morph.,
105: 193-292.

Anthony, J., and J. Guibé. 1952. Les affinités anatomiques de Bolyeria et de
Casarea (Boidés). Mem. Inst. Sci. Madagascar, Serie A, Vol. VII (2):
189-201.

Anthony, J., and R. G. Serra. 1950. Anatomie de l’appareil de la morsure
chez Eunectes murinus. Rev. Brasil. Biol., 10 (1): 23-44.

1951. Particularités anatomiques de l’appareil de la morsure chez

Constrictor constrictor et chez Epicrates crassus. Rev. Brasil. Biol., 11

(2): 203-210.

. 1955. Anatomie de l’appareil de la morsure chez Xenodon merremu.
Arq. Mus. Nac. Rio de Janeiro, 42 (1): 21-47.

Backstrom, K. 1931. Rekonstruktionsbilder zur Ontogenie des Kopfskelettes
von Tropidonotus natrix. Acta Zool., 12: 83-144.

Beebe, W. 1944. Field notes on the lizards of Kartabo, British Guiana, and
Caripito, Venezuela. Part 2, Iguanidae. Zoologica, 28: 195-216.

Bellairs, A. d’A., and G. Underwood. 1951. The origin of snakes. Biol. Rev.,
26: 193-237.

Bendz, H. 18438. Bidrag til den sammenligende anatomie af nervus glosso-
pharyngeus, vagus accessorius willis og hypoglossus, hos Reptilierne. K.
Danske Vidensk. Selsk., Afh. x: 113-152. (Not seen.)

101

102 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Buffa, P. 1904. Ricerche sulla muscolatura cutanea dei serpenti e con-
siderazioni sulla locomozione di questi animali. Atti Accad. sci. ven.-trent.-
istr., I: 145-228.

Camp, C. L. 1928. Classification of the lizards. Bull. Am. Mus. nat. Hist.,
48: 289-480.

Chaine, J. 1900. Anatomie comparée de certains muscles sushyoidiens. These
de la faculté des Sciences de Paris. (Not seen.)

Cope, E. D. 1900. The crocodilians, lizards, and snakes of North America.
Rept. U.S. Nat. Mus., 1898.

Cowan, I., and W. B. Hick. 1951. A comparative study of the myology of
the head region in three species of Thamnophis. Trans. roy. Soc. Canada,
Series III, 45 (5): 19-60.

Cuvier, G. 1836. Lecons d’anatomie comparée. Ed. 2. Bruxelles.

D’Alton, E. 1834. Beschreibung des Muskelsystems eines Python bivittatus.
Arch. Anat. Phys. wiss. Med.: 347-364, 432-450, 528-542.

DeBeer, G. R. 1937. The development of the vertebrate skull. Oxford Press,
London.

DeJong, J. K. 1924. Die Entwicklung der Zungenscheide bei Schlangen.
Tijdschr. ned. dierk. Ver., (2) 19: 107-125.

Dowling, H. G. 1959. Classification of the Serpentes: A critical review.
Copeia, 1959 (1): 38-52.

Dubois, E. 1886. Zur Morphologie des Larynx. Anat. Anz., 1: 225-235.

Dugés, A. 1827. Recherches anatomiques et physiologiques sur la déglutition
dans les reptiles. Ann. Sci. nat., 12: 337-395.

Dullemeijer, P. 1956. The functional morphology of the head of the common
viper (Vipera berus (L.)). Arch. neérl. Zool., 11: 387-497.

1958. A comparative functional-anatomical study of the heads of
some Viperidae. Morph. Jahrb., 99: 881-985.

Duméril, A., and H. Jacquart. 1865. Mémoire sur la déglutition chez les
ophidiens. Jour. l’anat. physiol., (11): 56-71.

Dunn, E. R., and J. A. Tihen. 1944. The skeletal anatomy of Liotyphlops
albirostris. Jour. Morph., 74: 287-290.

Duvernoy, G. L. 1832. De la langue, considerée comme organe de prehension
des alimens. Mém. Soc. Hist. nat. Strasbourg, Book I, Vol. I., 20 pp.

. 1832a. Mémoire sur les caractéres tires de l’anatomie pour distinguer
les serpens venimeux des serpens nonvenimeux. Ann. Sci. nat., 26: 113-
160.

Edgeworth, F. 1935. The cranial muscles of vertebrates. Cambridge Uni-
versity Press, Cambridge.

El-Toubi, M. R., and I. M. A. Magid. 1961. A comparative study of the
cranial osteology of the Egyptian vipers. Jour. Arab. Vet. Med. Assoc.,
21: 303-325.

Evans, H. E. 1955. The skeleton of Typhlops jamaicensis. Anat. Rec., 122:
381-396.

Fairley, N. H. 1929. The dentition and biting mechanism of Australian snakes.
Med. Jour. Australia, 1: 313-327.

LITERATURE CITED 103

Firbringer, M. 1922. Das Zungenbein der Wirbeltiere. Abhandl. Heidelberger
Akad. Wiss. Math-naturwiss., Kl. B., Abh. 11: 1-164.

Gaupp, E. 1904. Das Hyobranchialskelett der Wirbeltiere. Erg. Anat. entw.-
gesch., 14: SO8-1048.

Gnanamuthu, C. P. 1937. Comparative study of the hyoid and tongue of some
typical genera of reptiles. Proc. zool. Soc. London, (B) 107: 1-63.

Goéppert, E. 1900. Der Kehlkopf der Reptilien. Morph. Jahrb., 28: 1-27.

Haas, G. 1931. Die Kiefermuskulatur und die Schidelmechanik der Schlangen.
Zool. Jahrb. Anat., 53: 127-198.

1955. On the skull muscular anatomy of Lorocemus. Amer. Mus.
Novit., 1748: 1-8.

Hager, P. K. 1906. Die Kiefermuskeln der Schlangen, und ihrer Beziehungen
zu den Speicheldriisen. Zool. Jahrb. Anat., 22: 173-224.

Henle, J. 18389. Vergleichend-anatomische Beschreibung des Kehlkopfes. Leip-
zig. (Not seen.)

Hershkowitz, J. 1941. On the finer structure of the tongue of Lichanura
roseofusca. Jour. Morph., 68: 71-80.

Hoffmann, C. K. 1890. Reptilien, in Bronn’s Klassen und Ordungen des
Thierreiches, 6 (3). C. F. Winter, Leipzig.

Hubner, F. 1815. De organis motoriis Boae caninae. Diss. Berlin. (Not seen.)

Humphry, G. 1872. On the disposition of muscles in vertebrate animals.
Jour. Anat. Phys., 6: 293-376.

Kallius, E. 1901. Beitrige zur Entwicklung der Zunge. I. Teil Amphibien und
Reptilien. Anat. Hefte, 16: 529-760.

Kamal, A. M., and H. G. Hammouda. 1965. The development of the skull
of Psammophis sibilans. Jour. Morph., 116: 197-296.

Kellicott, D. S$. 1898. The dissection of the ophidian. Columbus.

Kesteven, H. L. 1944. The evolution of the skull and the cephalic muscles.
Aust. Mus. Mem. 8 (3): 1383-268.

Kochva, E. 1962. On the lateral jaw musculature of the Solenoglypha. Jour.
Morph., 110: 227-284.

List, J. C. 1966. Comparative osteology of the snake families Typhlopidae
and Leptotyphlopidae. Illinois Biological Monographs, No. 36. University
of Ilhnois Press, Urbana.

Losana, M. 1832. Essai sur l’os hyoide de quelques reptiles. Accad. Redle
Sci. Torino, 37: 1-24.

Lubosch, W. 1933. Untersuchungen iiber die Visceralmuskulatur der Saurop-
siden. Morp. Jahrb., 72. 584-666.

. 1938. Muskeln des Kopfes: Viscerale Muskulatur, in Bolk, Goppert,

Kallius, and Lubosch. Handbuch vergl. Anat. Wirbeltiere, V: 1011-1105.

Urban and Schwarzer, Berlin.

Ludwig Ferdinand vy. Bayern. 1884. Zur Anatomie der Zunge. T. Riedel,
Munchen.

Mahendra, B. C. 1938. Some remarks on the phylogeny of the ophidia. Anat.
Anz., 86: 321-368.

104: THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

McDowell, 8. B., and C. M. Bogert. 1954. The systematic position of
Lanthanotus and the affinites of the anguinomorphan lizards. Bull. Am.
Mus. nat. Hist., 105 (Art. 1): 1-142.

McKay, W. J. 1889. Osteology and myology of the death adder (Acanthophis
antarctica). Proc. Linn. Soc. N.S. Wales, 4: 893-986.

Minot, C. S. 1880. Studies on the tongue of reptiles and birds. Ann. Mem.
Boston Soc. Nat. Hist., 20 pp.

Mosauer, W. 1935. The myology of the trunk region of snakes and its sig-
nificance for ophidian taxonomy and phylogeny. Publ. Univ. California
L.A., 1: 81-120.

Nishi, 8. 1916. Zur vergleichenden Anatomie der eigenteilichen (genuinen)
Ruckenmuskeln. Morph. Jahrb., 50: 167-318.

. 1938. Muskeln des Kopfes, parietale Muskulatur, in Bolk, Goppert,
Kallus, and Lubosch. Handbuch vergl. Anat. Wirbeltiere, V: 447-466.
Urban and Schwarzer, Berlin.

Oelrich, T. 1956. The anatomy of the head of Ctenosaura pectinata. Misc.
Publ. Mus. Zool. Univ. Michigan, No. 94: 1-122.

Owen, R. 1866. On the anatomy of vertebrates. Vol. I, Fishes and Reptiles.
Longmans, Green and Co., London.

Parker, W. K. 1878. On the structure and development of the skull in the
common snake. Phil. Trans. roy. Soc. London, 169 (2): 3885-418.

Peyer, B. 1912. Die Entwicklung des Schadelskelets von Vipera aspis. Morph.
Jahrb., 44: 563-621.

Phisalix, M. 1914. Anatomie comparée de la téte et de Vappareil venimeux
chez les serpents. Ann. Sci. nat. Zool., 9th Serie, 19.

Pringle, J. A. 1954. Cranio-development in some South African snakes. Proc.
zool. Soc. London, 123: 813-865.

Radovanovic, M. 1935. Anatomische Studien am Schlangenkopf. Jena. Z.
Naturw., 69: 321-422.

Rathke, H. 1839. Entwickelungsgechichte der Natter (Coluber natriz).
Borntriger, Konigsberg.

Reese, A. M. 1932. The development of the snake’s tongue. Anat. Anz., 74:
207-218.

Richter, H. 1933. Das Zungenbein und seine Muskulatur bei den Lacertilia
vera. Jena. Z. Naturw., 66 (3): 395-480.

Romer, A. 8. 1956. Osteology of the reptiles. University of Chicago Press,
Chicago.

Rouvieré, H. 1906. Etude sur le devéloppement phylogénique de certains
muscles sus-hyoidiens. Jour. l’anat. physiol., 42: 487-540.

Schmidt, K. P. 1950. Modes of evolution discernible in the taxonomy of
snakes. Evol., 4 (1): 79-86.

Sewertzoff, S. A. 1929. Zur Entwicklungsgeschichte der Zunge bei den Rep-
tilien. Acta zool., 10: 231-341.

Smith, H. M., and R. Warner. 1948. Evolution of the ophidian hyobranchium
and its bearing on classification. Herpetologica, 4 (6): 189-193.

LITERATURE CITED 105

Sondhi, K. 1958. The hyoid and associated structures in some Indian reptiles.
Ann. Zool., Agra, II (11): 155-239.

Srinivasachar, H. R. 1954. Observations on the development of the chondro-
cranium in Vipera. Anat. Anz., 101: 219-225.

Stannius, H. 1846. Lehrbuch der vergleichenden Anatomie der Wirbeltiere.
Berlin. (Not seen.)

Stokely, P. 1947. Limblessness and correlated changes in the girdles of a
comparative morphological series of lizards. Am. Midl. Nat., 38: 725-754.

Taylor, E. H. 1939. Two new species of the genus Anomalepis Jan, with a
proposal of a new family of snakes. Proc. New Eng. zool. Club, 17: 87-96.

Teutleben, E. von. 1874. Uber Kaumuskeln und Kaumechanismus bei den
Wirbelthieren. Arch. Naturgesch., 40: 78.

Underwood, G. 1957. Lanthanotus and the anguinomorphan lizards: a critical
review. Copeia, No. 1: 20-31.

Versluys, J. 1936. Kranium und Visceralskelett der Sauropsiden, in Bolk,
Goppert, Kallius, and Lubosch, Handbuch vergl. Anat. Wirbeltiere, IV:
699-808. Urban and Schwarzer, Berlin.

Vogt, C. 1839. Zur Neurologie von Python tigris. Arch. Anat. Phys. wiss.
Med.: 39-58.

Walter, F. 1887. Das Visceralskelet und seine Muskulatur bei den einheimi-
schen Amphibien und Reptilien. Jena. Z. Naturw., 14: 1-45.

Warner, R. 1946. Pectoral girdles vs. hyobranchia in the snake genera Lio-
typhlops and Anomalepis. Science, 103 (2686): 720-723.

Watkinson, G. B. 1906. The cranial nerves of Varanus bivittatus. Morph.
Jahrb., 35: 450-472.

Wiedemann, E. 1932. Zur Ortsbewegung der Schlangen und Schleichen.
Zool. Jahrb., Abt. Zool., 50: 557-596.

Willard, W. A. 1915. Cranial nerves of Anolis carolinensis. Bull. Mus. comp.
Zool., 59: 17-116.

Zavattari, E. 1910. I muscoli ioidei dei sauri in rapporto. Parte I, Accad.
Reale Sci. Torino, Ser. 2a, 60: 351-392. 1911. Parte II, 61: 55-135.

; 4 bods wy us — = Se,
Cad e Ae ey at, ae 47)
7 sey Tek, itt ea ie dite ty .
4 4 ~_ t si ve aa ¢ i ci aae i ty he voy 8

Sol Afrne Soares =) os ty

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}

—
2

1
ef j
i

Explanation for Figures

The head muscle figures are of the ventral view unless otherwise
stated. Abbreviations used in the figures are:

bhy
Icb
IIeb
eel

basihyal

1st ceratobranchial

2nd ceratobranchial
costocutaneus inferior
costocutaneus superior
ceratomandibularis
ceratomandibularis,
medial slip

ceratohyal
cervicomandibularis
constrictor colli
constrictor of submandib-
ular gland
costomandibularis
dilator of submandibular
gland

unnamed muscle
geniohyoideus
geniohyoideus, medial slip
genioglossus
genioglossus, medial slip
geniotrachealis

hel
hhy
htr
ima
imp

ims
int

neu
omo
pro

rq
sh
ste
step
stes

sub
tbr

hyoglossus

hypohyal

hyotrachealis
intermandibularis anterior
intermandibularis
posterior profundus
intermandibularis
posterior superficialis
obliquus abdominis
internus
neuromandibularis
omohyoideus

processus lingualis
(lingual process)
retractor quadratus
sheath of tongue
sternohyoideus
sternohyoideus profundus
sternohyoideus

super ficialis

-submandibular gland

transversus branchialis

107

108

Figure 1. Various hyoids (some with only one side shown). Figures A-G are
hzards; H, J-M are snakes.

A —Varanidae: Varanus (from Gnanamuthu).

B —TIguanidae: Anolis chrysolepis (from Beebe) X6. A complete lizard
hyoid.

C —Amphisbaenidae: Amphisbaena darwini (from Richter) X10.
D — Anguidae: Gerrhonotus multicarinatus (from Cope).

EK — Geckonidae: Gehyra oceanica (from Richter) X2.

F —Scincidae: Mabowia carinata (from Richter) X2.

G — Xenosauridae: Xenosaurus grandis (from Camp) X2.

H —Anomalepididae: Liotyphlops albirostris X15. “M”’ type.

J —Typhlopidae: Typhlops schlegeli mucruso X11. “Y” type.

K — Leptotyphlopidae: Leptotyphlops maximus X7. “Y” type.

L — Boidae: Sanzinia madagascariensis X21. “V” type.

M — Crotalidae: Bothrops mexicanus 1%. Parallel type.

109

110

Ficurre 2. Various hyoids. A-E are lizards; F-H, J, K are snakes. Rib ends
are shown in the figures of snake hyoids. The bar represents 1 mm.

A —Anniellidae: Anniella pulchra (from Cope). Hypohyals and ceratohyals
not present.

B —Lanthanotidae: Lanthanotus borneensis (after McDowell and Bogert).
C —Anguidae: Anguwis fragilis (from Cope).

D — Helodermatidae: Heloderma suspectum (from Cope).

K —Amphisbaenidae: Rhineura floridana (from Cope). Ceratohyals prob-
ably not present.

F —Typhlopidae: Typhlops reticulatus (from List) X18. Note separation
of 1st ceratobranchials from basihyal.

G —Typhlopidae: Typhlops pusillus (from List) X18. 1st ceratobranchials
only.

H —Typhlopidae: Typhlops polygrammicus (from List) <8. Basihyal alone?
J —Leptotyphlopidae: Leptotyphlops dulcis dissectus (from List) X20.

K — Leptotyphlopidae: Leptotyphlops phenops (from List) x8.

Ars

oe Gs
uz

112

Fiaure 3. Various snake hyoids (from Smith and Warner). Sequential dashes
at left of drawing are corresponding ventral margins. The bar in drawing H
represents 10 mm. All drawings are approximately natural size.

A — Colubridae:
B — Colubridae:
C — Colubridae:
D — Colubridae:
E — Colubridae:
F — Colubridae:
G — Colubridae:

Salvadora grahamiae hexalepis.
Opheodrys vernalis.

Storeria dekayi.
Sibynomorphus catesbyi.
Tropidonotus natrix.

Tantilla gracilis.

Sonora s. semiannulata.

H — Elapidae: Micrurus fulvius.

114

Figure 4. More hyoids of various snakes (also from Smith and Warner).

drawings are approximately natural size. These genera are all colubrids.

A — Elaphe guttata.

B —Lampropeltis d. doliata.

C — Diadophis punctatus edwardsii.
D — Cerberus rhynchops.

E — Farancia abacura reinwardtit.
F — Coluber constrictor priapus.

G — Natriz s. sipedon.

H —Chersydrus granulatus.

J — Rhadinaea flavilata.

All

116

Ficure 5. Anniellidae: Anniella pulchra nigra (UI 4460) ; an anguinomorphan
lizard.

A — Ventral view. The constrictor colli is removed on both sides. The right
side shows the deep layer. The posthyoid muscle named the sternohyoideus
(ste) may be the omohyoideus. Note the simplified hyoid with only the Ist
ceratobranchials present as cornua. X13

B— Right lateral view. There is a snakelike arrangement of the cervico-
mandibularis (emn), and of what seems to be the neuwromandibularis (neu).
Note the slender cartilage, which apparently represents the scapula-procora-
coid, to which attaches the muscle designated as the sternohyoideus. 7

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Pe a0

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—[—=
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118

Ficure 6. Varanidae: Varanus monitor (UI 37536); a platynotan anguino-
morph.

A — Right lateral view. Note the distinct cervicomandibular and neuromandib-
ular muscles, and the hyoid with two pairs of cornua. 2.5

B— Ventral view. The constrictor colli and intermandibulars are removed.
Middle layer at left, deep at right. Note the two pairs of the geniohyoideus
(geh and geh’) inserting on the ceratohyal, and the neuwromandibularis par-
tially inserting into the ceratomandibularis (cer). The presence of a geniotra-
chealis (gtr) without a hyotrachealis is interesting and unique. 3.2

LLL

Zn eu

chy

LS)

Ficure 7. Anomalepididae: Lnotyphlops albirostris (MCZ 25232) X27. Note
the heavy geniotrachealis (gtr). The hyotrachealis (htr) attaches posteriorly
to the buccal floor. The intermandibulars are broad and generally transverse.
The geniohyoideus is prominent and runs between the lower jaw and the
hypohyal and ceratohyal. A slender muscle which is marked “cer” may well
represent a greatly reduced ceratomandibularis; it attaches posteriorly to the
recurrent cornu; the Ist ceratobranchial is of course missing in this family.
The hyoglossus (hgl) attaches posteriorly to the ceratohyal.

” 4

5 ss
PX pee een Sy

a2 & :

D $

rR ne

122

Ficure 8. Typhlopidae: Typhlops bibront (CNHM 17718) X7.

A— The costocutaneus superior muscles (ccs) are entirely removed in the
main figure, but are shown intact in the lower left inset. The intermandib-
ulars (ma and imp), constrictor colli, and neuromandibularis, are removed
at the right. The sternohyoideus is completed in (B). The slender tendon of
the ceratomandibularis is shown at the left; it is sectioned at the right.

B— Detail of the hyoid and the attached muscles. The fibers of the sterno-
hyoideus attach posteriorly to the midventral raphe. Note that the fibers of
the hyoglossi are always parallel and attach directly to the cornua.

Figure 9. Typhlopidae: Typhlops schlegeli mucruso (CNHM 81018).

A — Costocutaneus superior is removed. Deep layer is at the right. Note that
the hyotrachealis (htr) has a posterior attachment over the rib cage. 7
B— Completion of the tongue and hyoglossi, and showing the hyoid with
attached muscles. The sternohyoid fibers affix posteriorly to the midventral
raphe, but some of the fibers end blindly. Details of the sternohyoid attach-
ments to the hyoid are shown in the two small figures at the right. <7

C — The costocutaneus superior is shown intact. 3.5

125

rt re
+ Se ZK ET D

She ea ‘SH 5 i So ee oe
Sy WZ d z
eiNrs = LE 0 s = . <e
Z <i Aguiyis re say

Rt! : i , <e , Hj She sipesoes ous we Srey
fag =a ae ERIN oeaccaciaitein SSUZASOTAHATATA ee

ran Brae

126

Figure 10. Leptotyphlopidae: Leptotyphlops maximus (CNHM 38282) X11.

A — Costocutaneus superior is removed. Deep layer is at the right. Obliquus
internus (int) is removed at the right. The small inset at lower left shows the
costocutaneus superior intact; note the sample of ventral scale impressions on
the muscle.

B—Completion of the tongue and hyoglossi, and the sternohyoideus, which
has been shortened for the figure. Part of the sternohyoid fibers attach to the
midventral raphe, but the rest end blindly.

C — Genioglossus and sternohyoideus removed to show the bifurcate hyoglossi

and their relation to the hyoid. The hyoglossal fibers are parallel to the
cornua and are also encapsulated.

128

Figure 11. Uropeltidae: Rhinophis blythi (CNHM 25930) X12. The origin
of the costocutaneus superior on the jaw remains at the right. Note the large
omohyoideus-like muscle (omo). The intermandibularis anterior (ima) is
represented by a thin tendon. The neuromandibularis is separate, and the cera-
tomandibularis is reduced. The inset shows the costocutaneus superior intact.

129

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mime

130

Figure 12. The following all belong to the Anilidae.

A—Anilius scytale (CNHM 35683) 2.5. The hyotrachealis and the trans-
versus branchialis (tb) are sectioned at the right. The costomandibularis (cos)
is present. The neuwromandibularis is separate. Note that there is no inter-
mandibularis anterior.

B— Cylindrophis rufus (CNHM 67269) X38. The costocutaneus superior is
cut at the left. Note that some fibers of the ceratomandibularis run between
the cornua to end at the midventral raphe. The transition from costocutaneus
inferior (eci) to costomandibularis is shown. The intermandibularis anterior
is a very slender muscle. The inset shows the hyoid and its attached muscles
in detail.

C— Cylindrophis maculatus (MCZ 15795) 5. The costocutaneus superior
is cut at the left. The hyoid cornua are much reduced and so are the cera-
tomandibular slips attaching to each cornu. The costomandibularis joins the
ceratomandibularis, but the neuromandibularis is still separate. The inter-
mandibularis anterior is small.

131

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SSS Eee

Ficure 13. Xenopeltidae: Xenopeltis wnicolor (CNHM 15273) X3.5. Note
the lack of an intermandibularis anterior. The most important thing to ob-
serve 1s the presence of a neurocostomandibularis muscle, a complex which is
contributed to by the ceratomandibularis, neuromandibularis, and costomandib-
ularis. Note, however, that the costomandibular slip lies deep to the other
two contributing muscles.

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134

Ficure 14. The following all belong to the Boidae (sensu stricto).

A— Python sebae 2.4. Most costocutaneus superior fibers are removed.
The basihyal is definitely lacking. The intermandibularis anterior is weak.
There is still some overlap in the neurocostomandibular complex.

B—Eryz c. colubrinus (CNHM 81224) X2.4. All costocutaneus superior
fibers are removed; they attach to the hyoid. There is a small muscle present
which is conveniently called the omohyoideus. Note the spinal nerves lying
upon the internal oblique. The inset at the right shows the hyoglossus and
hyoid relationship plus the attachment of the hyotrachealis.

C— Epicrates cenchris (CNHM 31143) X1.9. The costocutaneus superior
fibers are particularly well shown here at left; ventral scale impressions upon
the fibers are illustrated. Note the well-developed neurocostomandibularis. The
costomandibularis has two slips. The inset at the right shows the attachments
of the hyotrachealis and the hyoglossus to the hyoid cornu.

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136

Figure 15.

A—Boidae (sensu lato): Tropidophis maculatus (USNM 56328) X4.6.
Note the weak intermandibularis anterior. The parallel type of hyoid and the
juxtaposed hyoglossi are of course important to notice. The neurocostomandib-
ularis is well developed and essentially presents a single layer. The hyotra-
chealis is omitted from the figure.

B—Colubridae: Achrochordus javanicus (CNHM 67268) 3.2. This colu-
brid has a remarkable set of independent variations: the very expansive
costocutaneus superior, with which the cervicomandibularis (not shown) par-
tially intertwines laterally; the independent ceratomandibularis; there seems
to be no neuromandibularis or costomandibularis. The hyoid and hyoglossi
are not shown completely, and the hyotrachealis is omitted. The intermandib-
ulars are relatively very large in this species.

C—Colubridae: Atretiwm schistosum (MCZ 1330) X3.7. Note the inter-
mandibularis posterior superficialis (ims) and the strong intermandibularis
anterior. There is a well-formed newrocostomandibularis with a distinct in-
scription. The hyoid cornua and hyoglossi are incomplete in the figure.

138

Ficure 16. The following all belong to the Colubridae.

A — Heterodon p. platyrhinos *2. Note the origin of the costomandibularis
from ribs 1-8, which are shown free from parietal muscles. The first slip of the
costocutaneus inferior is from rib 9. A small slip of the ceratomandibularis
passes external to the cornu to insert on the midventral raphe. The hyotra-
chealis is not shown. The hyoid and the hyoglossi are incomplete posteriorly.
B—Thamnophis s. sirtalis X3.4. A right lateral view. Note the distinct
tendinous inscription in the newrocostomandibularis. The constrictor colli is
very thin.

C—Thamnophis elegans vagrans 2.5. The innervation pattern is rather
completely shown; the common nerve trunk, composed of nerves X and XII
(and IX), is illustrated. The upper right inset shows a submandibular gland
with its dilator and constrictor muscles. The lower right inset shows the split
origin of the hyotrachealis; the ceratomandibularis is shown transparent; one
head of the hyotrachealis attaches to the tendinous inscription of the neuro-
costomandibularis. The hyoid and hyoglossi are incomplete posteriorly.

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140

Ficure 17.

A—Elapidae: Denisonia par (CNHM 41978) X2.3. The nerves are clearly
shown, particularly the large branch to the tongue entering just anterior to
the junction of the hyoglossus with the tongue sheath.

B—Hydrophidae: Aipysurus eydouxau (CNHM 11572) X34. There is no
apparent constrictor colli. Note the ceratomandibularis at the left and the
way part of it interleaves once with the intermandibularis posterior profundus
(amp). The cornua and hyoglossi are incomplete in the figure.

C — Viperidae: Cerastes vipera (CNHM 63115) X1.8. There is no dissect-
able constrictor colli. Many of the nerves are shown. Note the intermandib-
ularis posterior superficialis.

141

142

Ficure 18.

A —Crotalidae: Bothrops mexicanus X1.4. The intermandibularis posterior
superficialis is large.
B—A drawing of the ventral head region in a hypothetical primitive snake,
whose anatomy of the region is suggested by structures found in living snakes
and lizards. While this is only a presumed construction, it does satisfy condi-
tions which have been indicated by a study of the hyoid and associated muscles
in snakes. Note: the complete type of hyoid — basihyal, hypohyals, cerato-
hyals, Ist and 2nd ceratobranchials; the broad constrictor colli (inset); two
ramus-hyoid muscles — ceratomandibularis and geniohyoideus; at least two
posthyoid muscles — sternohyoideus (shown in two layers here, superficialis
and profundus), and omohyoideus; a separate neuromandibularis; the hyo-
trachealis, which attaches to the buccal floor; the broad, largely transverse
intermandibulars. The inset also shows a probably extensive costocutaneus
superior which likely would he superficial to the hyoid. The sternohyoidei and
the omohyoideus are shown incomplete posteriorly.

The hyoglossi are divergent and attach to the 1st ceratobranchials, which are
presumed to have been bony.

as
sone

144

Ficure 19. A diagram of a phylogenetic arrangement of the present-day
families of snakes which has been derived from the study of the hyoid appa-
ratus and its associated musculature. The diagram is also based on an assump-
tion of a monophyletic origin for snakes.

This diagram does not try to give a true relative picture of the possible
relationships of the various lines of evolution. For example, the black lines
merely indicate in a roughly relative way the numbers of genera and species
composing each family, and the vertical, or temporal, scale has no actual
definition.

Major events concerning the evolution of the hyoid and its musculature
are indicated by the rings along the main trunk and the offshoots. The six
lines of evolution which have been derived for the phylogeny of snakes are
noted by small numerals at the appropriate places.

Note: for Anomalepidae read Anomalepididae.

145

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INDEX

The f denotes that the page indicated is a figure page. The s means
that the name is a synonym on the indicated page.

Acanthophis antarctica: hyoid of, 31;
muscles of, 79

Achalinus spinalis: hyoid of, 23

Achrochordus javanicus: hyoid of, 23,
f137; muscles of, 59, 60, 61, 63, 66,
67, 69, 78, 79, 84, 86, 88, 90, 93,
136, £137; phylogenetic position of,
94-95

Adductor antérieur, s76

Adductor medius, s77

Adductor posterior, 78

Adelphicos veraepacis nigrilatus: hy-
oid of, 23

Agkistrodon contortrix: hyoid of, 34,
38; muscles of, 59, 68, 73, 79

Agkistrodon piscivorus: hyoid of, 35,
38; muscles of, 81

Aipysurus eydouxi: hyoid of, 33, 140,
f141; muscles of, 51, 54, 59, 73, 78,
79, 140, f141

Amblycephalus kuangtunensis: hyoid
of, 23; muscles of, 73, 77-79, 81

Amblycephalus stanleyi: hyoid of, 23-
24

Amphisbaena darwini: hyoid of, 7-8,
18, 108, £109

Amphisbaenidae: hyoid of, 7-8, 18,
108, £109, 110, f111

Anguidae: hyoid of, 108, £109, 110,
f1l11

Anguis fragilis: hyoid of, 110, f111

Aniliidae: hyoid of, 12, 20-21, 36, 41-
42, £131; muscles of, 51, 57-58, 60,
62-63, 65, 77, 80, 84, 86-87, 130,
f131; summary, 90; evolution of,
93, 100

Anilius scytale: hyoid of, 20, 36;
muscles of, 58, 60, 62, 65-66, 72, 76,
77, 80, 83; summary, 90; relation-
ships of, 93

Anniella pulchra: hyoid of, 7-8, 10,
14, 110, f111; muscles of, 49, 61, 71,
116, {117; comparison with snakes,
98

147

148

Anniellidae: comparison with snakes,
98; hyoid of, 110, f111; muscles of,
RTGS 7

Anolis: hyoid of, 18, 21

Anolis chrysolepis: hyoid of, 108, £109

Anomalepididae: hyoid of, 8-9, 19,
35, 41-42, 108, £109; muscles of, 51-
55 passim, 57, 60, 62-65 passim, 68,
70-71, 76-77, 79, 85-88 passim, 120,
f121; summary, 89, 99; evolution
of, 91; blind snake relationships of,
96-97; as snakes, 97, 100

Anomalepis: muscles of, 69

Anomalochilus: relationships of, 93

Aparallactus capensis: hyoid of, 24

Apostolepis quinquelineata: hyoid of,
24

Aspidelaps scutatus: hyoid of, 31

Aspidites melanocephalus: hyoid of,
AAI|

Aspis cerastes: hyoid of, 34, 38

Atheris nitschei: hyoid of, 34, 38

Atlanto-epistropheo-hyoideus, s73

Atractaspis microlepidota: hyoid of,
34, 38; muscles of, 59

Atretium schistosum: hyoid of, 24,
f137; muscles of, 57, 64, 73, 79, 136,
£187

Basihyal: in lizards, 6-7, 39, 41, 89,
98, £109, f111; in snakes, 9-18 pas-
sim, 36-42 passim, 89-90, 110, £111;
in primitive snakes, 91, 99; in
snake evolution, 93

Bitis cornutus: hyoid of, 34, 38

Bitis nasicornis: hyoid of, 34, 38

Blind snakes: relationships of, 96-97

Boa: hyoid of, 12, 39

Boa canina: hyoid of, 21

Boa cooku: hyoid of, 21; muscles of,
81

Boidae: hyoid of, 12, 108, £109; mus-
cles of, 62, 74-75, 84

Boidae (sensu lato): hyoid of, 21-23;
muscles of, 60, 62, 64, 76-77, 86,
136, £1387; evolution of, 93

Boidae (sensu stricto): hyoid of, 21-
23, 36, 41-42; muscles of, 51, 59,
85, 87, 134, £135; summary, 90;
evolution of, 93, 100

THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Boiga dendrophila latifasciata: hyoid
of, 24, 38

Bolyeria: hyoid of, 13, 36, 40, 42;
summary, 91; evolution and rela-
tionships, 93-94, 100

Bothrops atrox: hyoid of, 35

Bothrops mexicanus: hyoid of, 35,
108, {109; muscles of, 51, 59, 68,
73, (9; 142) fas

Branchio-mandibularis (part), s64

Branchiomandibularis spinalis, s56

Bungarus multicinctus: hyoid of, 32

Calabaria reinhardti: hyoid of, 21

Calliophis macclellandu: hyoid of, 32

Carphophis amoena vermis: hyoid of,
24

Casarea: hyoid of, 18, 36, 40, 42;
summary, 91; evolution and rela-
tionships of, 93-94, 100

Causus rhombeatus: hyoid of, 15, 34,
38

Cerastes vipera: hyoid of, 34, 38,
f141; muscles of, 59, 64-65, 79, SO,
140, £141

Ceratoglossus, s52

Ceratohyal: in lizards, 6-7, 41, 48,
f109, 110; in snakes, 9-18 passim,
52, 54, 68, 82, 85, 88, 89, f109; in
primitive snakes, 91, 99; in snake
evolution, 92

Ceratohyoideus: in Varanus, 48, 89;
missing in Anniella, 49

Ceratomandibularis: historical, 44; in
Varanus, 48; in Anniella, 49; snake
account of, 55-60, s78; discussion
of, 84; in lizards, 84; summary, 87,
89-91; in primitive snakes, 91; in
phylogeny, 92-93, 100

Cerato-vaginiens, sd2

Cerberus rhynchops: hyoid of, 24, 37,
114, f115; muscles of, 73

Cervico-hyoideus, s61, s63, s66

Cervico-mandibulaire (?), s60

Cervicomandibularis: in snakes, 61-
63 passim, 69; in lizards, 61, 63

Cervico-maxillaire, s60

Cervico-maxillaris, s60

Charina bottae: hyoid of, 12, 21

Chersodromus liebmanni: hyoid of,
24, 38

Chersydrus granulatus: hyoid of, 24,
38, 114, £115

Chondropython viridis: hyoid of, 21-
22

Chrysopelea ornata: hyoid of, 24

Clelia clelia: hyoid of, 24

Coluber constrictor constrictor:
oid of, 25

Coluber c. flaviventris: hyoid of, 25

Coluber c. priapus: hyoid of, 114,
f115

Colubridae: hyoid of, 23-31, 37-38,
ie iors 114, 9115; £137,
£139; muscles of, 51, 59, 64, 77, 79-
80, 86, 1386, £137, 138, f189; sum-
mary, 90; evolution of, 94, 100

Coniophanes imperialis copei: hyoid
of, 25, 37

Coniophanes i. proterops:
Loney

Conophis lineatus concolor: hyoid of,
25

Conopsis biserialis: hyoid of, 25

Constrictor colli: in Varanus, 49; in
Anniella, 49; snake account of, 73-
75; discussion of, 86; summary of,
87-88; in primitive snakes, 91, 99

Constrictor colli oralis and aboralis,
s73

Constrictor constrictor orton: hyoid
of , 22

Costocutaneus inferior: in snakes, 64,
68, 92

Costocutaneus superior: historical,
45; in Varanus, 48; in Anniella, 49;
snake account of, 66-69; discussion
of, 86; summary of, 87, 89-91; in
primitive snakes, 91, 99; in phy-
logeny, 91-94 passim

Costohyoideus, s64

Costomandibulaire (part), s55

Costo-mandibulaire (part), s63, s64

Costomandibularis: snake account of,
63-66; discussion of, 83-84; sum-
mary of, 87-88, 90-91; in primitive
snakes, 91; in phylogeny, 92-95
passim, 100

Costomandibularis (part), s55

Costo-mandibularis, s63, s64

Costo-mazillaire (part), s63

hy-

hyoid of,

INDEX 149

Costo-maxillien, s63

Crotalidae: hyoid of, 34-35, 38, 41-
42, 108, £109; muscles of, 51, 59, 64,
68, 73, 79-SO, {143; summary, 90;
evolution of, 94, 100

Crotalus cerastes: hyoid of, 35

Crotalus pricei pricei: hyoid of, 35

Crotalus tigris: hyoid of, 35

Crotaphopeltis hotamboeia hotambo-
ela: hyoid of, 25

Cutaneus externus, s66

Cyclagras gigas: hyoid of, 25

Cylindrophis: hyoid of, 36; muscles
of, 70-71, 76, 87, 88; summary, 90;
relationships of, 93, 98

Cylindrophis maculatus: hyoid of, 20,
36; muscles of, 58, 60, 62, 65, 67,
69, 72, 80, 86, 130, f131

Cylindrophis rufus: hyoid of, 20-21;
muscles of, 51, 60, 62, 65-66, 67, 72,
80, 83-85, 130, £131

Dasypeltis scaber: hyoid of, 15, 25

Demansia nuchalis: hyoid of, 32

Dendraspis viridis: hyoid of, 82

Dendrophidion vinitor: hyoid of, 25

Denisonia par: hyoid of, 832; muscles
of, 79, 140, f141

Depressor mandibulae, s61

Der grosse, aussere oder Seitenhaut-
muskel, s66

Diadophis punctatus arnyi: hyoid of,
2D

Diadophis punctatus edwardsu: hyoid
of, 25-26, 114, {115

Dibamus: hyoid of, 7, 14

Digastrique (?), s61

Dipsadoboa unicolor: hyoid of, 26

Dispholidus typus: hyoid of, 26

Doliophis bilineatus: hyoid of, 32;
muscles of, 73

Dromophis lineatus: hyoid of, 26

Drymarchon corais erebennus: hyoid
of, 26

Drymobius bifossatus: hyoid of, 26,
38

Drymobius margaritiferus margariti-
ferus: hyoid of, 26, 38; muscles of,
79

Dryophis mycterizans: hyoid of, 26

150

Echis carinatus: hyoid of, 34, 38

Elaphe: hyoid of, 16, 37

Elaphe guttata: hyoid of, 26, 114,
PS

Elaphe laeta: hyoid of, 26

Elaphe obsoleta obsoleta: hyoid of, 26

Elaphe obsoleta quadrivittata: mus-
cles of, 72, 79

Elaphe vulpina: hyoid of, 26

Elapidae: hyoid of, 31-33, 38, 41-42,
112, f113, f141; muscles of, 64, 73,
79, 140, f141; summary, 90; evolu-
tion of, 94, 100

Elapomorphus nuchalis: hyoid of, 26

Elapops modestus: hyoid of, 26

Elaps lacteus: hyoid of, 32

Elapsoidea sundervalli fitzsimonsi:
hyoid of, 32

Enhydris enhydris: hyoid of, 27, 37;
muscles of, 51, 59, 73, 78, 79

Enhydris plumbea: hyoid of, 27, 37

Enulius unicolor: hyoid of, 27

Enygrus bibroni: hyoid of, 22

Epicrates: hyoid of, 12, 22

Epicrates angulifer: hyoid of, 12, 22

Epicrates cenchris: hyoid of, 12, 22;
muscles of, 57, 66, 68, 74-75, 134,
£135

Eryx colubrinus colubrinus: hyoid of,
22; muscles of, 50, 70-71, 76, 85,
134, £135

Eryx jaculus: hyoid of, 22

Eryx john: hyoid of, 22

Eunectes gigas: hyoid of, 22

Facial nerve (VII): for constrictor
coli, 74

Farancia abacura abacura: hyoid of,
27, 37

Farancia abacura reinwardtu: hyoid
Oe 2iot, 114 fh

Ficimia publia: hyoid of, 27

Fimbrios klossi: hyoid of, 27; mus-
cles of, 78

First ceratobranchial: in lizards, 6-7,
48-49, 89, 98, £109, 110, f111; in
snakes, 9-18 passim, 36, 40-42, 56,
58, 84-86, 89-90, 94, 100, £109, 110,
f111; in primitive snakes, 91, 99

Furina annulata: hyoid of, 32

THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Geckonidae: hyoid of, 108, £109

Gehyra oceanica: hyoid of, 7, 12, 108,
£109

Genio-costalis, s63

Genio-glosse, s49, s50

Genioglossus: in Varanus, 48; in An-
niella, 49; snake account of, 49-51;
discussion of, 85; summary of, 87,
90; in primitive snakes, 91

Genioglossus profundus (geniovagina-
lis), s50

Genio-hyo-glossus, s50

Geniohyoideus: in Varanus, 48; miss-
ing in Anniella, 49; snake account
of, 54-55; discussion of, 85-86;
summary of, 87-89; in primitive
snakes, 91, 99; in phylogeny, 92, 99

Genio-hyoideus, s50

Geniohyoideus plus mylohyoideus, s56

Genio-hyoidien, s56

Genio-lateralis, s61

Geniotrachealis: in Varanus, 49; dis-
cussion of, 82; summary of, 88; in
primitive snakes, 91, 99

Geniovaginalis, s50

Genio-vaginien, s49

Genio-vaginiens, s50

Geophis semidoliatus: hyoid of, 27

Gerrhonotus multicarinatus: hyoid of,
7-8, 12, 108, £109

Haldea striatula: hyoid of, 27, 38

Haldea valeriae elegans: hyoid of, 27,
38

Haplopeltura boa: hyoid of, 27; mus-
cles of, 73, 74, 77-78, 79

Hautmuskel, s66, s73

Helminthophis flavoterminatus: hy-
oid of, 19

Heloderma suspectum: hyoid of, 7,
110, f111

Helodermatidae: hyoid of, 110, f111

Hemachatus hemachates: hyoid of,
HSS Sy Biss

Hemibungarus kelloggi: hyoid of, 32

Herabzieher des Kehlkopfes, s79

Heterodon nasicus nasicus: hyoid of,
27

Heterodon platyrhinos platyrhinos:
hyoid of, 27, 38, £189; muscles of,
59, 73, 79, 80, 138, £139

Homalopsis buccata: hyoid of, 28

Hydrophidae: hyoid of, 33-34, 38,
41-42, f141; muscles of, 51, 54, 59,
64, 73, 78, 79, 140, f141; summary,
90; evolution of, 94, 100

Hydrophis cyanocinctus:
33; muscles of, 73

Hyoglosse, s52

Hyoglossus: attaches to hyoid, 39; in
Varanus, 48; in Anniella, 49; snake
account of, 52-54; discussion of,
85; summary of, 87, 89-90; in
primitive snakes, 91; in phylogeny,
91-94

Hyo-glossus (?), s79

Hyoideo-laryngeus, s79

Hyoid of lizards: basic form of, 6-8,
39; composition of, 6-8; in Va-
ranus, 89; figured, 108-111

Hyoid of snakes: defined, 1-2; posi-
tion of, 2, 5-6; form of, 5-6; com-
position of, 8-18; types listed, 8;
“M” type, 8-9, 19, 35, 41, 99; “Y”
type, 9-12, 19, 35-36, 40-41, 43, 99;
“V” type, 12-13, 19-23, 36, 41, 99-
100; parallel type, 13-18, 23-35, 36-
38, 41-42, 100; descriptions of, 19-
35; variations of, 35-38; functions
of, 38-39, 42; phylogenetic signifi-
cance of, 39-43, 91-99 passim;
primitive form of, 39; evolutionary
trends of, 40-43; summary of, 87-
88, 89-90; in primitive snakes, 91,
99; evolutionary lines of, 91-94;
figured, 108-115

Hyo-laryngeus, s79

Hyomandibular (?), s56

Hyo-maczillaire superficiel, s56

Hyotrachealis: historical, 44; snake
account of, 79-81; discussion of, 83;
summary of, 87-88; in primitive
snakes, 91, 99; in phylogeny, 92, 95

Hyotrachealis (?), s52

Hyo-trachealis, s79

Hyo-vaginien, s52

Hypoglossal nerve (XII): for genio-
glossus, 52; for hyoglossus, 53; for
geniohyoideus, 54; for ceratoman-
dibularis, 56, 59-60; for sternohyoi-
deus, 70

hyoid of,

INDEX 151

Hypohyal: in lizards, 6-7, 41, 48, 89;
in snakes, 9-18 passim, 40, 41-42,
54, 68, 85, 88, 89; in primitive
snakes, 91, 99; in snake evolution,
92; figured, 109, 110

Iguanidae: hyoid of, 108, £109

Intermandibulaire superficial, s78

Intermandibulare antérieur, s76

Intermandibularis, s76

Intermandibularis anterior: in Va-
ranus, 49; in Anniella, 49; snake
account of, 76-77; discussion of, 86-
87; summary of, 87-91; in primi-
tive snakes, 91; in phylogeny of
snakes, 93-94, 99-100

Intermandibularis anterior, pars cu-
taneo-mandibularis, s76

Intermandibularis, longitudinal por-
tion, s77

Intermandibularis postérieur, s77

Intermandibularis posterior, s77; in
Varanus, 49, 89; in Anniella, 49;
summary of, 87-88; in primitive
snakes, 91

Intermandibularis posterior, pars an-
terior, s77

Intermandibularis posterior, pars pos-
terior, s78

Intermandibularis posterior profun-
dus: snake account of, 77-78; dis-
cussion of, 87, 90-91; in Achro-
chordus, 94

Intermandibularis posterior swperfi-
cialis: snake account of, 78-79;
discussion of, 87; in phylogeny, 94

Intermandibulars: in snakes, 75, 99-
100; in lizards, 76; discussion of,
86; in primitive snakes, 99

Intermazxillaris (part), s77

Kerilia jerdonu: hyoid of, 33, 38
Kieferzungenbeinmuskel, s55

Lachesis muta: hyoid of, 35

Lampropeltis: hyoid of, 37

Lampropeltis calligaster: hyoid of, 28

Lampropeltis doliata doliata: hyoid
of, 28, 114, £115

152 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Lampropeltis elapsoides
hyoid of, 28

Lampropeltis getulus holbrooki: hy-
oid of, 28

Lampropeltis g. splendida: hyoid of
28

Lampropeltis knoblochi: hyoid of, 28

Lamprophis: hyoid development of,
15

Lanthanotidae (Lanthanotus — bor-
meensis). shyoldsOlaee WO ssf ble
similar to leptotyphlopids, 98

Lapemis hardwicki: hyoid of, 33;
muscles of, 54, 79

Laringohyoideus, s79

Laryngohyoidien, s79

Laticauda colubrina:
muscles of, 59, 73

Latissimus ingluviei s. platysma myoi-
des, 844, s55

Leptodeira maculata: hyoid of, 28

Leptodeira septentrionalis polysticta:
hyoid of, 28

Leptomicrurus narducci: hyoid of, 32

Leptophis diplotropis: hyoid of, 28

Leptophis mexicanus mexicanus: hy-
oid of, 28

Leptotyphlopidae (Leptotyphlops):
hyoid of, 9-12, 15-16, 19, 36, 41-42,
108, £109, 110, f111; relationships
to typhlopids, 11-12, 15-16, 92;
muscles of, 51, 52-54, 55, 57-58, 60,
62-63, 64-65, 67, 69-70, 74-75, 76,
77, 80, 83-85, 87-88, 126, f127; sum-
mary, 90; evolution of, 92, 99;
blind snake relationships, 97; as
snakes, 97; comparison with An-
niella, 98

Leptotyphlops dulcis dissectus:
oid of, 110, f111

Leptotyphlops maximus: hyoid of, 19,
108, £109; muscles of, 58, 70, 80,
126, £127

Leptotyphlops phenops:
110, f111

Leptotyphlops septemstriatus: hyoid
of, 19

Tiasis albertisti: hyoid of, 22

Liasis childreni: hyoid of, 22;
cles of, 50, 66, 74, 75

elapsoides:

)

hyoid of, 33;

hy-

hyoid of,

mus-

Lichanura roseofusca: hyoid of, 22

Lingual process: in lizards, 6-7, 48,
98; in snakes, 10-18 passim, 19-42
passim, 58, 70, 78, 90; figured, 109,
111

Liotyphlops albirostris: hyoid of, 9,
19, 108, £109; muscles of, 51, 69, 77,
79, 82, 120, f121

Lizards: hyoid of, see Hyoid of liz-
ards; as ancestors of snakes, 39, 98-
99, 100

Loxocemus: relationship with Xeno-
peltis, 94

Loxocemus sumichrasti: hyoid of, 23;
muscles of, 75

Mabowia carinata: hyoid of, 18, 108,
£109

Manolepis putnami: hyoid of, 28

Masticophis flagellum flagellum: hy-
oid of, 28, 37

Masticophis f. flavigularis: hyoid of
28-29, 37

Maticora bivirgata: hyoid of, 32

Mazxillo-hyoideus and mylo-hyoideus,
so6

Mehelya nyassae: hyoid of, 29

Micropechis ikaheka: hyoid of, 32

Micruroides euryxanthus: hyoid of
32

Micrurus affinis affinis: hyoid of, 33

Micrurus fulvius: hyoid of, 33, 112,
f113

Micrurus latifasciata: muscles of, 79

Muscles, branchial arch: general, 46;
in lizards, 49; in snakes, 73-81

Muscles, hypo-branchial-spinal: gen-
eral, 45-46; in lizards, 47-49; in
snakes, 49-73

Mylohyoideus, s55

Mylo-hyoideus, s55

Mylohyoideus posterior, s73

Mylo-hyoidien, s55, s56

Mylo-hyoidiens, s56

Nackenzungenbeinmuskel (part), s60,
s63

Naja naja samarensis: hyoid of, 33

Nardoana boa: hyoid of, 28

Natrix cyclopion floridana: hyoid of,
29

Natrix erythrogaster erythrogaster:
hyoid of, 29

Natrix grahami: hyoid of, 29

Natrix piscator: hyoid of, 29; mus-
cles of, 70, 75, 79

Natrix septemvittata: hyoid of, 29

Natrix sipedon confluens: hyoid of,
29, 38

Natrizx s. sipedon: hyoid of, 114, f115

Neurocostomandibularis: ceratoman-
dibular part of, 56, 60; neuro-
mandibular part of, 62-63; costo-
mandibular part of, 64-66; discus-
sion of, 83-85; summary of, 87-88,
90-91; in phylogeny, 93, 95, 100

Neuro-costo-mandibularis, pars cost-
alis, s64

Neuro-costo-mandibularis, pars hy-
oidea, s56

Neuro-costo-mandibularis, pars verte-
bralis, s61

Neuro-costo-mandibularis (part), s56

Neuro-mandibulaire, s61

Neuromandibularis: in Varanus, 48,
61; m Anniella, 49, 61; snake ac-
count of, 60-63, s61; discussion of,
84-85; summary of, 87-91 passim;
in primitive snakes, 91; in phy-
logeny, 93-94

Neuro-mandibularis (part?), s66

Nina diademata diademata: hyoid
of, 29

Notechis scutatus: hyoid of, 33; mus-
cles of, 81

Nothopsis rugosus:
muscles of, 73

hyoid of, 29;

Obliquus abdominis internus: in
snakes, 68; discussion of, 82-83;
summary of, 88

Obliquus abdominis superficialis, s66

Obliquus externus, s66

Oesophageotrachealis, s79

Ogmodon vitianus: hyoid of, 33

Omohyoideus: in Varanus, 48; snake
account of, 70-71; discussion of, 87-
90 passim; in primitive snakes, 91,
99; in phylogeny, 92

INDEX 153

Omohyoideus plus sternohyoideus plus
sternothyroideus, s66

Opheodrys aestivus aestivus:
of, 29

Opheodrys vernalis: hyoid of, 29, 112,
f113

Oxybelis acuminatus: hyoid of, 29

Oxyrhabdinium leporinum: hyoid of,
29

hyoid

Peaucier du cou, 873

Peaussier, s66

Pelamis platurus: hyoid of, 33; mus-
cles of, 54

Petit oblique de abdomen, s63

Phylogeny: of snake hyoids, 39-43;
significance of hyoids and muscles
in, 95-96; of snakes shown by a
tree, 95-96, 99; of snakes, 95-98;
summary of, 99-100

Pituophis catenifer sayz: hyoid of, 13,
29-30

Platynotan lizards:
snakes, 99

Platyplectrurus madurensis: hyoid of,
19-20; muscles of, 51, 62, 75

Platysma, s73

Pliocercus: muscles of, 79

Primitive snakes: hyoid and muscles
of, 91, 142, [143; summary of, 99

Psammodynastes pulverulentus: hy-
oid of, 30

Psammophis sibilans: hyoid of, 16-17

Pseudaspis: muscles of, 80

Pseudechis: hyoid of, 14

Pseudelaps mulleri: hyoid of, 33

Pseudocerastes fieldi: hyoid of, 34, 38

Python: hyoid of, 12-13; muscles of,
73

Python molurus: hyoid of, 12; mus-
cles of, 73

Python regius: hyoid of, 22

Python sebae: muscles of, 73

as ancestors of

Quermuskel des Zungenbeins, s72

Rectus superficialis: in lizards, 86
Retractor laryngis, s79

Retractor trachea, s79

Retrahens laryngis, s44, s79

154

Rhadinaea flavilata:
114, £115

Rhadinaea laureata: hyoid of, 30

Rhadinella schistosa: hyoid of, 30

Rhineura floridana: hyoid of, 7-8,
110, f111

Rhinocheilus lecontei tessellatus: hy-
oid of, 30

Rhinophis blythi: hyoid of, 20; mus-
cles of, 51, 57, 62, 65, 67, 69, 70-71,
72; 75, 76, 80, 86, 128, 1129

Rhinophis planiceps: hyoid of, 20

Riickwartszieher des Kehlkopfes, s79

Riickwartszieher des Zungenbeins, s73

hyoid of, 30,

Salvadora grahamiae hexalepis: hy-
oid of, 30, 37, 112, £113
Salvadora intermedia richardi: hy-

oid of, 30

Salvadora mexicana: hyoid of, 30

Sanzinia madagascariensis: hyoid of,
23; muscles of, 51, 74-75

Scincidae: hyoid of, 108, £109

Second ceratobranchial: in lizards, 6-
7; im snakes, 13-18 passim, 40-42,
56, 59, 85, 89; in primitive snakes,
91, 99; in snake evolution, 92-95
passim; figured, 109

Sibynomorphus catesbyi: hyoid of, 30,
112, £113

Sibynophis collaris:
muscles of, 73

Silybura beddomiu: hyoid of, 20

Sistrurus miliarius: hyoid of, 35, 38;
muscles of, 79

Sistrurus ravus: hyoid of, 35, 38

Snakes: lizard ancestry of, 39, 98-99;
evolution of, 91-95, 99-100; phylo-
genetic tree of, 95-96, 99, 144, 145;
hyoid of, see Hyoid of snakes; su-
perfamilies of, see Superfamilies of
snakes

Sonora occipitalis occipitalis :
of, 30

Sonora semiannulata semiannulata:
hyoid of, 112, £113

Sonora taylori: hyoid of, 30

Sphincter colli, s73

Spinal nerves: for neuromandibularis,
62; for costomandibularis, 65; for

hyoid of, 30;

hyoid

THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

costocutaneus superior, 68; for ster-
nohyoideus, 70; for omohyoideus,
71; for transversus branchialis, 72

Squamo-costales, s66

Sternohyoid (?), s61

Sternohyoideus: in Anniella, 49; (?),
s66; in Leptotyphlops and Ty-
phlops, 67; snake account of, 69-
70; discussion of, 86; summary of,
87-90 passim; in primitive snakes,
91, 99; in phylogeny, 91-92, 99

Sternohyoideus profundus: im Vara-
nus, 48, 89

Sternohyoideus superficialis: in Vara-
nus, 48, 89

Sternothyroideus, s69

Stilosoma extenuatum: hyoid of, 30

Storeria dekayi: hyoid of, 31, 112,
f113

Submandibular gland: muscles of, 82,
88; constrictor of, 82; dilator of, 82

Submazillaris (part), s63

Superfamilies of snakes:
and Warner, 91

Superficial ventral constrictor, s73

of Smith

Tantilla gracilis: hyoid of, 21, 112,
f113

Temporalis (part), s61

Tendinous inscription: in neurocosto-
mandibularis, 58-59, 62, 84, f130,
138; for costomandibularis, 65-66

Thalassophina viperina: hyoid of, 34

Thamnophis: hyoid of, 18, 15, 37

Thamnophis elegans vagrans: hyoid
of, 31, £139; muscles of, 59, 64, 66,
73, 78-79, 80, 138, £139

Thamnophis eques: hyoid of, 31

Thamnophis melanogaster canescens:
hyoid of, 31

Thamnophis scalaris scalaris:
of, 31

Thamnophis sirtalis sirtalis: hyoid of,
f139; muscles of, 78, 138, £189

Thyro-hyoideus: of lacertilians, s52

Toluca lineata lineata: hyoid of, 31

Tongue: of snakes, 45-46; genioglossi
as protractors, 50-51; hyoglossi as
retractors, 52; short in Pelamis, 54

Tracheo-hyoideus, s79

hyoid

Trachyboa: hyoid of, 13, 36, 40, 42;
relationships of, 93-94

Trachyboa boulengeri: hyoid of, 22;
muscles of, 76; summary of, 91

Transverse, s72

Transversus abdominis:
82-83

Transversus branchialis: with other
muscle, 69; snake account of, 72-
73; discussion of, 83; summary of,
87-88

Transversus hyoideus, s72

Trigeminal nerve (V): for interman-
dibulars, 75

Trimeresurus wagleri: hyoid of, 35

Trimorphodon biscutatus biscutatus:
hyoid of, 31

Tropidoclonion lineatum: hyoid of, 31

Tropidonotus natrix: hyoid of, 14, 31,
112, f113; muscles of, 73, 75

Tropidophis: hyoid of, 13, 36; sum-
mary, 91; evolution and relation-
ships of, 93-94, 100

Tropidophis maculatus: hyoid of, 28,
36, 40, 42, 136, £137; muscles of,
64, 73, 76, 80, 136, £137

Tropidophis melanurus: hyoid of, 36

Tropidophis pardalis: hyoid of, 36

Typhlopidae (Typhlops): hyoid of,
8-12 passim, 19, 35-386, 41-42, 108,
£109, 110, f111; relationship to lep-
totyphlopids, 11-12, 15-16, 92;
muscles of, 50-51, 52-53, 55, 57-58,
60, 62-63, 64-65, 67, 69, 70, 74-75,
76-77, 80, 81, 83-84, 85, 122, £123,
124, 125; summary, 89-90; evolu-
tion of, 92, 99; blind snake relation-
ships of, 96-97; as snakes, 97, 100;
comparison with Anniella, 98

Typhlops bibroni: hyoid of, 8, 19;
muscles of, 58, 62, 70, 122, £123

Typhlops blanfordi lestradei: hyoid
i, 10; 11

Typhlops boettgeri: hyoid of, 11

Typhlops braminus: hyoid of, 11

Typhlops intermedius: hyoid of, 19;
muscles of, 58

Typhlops lumbricalis:
11

Typhlops platycephalus: hyoid of, 10

in snakes,

hyoid of, 10,

INDEX 155

Typhlops polygrammicus:
sea Peo a a

Typhlops punctatus: muscles of, 58

Typhlops pusillus: hyoid of, 10, 11,
110, f1l11

Typhlops reticulatus: hyoid of, 9, 11,
110, f111

Typhlops schlegeli brevis:
8, 11

Typhlops s. mucruso: hyoid of, 8, 11,
19, 108, f109; muscles of, 58, 70,
124, £125

Typhlops s. schlegeli: hyoid of, 11

Typhlops vermicularis: hyoid of, 11

hyoid of,

Ultrocalamus prussi: hyoid of, 33, 38

Ungaliophis continentalis: hyoid of,
23

Uropeltidae: hyoid of, 12, 19-20, 36,
41-42; muscles of, 51, 57-58, 60,
62-63, 65, 75, 80, 83, 84-87 passim,
128, £129; summary, 90; evolution
of, 92-93, 99

Vagus nerve (X): for hyotrachealis,
81

Varanidae: hyoid of, 108, f109; mus-
cles of, 118, £119

Varanus: hyoid of, 7-8, 12, 108, £109;
muscles of, 47-49, 83, 85; summary
of hyoid and muscles of, 89; com-
parison with snakes, 99

Varanus monitor: muscles of, 61;
hyoid of, 118, f119

Vertebrohyoideus, s61

Vertebro-hyoidien (?), s66

Vertebro-mandibulaire, s60, s61

Vertebro-mandibular (?), s60

Vipera aspis: hyoid of, 14, 34, 38

Vipera berus: hyoid of, 34; muscles
of, 79, 80, 84

Viperidae: hyoid of, 34, 38, 41-42,
f141; muscles of, 59, 73, 80, 140,
f141; summary, 90; evolution of,
94, 100

Vortszieher des Zungenbeins, s50

Vorwartszieher des Zungenbeins, s49,
s50, s56

Xenodermus javanicus: hyoid of, 31

156 THE HYOID AND ITS ASSOCIATED MUSCLES IN SNAKES

Xenodon: muscles of, 79 93, 100; relationship with Lozo-
Xenopeltidae (Xenopeltis wnicolor) : cemus, 94
hyoid of, 12, 21, 36, 41-42, £133; Xenosauridae: hyoid of, 108, £109
atieelas of, 50, 59-60, 62, 64, 72-73, Xenosaurus grandis: hyoid of, 7-9,
76-77, 80-81, 86-88 passim, 132, 108, £109
f133; summary, 90; evolution of, Zungenbeinzungenmuskel, s50

reat ay

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