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_^ OMOTOR MORPHOLOGY
OF THE VAMPIRE BAT,
DESMODUS ROTUNDUS
ALTENBACH
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A 46
HARVARD UNIVERSITY
Library of the
Museum of
Comparative Zoology
LOCOMOTOR MORPHOLOGY
OF THE VAMPIRE BAT,
DESMODUS ROTUNDUS
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This publication was hnanced in part by a gift from David Klingener.
LOCOMOTOR MORPHOLOGY
OF THE VAMPIRE BAT,
DESMODUS ROTUNDUS
By
J. SCOTT ALTENBACH
Department of Biology
University of New Mexico
Albuquerque, New Mexico 87131
SPECIAL PUBLICATION NO. 6
THE AMERICAN SOCIETY OF MAMMALOGISTS
Published 22 August 1979
131
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LIBRARY
OCT 11980
HARVARD
UNIVERSITY
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Library of Congress Catalog Card No. 79-53175
D 1979 by The American Society of Mammalogists
FOREWORD
ONE obvious objective of any functional morphological study is
to determine how anatomical features operate. Far more im-
portant, however, is the interpretation of the adaptive significance
of those anatomical features and the role their functioning plays
in the evolutionary, as well as the day-to-day, biology of an organ-
ism. Although morphological features have been used widely for
taxonomic purposes for centuries, only relatively recently has in-
terpretation of the functional significance of morphological fea-
tures been applied toward understanding the biology of organ-
isms. That this is especially true of locomotor morphology is
somewhat surprising, because locomotion plays such a critical role
in the survival of the vast majority of heterotrophic organisms.
Few, if any, groups of animals have as broad a spectrum of
locomotor styles as do mammals. Certainly much of their abun-
dance and general success has been a function of evolution of such
diversity in locomotor mechanisms. The locomotion of bats is es-
pecially interesting, because both pelvic and pectoral limbs are used
in aerial as well as terrestrial locomotion. Evolutionary compromise
has variously placed different bats on a spectrum between extreme
limb modification for certain types of flight and modification for
more efficient terrestrial locomotion.
The study of a biological extreme, whether it is a community,
an organism, or a functional system within an organism, can often
clarify the mechanisms of operation of the average or less extreme.
This is particularly true in the study of bat locomotion where the
outstanding locomotor specialization, flight, is rather poorly
understood. The common vampire bat {Desmodus rotundus) is an
ideal candidate for locomotor morphology studies because it rep-
resents an extreme in locomotor specialization. It seems logical that
a flying machine can vary or be modified evolutionarily in relatively
few ways and still fly. The vampire bat has seemingly approached
the limit of evolutionary modification by specializing in rapid and
effective terrestrial locomotion while retaining the ability to fly.
A functional morphological investigation of the vampire bat as a
flying machine should not only clarify the flight mechanics of oth-
er, less extreme, bats, but also facilitate interpretation of the role
of flight-associated morphology. Of equal interest is the study of
the terrestrial locomotor modifications that make the vampire so
extreme.
My study of the locomotor morphology of the vampire was un-
dertaken both to interpret the functional significance of its loco-
motor-associated anatomy to provide another viewpoint in our bi-
ological knowledge of this animal and to stimulate others to add
additional interpretation of functional morphology to bat biology,
as well as to the biology of other organisms. Only description of
the anatomical details of the pectoral girdle and limb is included
in this work. Admittedly the pelvic girdle and limb are important
in locomotion in the vampire bat and show specializations for its
unique locomotor mechanisms. However, I feel that the most spec-
tacular of the anatomical specializations for terrestrial locomotion
and certainly the most important specializations for flight are those
of the pectoral limb and girdle, and I have thus focused my atten-
tion on these structures. Perhaps this work will stimulate publica-
tions of functional morphological data on the pelvic girdle and
limb.
I want to thank Terry Vaughan for his encouragement at the
onset of this study. Paul Baldwin, Rowan Frandson, Thomas Bahr,
and Y. Z. Abdelbaki gave encouragement, generously loaned
equipment, and read the manuscript as prepared as a doctoral
dissertation. Marilyn Altenbach contributed countless hours in
help with surgical procedures, typing, and proofreading the
manuscript. Without her assistance and encouragement this work
would not have been possible. Sincere thanks are due to the per-
sonnel of the U.S. Fish and Wildlife Service at the Denver Wildlife
Research Center for the generous loan of living vampire bats and
to Northern Arizona University for the loan of preserved speci-
mens. I deeply appreciate the help of Janice Moore and Lyle Ber-
ger, who read proof of the final manuscript, and want to thank
James Findley, Patricia Freeman, and Michael Bogan, who criti-
cally read portions of the manuscript. I also thank James N. Layne
for his encouragement and his very time-consuming editorial
work, and Lorene Deckert who typed the final manuscript.
I would like to dedicate this monograph to my major professor,
the late Robert R. Lechleitner. He was the finest teacher I have
ever known and I can only hope to be a scientist of his competence
and a human being of his kindness. To his family I express sincere
thanks for the kindness and generosity shown to me and their
encouragement of my research.
CONTENTS
Introduction 1
Materials and Methods 5
Preservation and Dissection 5
Photographic Procedures 5
Electromyography 7
Locomotion 10
Standing Postures 10
Hanging Posture 12
Walking 12
Hopping Locomotion 14
Climbing 17
Jumping Behavior 18
Initial Flight Following a Jump 31
Slow Forward Flight 41
Alighting Maneuvers on Horizontal Surfaces 49
Alighting Maneuvers on Vertical Surfaces 51
Postcranial Osteology 52
Positional Terminology 52
Vertebral Column 53
Sternum 55
Ribs 56
Pectoral Girdle and Limb 56
Scapula 56
Clavicle 59
Humerus 60
Radius and Ulna 64
Manus 66
Digit I 68
Digit II 69
Digit III 69
Digits IV and V 70
Functional Myology of the Pectoral Girdle and Limb 72
Comments on Electromyographic Analysis 72
Muscles Unique to Bats 73
M. occipito-pollicalis 73
M. propatagialis proprius 74
M. coraco-cutaneus 75
Muscles of the Pectoral Girdle and Limb 75
Trapezius Group 75
M. clavotrapezius 75
M. acromiotrapezius 78
M. spirotrapezius 78
Costo-spino-scapular Group 79
M. levator scapulae 79
M. serratus anterior, anterior division 79
M. serratus anterior, posterior division 80
M. rhomoboideus 8 1
M. omocervicalis 83
Latissimus-subscapular Group 83
M. latissimus dorsi 83
M. teres major 84
M. subscapularis 84
Deltoid Group 84
M. clavodeltoideus 84
M. acromiodeltoideus 85
M. spinodeltoideus 87
M. teres minor 89
Suprascapular Group 89
M. supraspinatus 89
M. infraspinatus 90
Triceps Group 90
M. triceps brachii, caput lateralis 90
M. triceps brachii, caput medialis 90
M. triceps brachii, caput longus 90
Extensor Group of the Forearm 93
M. extensor carpi radialis brevis 93
M. extensor carpi radialis longus 93
M. supinator 95
M. extensor poinds brevis 95
M. abductor pollicis longus 96
M. extensor digiti quinti proprius 97
M. extensor digitorum communis 97
M. extensor carpi ulnaris 98
M. extensor indicis 99
Pectoralis Group 99
M. subclavius 99
M. pectoralis 100
M. pectoralis, anterior (clavicular) division 100
M. pectoralis, posterior (sternal) division 101
M. pectoralis abdominalis 102
Flexor Group of the Arm 102
M. coracobrachialis 102
M. biceps brachii 103
M. brachialis 104
Flexor Group of the Forearm 104
M. flexor carpi ulnaris 104
M. palmaris longus 105
M. flexor carpi radialis 107
M. pronator teres 108
M. flexor digitorum profundus 108
Extensors of the Manus 109
M. interosseus dorsale 109
Flexor Group of the Manus 110
M. abductor pollicis brevis 110
M. flexor pollicis brevis 110
M. adductor pollicis 111
Mm. interossei 112
M. abductor digiti quinti 1 14
M. opponens digiti quinti 115
Discussion 116
Terrestrial Locomotor Behavior 116
Flight and Aerodynamic Considerations 119
Anatomical Considerations 124
Summary 129
Literature Cited 132
Index 135
My study of the locomotor morphology of the vampire was un-
dertaken both to interpret the functional significance of its loco-
motor-associated anatomy to provide another viewpoint in our bi-
ological knowledge of this animal and to stimulate others to add
additional interpretation of functional morphology to bat biology,
as well as to the biology of other organisms. Only description of
the anatomical details of the pectoral girdle and limb is included
in this work. Admittedly the pelvic girdle and limb are important
in locomotion in the vampire bat and show specializations for its
unique locomotor mechanisms. However, I feel that the most spec-
tacular of the anatomical specializations for terrestrial locomotion
and certainly the most important specializations for flight are those
of the pectoral limb and girdle, and I have thus focused my atten-
tion on these structures. Perhaps this work will stimulate publica-
tions of functional morphological data on the pelvic girdle and
limb.
I want to thank Terry Vaughan for his encouragement at the
onset of this study. Paul Baldwin, Rowan Frandson, Thomas Bahr,
and Y. Z. Abdelbaki gave encouragement, generously loaned
equipment, and read the manuscript as prepared as a doctoral
dissertation. Marilyn Altenbach contributed countless hours in
help with surgical procedures, typing, and proofreading the
manuscript. Without her assistance and encouragement this work
would not have been possible. Sincere thanks are due to the per-
sonnel of the U.S. Fish and Wildlife Service at the Denver Wildlife
Research Center for the generous loan of living vampire bats and
to Northern Arizona University for the loan of preserved speci-
mens. I deeply appreciate the help of Janice Moore and Lyle Ber-
ger, who read proof of the final manuscript, and want to thank
James Findley, Patricia Freeman, and Michael Bogan, who criti-
cally read portions of the manuscript. I also thank James N. Layne
for his encouragement and his very time-consuming editorial
work, and Lorene Deckert who typed the final manuscript.
I would like to dedicate this monograph to my major professor,
the late Robert R. Lechleitner. He was the finest teacher I have
ever known and I can only hope to be a scientist of his competence
and a human being of his kindness. To his family I express sincere
thanks for the kindness and generosity shown to me and their
encouragement of my research.
CONTENTS
Introduction 1
Materials and Methods 5
Preservation and Dissection 5
Photographic Procedures 5
Electromyography 7
Locomotion 10
Standing Postures 10
Hanging Posture 12
Walking 12
Hopping Locomotion 14
Climbing 17
Jumping Behavior 18
Initial Flight Following a Jump 31
Slow Forward Flight 41
Alighting Maneuvers on Horizontal Surfaces 49
Alighting Maneuvers on Vertical Surfaces 51
Postcranial Osteology 52
Positional Terminology 52
Vertebral Column 53
Sternum 55
Ribs 56
Pectoral Girdle and Limb 56
Scapula 56
Clavicle 59
Humerus 60
Radius and Ulna 64
Manus 66
Digit I 68
Digit II 69
Digit III 69
Digits IV and V 70
Functional Myology of the Pectoral Girdle and Limb 72
Comments on Electromyographic Analysis 72
Muscles Unique to Bats 73
M. occipito-pollicalis 73
M. propatagialis proprius 74
M. coraco-cutaneus 75
Muscles of the Pectoral Girdle and Limb 75
Trapezius Group 75
M. clavotrapezius 75
M. acromiotrapezius 78
M. spirotrapezius 78
Costo-spino-scapular Group 79
M. levator scapulae 79
M. serratus anterior, anterior division 79
M. serratus anterior, posterior division 80
M. rhomoboideus 8 1
M. omocervicalis 83
Latissimus-subscapular Group 83
M. latissimus dorsi 83
M. teres major 84
M. subscapularis 84
Deltoid Group 84
M. clavodeltoideus 84
M. acromiodeltoideus 85
M. spinodeltoideus 87
M. teres minor 89
Suprascapular Group 89
M. supraspinatus 89
M. infraspinatus 90
Triceps Group 90
M. triceps brachii, caput lateralis 90
M. triceps brachii, caput medialis 90
M. triceps brachii, caput longus 90
Extensor Group of the Forearm 93
M. extensor carpi radialis brevis 93
M. extensor carpi radialis longus 93
M. supinator 95
M. extensor pollicis brevis 95
M. abductor pollicis longus 96
M. extensor digiti quinti proprius 97
M. extensor digitorum communis 97
M. extensor carpi ulnaris 98
M. extensor indicis 99
Pectoralis Group 99
M. subclavius 99
M. pectoralis 100
M. pectoralis, anterior (clavicular) division 100
M. pectoralis, posterior (sternal) division 101
M. pectoralis abdominalis 102
Flexor Group of the Arm 102
M. coracobrachialis 102
M. biceps brachii 103
M. brachialis 104
Flexor Group of the Forearm 104
M. flexor carpi ulnaris 104
M. palmaris longus 105
M. flexor carpi radialis 107
M. pronator teres 108
M. flexor digitorum profundus 108
Extensors of the Manus 109
M. interosseus dorsale 109
Flexor Group of the Manus 110
M. abductor pollicis brevis 110
M. flexor pollicis brevis 110
M. adductor pollicis 111
Mm. interossei 112
M. abductor digiti quinti 114
M. opponens digiti quinti 115
Discussion 1 16
Terrestrial Locomotor Behavior 116
Flight and Aerodynamic Considerations 119
Anatomical Considerations 124
Summary 129
Literature Cited 132
Index 135
INTRODUCTION
ALTHOUGH bats have been studied intensively for many years,
relatively little has been learned about the mechanisms of
locomotion and the anatomical features involved with locomotion
in this large order of mammals. The preliminary work in the field
of chiropteran locomotor morphology is restricted to relatively few
species of bats and emphasizes the need for investigation of ana-
tomical specialization and, particularly, the modes of locomotion
in other species.
Cuvier (1800, et seq.), Kolenati (1857), and Humphry (1869)
published papers on bat anatomy, but Macalister (1872) was the
first to standardize anatomical terminology for this order and to
correct errors of earlier investigators. Macalister described the
myology of 19 species representing the families Pteropidae, Rhi-
nolophidae, Megadermidae, Phyllostomatidae, and Vespertilioni-
dae, and his work remained the major reference in chiropteran
myology until 1959. Maisonneuve (1898) described the osteology
and myology of Vespertilio murinus and Levy (1912) described the
myology of the upper arm and shoulder of 16 species of bats.
Petersen (1923) studied the osteology of the arm and carpus of
Vespertilio murinus. Eisentraut (1936) published photographs of
Myotis myotis, Rhinolophus hipposideros, and Plecotus auritus in flight,
and presented the first analysis of the mechanics of flight in bats.
He carefully described the phases of the wingbeat and determined
where thrust and lift were generated. Although the photographic
material available to him was of poor quality, he was able to rec-
ognize that interspecific differences exist in flight mechanisms and
that different types of flight observed in a single species require
different movements.
Vaughan (1959) correlated differences in limb and girdle mor-
phology with differing modes of flight, terrestrial locomotion, and
roosting habits. This publication standardized chiropteran myo-
logical terminology and has remained the major reference on chi-
ropteran locomotor morphology. Later publications by Vaughan
(1966, 1970a, 1970^, 1970c, 1970^, 1970^) further illustrate ana-
tomical specialization to fit a particular mode of locomotion or
behavior. Struhsaker (1961) attempted to correlate interspecific
differences in flight patterns with differences in relative weights
2 Spec. Publ. Amer. Soc. Mamm. 6
of specific flight muscles and the dimensional relationships of the
flight membranes. However, incorrect analysis of the mode of
flight of one species makes certain of his conclusions questionable.
His paper does provide dimensional relationships that are valuable
for comparison. Hartman (1963) calculated dimensional and di-
mension/weight ratios for 12 species of bats, including the vampire
bat, of five families. His data are useful for comparison and show
interesting aerodynamic relationships. Gaisler (1964) published
observations on the flight of several European species and con-
firmed some of the conclusions of Eisentraut. Findley et al. (1972)
presented data on morphologic properties of bat wings and spec-
ulated on their functional significance.
Altenbach (1968) described the appendicular anatomy and flight
of a hovering species (Leptonycteris sanborni) and compared them to
those of a species {Eptesicus fuscus) that flies rapidly and cannot
hover. The contrasts clarified the significance of many anatomical
features of both species. Walton (1968) described the appendicular
osteology in members of the family Phyllostomatidae. This paper
did not consider functional significance but is a valuable anatomical
reference for this family. Vaughan and Bateman (1970) correlated
differences in foraging behavior with variations in forelimb mor-
phology in the families Mormoopidae and Phyllostomatidae.
Norberg (1970a, 1970^) published a beautifully illustrated de-
scription of the osteology and myology of the pectoral limb of
Plecotus auritus, and an account of hovering flight in this species.
Norberg (1969) also discussed the bracing system that is seen in
the leading edge of the "hand-wing" of bats.
The difficulties encountered photographing small flying animals
in anything but highly restrictive enclosures are severe. Virtually
no detailed research on bat locomotion has been attempted except
by Eisentraut (1936), and the data he had to work with did not
allow thorough analysis of the mechanisms involved.
Much of the literature concerning bat locomotion, particularly
flight, is based on indirect evidence. Dimensional relationships of
flight membranes, dimension/weight relationships, positional re-
lationships of myological and osteological components of the gir-
dles and appendages, and visual observations of bats in flight and
terrestrial locomotion can lead to reasonably accurate conclusions
about the mechanics of locomotion. However, only high-speed
photography can clearly illustrate the mechanisms involved and
Altenbach — Vampire Locomotor Morphology 3
the often subtle interspecific differences. When high-speed pho-
tographic data are available, anatomical features can be correlated
with movements that are peculiar to specific types of locomotion.
The objectives of this study were: (1) to analyze through the use
of high-speed still and motion picture photography the mecha-
nisms of walking, hopping, jumping, climbing, and flight used by
Desmodus rotundus; (2) to describe the pectoral girdle and the ap-
pendicular osteology and myology by dissection of preserved spec-
imens and examination of skeletons; (3) to determine how some
of the muscles involved with locomotion function during normal
movements by simultaneous photography and electromyography;
(4) to determine the functional significance of pectoral girdle and
appendicular anatomy in the locomotion of Desmodus; and (5) to
determine, if possible, the significance of specialized locomotor
behavior in Desmodus.
It is surprising that the locomotion of the common vampire bat
has not heretofore been investigated in detail and that not more
than a cursory examination of its appendicular anatomy has been
attempted. In contrast, the distribution, feeding behavior, and par-
ticularly the role of this species as a vector of disease of man and
domestic animals have been the subject of many published ac-
counts.
The agility and delicate walking behavior of this species were
described by Beebe (1927) and Price (1950) from observations
made on vampires attempting to feed on them. Ditmars and
Greenhall (1935, 1960) related the account of an explorer who
noted that Desmodus "walked" or "hopped from one spot to
another." These authors described the ability of vampires to walk,
climb, and jump into flight from the ground and published the
first photographs of the terrestrial locomotion of this species (Dit-
mars, 1934; Ditmars and Greenhall, 1935, 1960). The photographs
illustrate the characteristic walking gait of the bat, the posture
when drinking from a dish, and the feeding posture on the back
of a live goat. The authors commented that Desmodus moved rap-
idly over the back of the goat to avoid being brushed off as the
animal walked under obstacles.
Dalquest (1955) noted the extreme terrestrial agility oi Desmodus,
its ability to hop and to jump into flight from the ground, and its
characteristic swift and direct flight. Wimsatt (1959) noted that
Desmodus could rapidly "scramble" across vertical surfaces and used
4 Spec. Publ. Amer. Soc. Mamm. 6
hopping and leaping jumps in terrestrial locomotion. He also re-
marked on its strong, swift flight and its habit of flying within a
meter of the ground. Mohr (1955) also mentioned the agility of
this bat and the "crab" or "spider-like" way it moves over vertical
surfaces. He also observed vampires taking flight from the ground
after being knocked from a roost by the blast of a gun. Leen and
Novick (1970) referred to the jumping behavior of Desmodus and
published photographs of individuals standing and jumping.
Many authors have suggested that the terrestrial locomotor abil-
ity of the vampire is useful in feeding behavior but provide only
scant evidence to support this hypothesis. An account by Hensel
(1869) stated that in South America cattle are bitten by Desmodus
about the hooves, and recent evidence from Mexico (Mitchell, 1970;
Robert Tigner, personal communication) indicates that individuals
often feed from the ground by biting cattle on the fetlock and, if
necessary, follow the animal while taking blood from the wound.
The agility and the ability to jump appear necessary to avoid being
crushed while feeding and to take flight from the ground. Motion
pictures taken by A. M. Greenhall show Desmodus feeding on un-
restrained guinea pigs and illustrate the use of the terrestrial agility
and walking behavior to catch and feed on these active rodents.
Although a few other species of bats move readily on the ground
(Burt, 1934; Vaughan, 1959, 1970^; Leen and Novick, 1970) and
some can take off from the ground (Eisentraut, 1936; Vaughan,
1959; Anonymous, 1969), no other species possesses the extreme
terrestrial agility and jumping ability of Desmodus.
MATERIALS AND METHODS
Preservation and Dissection
TEN Desmodus rotundus from near San Bias, Nayarit, and eight
from near Mazatlan, Sinaloa, were preserved in 10 per cent
formalin and stored in 70 per cent ethyl alcohol. Additional frozen
specimens were obtained from the Denver Wildlife Research Cen-
ter of the U.S. Fish and Wildlife Service and were preserved and
stored in the same manner.
Several preserved bats were dissected under a binocular micro-
scope with variable magnification from seven to 30 power. These
bats were stored in a solution of one part glycerin and eight parts
70 per cent ethyl alcohol, which prevented desiccation and soft-
ened muscles. Photographs of the dissections were taken with a 35
mm camera for aid in preparation of anatomical drawings.
Skeletons of a male and a female bat from the collection of
Northern Arizona University were used for a description of osteo-
logical features. A bat from Nayarit, Mexico, was cleared in two
per cent KOH solution, stained with Alizarin Red S, and stored in
glycerin for use in description of osteological features of the car-
pus. X-ray photographs of another of the Nayarit specimens were
taken by Y. Z. Abdelbaki of the Anatomy Department, Colo-
rado State University, for preparation of anatomical drawings.
Photographic Procedures
Patterns of terrestrial and aerial locomotion were analyzed by
means of high-speed still and motion pictures. Bats used in this
phase of the study were maintained in the laboratory on a diet of
defibrinated beef blood and housed in separate containers made
from 2-liter freezer cartons.
All still photographs were taken with a Praktiflex 35 mm single
lens reflex camera on Kodak Panatomic X film with illumination
provided by a 100 watt second electronic flash unit of my own
design. The V15000 second flash eliminated blur and permitted
an aperture of f/16 with the three lamp heads positioned 50 cm
from the bat. A black velveteen backdrop was positioned be-
hind the flight path of the bat and the camera shutter was
6 Spec. Puhl. Amer. Soc. Mamm. 6
wire cage
\
black backdrop
Hycam K2004E
50 mm lens
— light trap
Tektronix 502 A
oscilloscope
Fig. 1 . Diagram of the equipment used in the electromyographic experiments.
Two additional lights not illustrated were positioned above the wire cage. The plug
and cable, preamplifier, and oscilloscope were not used in general high-speed pho-
tography of locomotion, but the position of the lights, wire cage, and camera was
similar.
Altenbach — Vampire Locomotor Morphology 7
opened prior to the exposure. After the flash was triggered, the
shutter was closed. Since light in the room was normally low, no
fogging of the film occurred; the only exposure was produced by
the V15000 second flash. Photographs of the bats in motion were
taken as they interrupted a light beam directed on a photocell that
in turn activated an advance relay triggering the flash. Bats were
directed into a prescribed area by baffles or released from beneath
an inverted bowl. Photographs of bats standing and climbing were
taken manually by use of a toggle switch that triggered the flash.
High-speed motion pictures were taken with a Hycam K2004E
camera. Kodak Four-X reversal 16 mm film was used in 100-foot
rolls and forced to ASA 800 during development. Four lights to-
taling 3400 watts output provided sufficient illumination to use an
aperture of f/8 at 250 fps (frames per second), 5.6 at 500 fps, and
4 or 2 at 1000 fps. The bats were positioned under an inverted
cup in an open-fronted wire flight compartment 0.6 m wide,
0.9 m high, and 0.9 m deep that was lined on the bottom
and back with black velveteen. The camera was focused on the
center of this compartment and the lights were positioned in front
of it (Fig. 1). In photographing bats with this set-up, the lights
were switched on, the camera started, then the cover pulled off
the bat. Motion pictures of flight from the side were taken as the
bat flew from baffles into a room.
Electromyography
To determine the temporal sequence of contraction of certain
muscles during normal movements, stainless steel electrodes 0.001
inch in diameter were implanted in the muscles and exteriorized
through an implanted silicone rubber plug (Altenbach, 1972). A
two-conductor shielded cable 1 m long with a soft plastic in-
sulator was adapted with a three-pin male plug for attachment to
the female plug sutured to the bat. The contacts could be adjusted
to allow separation of the plugs with a gentle tug, preventing injury
to the bat when it moved beyond the length of the connecting
cable. The cable connected to a Grass model PI 5- A AC preampli-
fier that provided a gain of 10, 100, or 1000 to the myopotential
changes monitored in the bat. The connecting cable and pream-
plifier were arranged in a grounded cage of 6-mm hardware cloth
8 Spec. Publ. Amer. Soc. Mamm. 6
with the cable running through a wire partition (Fig. 1). A heavy
shielded cable connected the preamplifier to a Tektronix 502-A
dual beam oscilloscope.
The high-speed motion picture camera and lights were posi-
tioned in front of the cage as described in the section on pho-
tography. The objective lens was focused on the flight com-
partment of the cage and a 50-mm lens mounted on the rear
focusing aperture was focused on the screen of the oscilloscope
60 cm behind the camera. This technique superimposed an
electromyographic trace over the frame by frame record of the
action in the cage. In this type of oscillography the cathode beam
is not swept by a horizontal amplifier but is positioned in the center
of the tube. The deflections are vertical and correspond, in this
case, to potential changes in a muscle.
The camera was operated at 200, 250, and 500 fps for the elec-
tromyographic experiments, and the same film and processing de-
scribed for motion picture photography were used. The oscillo-
graphic trace was transferred to paper tape for analysis by a device
that moved the film and paper tape parallel to each other at dif-
ferent speeds. A stylus was moved to follow the vertical deflections
in the myographic trace on the film, and a pen attached to the
stylus transcribed the trace onto the paper tape. This method al-
lowed the trace reproduced on the paper tape to be condensed
horizontally to readable and reproducible proportions. For ex-
ample, if the film was moved past the stylus at twice the speed of
the tape, the trace on the film was condensed 50 per cent on the
tape. Register marks were put on every fifth frame of the motion
picture film and at corresponding points on the tape to correlate
the myographic streak with the movements of the bat.
Because myopotential changes seldom exceeded 2 millivolts, a
gain of 100 was sufficient for preamplification and the oscilloscope
vertical amplifier was set at 50 millivolts/cm. Thus a potential
change of 2 millivolts produced a 4-cm deflection of the elec-
tron beam.
Tracings were made from the films for illustration of the move-
ments for correlation with the electromyographic traces. No timing
marks were put on the film because the camera was speed regu-
lated to ± 1 per cent and periodically checked for accuracy. Dif-
ferences of 1 per cent are negligible and calculations of elapsed
time can be made by frame counts. Slight differences in speed of
Altenbach — Vampire Locomotor Morphology 9
Fig. 2. Alert standing postures oi Desmodus rotundus: A, inclined slighdy; B,
horizontal; C, steeply inclined.
10 spec. Publ. Amer. Soc. Mamm. 6
the film do not affect the correlation of movement with myopo-
tential changes inasmuch as the two are recorded simultaneously.
LOCOMOTION
Standing Postures
IN alert standing postures, Desmodus often holds the body 2 or 3
cm above the substrate and inclined upward between 10 and
50 degrees above the horizontal (Fig. 2A). The thighs are oriented
laterally and the knees are flexed 60 to 90 degrees and usually
oriented perpendicular to the substrate, with the feet directed pos-
terolaterally. The weight of the hind body rests on the heel pads,
the pads at the metatarsophalangeal junction, and perhaps on the
claws, which are usually spread slightly. The brachii are directed
posterolaterally and dorsally and the forearms are directed an-
terolaterally. If the body is not steeply inclined, the brachii are
inclined up to 40 degrees above horizontal and inclined postero-
laterally (Fig. 2B). The elbows are strongly flexed, and the fore-
arms are oriented anterolaterally and inclined 50 to 60 degrees
above horizontal. The thumbs are directed laterally, and the weight
rests on the basal and distal thumb pads.
If the body is inclined more steeply, the brachii are adducted
but still directed strongly posteriorly. The forearms are extended
slightly and oriented strongly anteriorly and slightly laterally. Pho-
tographs of the bats in an inclined stance indicate that the first
metacarpals are directed ventrally and the weight is concentrated
on the distal thumb pads and phalanges, which are hyper-extended
anteriorly and laterally from the metacarpal (Fig. 2C).
When feeding terrestrially on the fetlock of a large ungulate,
the bat assumes a posture that is similar to that of the elevated
stance in Fig. 2C (Mitchell, 1970). The hind limbs are almost fully
extended as in a jump, occasionally so much so that the weight
rests on the pads at the metatarsophalangeal junctions. The brachii
are adducted and oriented ventrally in a plane parallel to a sagittal
plane through the body. The elbows are fully extended, and the
forearms are directed nearly vertically. The thumbs are often ad-
ducted in line with the long axis of the forearm, with the weight
Altenbach — Vampire Locomotor Morphology 1 1
Fig. 3. Hanging posture of Desmodus.
resting on the terminal phalanges and claws as in Fig. 2C. The
body is thus steeply inclined, and the lips can reach up to 8 or 10
cm above the substrate.
The transition from these postures, with the exception of the
fully elevated feeding posture, to terrestrial locomotion is simple
and involves only alternate strokes with the limbs.
12 Spec. Publ. Amer. Soc. Mamm. 6
Hanging Posture
When a bat is fully alert and hanging on a vertical surface, the
body is held as far as a centimeter away from the surface and is
inclined anteroventrally with the head sharply turned upward or
directed toward an observer (Fig. 3). The thighs are oriented lat-
erally and shghtly dorsally, relative to the animal, and the shanks
are flexed and directed upward, often slightly medially, and to-
ward the vertical surface. The feet are oriented upward and the
weight is on the claws which are slightly spread. The brachii are
oriented posterolaterally at the level of midbody and the forearms
are directed ventrolaterally. The thumbs are directed laterally or
slightly dorsolaterally, with the weight supported by the basal pads
and the claws. The inclination of the body and its position away
from the surface tend to force the thumb toward the surface, using
the hind feet as a fulcrum. This provides good traction for the
forelimbs and allows sudden lateral or dorsal movements powered
by the forelimbs.
A resting position is similar, except that the body is close to the
surface and the forelimbs are not directed laterally. When the bat
is resting pendant from a steeply inclined overhead surface with
sufficient irregularities to give the claws purchase, the hind limbs
often are fully extended and the forelimbs are flexed toward the
brachium and not in contact with the surface. However, when the
animal is disturbed in this position, the hind limbs are flexed, draw-
ing the body toward the surface, as the forelimbs are extended
posteriorly or ventrally, relative to the bat, to bring the thumbs in
contact with the surface. This allows the forelimbs to be used in
an evasive drop into flight or terrestrial locomotion.
Walking
The walking gait of Desmodus on a horizontal surface, like all
other locomotion in this species, is highly variable, the particular
pattern depending upon a number of factors. When unhurried,
bats accustomed to captivity and observation walk in a deliberate
and even gait. However, under experimental conditions, this type
of walking was infrequently observed; the animals usually em-
ployed a faster walking gait. Analysis of films of slightly hurried
locomotion of a bat approaching and starting up an inclined sur-
AUenbach — Vampire Locomotor Morphology 13
face indicates that at the start of a stride the hind limbs are flexed
at the knee and oriented in reptilian fashion, with the plane of the
limbs and feet directed posterolaterally (Fig. 4A). The brachii are
inclined posterodorsally and the forearms are partially flexed, with
the carpi and thumbs contacting the substrate roughly two cm lateral
to the sides at midthorax. The body is about a centimeter above
the substrate at the start of the stride. The hind limbs are extended
at the knees as slight adduction of the brachii and extension of the
right elbow lift the body and shift it to the left (Fig. 4B-C). Exten-
sion of the left hind limb continues as the right hind limb is lifted
by abduction of the femur and slight flexion of the knee and
brought anteriorly (Fig. 4C-D). Almost concurrently the left fore-
limb is lifted off the surface and extended forward and to the
left (Fig. 4D). Within eight milliseconds the right forelimb is lifted
after a lateral and posterior thrust and is brought forward by flex-
ion of the elbow (Fig. 4D-F). Only the right hind limb remains in
contact with the substrate, and extension of the right knee and a
posterior swing of the femur provide forward thrust to the body.
The right hind limb reaches the end of its forward swing and
contacts the substrate as the left forelimb contacts the inclined
surface toward which the bat is walking (Fig. 4F). Simultaneously
the left hind limb is raised by abduction of the femur and begins
a forward swing. Meanwhile, the left forelimb begins to pull the
body forward and up the incline by movement of the brachium,
which draws the distal end of the partially flexed forearm down-
ward and posteriad (Fig. 4F-G). The right forelimb contacts the
substrate, and extension of the forearm and slight adduction of
the brachium drive the body forward and toward the incline (Fig.
4H-I). The right hind foot is raised and swung forward as the bat
pushes off the substrate with an extension of the left hind limb
followed by a powerful adduction or flexion of the right thumb
(Fig. 4I-K). As the right thumb is adducted, the left forelimb is
lifted and the bat becomes airborne for about 10 milliseconds (Fig.
4L-M). The right hind foot is extended laterally and ventrally to
contact the substrate simultaneously with the left forelimb. The
left hind limb reaches the end of its anterior swing and, with the
knee flexed, contacts the inclined surface as the right forelimb
contacts the substrate after flexion of the elbow to advance the
arm. Both hind limbs extend, along with extension of the elbow
and inclination of the brachium of the right forelimb, to thrust the
14 Spec. Publ. Amer. Soc. Mamm. 6
Jf^ J^ -4^ ^ -^
'j)-Ar-'^
Fig. 4. Drawings at 40 millisecond intervals of Desmodus walking rapidly on a
horizontal surface (A-H) and up an incline (I-R).
body up the incline, while the left forelimb is extended forward to
grasp higher up (Fig. 4N-R).
After the series of pictures upon which this description is based
was taken, the bat executed a turn on the inclined surface and
used the typical backward climbing method to climb it vertically.
Hopping Locomotion
When Desmodus further accelerates its movement on a horizontal
surface, a hopping gait is employed, which leads to a rapid leaping
type of locomotion if a sufficiently open expanse of substrate is
available. Fig. 5A-E illustrates a turn prior to the initiation of hop-
ping locomotion. The bat pivots to the right around the right hind
foot by the force of the left forelimb pushing against the inclined
surface immediately behind (Fig. 5A-C). The left hind limb is
raised, pulled forward, and positioned lateral to the body (Fig. 5C-
D). As the right forehmb is moved laterally during the last of the
turn, the right hind limb is lifted slightly, and when the forelimb
contacts the substrate, the right hind limb is powerfully extended
(Fig. 5D-G). Both brachii are inclined and the forearms are ex-
tended to drive the body forward and upward. The left hind limb
Altenbach — Vampire Locomotor Morphology 15
/^ Jk^" J'-f^ J^ I^
i).
1^=^ \.^^ l4
#^ ^
M NO P Q R
Fig. 5. Drawings at 40 millisecond intervals of Desmodus in typical hopping
locomotion on a horizontal surface.
is raised as the right hind limb is extended, and both are pulled
strongly forward. The forelimbs leave the substrate after the ter-
minal adduction of the thumb for thrust and the bat is airborne
for about 70 milliseconds (Fig. 5H-K). The forelimbs are then
moved upward by adduction of the brachium and then anteriorly
by simultaneous adduction, supination, and subsequent anterior
swing of the brachii. The bat alights simultaneously on the antero-
laterally directed hind feet and ventrally oriented thumbs (Fig.
5L).
Transition to a more vigorous hopping locomotion is accom-
plished when the bat maintains forward momentum by inclination
of the brachii and extension of the elbows (Fig. 5M-Q). The thighs,
which were partially abducted as the bat alighted, are swung pos-
teriorly, and the knee is extended to drive the body forward and
upward, much as in a jump into flight. The hind feet leave the
substrate as the forearms are extended (Fig. 5P-Q). A slight ad-
duction of the brachii, with the forearms extended at right angles
to them, provides upward momentum to carry the bat higher than
in the previous hop. The thumbs are not forcefully flexed as the
forelimbs leave the substrate, as in a typical jump. In addition, the
weight is transferred from the thumb pads to the anterior surface
of the carpi when the forelimbs are inclined.
16 Spec. Publ. Amer. Soc. Mamm. 6
^■:D|
Fig. 6. Drawings at 44 millisecond intervals of Desmodus climbing on a vertical
surface. Horizontal lines (1-5) on the surface behind bat are included as spacial
reference points.
Altenbach — Vampire Locomotor Morphology 17
Hopping locomotion can carry the bat over a horizontal surface
at rates of up to two m per second with surprising agility. The animal
can readily hop over or around obstacles in its path with little
noticeable reduction of speed. The hopping locomotion often al-
ternates with short flights varying from slightly less than half a
meter to several meters in length and 0.3 m or less in height.
Often, only two or three hops are made between these flights. If
there is an unobstructed path ahead of the bat, continuous forward
flight is initiated by a more powerful jump.
Climbing
Although able to climb a vertical surface forward or sideways,
Desmodus normally climbs backward, and, if hurried, slightly side-
ways. I have observed this behavior in the wild as well as in the
laboratory. The bats are exceptionally alert while climbing. The
presence of an observer may influence the frequency of backward
climbing, as this form of locomotion allows the bat a good view of
the observer. Thus it is possible that when undisturbed, vampires
may use other types of climbing. However, this seems unlikely.
The following description of backward climbing is based on pic-
tures of a subject climbing a vertical strip of 6-mm hardware cloth
angled 25 degrees from parallel to the line of view (Fig. 6).
A cycle begins with the left hind limb extended and grasping
the wire (Fig. 6A). The right hind limb is flexed in a plane parallel
to the wire after the. foot has released its grip through extension
of the phalanges. The claws and basal and distal pads of the
thumbs of both forelimbs are in contact with the wire. The right
forelimb is slightly flexed and positioned anterior to the head while
the left forelimb is strongly flexed and positioned caudad of the
head. The left hind limb flexes at the knee and both forelimbs
extend, driving the body upward while the right hind limb pulls
away from the wire and reaches backward toward a higher grip
(Fig. 6B-C). As the hind limbs are nearly side by side, the weight
is transferred to both left limbs, and the right forelimb releases
contact with a push that swings the body away from the wire (Fig.
6D-F). (This maneuver was noted in nearly all of the motion pic-
tures of climbing and may be the result of avoidance of the wire
surface during movements of the limbs. The long, recurved claws
of Desmodus are better suited for climbing on rough stone than on
18 Spec. Publ. Amer. Soc. Mamm. 6
screening where they easily become hooked over the wire strands.)
The right brachium is pulled caudally and the forearm is flexed,
thus lifting the right carpus to the level of the left. As the body is
pulled toward the level of the left hind foot and shank, the right
hind foot is fully extended and gains purchase on the wire as the
right forelimb contacts it (Fig. 6E-G). Although the claws do not
actually grasp the wire, the right forelimb provides support
through contact of the thumb pads with it. Simultaneous flexion
of the shanks of both hind limbs and a cranial and dorsal swing of
the thighs lift the body, and the left forelimb releases its grip and
is pulled upward by flexion of the elbow and upward rotation of
the brachium (Fig. 6H-K). When the left forelimb contacts the
wire, the left hind limb is released and extended upward, and the
right forelimb is raised, as described for the left forelimb (Fig. 6J—
M). Flexion of the right hind limb and extension of the right fore-
limb lift the body, and the left hind limb is fully extended for a
new grip (Fig. 6N). The left forelimb is raised by extension of the
elbow to obtain a grip considerably lateral to the climbing path.
When the left hind limb grasps the wire and begins flexion to raise
the body, the right forelimb is flexed slightly at the elbow (Fig. 60)
to give the thumb a grip higher on the screen. Its thumb is flexed
to the level of the distal pad, which rests against the wire. From
this position the bat assumes a horizontal resting posture against
the wire (Fig. 6P-T).
When vampires descend a vertical surface, the posture and ori-
entation of the body are similar to those seen in climbing, and the
movements are also quite similar. Although this behavior was ob-
served on several occasions, it was not photographed for detailed
analysis. The bats literally ran down the wire screen on the side of
the flight compartment and could stop or change direction almost
instantly, indicating sufficient contact of the limbs with the wire to
allow control.
Jumping Behavior
The jumping behavior of Desmodus is perhaps the most striking
and unique feature of its locomotion and is vital to the terrestrial
feeding behavior of this genus. Although several other bats can fly
from the ground, descriptions of this behavior (Eisentraut, 1936;
Orr, 1954; Vaughan, 1959; Altenbach, 1968; Anonymous, 1969)
Altenbach — Vampire Locomotor Morphology 19
Fig. 7. Multiple exposure photograph of D esmodus ']um^mg into flight through
an angle of about 60 degrees.
20 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 8. High-speed photographs of Desmodus in the thrusting phase (A-E) and
the coasting phase (F-H) of a jump into flight.
Altenbach — Vampire Locomotor Morphology 21
Fig. 9. High-speed photographs of Desmodvs in the last of the coasting phase
(I-J) and the initiation of the first downstroke (K) following a jump into flight.
indicate that flight is effected by an adduction of fully or partially
extended wings or, on an open surface, by a series of these motions
combined with several shallow hops to gain forward speed. Only
Desmodus launches itself into flight almost vertically from a typical
terrestrial stance with folded wings. Several authors (Ditmars and
Greenhall, 1935, 1960; Dalquest, 1955; Leen and Novick, 1970)
have commented upon the jumping behavior but none has de-
scribed it in detail nor pointed out its significance.
Recent investigations in Mexico (Robert Tigner, personal com-
munication; Mitchell, 1970) and the observations of Hensel (1869)
establish that Desmodus does feed from the ground at least occa-
sionally and often moves about on the ground before and after
feeding (Ditmars and Greenhall, 1960). Wimsatt (1969) reported
that under natural conditions Desmodus often consumes more than
50 per cent, and occasionally more than 100 per cent, of its body
22 Spec. Publ. Amer. Soc. Mamm. 6
^t ^ ^
A .000 B .020 C .040 D oeo
E .080 F .092 G .104
N .182
O .208
P .214 Q .226
R .264
Fig. 10. Drawings of Desmodus jumping into flight and corresponding elapsed
time in seconds.
weight in blood in a single feeding period. Thus, jumping behavior
functions to get a heavily loaded bat into flight from a horizontal
surface. In addition, this behavior probably enables the bat to avoid
sudden movements of a large host animal that could crush a bat
with its foot or to avoid a terrestrial predator such as a snake or
carnivorous mammal.
In the laboratory, it was difficult to photograph the bats jumping
from an undisturbed walking gait or when startled from a typical
terrestrial feeding posture. Thus the majority of the photographic
records are of bats suddenly released from beneath a small enclo-
sure. The photographs certainly show typical jumping behavior,
especially hurried jumps, which probably are normal in avoidance
reactions.
Figure 7 is a multiexposure photograph of a vampire bat jump-
ing into flight through an angle of approximately 60 degrees. It
is included to give the reader a better perspective of the direction-
ality and distance involved in a typical jump. The details are de-
scribed below.
Prior to a jump, Desmodus normally crouches with the body close
Altenbach — Vampire Locomotor Morphology 23
to the substrate (Figs. 8A, lOA). The brachii are highly abducted
and inclined posteriorly five to 10 degrees above horizontal. The
elbows are fully flexed, the forearms inclined about 15 degrees
anteriorly and slightly laterally, and the thumbs directed laterally
with the weight resting on the basal and distal pads. The thighs
are abducted roughly 40 degrees above horizontal and directed
slightly anterolaterally, laterally, or posterolaterally from the body.
The knees are flexed between 90 and 120 degrees and the shanks
are inclined posteriorly, posterolaterally, or occasionally postero-
medially. The orientation of the hind feet varies between posterior
and lateral with the toes slightly spread and the weight resting on
the heel pads, the pads at the distal tips of the metatarsals, and the
claws. The prejump position is variable, depending upon the na-
ture of the substrate and how rapidly the animal initiates the jump
from another posture such as walking or feeding positions. High-
speed motion pictures indicate that the bats can jump short dis-
tances from nearly any position, but when jumping into flight from
a static position on a horizontal surface they usually assume a po-
sition similar to that shown in Fig. 8A.
The sequence of movements is highly variable, depending upon
the angle of the jump, the plane of the substrate, the orientation
of the bat on the substrate, and individual differences. In most of
the high-speed photographs of bats jumping into forward flight
from a flat, horizontal surface, the jump path was at an angle
between 50 and 70 degrees above horizontal. The following de-
scription of the movements involved in jumping into forward flight
will emphasize this type of jump, which under experimental con-
ditions appears to be the most frequently used. However, Desmodus
is capable of jumping into flight through angles of 35 degrees to
more than 80 degrees. Even in jumps that appear to be nearly
identical, careful analysis of motion picture film reveals consider-
able variation in the magnitude and temporal sequence of the var-
ious movements.
The jump is initiated by an inclination of the brachii and resul-
tant declination of the highly flexed forearm (Figs. 8B, lOB-C).
This movement shifts the center of gravity at midthorax in a line
through the contact of the pectoral limbs and substrate and the
direction in which the jump progresses. Extension of the hind
limbs, which begins either a few milliseconds before or within 20
milliseconds after the initiation of this movement, aids in the an-
24 Spec. Publ. Amer. Soc. Mamm. 6
terior shift of the body and supplies upward momentum to the
posterior half of the body. As the brachii reach an inclination of
between 40 and 55 degrees above horizontal, about 60 milliseconds
after initiation of the jump, they are adducted to begin the upward
thrust of the jump (Figs. 8B-C, lOC-D). Extension of the elbow
normally begins concurrently or within two to five milliseconds after
the adduction of the brachium, but if the jump is directed strongly
anteriad, extension of the elbow precedes the adduction of the
brachium by up to 10 milliseconds and increases the forward shift
of the body.
As the hind limbs reach almost full extension, the feet are ad-
ducted to provide anterior and upward thrust to the body (Figs.
8C, lOD). Because the center of gravity is positioned over the pec-
toral limbs in hne with the angle of the jump, the last thrust from
the hind limbs probably tends to stabilize the position of the body
rather than supply much power to the jump.
Adduction of the brachii and extension of the elbows continue
about 20 milliseconds and accelerate the bat upward and forward.
Although measurement of the movement of parts of the thorax is
difficult from photographs of an animal covered with hair, depres-
sion of the shoulder joint is evident during adduction of the hu-
merus. This can be partially explained by the humerus being
locked dorsally with the lateral scapular border as the lateral scap-
ular border is rocked ventrad, but the depression appears more
pronounced than would be accounted for by this movement. The
frontal, still photographs of the jump illustrate this best and sug-
gest that depression of the entire shoulder girdle occurs, which
necessitates a ventral swing of the distal end of the clavicle (Fig.
8B-E). The depression of the shoulder during adduction of the
brachium would add to the upward momentum of the body and
thus would certainly be advantageous in jumping. Although no
direct evidence is available concerning the exact mechanism of the
shoulder depression, analysis of the motion picture films indicates
it does occur, and that it begins concurrently with adduction of the
brachium and continues through all but the last few degrees of
this movement.
Between five and 15 milliseconds before the brachium is fully ad-
ducted and the elbow is fully extended, flexion of the thumb begins
(Figs. 8D-E, lOE). High-speed photographs show that the thumb
remains relatively straight during adduction to provide a lever arm
Altenbach — Vampire Locomotor Morphology 25
of maximal length (Figs. 8E, lOE-F). The upward thrust provided
by the movements of the body, brachium, and elbow is completed
as the thumb leaves the substrate or within a few milliseconds be-
fore; thus the thumb provides the last component of thrust in the
jump. The contact with the substrate is broken when the thumb
is adducted to within about 40 degrees of the long axis of the
forearm. After adduction to this point, the forearm is raised almost
imperceptibly, and the upward movement of the body facilitates
the lift of the thumb off the substrate. Adduction of the thumb
continues until it is parallel with the long axis of the forearm. This
movement appears to have no function and is probably only a
follow-through, as the thumb no longer meets resistance (Figs. 8F,
lOG).
Although there is considerable variation among the jumps re-
corded on motion picture film, the velocity imparted to the body
by the jump can readily be measured from the film. The highest
velocity recorded as the bat broke contact with the substrate was
2.4 m per second. In 10 other jumps into forward flight, the ve-
locity varied between 1.3 and 2.2 m per second. Although jumping
movements are used both in transition from terrestrial stance into
flight, and in hopping terrestrial locomotion and avoidance move-
ments, I did not attempt to calculate velocities imparted by jumps
except those leading into flight. Simple calculation without consid-
eration of air resistance indicates that an upward velocity of 2.4 m
per second will carry an object to a height of about 30 cm. When
compared with the motion pictures of the Desmodus jumping, this
height seemed too great, but the bats normally jumped forward
and upward at an angle of between 35 and 70 degrees above hor-
izontal, thus much of the velocity imparted to the body was di-
rected anteriorly.
During the thrust phase of the jump, the long axis of the body
is normally inclined upward between five and 20 degrees. The
angle appears greater, as the head is often strongly upturned dur-
ing the jump. The stability of the angle of the body indicates that
the weight is effectively centered over the thrusting pectoral limbs
and that perhaps the thrust from the pelvic limbs early in the jump
counteracts forces that would incline the body.
When the forelimbs leave the substrate, the powered phase is
complete and a coasting phase begins with almost immediate flex-
ion of the elbows (Figs. 8F-G, lOG-H). Abduction and supination
26 Spec. Publ. Amer. Soc. Mamm. 6
of the brachii and flexion of the elbows raise the forearms nearly
parallel to a saggital plane through the body (Figs. 8F-H, lOG-I).
As the forearms reach the level of the lower body, extension of the
elbows and digits begins (Figs. 8H, 101). The abduction of the
brachii continues, but the supination ceases as the forearms reach
the level of the body. Thus the remainder of the wing positioning
is a result of abduction and pronation of the brachii and extension
of the forearms and digits. Figure 9I-K illustrates the remainder
of the coasting phase and the beginning of the first downstroke.
The angle of inclination of the body during this coasting phase
of the jump is variable and seems directly related to the flight path
during the first few wingbeats. The inclination is often as much as
35 degrees during a coasting phase prior to the first wingbeats of
climbing flight. Prior to and during the first wingbeat of nearly
horizontal flight, the inclination of the body is reduced to orient
the long axis of the body horizontally. This movement is easily
explained by the rapid posterior and dorsal movement of the un-
folding wings, which imparts a forward and downward force to
the anterior body.
The sequence of movements in a more vertical jump is different
from those of an anteriorly directed jump. There appears to be
little or no inclination of the brachii, and the jump is initiated by
adduction of the brachii followed in roughly two to six milliseconds
by extension of the elbows. Extension of the hind limbs starts about
four to six milliseconds after adduction of the brachii and is directed
downward, thus providing little or no forward momentum to the
body. The forward thrust that is produced comes from the exten-
sion of the elbows, since the brachii are oriented strongly poste-
riorly during adduction. Adduction of the hind feet is similar to
that seen in an anterior jump but provides primarily upward
thrust, because the hind limbs are oriented ventrally instead of
posteroventrally. Strong flexion of the thumb is initiated prior to
the completion of brachial adduction and extension of the elbow
to provide the last upward thrust. It appears that a jump forward
and upward provides more upward momentum and is better suit-
ed to initiating flight from the ground than is a laterally or pos-
teriorly directed jump. A rapid turn made immediately after the
jump is usually used in favor of a jump directed laterally.
Lateral and posterior jumps are typically used in avoidance re-
actions, particularly if the bat is not oriented toward an open flight
u*.
A .000
H .117
Altenbach — Vampire Locomotor Morphology 27
M. n
B .020
C .035
D .050 E .070
F .092
J .14 2
K .152
L .162
G .102
M .172
Fig. 11. Drawings of Desmodus performing an anterolateral jump and turn into
horizontal flight. Numbers are elapsed time in seconds.
path that would allow a forward jump into flight. Most of the
lateral and posterior avoidance jumps were recorded only on high-
speed still photographs, which prevents detailed description of the
movements involved. However, one motion picture sequence of an
anterolateral jump was obtained. In this sequence, the hind limbs
initially shift the center of gravity slightly forward and laterally
into the line of the jump over the pectoral limbs. The major thrust
of the hind limbs, however, is almost vertical. Because the body is
accelerated laterally, the vertical thrust component of the hind
limbs imparts a yaw to the body so that its long axis swings per-
pendicular to the prejump axis (Fig. IID-E). The body appears
shifted to the left by shght flexion of the left elbow toward the
inclined brachium (Fig. IIA-C). Adduction of the right brachium
and extension of the right elbow begin and continue to shift the
body, and thus the center of gravity, laterad over the left forelimb
(Fig. 11 D). Adduction of both brachii and extension of the elbows
now thrusts the bat upward, slightly forward, and strongly to the left
(Fig. IIE-F). The flexion of the right thumb and simultaneous pos-
terior swing of the right forearm swing the long axis of the body to-
ward a position perpendicular to its prejump axis. Flexion of the left
thumb supplies the final upward thrust (Fig. IIG). During the
coasting phase, the momentum imparted by the right limb swings
the body perpendicular to the prejump position (Fig. IIH-M).
A single high-speed photograph of a posterior jump (Fig. 12)
indicates that the hind limbs impart slight upward and backward
28 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 12. High-speed still photograph of Desmodus 100 milliseconds after initia-
tion of a posterior jump.
momentum by extension of the knees and adduction of the thighs.
The pectoral limbs are probably adducted and extended from the
prejump posture with no prior inclination of the brachium, as the
extended limbs are seen to be thrust strongly anteriad at the instant
of the exposure, about 100 milliseconds after initiation of the
jump. It appears improbable that flight could be initiated from a
jump of this type, as it did not progress more than a few centi-
meters vertically and thus would not allow for a full downstroke,
although a rolling maneuver could perhaps orient the body in the
opposite direction. Jumps such as this are obviously necessary to
avoid sudden movements of a host animal, obstacles the host ani-
mal brushes by, or predators the bat might encounter on the
ground. Flight could readily be initiated after a posterior jump by
Altenbach — Vampire Locomotor Morphology 29
Fig. 13. Drawings of Desmodus jumping into flight from a walking gait: A-D,
10 millisecond intervals; D-E, 8 millisecond intervals; E-G, 6 millisecond intervals;
G-J, 4 millisecond intervals; J-N, 8 millisecond intervals.
alighting, executing a partial turn, and then jumping anterolat-
erally or forward.
Figure 13 illustrates a jump into flight following the completion
of a stride at a walking gait. As the left forelimb contacts the sub-
strate after a forward swing (Fig. 13 A-D), simultaneous brachial
adduction and extension of the hind limbs thrust the body forward
and upward (Fig. 13E-N). The thumbs supply the final upward
thrust typical of jumps initiated from a stationary position.
Desmodus uses the jump to initiate flight from a vertical roosting
surface or from the side of a host animal. In the prejump posture
on a vertical surface, and brachii are nearly parallel with the long
axis of the body, and the forearms are partially extended with the
thumbs oriented dorsally and laterally against the surface (Fig.
14A). The hind limbs, which support much of the weight, are held
with the knees slightly flexed. The jump is initiated by adduction
of the brachii and extension of the forearms with no preliminary
inclination of the brachii (Fig. 14B-D). Because the hind feet retain
their grip on the surface for a few milliseconds, the thrust of the
pectoral limbs sharply inclines the body relative to the vertical sur-
face. The momentum imparted by this movement orients the long
axis of the body horizontally in the coasdng phase of the jump. As
30 Spec. Publ. Amer. Soc. Mamm. 6
.A
€^
O p Q
Fig. 14. Drawings at 12 millisecond intervals of Desmodus in a jump into flight
from a vertical surface.
the adduction of the brachii and extension of the forearms pro-
gress, the hind limbs release the surface and the body is thrust
laterad and slightly ventrad (Fig. 14D-E). The thrust is completed
by extension of the thumbs as in a jump from a horizontal surface
(Fig. 14E-F). The elbows remain extended, and the wings are po-
sitioned for the downstroke by abduction of the brachii and ex-
tension of the digits as the long axis of the body becomes nearly
horizontal (Fig. 14G-K). As the airspeed is high because of the
lateral thrust of the jump, a downstroke of high amplitude is ap-
parently not necessary and the wings are abducted only 20 degrees
above horizontal prior to the first downstroke, which is similar to
one seen in level forward flight several wingbeats after a jump
from a level surface (Fig. 14L-Q).
Altenbach — Vampire Locomotor Morphology 31
Initial Flight Following a Jump
In initial flight following a jump, the position of the body, move-
ments of the wings, and direction of the flight path are variable
and, as in other types of locomotion, are dependent upon many
factors. A description of the movements recorded on a single high-
speed motion picture film would not adequately cover this aspect
of locomotion. Still photographs and drawings from films of sev-
eral different flights will be discussed in an attempt to describe at
least most of the characteristics of the flick of Desmodus.
When jumping into flight from the ground, Desmodus does not
have the advantage of species that begin flight from a high roost
and can build airspeed by a vertical drop or by a shallow dive
during the first few wingbeats (Eisentraut, 1936; Vaughan, 1959,
1970^; Hayward and Davis, 1964; Altenbach, 1968). Although
some other bats can take flight at a steep angle from a horizontal
surface, the majority of these have light wing loading or complex
modifications of the wingbeat cycle that allow hovering. Desmodus
is heavily loaded (Struhsaker, 1961; Hartman, 1953), and my in-
vestigation revealed no extreme wingbeat modifications typical of
heavy-bodied, hovering species (Altenbach, 1968). The only for-
ward airspeed available to Desmodus after a jump is provided by
the momentum of the jump.
During photography of jumps into flight, bats normally did not
fly higher than 0.3 to 0.6 m above the level of the surface from
which they jumped. Thus the flight path was usually inclined no
more than 15 degrees above horizontal, although in a few instances
bats flew upward at an angle of 60 or 70 degrees above horizontal.
When released on the laboratory floor, Desmodus typically jumped
from the floor and flew within less than a meter of it for as far as
10 m. Dalquest (1955) and Wimsatt (1959) commented that Des-
modus flies within a meter of the ground.
Coasting phase and initial flick. — In a jump into a forward flight
with a climb path of five to 10 degrees (Fig. 15), the body is slighdy
inclined during the coasting phase. As the wings are abducted to
the level of the body (Fig. 15G-I), within about 100 milliseconds
of initiation of the jump (Fig. 151), the forward motion imparted
by the jump is only about 0.2 m per second. However, as the
forearms and digits are extended and the wings are abducted, the
distal half of the wings assumes a configuration that provides for-
32 Spec. Publ. Amer. Soc. Mamm. 6
'^
<S7^
J^
Fig. 15. Drawings at 20 millisecond intervals of Desmod-us in a jump into nearly
horizontal flight.
ward thrust (Fig. 15I-J). As extension of the wings begins, the
digits are inclined posteroventrally between 60 and 80 degrees
below horizontal. In the next 30 milliseconds, the digits are fully
extended and inclined posteriorly through an arc of roughly 70
degrees, as the wings are raised 50 to 60 degrees. The movement
of the distal half of the wings is rather complex and is the result
of several movements of the arms and hands. Extension of the
digits and extension of the forearms impart a rapid lateral move-
ment to the wingtip. Abduction of the arm adds a vertical com-
Altenbach — Vampire Locomotor Morphology 33
ponent to this movement, and pronation of the arm and extension
of the phalanges add a posterior component. Through the first
half of this movement, while the digits are still directed strongly
ventrally, the distal half of the chiropatagium attains velocities of
11 to 12 m per second. During this phase, the average forward
velocity of the bat increased from 0.2 m per second to 0.56 m per
second, indicating that forward thrust was being produced. In de-
scriptions of forward and hovering flight in other species of bats,
Eisentraut (1936) and Norberg (1970a) indicated that, in the last
phase of the upstroke, similar movements produce strong forward
thrust.
As the wing reaches a fully abducted position prior to the initi-
ation of the downstroke (Fig. 15J-K), decreased velocity at the
distal chiropatagium probably reduces forward thrust.
First downstroke. — The transition from upstroke to downstroke is
not clearcut, but is marked by a progressive change in the direction
of movement. At peak upstroke the wings are positioned about 60
degrees above horizontal and full extension of the digits has ori-
ented the distal plagiopatagium and all but the trailing edge of the
chiropatagium almost behind the leading edge (Fig. 15K). The
terminal phalanges of digits III, IV, and V still are slightly flexed
ventrally from the dorsal air pressure during abduction, thus the
trailing edge of the chiropatagium is below the plane of the rest
of the wing. The hind limbs are fully extended posterior to the
body and parallel with its long axis.
The downstroke begins with a slight anterior swing of the brachii
(Fig. 15L) accompanied by adduction and pronation of the arms.
This movement depresses the leading edge of the wings and elim-
inates the ventral flexion of digits IV and V. Eisentraut (1936)
maintained that complete extension of the phalanges of digits IV
and V is the result of air pressure against the membrane adjacent
to them. However, analysis of several high-speed motion picture
films of the start of the downstroke leads me to believe that, al-
though adduction of the wing is evident and air pressure from
below contributes to this movement, an active dorsal extension of
the digits also is involved. The movement of the wing is slight as
the phalanges are rapidly extended. There appears to be no pro-
nounced dorsal billowing of the chiropatagium between digits III,
IV, and V as would be expected if the force of the air were causing
the movement of the phalanges. As adduction of the wings pro-
34 Spec. Publ. Amer. Soc. Mamm. 6
gresses ventrally and slightly anteriorly, the arms remain strongly
pronated. The pronation and the force against the air below the
wings cause the trailing edges of the distal half of the plagiopata-
gium and the chiropatagium to be about 10 degrees above the
leading edges (Fig. 15L-M). This portion of the wings is thus in
a thrusting configuration, as the air is readily accelerated poste-
riorly to impart a forward component of force to the wing, as
described by Eisentraut (1936) for this phase of the wingbeat in
forward flight of other bats. The leading edge of the chiropata-
gium, or digits II and III, is depressed relatively more than the
membranous propatagium because of the strong pronation of the
brachium. Even when the limb is in a fully extended position, the
long axis of the forearm is angled between 30 and 40 degrees
ahead of the axis of the brachium; thus pronation of the brachium
imparts a ventral swing to the distal forearm and anterior digits
(Fig. 15M). Air pressure tends to bend the phalanges of digit IV
dorsad thus adding to the thrusting configuration of the wing. The
dorsal bending of the fourth digit to produce the thrusting of the
distal chiropatagium is described by Vaughan (1959, 1970c?,
1970^), who estimated that in the species of bats he studied no
more than 20 per cent of the wing produced thrust during any
phase of the wingbeat cycle (Vaughan, \910d). It is evident from
analysis of the motion pictures of Desmodus in flight that probably
60 to 80 per cent of the wing provides thrust. This thrust is greater
distally than proximally because of the greater angle of anteroven-
tral inclination of the chiropatagium and the more rapid move-
ment of the wing distally. The extremely large part of the wing
producing thrust is probably necessitated by the high wing loading
in this species coupled with the habit of taking off from the ground
where high thrust is vital to gain sufficient airspeed for more ef-
ficient flight.
The hind limbs are depressed concurrently with, or slightly later
than, the adduction of the brachii and thus depress the trailing
edge of the plagiopatagium, which in turn shapes the medial half
to one quarter of the plagiopatagium into a more cambered surface
than at the start of the downstroke.
Superimposition of successive motion picture frames of the
coasting phase of a jump and the first wingbeat indicates that, prior
to the beginning of the downstroke, the upward velocity has
dropped to about 0.3 m per second although the forward speed
Altenhach — Vampire Locomotor Morphology 35
has been increased by the flick phase of the upstroke. By the end
of the first half of the downstroke, upward velocity of the body
increases to an average of 0.5 m per second indicating production
of lift. Forward velocity also increases, indicating production of
thrust during the downstroke. The magnitude of this acceleration
was not calculated because the bat was flying toward the camera.
Direct observation of the motion pictures projected at 16 frames
per second shows a definite upward "hop" of the bat during the
first downstroke. The amplitude of the hop varied between dif-
ferent films but was as great as 12 mm during the first half of the
stroke. This hop is equally evident in flights where the forward
speed at the start of the downstroke was extremely low (about 0.1
m per second). It seems obvious that an upward and forward ac-
celeration of the bat results from a downward and backward ac-
celeration of air as the wings are swept through the downstroke.
From the level of the body, the path of the downstroke becomes
increasingly more anterior. The arms remain strongly pronated as
the wings are adducted past the level of the body, but as they reach
an angle of approximately 30 degrees below a horizontal plane
through midbody, the pronation is lessened (Fig. 15N). The up-
ward bending of the phalanges of digit IV continues, although the
anteroventral inclination of the leading edge is reduced. The up-
ward deflection of digit V is eliminated by flexion of the phalanges,
thus increasing supination of the wing, and continuous depression
of the hind limbs depresses the trailing edge of the entire plagio-
patagium below the leading edge of the wing. Air acceleration
during this phase of the stroke would be strongly downward and
would supply a component of high lift.
As the wings reach an angle of roughly 50 degrees below hori-
zontal, the adduction of the brachii is almost stopped and a flexion
of the forearms and pronounced supination of the arms begin
(Fig. 15N-0). This movement strongly supinates the distal half of
the wings and swings them anteriad and mediad. The air accel-
eration from the more medial portions of the wing is directed
somewhat downward by these movements thus producing more
lift and thrust while air acceleration from the chiropatagium still
produces thrust.
Upstroke and flick. — There is no sudden transition into the up-
stroke, rather a uniform transition to a different direction of move-
ment. As the opposing planes of chiropatagii become parallel, con-
36 Spec. Publ. Amer. Soc. Mamm. 6
tinuing flexion of the forearms and supination of the brachii lift
them vertically in this position (Fig. 150) toward the level of the
body. The digits remain fully extended during this movement and
the vertical orientation of the entire chiropatagium and much of
the distal plagiopatagium keeps the air resistance to this movement
minimal.
Abduction of the brachii begins with the vertical movement of
the forearms and occurs simultaneously with abduction of the hind
limbs. The elastic properties of the plagiopatagium, and perhaps
also contraction of the M. coraco-cutaneous, appear to reduce its size
when the wings are in an anterior position and probably help to
reduce drag. The hind limbs maintain tension posteriorly to stretch
the membrane and prevent it from flapping from the forward
motion of the body. Since the bat is rapidly accelerating during
the first few wingbeats, reduction of drag is vital.
There is considerable flexion of the phalanges of digits III, IV,
and V during this phase of the stroke, probably the result of sud-
den loss of pressure against the ventral surface of the chiropata-
gium and distal plagiopatagium while this membrane is raised ver-
tically. Considerable flexion of the digits (metacarpals) toward the
forearm also occurs during the last phase of this part of the stroke.
Flexion of the phalanges at this stage is of functional importance
since their extension during the next stage provides increased
thrust.
As abduction and supination of the brachii raise the carpi above
the level of the body, extension of the forearms begins. Extension
of the forearms and digits and abduction of the brachii swing the
chiropatagii first laterally and then posterodorsally (Fig. 15P). The
posterodorsal swing is exaggerated by a pronation of the brachii
when they reach their highest angle of inclination (Fig. 15Q). This
is the thrusting phase described in the upstroke of other species
of bats by Eisentraut (1936) and Norberg (1970a), who termed it
the "flick phase." As the chiropatagium is extended, supinated,
and abducted from a vertically oriented position anterior to the
head, its movement against the airstream imparts a large compo-
nent of forward thrust to the wings.
There is extreme variation in the first wingbeat cycle, and the
above description pertains only to flight that is nearly horizontal.
Frequently the digits are not fully extended at the beginning of
the downstroke and the phalanges of digit III remain flexed at the
jf^
Altenbach — Vampire Locomotor Morphology 37
13^
V
-c?
s
?fsr
(rw
rCP^ <
w
BB
~y<
^-.
^■/=
cc
Fig. 16. Drawings at 15 millisecond intervals of Desmodus in a jump into flight
with the digits not fully extended.
38 Spec. Publ. Amer. Soc. Mamm. 6
TABLE 1
Relative Lengths of Time (in Seconds) of Phases of Wingbeat Cycles of
Desmodus rotundus Following a Jump into Flight in Five Trials of Individuals.
Abbreviations: L Initial flick; D, Downstroke; U, Upstroke prior to Flick;
F, Flick.
Wingbeat
number
Phase
Trial number
1
2
3
4
5
I
.030
.048
.036
.040
.038
1
D
.052
.040
.048
.048
.052
U
.020
.020
.024
.024
.024
F
.018
.022
.024
.018
.028
2
D
.048
.054
.050
.048
.056
U
.014
.028
.026
.026
.022
F
.022
.016
.020
.018
.018
3
D
.052
.058
.052
.050
.050
U
.014
.020
.020
.018
F
.026
.018
.018
.020
4
D
U
F
.058
.020
.024
second and third interphalangeal joints. This illustrates the im-
portance of the thrust produced by the medial chiropatagium and
distal plagiopatagium as the leading edge of the wing is declined
below the trailing edge. The view that thrust is produced only by
the propeller configuration of the distal chiropatagium between
digits III and IV as the phalanges of digit IV bend upward ob-
viously does not apply to the initial flight of Desmodus. Figure 16
illustrates this in a bat jumping into a flight path that is inclined
upward about 10 degrees. The upward and forward momentum
imparted by the jump was low and the bat initiated flight with an
air speed of about 0.2 m per second. The first downstroke starts
with the digits partially extended from the forearm and the pha-
langes of both third digits flexed in a configuration typical of a
folded wing (Fig. 161). Because the bat is flying toward the camera,
the forward speed is nearly impossible to calculate without complex
photogrammetric procedures. However, forward acceleration was
reflected in the increasing size of the image of the bat on the film.
The drawings in Fig. 16 all are to the same scale and do not reflect
increasing size of the photographic images. The digits are not fully
extended until the last of the third wingbeat cycle (Fig. 16CC), yet
Altenbach — Vampire Locomotor Morphology 39
prior forward acceleration (Fig. 16G-CC) indicates thrust was pro-
duced. The propeller configuration of the chiropatagium noted
above, and described earlier by Vaughan (1959), was certainly not
possible, thus thrust was probably produced by the distal portion
of the plagiopatagium and the proximal portion of the chiropa-
tagium during the downstrokes. No doubt the initial flick and the
flicks in the subsequent wingbeat cycles produced additional thrust.
Time periods for the initial flick and for portions of initial wing-
beat cycles in several flights are presented in Table 1. Although
there is considerable variation between flights, it is evident that the
initial flick, because of its greater amplitude, lasts longer than sub-
sequent flicks and provides thrust over a longer period. The up-
strokes (including the flick) require less time than the downstrokes,
as Eisentraut (1936) described for other species, and reflect the
low resistance of the wing against the air stream initially, and the
rapidity of the flick.
Steeply inclined flight and turning maneuvers. — If the flight path is
inclined steeply upward or if the bat executes a relatively sharp
turn during the first few wingbeats after a jump, the angle of the
long axis of the body is usually steeply inclined during the coasting
phase of the jump and initial wingbeats. Figure 17 illustrates a
jump from an inclined surface and an immediate right turn into
nearly level flight. Both upward and forward velocities were low
(about 0.2 m per second) at the start of the initial flick. The body
is inclined upward at about 60 degrees during the coasting phase
of the jump and remains in this attitude during the entire turn.
The flick progresses as described above, but the inclination of the
body directs more of the air acceleration downward thus providing
both upward and forward acceleration to the body (Fig. 17I-K).
The downstroke is similar to the one described above and is char-
acterized by strong pronation that orients the leading edge of the
wing approximately 20 degrees below the trailing edge over the
distal two-thirds of the plagiopatagium and entire chiropatagium.
The inclination of the body directs much of the air acceleration
downward, thus supplying high lift and upward momentum. The
downstroke progresses far ventrally, relative to the bat, apparently
to provide air acceleration for a relatively longer time than in hor-
izontal flight after a jump (Fig. 17L-M). The bat has jumped into
a virtual stall and needs all possible downward air acceleration to
remain airborne. The turn is initiated at the flick phase of this
40 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 17. Drawings at 20 millisecond intervals oi Desmodus in a jump into steeply
inclined initial flight.
wingbeat, but the unilateral differences that effect the turn are
subtle. In another series of drawings of a turn following a jump,
the right hind limb is depressed far below the left early in the first
two downstrokes (Fig. 18I-J, 180-P). This provides greater drag
on the right side of the body as well as reduced thrust resulting
from reduction of the area of the wing oriented to provide thrust.
The resultant differences in forward velocity of the wings appar-
ently produce a right turn. The upstroke effects a horizontal ori-
entation of the body, and the flight progresses horizontally at near-
ly a right angle to the direction of the jump (Fig. 18R-U).
In flight inclined at greater angles, the wing movements are
similar but the inclination of the body is greater. High amplitude
downstrokes occur at about the same angle relative to the bat, but
the resultant air acceleration is directed downward to provide up-
ward momentum.
Altenbach — Vampire Locomotor Morphology 41
1> i> 4^ -f^ f ? '"i
J
If"
Fig. 18. Drawings at 20 millisecond intervals of Desmodus in a jump into flight
followed by a turn during the first two wingbeats.
Slow Forward Flight
High-speed still photographs (Figs. 19, 20) taken from the side,
about four to eight wingbeats after a jump into horizontal flight,
illustrate changes that occur in the wingbeat cycle and show rather
subtle features of the wings that are not apparent in the motion
pictures. This series of pictures was selected from nearly 300 still
photographs of flight sequences of different individuals to best
illustrate particular features of the wingbeat cycle.
42 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 19. High-speed still photographs of stages in the downstroke of Desmodus
in slow, forward flight.
After the first four to eight wingbeats in level flight the bat has
accelerated to about 2 m per second and its aerodynamic require-
ments have changed somewhat from those in the wingbeats im-
mediately following a jump into flight. The bat is still accelerating
to a flight speed that is typically over 5 m per second and the
Altenbach — Vampire Locomotor Morphology 43
wingbeat must still produce lift and thrust. However, the bat has
the advantage of air speed that will allow the deflection of air by
the wings as the bat passes through it.
Downstroke. — At the start of the downstroke the strong pronation
characteristic of the beginning of adduction is evident (Fig. 19A).
As the downstroke progresses, pronation of the entire arm is evi-
dent, and an upward deflection of the terminal two bony phalanges
of digit III and the phalanges of digits IV and V can be seen (Fig.
19B-C). This upward deflection is the result of the upward pres-
sure of air as the wing is adducted and perhaps contraction of the
phalangeal extensors as well. The deflection is most obvious in
digits III and IV (about 30 degrees above the long axis of the
metacarpals) and only slight in digit V (about eight degrees above
the long axis of metacarpal V). The upward deflection of the pha-
langes of digit V appears unique and has not been described for
any other bat. This configuration increases the posterodorsal in-
clination of the medial wing and, along with the upward billowing
of the distal half of the plagiopatagium, produces a thrusting sur-
face for this part of the wing. The upward deflection of digit IV
is typical of all bats during the downstroke, and serves primarily
to increase the upward inclination of the chiropatagium between
digits III and IV to provide a high thrust component, as this part
of the wing is adducted at a higher velocity than the more medial
parts of the wing. The upward inclination of the phalanges of digit
III is more difficult to explain functionally. It reduces the forward
thrusting capabilities of the distalmost part of the wing and directs
forces on the membrane between the phalanges of digits III and
IV medially, rather than anteriorly, as exhibited in other species
of bats (Eisentraut, 1936; Vaughan, 1959, 1970^, 1970^; Alten-
bach, 1968). Due to the posterior curve of the distal part of the
leading edge of the chiropatagium and the strong pronation of the
arm, low resolution photographs of the bat flying toward the cam-
era do not show this condition, although it may be present. Al-
though this configuration of the distal wing is perhaps important
in providing lift later in the downstroke, it may function at this
stage to alter the tip vortex. The bat has an air speed of about 2
m per second at this time, and certainly tip vortices could alter
airflow characteristics across more medial parts of the wing. Des-
modus has an extremely high wing loading and does not have a
long wing to displace the tip vortices distally as do some of the
44 Spec. Publ. Amer. Soc. Mamm. 6
equally heavily loaded molossid bats, such as Eumops perotis and
Tadarida molossa (Vaughan, 1959, 1966), and Molossus ater (Hart-
man, 1963). Other means of reducing the vortices may be essential
in Desmodus. Photographic evidence for heavily loaded, low aspect
ratio bats like Artibeus jamaicensis would be interesting to analyze
to see if this phenomenon also occurs in them.
As the wing is adducted to the level of the body, the dorsal
deflection of phalanges of digit V is first reduced and then elimi-
nated by ventral flexion (Fig. 19D-E). Adduction of the hind leg
during this stage depresses the trailing edge of the plagiopatagium
and increases the camber to deflect and accelerate air downward
to provide an increasing component of lift (Fig. 19D-F). As the
wing is adducted below the body (Fig. 19F-G), flexion of the pha-
langes of digit V becomes more pronounced and, along with con-
tinued adduction of the hind limbs, increases the camber and angle
of attack of the entire plagiopatagium and medial half of the chi-
ropatagium between digits IV and V. The phalanges of digits IV
and III remain deflected upward to maintain the thrusting con-
figuration of the lateral chiropatagium between the phalanges of
digits V and IV, and of all the surface between the phalanges of
digits III and IV. As the stroke progresses anteriad and ventrad,
the configuration of the lateral chiropatagium that produces pos-
terior air acceleration and thrust in the middle of the downstroke
now produces increasing lift generation from this portion of the
wing (Fig. 19H-I).
Upstroke and flick. — The flexion of the forearms approximates
the distal plagiopatagii and chiropatagii as described in initial
flight, and supination and abduction of the brachii raise the fore-
arms, and thus the vertically oriented wings, parallel and anterior
to the body (Fig. 20J-L). The smooth transition from downstroke
to upstroke by an anterior and medial movement of the wings is
important for two reasons. First, this type of transition allows for
a wing configuration that permits a thrust and lift generating
movement during the upstroke. Second, the waste of muscular
effort to reverse direction of movement is reduced by a transition
involving only gradual change of configuration and direction of
movement. At the level of the upper body, flexion of the digits is
noticeable (Fig. 20M), and the flick phase is initiated by extension
of the forearm and digits, and by abduction and pronation of the
arm at the brachium (Fig. 20N-O). The phalanges of digits III,
Altenbach — Vampire Locomotor Morphology 45
Fig. 20. High-speed still photographs of stages in the upstroke and flick of
Desmodus in slow, forward flight.
IV, and V remain ventrally flexed during this rapid movement
and help maintain an efficient thrusting surface. Although Eisen-
traut (1936) described this flick phase in detail and suggested it
provided a strong forward thrust, it has not been credited with
providing thrust by more recent investigators of bat flight. Most
other descriptions of bat flight, except that of Eisentraut (1936),
imply that the upstroke in bats is typically a recovery stroke, as it
is in most birds (Storer, 1948), and provides no forward thrust.
The strongest evidence that the flick phase actually produces thrust
46 Spec. Publ. Amer. Soc. Mamm. 6
is the acceleration seen during the flick phase prior to the initial
downstroke after a jump into flight described earlier. The still
photographs illustrate the ventral and anterior billowing of the
chiropatagium between digits III, IV, and V (Fig. 20O) as the
chiropatagium swings laterad, posteriad, and dorsad. Similar bil-
lowing of the plagiopatagium immediately medial to digit V of the
chiropatagium and between the phalanges of digits V, IV, and III
is evident in Fig. 20P-Q, indicating that an anterior force is gen-
erated here by the pressure of the airstream. The billowing of the
patagii anteriorly, the rapidity of the movements of the flick phase,
and the acceleration evident during a similar movement after a
jump provide convincing evidence that considerable forward
thrust is produced.
Motion picture data on slow forward flight. — A series of drawings
from motion picture film taken of the third and the beginning of
the fourth wingbeat after a jump into horizontal flight further
illustrates some of the features considered previously (Fig. 21).
The pronation at the first of the downstroke is seen at A and B.
The leading edge of the wing at the level of digit V is depressed
fully 15 degrees below the trailing edge. Although not visible, the
phalanges of digit V are probably deflected upward, because the
upward deflection of the phalanges of digits III (second and third
phalanges), and IV can readily be seen in the right wing (Fig. 2 IB).
As the wing is adducted, the effect is no longer obvious, illustrating
that the angle of the wing relative to the camera can easily obstruct
the view of critical details of the flight mechanism. In Fig. 21D-H,
the adduction is clearly seen as is a decrease in pronation and
increase in medial camber accompanying depression of the hind
limbs during the last half of the downstroke. Flexion of the fore-
arms (Fig. 21G-I) brings the wing medially and strongly anteriorly.
The flick phase is initiated at Fig. 21J and terminates about 22
milliseconds later between M and N. Fig. 21N-Q shows the begin-
ning of adduction and pronation of the wing and establishment of
the upward deflection of the phalanges of digits III and IV.
Although they do not show the upward deflection of the pha-
langes of digit V, drawings of frames of motion picture film taken
from the side of a bat in forward, horizontal flight at about 2.5 m
per second show the upward deflection of the phalanges of digits
III and IV, the purely ventral movement of the strongly pronated
wing to the level of the body, and the decrease in pronation after
AUenbach — Vampire Locomotor Morphology 47
tj^ "^y
i^-^
'C^..
Fig. 21. Drawings of a head-on view of Desmodus in slow forward flight. Time
intervals (milliseconds) between successive positions are: A-B, 6; B-C, 12; C-D, 8;
D-E, 8; E-F, 8; F-G, 10; G-H, 8; H-I, 6; I-J, 6; J-K, 8; K-L, 6; L-M, 6; M-N,
4; N-O, 2; O-P, 2; P-Q, 6.
48 Spec. Publ. Amer. Soc. Mamm. 6
^3 ^v,
F G -^ H '<-! V\ % J
P
i3
S T U
Fig. 22. Drawings at 5 millisecond intervals of a side view of Desmodus in slow,
forward flight.
Altenbach — Vampire Locomotor Morphology 49
that point (Fig. 22A-G). It is certainly possible that at this airspeed,
the upward deflection of the phalanges of digit V may be oblit-
erated or prevented in the early downstroke by phalangeal flexors.
Sufficient thrust may be generated by posterior air acceleration
from more distal parts of the wing, and it may be advantageous to
maintain a cambered medial wing to deflect air downward and
produce lift. In the last part of the downstroke, the wing is oriented
more anteriorly and adducted to about 70 degrees below horizon-
tal. The deep amplitude of the downstroke seems characteristic of
slow, stable, accelerating flight and is probably an effort to get as
much forward thrust and lift as possible from the downstroke. The
initiation of the upstroke begins with flexion of the strongly ad-
ducted forearm, which raises the vertically oriented distal segment
of the wing. Abduction and supination of the brachium begin rel-
atively later than in the initial few wingbeats, perhaps to delay the
flick phase until the wing is slightly above the level of the body.
Early initiation of the flick phase from a ventral position would
necessitate the abduction of the plagiopatagium in a relatively hor-
izontal position over a fairly wide arc, and thus would require
considerable energy. When the flick phase is delayed until the wing
is above the body, the plagiopatagium is raised to the level of the
body in an anteriorly oriented, stretched, low drag configuration
(Fig. 22K-0). During the flick phase, the lateral plagiopatagium
produces thrust along with the chiropatagium (Fig. 22P-S). As
flight speed increases, the flick probably plays a lesser role in thrust
generation.
Alighting Maneuvers on Horizontal Surfaces
As Desmodus is so highly terrestrially oriented in feeding behav-
ior, the transition between flight and terrestrial locomotion on a
horizontal surface is an important aspect of its locomotor behavior.
Again, the maneuvers in this phase of locomotion are quite dif-
ferent depending upon differences in the flight prior to alighting,
the contour of the surface, and, no doubt, individual differences.
Tracings from a high-speed motion picture film of a bat alighting
from slow, almost hovering flight (about 0.2 m per second), show
that as the wings are in position for a downstroke, there is a strong
anterior movement of the forearms by an anterior swing of the
brachii and flexion of the elbows (Fig. 23A-B). The forearms.
50 Spec. Publ. Amer. Soc. Mamm. 6
\f ^^ ^"^ "^^ ^% -"^
O H . ^ - \ . " .
Fig. 23. Drawings at 10 millisecond intervals of Desmodus alighting on a hori-
zontal surface.
oriented parallel to the long axis of the body, which is inclined
anteriorly, are lowered by adduction of the brachii to the level of
the body (Fig. 23B-D), and the digits are folded toward the con-
figuration seen in terrestrial locomotion. Strong flexion occurs at
the joints between phalanges two, three, and four of digit III, and
between phalanges one and two of digits IV and V. As the brachii
are adducted below the middle of the body, pronounced extension
of the elbows begins (Fig. 23D-E). Adduction and an anterior
swing of the brachii orient the forelimbs almost vertically beneath
the shoulders. Prior to contact with the substrate, the thumbs are
nearly in line with the long axis of the forearms (Fig. 23E). As the
thumbs contact the substrate, they bend upward at the metacar-
pophalangeal joints to begin absorption of the impact. A posterior
swing and abduction of the brachii shift the center of gravity an-
teriorly over the forelimbs and, in combination with flexion of the
elbows, begin to break the fall (Fig. 23F-I). Dorsolateral bending
of the first metacarpals lowers the carpi to the substrate during
these movements and also probably helps break the fall. The body
remains inclined anteriorly below horizontal, but the hind limbs
are flexed at the knees and adducted posterolaterally to accom-
modate the ventral pull of the plagiopatagii. As the brachii are
abducted to the level of midbody, the inclination of the body is
reduced, thus dropping the hind limbs toward the substrate (Fig.
23H-L). The folding of digits of the forelimbs is complete before
Altenbach — Vampire Locomotor Morphology 51
the hind limbs contact the substrate (Fig. 23L). Nearly all of the
shock of the landing is absorbed by the pectoral limbs, and the
hind limbs appear to absorb little of the energy.
Many parts of the fall-breaking maneuver are similar to the
movements seen in a jump, although the direction of movement
is reversed. No electromyographic data are available, but no doubt
the muscles that power the jump supply force to break a fall in a
sequential series of contractions. The pelvic limbs play an even
lesser role in alighting on a horizontal surface than during a jump.
When released in confined and unfamiliar surroundings, Des-
modus often lands on the floor with a solid "plop," indicative of
little or no breaking of the fall. However, when accustomed to the
surroundings, as in a large flight cage or in a roost, the alighting
is delicate and almost noiseless. I assume that, when alighting on
a horizontal surface from flight, the breaking maneuver of the
pectoral limbs is used consistently. This behavior is of obvious ad-
vantage to avoid internal injuries from a hard fall, and perhaps to
lessen the noise of alighting when intending to feed on a host
animal from the ground or to lessen the impact when alighting
directly on the animal. Because my observations and those of oth-
ers indicate that Desmodus often flies close to the ground (Wimsatt,
1959), a simple stalling or braking maneuver could cut air speed
and allow a short drop to the ground that would not necessitate
strong breaking of a fall.
Alighting Maneuvers on Vertical Surfaces
When alighting on a vertical surface from forward flight, Des-
modus characteristically executes a steep bank during the flick phase
of the upstroke and brakes with a shallow downstroke. As the bat
slows, its digits are rapidly flexed toward the forearm and the
phalanges of digits III, IV, and V are flexed ventrally. The fore-
limbs and hind limbs appear to contact the surface simultaneously
in a spread position, as described by Eisentraut (1936) for Myotis
myotis. In Desmodus, the hind limbs are flexed at the knee and
oriented posterolaterally. The forelimbs are only slighdy flexed at
the elbow, and the thumbs are directed laterally. Immediately
upon alighdng, the bat turns head down by alternate flexion of
the hind limbs, and hangs in the characteristic posture with the
hind legs flexed at the knee and the forelimbs slighdy flexed and
52 Spec. Publ. Amer. Soc. Mamm. 6
oriented laterally. The thumbs are directed dorsolaterally, with the
weight distributed between the daws and the two pads, which press
into depressions in the surface. The head is strongly upturned,
and the body is inclined outward between 10 and 20 degrees from
the surface. From this position the bat can climb or jump into
forward flight as described earlier. The turn after alighting is so
rapid that the bat appears to alight upside down after a sharp
banking turn toward the surface.
POSTCRANIAL OSTEOLOGY
Positional Terminology
FOLLOWING the practice of Vaughan (1959, 1966, 1970^, 1970c,
1970rf), I have used the same positional terms for the bat body
as employed for other vertebrates. The arm and manus (wing) are
described as though fully extended in the middle of the downstroke
(Fig. 24). The pollical side of the manus is anterior, digit V is
directed posteriorly, digit IV is directed posterolaterally, and digits
III and II are directed laterally to the level of the first interphal-
angeal joint of digit III. The terminal phalanges of digit III are
oriented posterolaterad. The palmar surface of the hand and wing
is considered ventral and the opposite side is considered dorsal.
Following Norberg (19706), the upper side of the bones of the arm
is considered as dorsal, the lower side as ventral. Thus the ulnar
side of the radius is posterior, the opposite side anterior. When
strongly flexed, the forearm opposes the anterior surface of the
humerus.
The hind limbs of a bat are oriented differently from those of
other mammals, and positional terms for them are confusing. This
problem is particularly severe in Desmodus, because the hind limbs
are extremely mobile and can be oriented in more positions than
those of other bats. For general descriptive purposes, the limb is
considered as in flight during the first part of the downstroke (Fig.
19A) when it is oriented similarly to the hind limb of Macrotus
(Vaughan, 1959). The plagiopatagial side of the limb is considered
lateral, the opposite side is medial; thus the tibia is lateral, and the
fibula is medial. The hind foot is oriented with the plantar side
Altenbach — Vampire Locomotor Morphology 53
chiropatagium
Fig. 24. Ventral view of Desmodus with parts of the flight membranes and po-
sitional terms relative to the arm, hand, and pelvic limb: I-V are metacarpals of
corresponding digits and 1-4 are phalangeal elements; superscript "c" indicates the
phalanx is cartilaginous. The right wing is folded as in terrestrial locomotion and
the left wing is extended as in mid-downstroke of forward flight.
ventral and the opposite side dorsal. Movements in the plane of
the wing membranes are termed either tibial or fibular. Digit V is
located on the medial side of the foot and digit I on the lateral
side.
Vertebral Column
Desmodus has seven cervical, 12 thoracic, six lumbar, five sacral,
and no caudal vertebrae. Only the most significant features of the
vertebrae are described below.
Cervical vertebrae. — The atlas and axis allow extreme lateral and
vertical mobility of the skull, which is advantageous for making
incisions in a host animal prior to feeding. The remainder of the
cervical vertebrae are relatively short and broad and have well-
developed transverse processes. These processes have a broad,
flange-like projection ventrally and a thin posterodorsal projection
that serves for the origin of the four slips of the M. levator scapulae
on the last four vertebrae.
Thoracic vertebrae. — Anteriorly the vertebrae are relatively short
54 Spec. Publ. Amer. Soc. Mamm. 6
lateral process
articular facet for clavicle
1st costal cart.
manubrium
body
xiphoid process
ventral process
posterior process
Fig. 25. Sternum and first costal cartilages of Desmodus. A, ventral aspect; B,
lateral aspect.
and wide, and become increasingly longer and narrower poste-
riorly. The articulations between these vertebrae are similar to
those of Macrotus as described by Vaughan (1959), but are more
rigid, and the vertebral elements are closer together, providing a
sturdy chain of bone.
A solid, tubercle-like, spinous process projects 1 mm dorsally
from the mid-dorsal portion of the vertebral arch of the first tho-
racic vertebra. Bordered laterally by ridges that give rise to thin
projections extending posteriorly beyond the border of the ver-
tebra, it serves for the point of origin of the thickest portion of the
trapezius muscles. The spinous processes of the next two vertebrae
are represented by slight mid-dorsal elevations bounded laterally
by prominent, posteriorly projecting ridges similar to those de-
scribed on the first thoracic vertebra. On more posterior vertebrae,
these ridges converge toward the midline and at the fifth thoracic
vertebra, fuse medially to form a mid-dorsal ridge approximately
0.5 mm wide. On the sixth and successive vertebrae these ridges
widen posteriorly to form a triangular dorsal prominence. The
apex of the prominence on the last thoracic vertebra is directed
anteriorly and is 1.2 mm in width at the posterior margin of the
vertebra.
Lumbar vertebrae. — The mid-dorsal spinous processes are more
Altenbach — Vampire Locomotor Morphology 55
pronounced on the lumbar vertebrae. They become arrowhead-
shaped, and the anterior point of one vertebra projects into a pos-
terior indentation on the one before it. The spinous processes on
the third, fourth, and fifth lumbar vertebrae are extremely high,
and those of the fourth and fifth are low anteriorly and project
strongly upward and backward. The centrum of the last lumbar
vertebra is fused with the centrum of the first sacral vertebra and
its transverse processes articulate laterally with the medial borders
of the ilia.
Sacral vertebrae. — These are completely fused to each other and
laterally to the medial aspect of the ilia. The fused vertebrae taper
posteriorly into a laterally compressed rod of bone that arches
posterodorsally for almost the length of the pelvic girdle. The pos-
teroventral margins of the fused vertebrae are fused to the ischia
immediately dorsal to the ischial tuberosities.
Sternum
In Desmodus, the sternum is composed of three distinct parts —
manubrium, body, and xiphoid process — joined by thin cartilagi-
nous discs. The manubrium has a laterally compressed and slightly
anteriorly directed ventral process (Fig. 25A-B). Lateral processes
project about 15 degrees dorsally and swing slightly anteriorly to
enlarged distal ends, which have an anterolaterally and slightly
dorsally oriented articular surface for the clavicle and a laterally
directed articular surface for the first costal cartilage (Fig. 25A-B).
A posterior process, approximately 2.5 mm long and triangular in
cross-section, has a ventral apex that forms a thin ridge continuous
anteriorly with the posterior edge of the ventral process. The ar-
ticular facets of the costal cartilages of the second pair of ribs are
located on the posterolateral surfaces of the posterior process.
The elongate body of the sternum is about 8 mm in length. It
is roughly triangular in cross-section, slightly rounded dorsally,
and, unlike many phyllostomatid bats, has no enlarged midventral
keel. Articular facets for the costal cartilages of ribs three through
six are arranged along the lateral borders at progressively shorter
intervals (Fig. 25A-B).
The xiphoid process is slightly less than half the length of the
body and is almost square in cross section in its anterior region.
56 Spec. Publ. Amer. Soc. Mamm. 6
The costal cartilages of the seventh pair of ribs articulate on the
anterolateral aspects of the xiphoid process. Posteriorly the xi-
phoid process becomes dorsoventrally flattened and terminates in
an expanded flange.
Ribs
The rib cage is about 1.4 times as broad and 1.1 times as deep
as it is long. In one specimen, it was about 5 mm deep and 13.5
mm wide at its anterior end, and was expanded posteriorly to a
depth of about 18 mm and breadth of 26 mm.
The first rib is strongly thickened anteroposteriorly as described
by Vaughan (1959, 1970^) for other species of bats. A stout tu-
bercle is found on the dorsal aspect immediately distal to the tu-
berculum. The rib arches gently dorsad and terminates in an ex-
panded tip, which articulates with the thick, first costal cartilage.
The costal cartilage is parallelogram-shaped and articulates on its
dorsal surface with the first rib and on its medial surface with the
lateral process on the manubrium. Inasmuch as the remaining cos-
tal cartilages of the sternal ribs are thin, the first costal cartilages
provide much of the support of the sternum and reinforce it
against the powerful dorsolateral pull of the sternal M. pectoralis.
The second and third ribs are anteroposteriorly flattened, but cau-
dally the ribs become dorsoventrally and laterally flattened. Rib
seven is the last sternal rib, and the costal cartilage of rib eight
connects with its costal cartilage. The cartilage of rib nine attaches
to the costal cartilage of rib eight, but the cartilage of rib 10 con-
nects directly with rib nine and the cartilage of rib 1 1 connects to
rib 10. The twelfth rib is normally less than a millimeter long and
has poorly defined distal connection.
Pectoral Girdle and Limb
Scapula (Fig. 26). — Viewed dorsally, the scapula is roughly elip-
tical posteriorly, truncate anteriorly, and about 41 per cent as wide
as it is long. The glenoid fossa is directed slighdy craniolaterally.
The ardcular surface is anteroposteriorly elongated and is twice as
high posteriorly as anteriorly. The posterior half of the fossa is
deeply concave and strongly reinforced posteriorly by the expand-
Altenbach — Vampire Locomotor Morphology 57
coracoid process
coracoid proc.
scapular flange
onnective tissue b
supraspinous fossa
spine
anteromedial
facet
ntermediate
facet
posterolatera
facet
glenoid fossa
lateral border
supraglenoid tuberosity
coracoid process
acromion process
scapular flange
Fig. 26. Scapula and proximal portion of humerus of Desmodus: Ventral view
of right humerus (A) and scapula (B); dorsal view of right humerus (D) and scapula
(C); anterior view of right scapula (E).
ed lateral scapular border. Paired infraglenoid tuberosities are sit-
uated immediately posterior to the fossa and serve as points of
origin for slips of the long head of the M. triceps brachii. The thick
lateral scapular border slopes gently posteromedially and becomes
progressively thinner toward the rounded posterior margin. The
medial border, which is not as thick as the lateral border, is nearly
parallel with the long axis of the body. Anteriorly, the medial bor-
der is thickened dorsoventrally and curves laterally to form the
scapular flange. Lateral to the flange, the anterior scapular border
is concave for about 2 mm, and then becomes thickened and di-
rected anteriorly to form the projection that is the base of the
coracoid process. Laterally, the thickened anterior process bears
a small supraglenoid tuberosity that lies immediately anterior to
the glenoid fossa.
The anteroposteriorly flattened coracoid process extends ven-
trally from the thickened anterior projection of the scapula, medial
to the supraglenoid tuberosity, and then curves laterally and slight-
ly posteriorly. The tip of the coracoid process is expanded and lies
below and slightly lateral to the middle of the glenoid fossa.
The dorsal surface of the scapula is transected by the scapular
58 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 27. Diagrammatic frontal view of the pectoral girdle of Desmodus: A, right
clavicle and scapula tipped ventrally and right humerus fully adducted as might
occur at the end of a jump; B, position of left clavicle, scapula and humerus at the
start of a jump or downstroke. The lateral scapular border is tipped upward and
the humerus is locked dorsally with the scapular border.
spine, which runs from the medial border anterolaterally toward
the posterior half of the glenoid fossa. Quite low medially, the
spine becomes progressively higher laterally and, about 4 mm from
the glenoid fossa, curves sharply cranially and dorsally to the
anteroposteriorly flattened acromion process. The distal 3 mm of
the acromion process is thickened and strongly anteroventrally
curved so that it lies medial to, and above, the glenoid fossa. The
lateral border of the acromion process arises about a millimeter
medial to the highest point of the glenoid fossa. A strong band of
connective tissue runs from the dorsolateral aspect of the flange
to the medial surface of the expanded tip of the acromion process,
and helps brace the latter against the pull of the abductors and
supinators of the humerus. The anteroposterior flattening of the
process and the increased height of the scapular spine also aid in
resisting these forces.
In Desmodus, the supraspinous fossa is smaller relative to the
Altenbach — Vampire Locomotor Morphology 59
infraspinous fossa than in some of the closely related phyllostom-
atids. A thickened ridge extending from the base of the acromion
process to the anteromedial edge of the posterior border separates
the large anteromedial facet from the small and nearly vertically
oriented intermediate facet. Another thickening separates the in-
termediate facet from the nearly horizontally-oriented postero-
lateral facet. The vertical orientation of the intermediate facet pro-
vides a solid surface for muscular attachment and reduces the
relative width of the entire facet. This suggests that the muscle
mass that originates there, the M. infraspinatus, is suited for pow-
erful contraction in a limited direction. Posteriorly the scapula ter-
minates in a cartilaginous extension typical of many other bats.
Clavicle (Fig. 27). — The proximal articular surface is greatly en-
larged, rather ovoid, and elongate laterally. Within 2 mm of the
articular surface, its diameter constricts to about a millimeter. At
this point the clavicle is nearly circular in cross-section, but becomes
laterally compressed distally.
In specimens preserved with the wing folded in the typical pos-
ture seen in hanging, the long axes of the proximal half of the
clavicles are oriented about 20 degrees anterolateral and about 30
degrees anterodorsal to the long axis of the body. From their prox-
imal articulations, the clavicles curve gently posterodorsally and,
over the proximal 80 per cent of their length, become increasingly
deeper (anteroposteriorly) in cross-section. The distal 20 per cent
of each clavicle is curved sharply posteriorly, and the slightly ex-
panded distal tip is displaced about 3 mm posterior to the long
axis of the proximal shaft.
The ventrolateral aspect of the distal 1.5 mm of the clavicle is
bound by tough connective tissue to the ventromedial surface of
the anterior tip of the scapula. The articular surface is elongate
and nearly horizontal, a configuration that permits the scapula to
tilt about its long axis relative to the clavicle. Angular displacement
of the long axis of the scapula is hmited to only a few degrees by
the articulation. However, when the lateral scapular border is
rocked strongly ventrally, the articulation allows the long axis of
the scapula to be inclined upward posteriorly between 10 and 15
degrees. This suggests that the anterior end of the scapula is com-
monly tipped ventrally when the lateral scapular border is tipped
ventrally, as in a jumping maneuver or in certain terrestrial feeding
postures. This helps explain the apparent depression of the shoul-
60 Spec. Publ. Amer. Soc. Mamm. 6
der joint during these movements. The curvature of the posterior
surface of the clavicle, adjacent to its distal tip, perfectly matches
the curvature of the coracoid process, and allows the coracoid pro-
cess to swing behind the clavicle (Fig. 27 A). The scapula can be
rotated about its long axis to position the coracoid process directly
behind the clavicle. When the clavicle is inclined a normal 40 de-
grees above horizontal (viewed frontally), this rotation of the scap-
ula orients the short scapular axis vertically, thus directing the
glenoid fossa ventrally. This is the most striking feature of the
pectoral girdle osteology of Desmodus and is partly responsible for
the high quadrupedal stance and remarkable jumping ability of
the species, as it allows the humerus to be directed completely
ventrally.
At the clavo-scapular articulation, the surfaces of both the clav-
icle and scapula are bordered dorsally by nearly vertical bony sur-
faces that limit upward rotation of the lateral scapular border.
When the short axis of the scapula is within a few degrees of being
parallel to the long frontal axis of the clavicle, following upward
rotation of the lateral scapular border (Fig. 27B), the supra-arti-
cular surfaces meet and stop further rotation. Rotational forces
applied to the scapula are thus transferred to the clavicle. A strong
connective tissue band runs from the middle anterior surface of
the clavicle to the middle of the coracoid process and aids in stop-
ping the upward lateral rotation of the scapula. The articulation
of clavicle and scapula allows rotation of the short axis of the scap-
ula through an arc of fully 120 degrees.
Humerus (Figs. 26-28). — This bone is relatively stocky in Desmo-
dus; the greatest diameter of the middle diaphysis is about 5.4 per
cent of the length. The head is directed posterior to the proximal
end of the shaft. Anterior to the head is a deep depression (Fig.
28E) into which the supraglenoid tuberosity fits when the humerus
is extended anteriorly. The greater tuberosity extends postero-
dorsally and medially from the medial end of the shaft. The ridge
of bone that runs between the tuberosity and the dorsal aspect of
the head articulates with the dorsal border of the glenoid fossa to
stop abduction of the humerus (Fig. 27B). Anteriorly, the greater
tuberosity gives way to a ridge that projects anteroventrally to meet
the medial end of the pectoral ridge. The lesser tuberosity projects
posteroventrally and medially from the medial end of the shaft,
and is continuous laterally with a low midventral ridge that extends
Altenbach — Vampire Locomotor Morphology 61
pectoral ridge
dorsal epicondyle
spinous process
greater tuberosity
pectoral ridge
dorsal epicondyle
capitulum
trochlea
spinous process
head
cap.
troch.
spin, proc
greater tuberosity
pectoral ridge
cap. —
troch.
spin. proc.
lesser tuberosity
Fig. 28. Humerus of Desmodus: A, dorsal view; B, ventral view; C, anterior view
of proximal end; D, posterior view of proximal end; E, medial view of proximal
end; F, anterior view of distal end; G, posterior view of distal end; H, lateral view
of distal end.
62 Spec. Publ. Amer. Soc. Mamm. 6
for several millimeters along the shaft and ends in a small tubercle
about 6.5 mm distal to the tip. A ridge runs anterodorsally from
the lesser tuberosity to the ventromedial base of the pectoral ridge.
The importance of the rotative forces applied by the muscles that
insert on the greater and lesser tuberosities is reflected by the
ridges that run from their bases anteriorly to the medial end of
the pectoral ridge.
The pectoral ridge projects anteriorly about a millimeter from
the middle of the proximal end of the shaft, beginning adjacent
to the head, and continues distally for about 8 or 9 mm. The ridge
is divided in its middle part into two ridges, one below the other,
but it becomes quite thin about 2.5 mm distal to that point and is
thin for the remainder of its length.
For the first one-fourth of its length, the shaft is quite straight
and roughly circular in cross section except for the pectoral ridge.
The distal three-fourths of the shaft is strongly bowed posteriorly
and compressed anteroposteriorly. The anterior aspect of the dis-
tal half is slightly concave. These structural features apparently
strengthen the distal shaft against the torque and strong upward
forces encountered in the wingbeat cycle and terrestrial locomo-
tion. The bowing of the distal three-fourths accomodates the
prominent forearm musculature when the forearm is strongly
flexed toward the humerus during terrestrial locomotion.
The locking mechanism between the humerus and scapula of
other bats described by Vaughan (1959) and others is quite evident
in Desmodus and limits adduction and abduction to about 30 de-
grees above and below the short axis of the scapula (Fig. 27). How-
ever, the depression anterior to the head of the humerus is suffi-
ciently deep, and the supraglenoid tuberosity is sufficiently small
and anteriorly positioned, that the humerus can be extended to
within 30 degrees of the long axis of the lateral scapular border
before being stopped by this locking mechanism. Anterior exten-
sion of the humerus is necessary for alighting on a horizontal sur-
face (Fig. 23), a backward jump (Fig. 12), and climbing on a vertical
surface (Fig. 6).
Fig. 29. Right radius and ulna oi Desmodus. A, dorsal view; B, ventral view; C,
anteromedial view of proximal end; D, ventral view of proximal end; E, dorsal view of
proximal end.
Altenbach — Vampire Locomotor Morphology 63
sesamoid for triceps tendon
radius
ulna
radius
flexor fossa for biceps tendon
ulna
ulna
radius
64 Spec. Publ. Amer. Soc. Mamm. 6
The distal articular surfaces formed by the capitulum and the
trochlea are displaced anteriorly and slightly dorsally to the axis
of the shaft (Fig. 28F-H). The groove separating the two inclined
surfaces of the capitulum is rather shallowly concave, whereas the
groove separating the capitulum from the ventral trochlea is deep-
er and rather V-shaped in section. The prominent ventral flange
of the trochlea continues to the posterior side of the epiphysis,
where the groove above it is broadened and bordered above by
the ridgelike, posterior continuation of the dorsal side of the ca-
pitulum. The ulna and the elongate sesamoid of the M. triceps
brachii tendon (Fig. 29A-B) run into this groove as the forearm is
extended. The epicondyle above the capitulum is indented (Fig.
28 A), and the M. supinator arises from the center of this indenta-
tion. Proximally, a small ridge runs posteromedially to the shaft
and serves for the point of origin of the M. extensor carpi radialis
longus and M. extensor carpi radialis brevis. Ventrally, the epicondyle
(medial epicondyle) extends slightly more than 2 mm to form a
spinous process (Fig. 28B, 28F-G). The tip of this process is located
directly below the center of rotation of the radius; thus, flexion
and extension of the radius do not affect the length of the muscles
that originate on the spinous process.
Radius and ulna (Fig. 29). — The radius is about 1.6 times the
length of the humerus and over its proximal half curves strongly
posteriorly and ventrally (Fig. 29A-B). The proximal articular sur-
face is directed anteromedially and has a central concavity that is
bordered dorsally and ventrally by low ridges and adjacent flat-
tened areas (Fig. 29B-D). The rounded ventral part of the capit-
ulum fits into the central concavity, and the inclined dorsal portion
of the capitulum and the ventral trochlea articulate with the nar-
row flattened surfaces above and below the concavity. The con-
cavity is in line with the axis of the shaft and is bordered ventrally
by a flange that makes up the ventral articular surface. A promi-
nent ridge of bone extends from the anterior border of this sur-
face, at the level of the bottom of the concavity, laterally for about
5 mm (Fig. 29B, 29D). Posterior to this ridge is a flattened, pos-
terodorsally inclined surface that ends in a deep groove (the flexor
fossa) on the posterior face of the radius. The tendons of the M.
biceps brachii and M. brachialis run ventrally over the ridge imme-
diately distal to the ventral flange and insert into the flexor fossa.
Thus, contraction of these muscles exerts both a flexive force to
Altenbach — Vampire Locomotor Morphology 65
the forearm and a powerful supinating force to the entire arm, as
the articulation of the humerus and radius severely limits any
movement except flexion and extension.
The thickened proximal end of the ulna is positioned posterior
to the ventral half of the proximal articular surface of the radius
and projects 1.5 mm beyond its proximal tip (Fig. 29A, 29D). A
vertical groove on the anterior surface of the ulna articulates with
a ridge on the posterior surface of the radius about 1.5 mm distal
to its end. A groove distal to the ridge on the radius accepts a ridge
on the ulna. This tongue-in-groove mechanism stabilizes the ulna
against the medial pull of the M. triceps brachii. Distal to the thick-
ened proximal articular area, the shaft of the ulna is thin and
concave anteriorly. The ulna is fused distally to the posterodorsal
surface of the radius at about the middle of the radial shaft. The
rigid fusion distally and strong articulation proximally suggest that
the ulna is important in bracing the radius against forces directed
toward its long axis during terrestrial locomotion or jumping. It
also affords a rigid structure for muscle attachment. Distal to the
fusion of the ulna and radius, a thin ridge runs along the postero-
dorsal surface of the radius to within 5 mm of its distal end. The
ridge is the same thickness and width as the ulna before its fusion
to the radius. Although no embryologic evidence is available, this
ridge may represent the distal end of the fused ulna. The concave
underside of this ridge serves for muscle attachment. Distal to the
fusion of the ulna with the radius, the radius is diamond-shaped
in cross section. The broad, anterodorsal surface of the distal 2 or
3 mm is divided by bony ridges into grooves for the tendons of
several of the forearm muscles (Figs. 30-31). Anteroventrally, two
ridges of bone make a deep channel for the M. abductor pollicis
longus. The large, posterodorsal ridge bordering this channel is the
anteroventral edge of a pair of channels divided by a small median
ridge. The lower channel accommodates the M. extensor carpi ra-
dialis longus and the upper accommodates the M. extensor carpi ra-
dialis brevis. Posterodorsally, a broad flat surface separates these
channels to form a prominent posteriorly-projecting flange at the
distal tip of the radius. This flange is the dorsal edge of a channel
bordered ventrally by a median projection of the cuneiform. The
tendons of the M. extensor pollicis brevis, M. extensor digitorum com-
munis to digits III and IV, and the M. extensor indicis run through
this channel. On the posterior surface of the radius medial to this
66 Spec. Publ. Amer. Soc. Mamm. 6
Fig. 30. Dorsal view of the right carpus and first digit of Desmodus.
channel is a large backward-projecting flange of bone that supports
the tendons ventrally and functions as a posterior extension of the
ventral aspect of the channel described above. This flange on the
radius also forms a shelf for the tendon of the M. extensor digiti
quinti proprius to digit V and the tendon of the M. extensor carpi
ulnaris. The tendons are bound to this shelf of bone by a tough
ligamentous band, which runs from the posterior tip of the shelf
to the posterior tip of the cuneiform. The exceptional investrrient
of the distal portion of the radius with grooves and ridges of bone
to confine tendons reflects the great forces placed upon the ten-
dons, and thus elements in the hand, during terrestrial locomotion,
jumping, and initial flight.
The distal articular surface of the radius is deeply concave and
directed posterolaterally from the long axis of the shaft. The pos-
teroventral surface of the border of the articular surface bears a
prominent lateral projection, which interlocks with the deep notch
in the posterior aspect of the lunar. The edge of the articular
surface posterodorsal to the projection forms a ridge that serves
to hold the lunar in position. Anteroventrally, the projection con-
tinues as a ridge of bone that confines the lunar ventrally and helps
limit it to movement on only one plane.
Manus (Figs. 30-31). — The lunar is the largest of the eight car-
pals and is elongate parallel to the long axis of the distal articular
surface of the radius. The body of the lunar is offset posteroven-
trally to the long axis of the shaft and bound to the shaft by heavy
ligaments on the posterodorsal surface. On the posteromedial as-
pect of the lunar is a deep groove that interlocks medially with the
Altenbach — Vampire Locomotor Morphology 67
scaphoid
Fig. 31. Ventral view of the right carpus and first digit of Desmodus.
distal projection on the posteroventral side of the articular surface
of the radius and limits flexion of the lunar. The cuneiform is
tightly bound to the radius posterodorsally to the lunar and bears
a posteromedial projection that forms the ventral half of the deep
channel described above. The posterior tip of this projection
curves strongly dorsally, making the channel almost tubular (Fig.
30).
A cylindrical anteroventral projection of the lunar bears a
smooth surface anteriorly on which the small ovoid scaphoid rests.
A deep circular groove separates the projection posterodorsally
from an expanded circular ridge perpendicular to the long axis of
the lunar. This groove accommodates a prominent anteromedial
projection from the flattened trapezium and stabilizes it as the
carpus is flexed and extended. The anterodorsal surface of the
lunar posterior to the lateral ridge is saddle-shaped and accom-
modates an anteromedial projection of the small trapezoid that
projects from beneath the overlying trapezium. The lateral artic-
ular surfaces of the lunar limit the movements of the trapezium,
trapezoid, magnum, and cuneiform to a single plane, that of lateral
extension and medial flexion.
Distally, the cuneiform projects anteroventrally parallel to the
long axis of the lunar and forms a broad articular surface that
contacts the posteromedial aspect of the cuneiform. The trapezoid,
which rides against the posterodorsal surface of the ridge on the
lunar, serves as a spacer between the trapezium and the adjacent
68 Spec. Publ. Amer. Soc. Mamm. 6
magnum. The magnum bears a prominent posteroventrally-di-
rected spine beneath the rounded articular surface, which slides
against the deep lateral depression of the lunar. As the magnum
is flexed, this spine locks against the posterior surface of the lunar.
Distal to its articulation with the lunar and the cuneiform, the
unciform is expanded and bears on its posterior surface a deep
groove bordered above and below by slightly convex articular sur-
faces. The long axis of the groove is inclined medially, slightly
above the long axis of the radius, and accommodates the fingerlike
projection on the proximal end of metacarpal IV. The surfaces
above and below the groove accommodate proximal portions of
metacarpals IV and V, respectively. Distally, the arrangement of
the trapezium, trapezoid, magnum, and cuneiform produces deep
notches on the posterolateral surface of the carpus, which receive
the proximal processes of metacarpals II and III.
The long axis of the rodlike pisiform is oriented obliquely across
the posterior surface of the carpus from the medial projection of
the trapezium adjacent to its articulation with the lunar postero-
dorsally to the posteromedial tip of the cuneiform. Heavy liga-
ments bind the pisiform to the posteromedial tip of the cuneiform,
the posteromedial surface of the magnum, and the medial tip of
the trapezium. A large tubercle projects from the posterior surface
of the pisiform immediately ventrad to its dorsal tip, which is flat-
tened into a smooth articular surface. This dorsal articular surface
meets the flattened and slightly ovoid ventral surface of the prox-
imal tip of metacarpal V. The articular facet on the metacarpal is
oriented ventral and perpendicular to the slightly concave proxi-
mal articular facet that contacts the cuneiform.
Digit I (Figs. 30-31). — The proximal articular surface of the first
metacarpal slopes anterolaterally from its ventral ligamentous at-
tachment to the broad, flattened, distal surface of the trapezium,
which slopes anteromedially. The articulation allows considerable
freedom of movement, and the first metacarpal can be adducted
or abducted through an angle of about 130 degrees. The first
metacarpal is the thickest of the metacarpals and about 7 mm long,
longer than the entire pollux of most other microchiropteran bats.
Its thickness reflects the forces it bears in terrestrial locomotion
and jumping. The distal articular surface is rounded, allowing
movement of the first phalanx in almost any plane. The proximal
articular surface of the first phalanx is deeply concave to accom-
Altenbach — Vampire Locomotor Morphology 69
modate the rounded articular surface of the metacarpal, and the
hingelike distal articular surface limits movement of the short sec-
ond phalanx (which bears a recurved claw), to flexion and exten-
sion.
Digit II (Figs. 30-31). — The proximal end of the second meta-
carpal is vertically expanded and compressed anteroposteriorly
into a rounded flange, which articulates in the groove between the
trapezium and the magnum. The anterior tip of the flange rests
against the posterolateral tip of the trapezoid. Distally, there is a
ventral tubercle that articulates with the proximal part of meta-
carpal III. Two milhmeters distal to this tubercle there is a small
posterodorsal saddle, bordered distally by a tubercle, into which
articulates the large, anterodorsal tubercle of metacarpal III. This
is the spacer described by Vaughan and Bateman (1970) that main-
tains the spread of the second and third metacarpals in bats with
a large dactylopatagium minus. Because Desmodus does not have
a large dactylopatagium minus, this tubercle is quite small.
The second metacarpal is approximately 81 per cent of the
length of metacarpals III through V. Its distal articular surface
and the proximal articular surface of the first phalanx are ex-
panded, flattened, and nearly perpendicular to the long axis of the
digit. Firm ligamentous binding of the joint limits movement and
stabilizes the leading edge of the chiropatagium. The second pha-
lanx is cartilaginous and serves only as a connection between the
second and third digits to stabilize the leading edge of the chiro-
patagium.
Digit III (Figs. 30-31). — Medially the metacarpal is enlarged and
flattened into a vertically-oriented flange similar to, but larger
than, the flange of metacarpal II. The flange fits into a shallow
curved depression on the posterior surface of the magnum and is
bordered posteriorly by the concave, flattened anterolateral por-
tion of the distal part of the cuneiform. There is a prominent
depression on its posterior surface that accommodates an ante-
riorly-directed process on the anteroventral aspect of the proximal
tip of metacarpal IV. The distal articular surface of metacarpal III
is expanded to one and a half times the diameter of the distal shaft
and, along with the proximal articular surface of the basal phalanx,
is perpendicular to the long axis of the shaft. The long axis of the
shaft of the basal phalanx is offset dorsally and in line with the
dorsal aspect of the shaft of the metacarpal. The metacarpopha-
70 Spec. Publ. Amer. Soc. Mamm. 6
langeal joint allows limited movement in any direction, but liga-
mentous binding limits upward deflection. Much of the stability of
this joint is provided by medially directed forces imparted by the
tendons inserting on the first phalanx. Compression of the shaft
forms a ventral notch proximal to the distal articular surface. The
trochlealike articular surface bears a shallow vertical groove on its
dorsal and distal surface. The proximal articular surface of the
second phalanx is deeply concave and bears a dorsomedian process
that curves strongly proximad to articulate dorsally with the groove
of the distal surface of phalanx one. Lateral processes of phalanx
two articulate medially with the lateral edges of the trochlea of the
first phalanx and limit the movement of this joint to a vertical
plane. The second phalanx can be deflected about 30 degrees
above the long axis of the metacarpal and first phalanx, but this
movement is then stopped by the dorsomedian process of the sec-
ond phalanx. Ventral flexion through an arc of more than 90
degrees is possible as the ventral aspect of the articular surface of
phalanx two fits into the notch proximal to the distal tip of the
first phalanx. The second interphalangeal joint is flattened and
similar to the metacarpophalangeal joint. All but ventromedial
flexion is restricted by a firm ligamentous binding.
Digits IV and V (Figs. 30-31). — From the anterolateral aspect of
the proximal articular surface of metacarpal IV, a spine projects
anteriad to fit into the depression on metacarpal III. This serves
as a center of rotation that allows upward deflection of the fourth
metacarpal. However, if the hand is extended, a flange on the
anterodorsal edge of metacarpal IV slides into the posteriorly-
turned dorsal edge of the articular flange of metacarpal III and
stops this movement. This effectively braces the fourth metacarpal
against upward displacement from the forces of the airstream as
the extended wing is adducted. A posteromedially directed fin-
gerlike projection of the proximal articular surface of metacarpal
IV articulates with the groove in the distal surface of the cunei-
form. The depression dorsal to the projection fits over the convex
surface above the groove on the cuneiform. This arrangement
prevents any rotation of the shaft, which would reduce the effec-
tiveness of the dorsal bracing previously described.
The proximal surface of metacarpal V bears a central notch that
fits against the fingerlike posteromedial projection of the fourth
metacarpal. Dorsally, a projection of the fifth metacarpal fits into
AUenbach — Vampire Locomotor Morphology 71
a depression on the posteromedial and dorsal aspect of the fourth
metacarpal and prevents upward deflecdon of the fifth metacarpal
when the wing is extended and forced downward against the air-
stream.
The ventromedial surface bears a tubercle that projects antero-
laterally and fits into a groove on the posteromedial and ventral
part of metacarpal IV. Strong tendinous binding here further
braces the fifth metacarpal against upward deflection by the air
stream. Medial to the central notch, a flat articular surface curves
posteriorly and articulates with the flattened distal surface of the
cuneiform below the groove that accommodates the fingerlike pro-
jection on metacarpal IV. The distal articular surfaces of the fourth
and fifth metacarpals are similar to that of the third, but typically
slope proximally on their ventral edge, allowing ventral flexion of
the first phalanges through an arc of more than 90 degrees as the
wing is folded. The proximal articular surfaces of the first pha-
langes of digits III and IV are flattened and similar to that of the
first phalanx of digit III.
The first interphalangeal articulations of digits IV and V are
similar to the first interphalangeal articulation of digit III. Digits
IV and V have similar dorsomedial projections on the proximal
articular surfaces of the second phalanges, which, unlike the less
restrictive arrangement seen at the first interphalangeal joint of
digit III, limit upward deflection of the second phalanges to a
position parallel to the long axis of the basal phalanges. As the
metacarpophalangeal joints allow considerable upward deflection,
there is little need for additional deflection at the interphalangeal
joints. However, ventral flexion through an arc of more than 100
degrees is permitted to facilitate folding of the wing. Lateral move-
ments of the distal phalanges of digits IV and V are limited by
ligamentous binding, which holds the second phalanges by their
lateral articular surfaces against the distal articular surface of the
basal phalanges, and by proximolateral projections, which articu-
late with the distolateral surfaces of the basal phalanges.
FUNCTIONAL MYOLOGY OF THE
PECTORAL GIRDLE AND LIMB
IN the following descriptions I follow the system of muscle ter-
minology used by Vaughan (1959) who, in turn, followed those
of Hill (1937) and Rinker (1954). However, I have used the same
positional terms as in the previous section on osteology. Thus, the
body, arm, and hand are described as in forward flight with the
wing fully extended in mid downstroke.
Comments on Electromyographic Analysis
Without implant of a tension transducer in series with the in-
sertional tendon of a specific muscle, there is no way of determin-
ing the exact amount of tension that a muscle exerts on its insertion
and origin or the temporal distribution of that tension in normal
movements.
However, electromyography provides useful information about
both parameters if the electromyographic record is accurately in-
terpreted. Bigland and Lippold (1954) and Bergstrom (1959) have
demonstrated that tension varies directly with the integrated po-
tential changes and that spikes of an electromyogram can be used
to estimate the relative tension generated by a given muscle. Bas-
majian (1962) suggested that the number of spikes, the degree of
their superimposition, and their relative height and type, are im-
portant factors in analysis of muscular function through an elec-
tromyogram. He stated: "Experience has shown that the easiest,
and in most cases, most reliable evaluation is by the trained ob-
server's visual evaluation of results colored by his knowledge of
the technique involved." I have made no attempt to precisely quan-
tify the data, but have discussed it in such relative terms as "no
contraction," "slight contraction," or "strong contraction." Until
electromyographic data are available for all the major muscles of
a particular part of the girdle or limb, or the exact force produced
can be determined from implanted tension transducers, any at-
tempt at a more precise quantification easily could be misleading.
Electromyographic data, however, do allow more accurate anal-
ysis of the function of many muscles than heretofore has been
72
Altenbach — Vampire Locomotor Morphology 73
possible. All of the literature on the function of muscles in bats is
centered around predictions about the role of a given muscle based
on strictly positional criteria. Although reasonably reliable conclu-
sions can be drawn from positional relationships, they can be nicely
supplemented and clarified by electromyographic data.
The temporal lag between myopotential changes and force gen-
erated by a muscle, which is a function of the time between de-
polarization and shortening of the fibers and the time required to
stretch the elastic components of the muscle, probably varies be-
tween muscles in Desmodus. For the coracoid head of the M. biceps
brachii, this delay was experimentally determined to be approxi-
mately 10 milliseconds. A tension transducer was attached to the
insertional tendon of this muscle and the electromyogram from
the muscle and output from the transducer were recorded simul-
taneously with the high-speed camera. Restraints of time and avail-
ability of additional living specimens for these experiments pre-
vented doing this with other muscles. When such data are available,
the electromyographs might be interpreted differently. However,
as presently interpreted, they provide considerable insight about
the function of muscles in the pectoral girdle and limb.
The points on the electromyographic traces in Figs. 32-33, and
35-41 coincide temporally with corresponding drawings of the lo-
comotor behavior. Both the electromyogram and drawings are la-
beled with upper case letters. The probable time of muscular con-
traction, represented by a solid line, is displaced to the right along
the horizontal axis of the electromyogram, a distance correspond-
ing to 10 milliseconds. A scale indicating the magnitude of the
potential changes on the vertical axis and time on the horizontal
axis is included in each figure.
Muscles Unique to Bats
M. occipito-poUicalis (Figs. 42, 44). — The anatomical modification
of this muscle in Desmodus seems quite different from that in other
bats (Macalister, 1872; Humphry, 1869; Vaughan, 1959; Norberg,
1970/;). There is considerable variability between species in the
relative length of the fleshy belly distal to its origin on the cranium,
and in some bats, such as Plecotus auritus (Norberg, 19706) and
Pteropus edwardsi (Humphry, 1869), there is a second, distal belly.
74 Spec. Publ. Amer. Soc. Mamm. 6
However, descriptions of this distal belly indicate it is relatively
fusiform and originates almost entirely on the rather compact in-
sertional tendon of the proximal belly, which runs along the lead-
ing edge of the propatagium (Fig. 24). In Desmodiis, the proximal
belly inserts rather diffusely into the proximal propatagium. A
broad, flat belly originates from fibers in the anterior half of the
propatagium anterior to the radius, about one-third the distance
toward its distal tip, and from some of the small insertional tendons
of the proximal belly. Schuinacher (1932) described a M. propa-
tagialis proprius in Pteropus that was innervated by nerves of the
cranial portion of the brachial plexus, whereas Macalister (1872)
found the proximal belly in three other genera to be innervated
by the spinal accessory nerve. I was unable to trace the innervation
of either muscle, but on strictly positional criteria, I designate the
proximal belly as M. occipito-pollicalis and the distal belly as M.
propatagialis proprius.
Origin is primarily on connective tissue lateral to the midline
from the posterior tip of the saggittal crest and down the supraoc-
cipital for 2 mm. A distal slip originates from fibers of the clavicular
M. pectoralis. Insertion is by a finely branched tendon onto the
connective tissue fibers of the propatagium at the level of the base
of the forearm.
In contrast to the condition in most other bats, the M. occipito-
pollicalis tenses the propatagium directly by drawing its elastic fi-
bers anteromediad. As in other bats, it depresses and tightens the
leading edge of the propatagium. Contraction of the fibers of the
clavicular M. pectoralis, which insert on this muscle, draws the me-
dial half of the propatagium strongly ventrad and increases the
camber of the medial portion of the wing.
M. propatagialis proprius (Fig. 46). — The origin is from the fibers
in the anterior half of the middle propatagium and on some of the
insertional fibers of the M. occipito-pollicalis. Insertion is by an apo-
neurosis over the medial aspect of metacarpal I, a thin tendon to
an aponeurosis over the metacarpophalangeal joint of digit I, and
a tendon on the middle of the anterior surface of the first phalanx
of digit II.
This muscle is not effective in moving the digits, but uses them
as a fulcrum to tense the propatagium. The vertical orientation of
the wing during the first half of the upstroke and its position an-
terior to the body may have necessitated the development of this
Altenhach — Vampire Locomotor Morphology 75
muscle. When the wing is highly flexed in this phase of the up-
stroke, contraction of the M. occipito-pollicalis would have only lim-
ited effect if it inserted on the hand. However, tension from both
proximal and distal sides of the propatagium, directed against the
fibers posterior to the leading edge, is effective in reinforcing it
for a firm airfoil. Contraction of both muscles at the start of the
coasting phase of the jump would keep the propatagium oriented
ahead of the arm and somewhat reduce its area and drag. This
muscle also serves to help brace the leading edge of the medial
wing as it is deeply pronated for thrust production in the down-
strokes during accelerating flight.
M. coraco-cutaneus (Fig. 44). — Origin is on the medial aspect of
the tip of the coracoid process of the scapula. The belly gives rise
to a second belly about 5 mm distal to the origin on the coracoid
process, and both bellies insert onto elastic fibers in the plagiopa-
tagium posterior to the brachium and proximal one-fourth of the
forearm.
When the wing is adducted in the downstroke, contraction helps
reinforce the plagiopatagium and reduce billowing from the force
of the air stream. In the first half of the upstroke, when the distal
half of the wing is oriented vertically and raised anterior to the
body (Fig. 20), contraction of this muscle and pull from the hind
limbs probably help maintain tension on the plagiopatagium to
reduce its surface area and minimize drag.
Muscles of the Pectoral Girdle and Limb
Trapezius Group
M. clavotrapezius (Fig. 42). — This muscle has its origin on a tough
tendinous sheet bound to the anterior tip of the dorsal process on
the first thoracic vertebra and to a dorsal tubercle on the first rib.
It inserts over the dorsal surface of the clavicle, beginning about
9 mm distal to its proximal tip and continuing to within 2 or 3 mm
of its distal tip.
In contrast to the condition in many other species of bats, the
clavotrapezius is separate from the acromiotrapezius. It is much
larger than the anterior portion of the united clavotrapezius and
acromiotrapezius, which insert on the clavicle of other species.
Contraction pulls the distal end of the clavicle, and thus the an-
terior end of the scapula, dorsomedially. The relatively free artic-
76 Spec. Publ. Amer. Soc. Mamm. 6
A B C D E F
Fig. 32. Electromyogram of right M. davotrapezius of Desmodus and correspond-
ing locomotor behavior. The contraction of the muscle occurs slightly after the
electrical event and is shown as a solid line above the electromyographic recording.
Corresponding locomotor stages and portions of the electromyogram are indicated
by the same letters.
ulation of the scapula and clavicle of Desmodus requires that the
clavicle be firmly braced to provide a solid fulcrum on which the
scapula can rock about its long axis, as described in other species
of bats by Vaughan (1959). However, more importantly, the an-
terior tip of the scapula, and thus the shoulder joint, can be pulled
dorsomediad by this muscle. This movement is important in Des-
modus to position the wing prior to the first downstroke after a
jump. The shoulder is pulled ventrad during the jump and must
be positioned dorsally to give the ventral flight musculature a good
mechanical advantage on the downstroke. Electromyographic data
illustrate that the contraction of this muscle probably occurs during
the powered phase of the jump to stabilize the clavicle. Assuming
a 10 millisecond temporal lag between the myopotential changes
and the generation offeree by the muscle, power should be applied
roughly from before B, through C, and nearly to D in Fig. 32. The
contraction could certainly be overpowered by the M. subclavius
during any of the powered phase of the jump, although the qui-
escence before and after D indicates probable shoulder joint
depression late in the jump. The jump on which electromyograph-
ic data are available did not lead to flight (the bat landed on the
side of the flight chamber after the jump). Thus, the flick and
subsequent first downstroke do not occur and the contraction to
Altenbach — Vampire Locomotor Morphology 77
I I I I I I I I I I I I I I I III
ABCDEFGH IJ KLMNO PQR
Fig. 33. Electromyogram of right M. spinotrapezius of Desmodvj and correspond-
ing locomotor behavior. The contraction of the muscle occurs slightly after the
electrical event and is shown as a solid line above the electromyographic recording.
Corresponding locomotor stages and portions of the electromyogram are indicated
by the same letters.
78 Spec. Publ. Amer. Soc. Mamm. 6
raise the clavicle and shoulder from the adducted position is not
seen. A short burst of activity after the powered phase of the jump
might be the beginning of such a contraction.
M. acromiotrapezius (Fig. 42). — The origin is on the dorsal midline
from the posterior tip of the tubercle on the first thoracic vertebra
to the posterior tip of the fifth thoracic vertebra. Insertion is onto
the tendon of origin of the M. acromiodeltoideus from a point about
half a millimeter anterior to the tip of the acromial process and
posteriorly for 7.5 mm along the lateral aspect of the acromial
process and scapular spine.
The anterior portion of the acromiotrapezius, which inserts on
the enlarged area of the acromion process, is three times as thick
as any portion posterior to it. The combined clavotrapezius and
acromiotrapezius is thicker anteriorly in many other bats
(Vaughan, 1959; Norberg, 1970^), but the thickened anterior por-
tion is usually considered the M. clavotrapezius. In Desmodus, the
thick anterior portion is suited to powerfully tip the acromial pro-
cess mediad and thus the medial scapular border ventrad, inde-
pendent of movement of the clavicle. As Vaughan (1959) noted,
this action can initiate abduction of the humerus when the latter
is locked with the ventral scapular border. In addition, this muscle
probably helps steady the scapula when the bat is moving on the
ground and the lateral scapular border is tipped strongly ventrally.
M. spinotrapezius (Fig. 42). — Origin is on the dorsal midline from
the eighth thoracic vertebra to the posterior tip of the second lum-
bar vertebra. Insertion is from the dorsolateral aspect of the thick-
ening at the junction of the spine and medial scapular border to
a point about 5 mm anterior.
As in other bats (Vaughan, 1959; Norberg, 1970^), this muscle
is situated to exert a strong posterior pull on the medial scapular
border. This is important, because the fulcrum of scapular motion
is the anterior articulation with the clavicle. A posterior anchor is
necessary if the muscles applying ventral force to the medial and
lateral scapular borders are to be effective in rocking the scapula
and the wing when the humerus and scapular border are locked.
Assuming a 10 millisecond temporal delay, electromyographic data
illustrate continuous, probably moderate, contraction during the
jump and quiescence at its end (Fig. 33A-F). Activity during the
coasting phase may reflect initial limb abduction and scapular sta-
bilization (Fig. 33G-J), but it is much better positioned for the
Altenbach — Vampire Locomotor Morphology 79
latter. However, the relatively great activity around G suggests this
muscle may be important in reorienting the scapula after its lateral
border is so highly depressed during the jump. The posteriorly
elongate scapula in this species is a feature that aids scapular sta-
bilization by the M. spinotrapezius during movements in flight and
terrestrial locomotion. Function in the former role is suggested by
nearly continuous activity during the next two wingbeats (Fig.
33K-R).
Costo-spino-scapular Group
M. levator scapulae (Fig. 42). — The origin of this muscle is by four
slips onto the dorsal projections of the transverse processes of the
fourth through seventh cervical vertebrae. Insertion is on the me-
dial scapular border, beginning about 5 mm posterior to the an-
terior tip of the scapular flange and continuing posteriorly to the
junction of the spine and medial border.
As in other bats (Vaughan, 1959; Norberg, 1970/>), this muscle
tips the medial scapula border ventrad and, along with the M.
acromiotrapezius and the anterior division of the M. serratus anterior,
can brace the scapula or aid in the upstroke. The deep, ventral
arch of the cervical vertebrae and the relatively high position of
the scapula separate the origin and insertion of this muscle more
than in most bats and allow it to exert nearly constant force, ir-
respective of the position of the scapula.
M. serratus anterior, anterior division (Figs. 42, 45). — The origin
of the muscle is by two large bellies: one from the anterior face of
the first rib adjacent to its articulation with the first costal cartilage,
and the other by a slip from a tubercle lateral to the transverse
foramen of the sixth cervical vertebra and a slip from a tubercle
ventral to the dorsal projection on the transverse process of the
seventh cervical vertebra. Insertion is onto the medial scapular
border from the anterior tip of the flange posteriorly to within
about 4 to 5 mm of the junction of the spine and medial border.
The anterior portion of the serratus, anterior division, is thick;
the posterior portion is thin and membranous. Thus, most of the
contractile force is exerted on the enlarged scapular flange and
tilts the medial border ventrad. Along with the M. levator scapulae,
M. acromiotrapezius, and M. rhomboideus, this muscle aids in abduc-
tion of the arm when the humerus is locked ventrally with the
80 Spec. Publ. Amer. Soc. Mamm. 6
subclavius
M. serratus anterior
post. div.
pectoralis
sternal div.
Fig. 34. Diagram of anterior view of the rib cage, pectoral girdle, and proximal
end of the humerus of Desmodus showing primary adductive forces during the
powered phase of a jump or during the downstroke in initial flight following a
jump. The humerus is dorsally locked with the scapular border.
lateral scapular border and probably steadies the scapula during
jumping behavior and terrestrial locomotion.
M. serratus anterior, posterior division (Figs. 34, 42, 44-45). — The
origin extends from the lateral aspect of the first costal cartilage
in a line along the junctions of the second through sixth ribs and
their costal cartilages, then dorsally along the costal cartilages of
ribs seven and eight to the level of the junction of rib eight and its
costal cartilage. Insertion is on the lateral and ventral aspect of the
lateral scapular border, from the posterior tip of the posterior
cartilaginous extension anteriorly to within about 3 mm of the
glenoid fossa.
As in other bats (Macalister, 1872; Vaughan, 1959; Norberg,
Altenbach — Vampire Locomotor Morphology 81
1970^), the posterior division of the serratus is massive. When the
humerus is locked with the dorsal scapular border, this muscle can
adduct the brachium, as in the first portion of the downstroke or
in much of the powered phase of the jump (Fig. 34). A tremendous
amount of power is required in the jump to accelerate the bat
upward with a heavy load of blood. This muscle is probably able
to assist the sternal M. pectoralis in this movement through an arc
of more than 130 degrees.
The posterior division of the M. serratus anterior also is vital in
the first of the downstroke where it assists the M. pectoralis in ad-
ducting the extended wing, as described by Vaughan (1959) in
other bats. Following a jump, air speed is low and the first few
wingbeats must rapidly accelerate the bat. By functioning simul-
taneously in the first half of the downstroke, the posterior division
of the M. serratus anterior and the M. pectoralis supply maximal
power to the wing when it is configured to provide both thrust and
lift. During faster and more efficient flight, a division of labor,
suggested by Vaughan (1959) for other species of bats, between
the M. serratus anterior, M. pectoralis, and M. subscapularis may occur
and the muscles may not contract simultaneously.
During terrestrial locomotion, forces acting on the pectoral limb
are transferred to the lateral scapular border by the humerus.
During locomotion with the body extremely elevated, as seen in
terrestrial feeding behavior, this muscle tips the short axis of the
scapula nearly vertically, thus directing the forces acting against
the pectoral limbs directly upward against the scapula, with little
or no rotational component. The M. serratus anterior and the clav-
icle thus act as a sling to support the body.
M. rhomboideus (Fig. 42). — The origin is a large belly from tho-
racic vertebrae one through six; a small anterior slip on the ten-
dinous sheet that is the origin of the M. clavotrapezius; and a third
slip on the dorsal spinal musculature adjacent the first thoracic
vertebra. Insertion is on the ventral and medial aspect of the pos-
terior cartilaginous extension of the scapula and anteriad along
the medial scapular border to its junction with the scapular spine.
Thin anteriorly, the rhomboideus becomes thick posteriorly in
the region of its insertion on the posterior cartilaginous extension
of the scapula. This suggests the major function is to shift the
scapula anteriad and tilt its medial border ventrad. As in other
bats (Vaughan, 1959; Norberg, 19706), this muscle functions with
82 Spec. Publ. Amer. Soc. Mamm. 6
AA
»-'»v^\j|^I^W~-
-^^\^w^
Q R S T U 20msec
Fig. 35. Electromyogram of right M. latissimus dorsi of Desmodus and corre-
sponding locomotor behavior. The contraction of the muscle occurs slightly after
the electrical event and is shown as a solid line above the electromyographic re-
cording. Corresponding locomotor stages and portions of the electromyogram are
indicated by the same letters.
Altenbach — Vampire Locomotor Morphology 83
the M. acromiotrapezius, M. levator scapulae, and the anterior division
of the M. serratus anterior to power the initial abduction of the arm
or to steady the scapula when contracting against the antagonistic
posterior division of the M. serratus anterior. Anteroposterior move-
ments of the scapula probably aid in balancing the bat over the
line of force exerted by the pectoral limbs during a jump and in
stabilizing the shoulder girdle during turning maneuvers (Fig. 18).
M. omocerzncalis (Fig. 42). — Origin is on the ventral arch of the
atlas. Insertion is onto the dorsal border of the clavicle and half a
millimeter of the adjacent M. subclavius, 7 mm distal to the sternal
articulation of the clavicle.
The omocervicalis probably aids in the movement of the head.
Insertion on the central clavicle instead of the acromial process (as
in many other bats) is indicative of the great motility of the head
in this species.
Latissimus-subscapular Group
M. latissimus dorsi (Fig. 42). — Origin is on the dorsal midline from
the posterior tip of thoracic vertebra nine to the anterior tip of
lumbar vertebra three. Insertion is in common with the M. teres
major on the low ridge on the ventral aspect of the humerus be-
ginning about 3.5 mm distal to the tip of the lesser tuberosity.
The latissimus dorsi and the teres major are well suited to pro-
nate the humerus and thus the entire arm, as well as to flex and
abduct the humerus. These movements are important in terrestrial
locomotion when the pectoral limbs are pulled posteriad and pro-
nated in the power stroke. Figure 35 illustrates the function of this
muscle during a jump into flight and the initial two wingbeats. A
10 millisecond temporal delay between myopotential changes and
contraction is assumed. Contraction begins at the onset of the
coasting phase (Fig. 35E) and probably helps abduct the wing.
During the early part of the initial flick (Fig. 35H), contraction
helps pronate the arm to drive the digits upward and backward
against the airstream and help position the wing for the first down-
stroke. Slight electrical activity indicates weak contractions during
the downstroke that perhaps help stabilize the angle of attack and
may reinforce the strong pronation of the wing. After flexion and
supination of the arm in the first of the upstroke, sudden con-
traction helps pronate and abduct the arm early in the flick phase
(Fig. 35L to between M and N). This myopotential burst indicates
84 Spec. Publ. Amer. Soc. Mamm. 6
Strong, perhaps maximal, contractive force during this movement.
Feeble contractions again occur periodically during the down-
stroke, perhaps for fine control of wing orientation, and a strong
contraction occurs early in the flick phase (Fig. 35R to between S
and T).
M. teres major (Fig. 42). — Origin is on the lateral scapular border
from the level of the junction of the spine and medial border to
within about a millimeter of the posterior tip. Insertion is with the
M. latissimus dorsi on the ventral aspect of the humerus distal to the
lesser tuberosity.
The function of the teres major is essentially similar to that of
the M. latissimus dorsi, except that it is not suited to abduct the
humerus. It probably functions primarily in the flick phase of the
upstroke in flight, in terrestrial locomotion, and in climbing.
M. subscapularis (Fig. 45). — Origin is on the ventral aspect of the
scapula and posterior cartilaginous extension to within 2 mm of
the base of the coracoid process and within 2 mm of the posterior
edge of the glenoid fossa. Insertion is onto the posterior and me-
dial aspect of the tip of the lesser tuberosity of the humerus.
Although no electromyographic data are available, the subscap-
ularis almost certainly functions to adduct the humerus after it is
unlocked from the dorsal scapular border in the last of the down-
stroke in forward flight, as described by Vaughan (1959). In an
alighting maneuver (Fig. 23), the subscapularis, along with the cla-
vicular M. pectoralis, extends and adducts the humerus prior to
contact of the substrate by the forelimbs and probably helps cush-
ion the impact by contraction as the humerus is forced upward
and backward.
Deltoid Group
M. clavodeltoideus (Figs. 42, 44). — Origin of a large belly is from
the anterodorsal aspect of the clavicle for about 9 mm beginning
approximately 2.5 mm from its distal tip; and a small belly, deep
to the first, from about 2 mm of the anteroventral surface of the
clavicle in the region of the sharp posterior curve of the clavicle
before its articulation from the scapula. Insertion of the larger
belly is onto the anterior aspect of the expanded proximal tip of
the pectoral ridge and laterally for 9 mm. The second belly inserts
onto the dorsomedial aspect of the proximal end of the pectoral
Altenbach — Vampire Locomotor Morphology 85
ridge and onto a ridge on the anterior base of the greater tuber-
osity.
Both bellies are clearly separate from the clavicular portion of
the M. pectoralis. The clavodeltoideus powers the forward, recovery
stroke of the brachium during terrestrial locomotion and the
thrusting stroke of the brachium during backward climbing. It is
probably aided in this movement by the clavicular M. pectoralis and
somewhat by the M. subscapularis. Its clear separation from the
clavicular M. pectoralis suggests that the clavodeltoideus is impor-
tant in powering the complex movements of terrestrial locomotion
and climbing.
The clavodeltoideus cannot assist in adduction of the brachium
during the powered phase of the jump or in the downstroke of
forward flight, but it is important in controlling the angle through
which adduction progresses. Steady contraction during a down-
stroke would direct the stroke strongly forward. In a braking ma-
neuver, this muscle functions to anteriorly brace the wing as it
remains extended at a high angle of attack.
M. acromiodeltoideus (Fig. 42). — The origin is on the tendon of
insertion of the M. acromiotrapezius at a point anterior to the acro-
mion process and extending for 6 mm along the lateral aspect of
the acromion process and scapular spine. Insertion is on the an-
terior 2 mm of the dorsal aspect of the pectoral ridge beginning
5 mm distal to the tip of the greater tuberosity and continuing
lateral for 1 1 mm.
The acromiodeltoideus is situated to abduct, slightly flex, and
impart a strong supinating force to the humerus. The relatively
long scapula, along with bracing supplied by the M. spinotrapezius,
provides a stable origin for the muscle to supinate the brachium
and thus raise the wing when the forearm is flexed toward the
brachium, as occurs at the beginning of the upstroke. An electro-
myographic record during a jump and initial flight indicates a
relatively long contraction during the adduction of the brachium
(Fig. 36D-G). This seems surprising, but possibly the acromiodel-
toideus stabilizes the dorsal locking of the scapula and humerus
throughout the entire powered phase of the jump, thus suggesting
that the humerus is not adducted relative to the scapula during
even the last of the jump. The posterior division of the M. serratus
anterior and the sternal M. pectoralis thus would supply the power
for the entire adduction of the brachium. The relatively free ar-
86 Spec. Publ. Amer. Soc. Mamm. 6
oV
^/% (zljK '^if% '^^fx ""^Z
A B C D E
f',
2 tnv
P
20 msec
Q
1 1 1 1
J K L M
1
A
1 1 1 1 1 1 1 1
B C D E F G H 1
1
N
1 r 1
P Q
Fig. 36. Electromyogram of right M. acromiodeltoideus of Desmodus and corre-
sponding locomotor behavior. The contraction of the muscle occurs slightly after
the electrical event and is shown as a solid line above the electromyographic re-
cording. Corresponding locomotor stages and portions of the electromyogram are
indicated by the same letters.
Altenbach — Vampire LtPcomotor Morphology 87
ticulation of the scapula and clavicle allows the two largest muscles
in the bat to power the adduction of the brachium during the
jump. The M. subscapularis apparently does not aid the adduction
during the jump as perhaps it does in the downstroke of forward
flight, as Vaughan (1959) suggested for other bats. However, the
electromyographic data provide no evidence that the M. subscap-
ularis does not overpower the deltoid group and adduct the hu-
merus relative to the scapula at the very last of the powered phase
of the jump.
Contraction of the M. acromiodeltoideus probably continues dur-
ing the first part of the coasting phase of the jump, or until the
initiation of the flick phase (Fig. 36, between G and H). Activity
depicted at Fig. 361 suggests the muscle again stabilizes the dorsal
locking of scapula and humerus prior to the downstroke. Only
slight activity is apparent in the first downstroke, but contraction
again occurs at the last of the downstroke and onset of the up-
stroke, and continues to the initiation of the flick phase (Fig. 36,
K to between L and M). Contraction at the end of the upstroke
again indicates stabilization of dorsal locking of scapula and hu-
merus. The muscle probably functions to supinate and abduct the
brachium during the very last of the downstroke and first half of
the upstroke. Final positioning of the brachium prior to the down-
stroke appears to be the function of the M. latissimus dorsi and M.
teres major.
M. spinodeltoideus (Fig. 42). — Origin is by a tendinous raphe over
the scapular spine and then along the dorsal aspect of the thick-
ened medial scapular border to its posterior tip. Insertion is by a
flat tendon posterior to the proximal 2.5 mm of the insertion of
the M. acromiodeltoideus.
The spinodeltoideus is relatively thin and situated to slightly
abduct, flex, and supinate the humerus. An electromyographic re-
cording during a jump into flight (Fig. 37) illustrates contractions
similar to those of the M. acromiodeltoideus (Fig. 36). Initially, there
is a contraction that, along with the other deltoid muscles, probably
stabilizes the locking of the humerus and dorsal scapular border.
The contraction continues during the powered phase of the jump,
but becomes less intense over the last half of the adduction of the
brachium (Fig. 37F). At the beginning of the coasting phase (Fig.
37G), contraction aids the supination and perhaps the abduction
of the brachium. In the flick phase, shght contraction apparendy
spec. Publ. Amer. Soc. Mamm. 6
Mh^ Mh^ £^ J^ Jh^
A
m^ w
fr
I t I I I I I I I I I I I I I I I I
H I
M N
Fig. 37. Electromyogram of right M. spinodeltoideus of Desmodus and corre-
sponding locomotor behavior. The contraction of the muscle occurs slightly after
the electrical event and is shown as a solid line above the electromyographic re-
cording. Corresponding locomotor stages and portions of the electromyogram are
indicated by the same letters.
Altenbach — Vampire Locomotor Morphology 89
helps pull the brachium mediad prior to the downstroke (Fig. 371-
J). The supinating force imparted by this contraction is probably
offset by the pronating force of the M. latissimus dorsi, M. teres
major, and M. pectoralis. With the wing at the level of midbody,
another contraction occurs that probably tends to reduce some of
the pronation imparted by the M. pectoralis and conforms the wing
into more of a lift-generating structure (Fig. 37K to between L and
M). As the humerus probably is locked with the dorsal scapular
border at this point, this contraction does not detract from the
adductive forces applied to the brachium. The contraction contin-
ues into the first phase of the upstroke to help supinate the wing
and again in the flick phase to position the brachium for the down-
stroke. Another contraction early in the downstroke (Fig. 37P-Q)
probably reinforces the scapulo-humeral locking and stabilizes the
arm against some of the pronating force applied by the M. pecto-
ralis.
M. teres minor. — The origin is on the posterodorsal aspect of the
rim of the glenoid fossa and onto the tendon of origin of the long
head of the M. triceps brachii. Insertion is on the dorsal surface of
the greater tuberosity of the humerus for 1.5 mm distal to the
insertion of the M. infraspinatus. The small teres minor is a weak
supinator and flexor of the humerus.
Suprascapular Group
M. supraspinatus (Fig. 42). — The origin is from the medial 3 mm
of the supraspinous fossa and adjacent ligamentous raphe over the
scapular spine, and from the dorsolateral aspect of the scapular
flange. Insertion is by a heavy tendon onto a groove on the medial
surface of the greater tuberosity of the humerus.
As in other bats (Vaughan, 1959; Norberg, 1970^), the supra-
spinatus abducts, slightly supinates, and extends the humerus.
Along with some of the deltoid group (Figs. 36-37), it probably
stabilizes the dorsal locking of the scapula and humerus and helps
abduct the humerus relative to the scapula during the upstroke in
forward flight. In terrestrial locomotion, it is best suited to swing
the humerus forward and, by supinating and slightly abducting
the humerus, to lift the carpus off the substrate for the forward
swing. In terrestrial feeding postures, when the short axis of the
scapula is oriented nearly vertically, this muscle, along with the M.
90 Spec. Publ. Amer. Soc. Mamm. 6
infraspinatus and M. subscapularis, is important in moving the pec-
toral limb.
M. infraspinatus (Fig. 42). — Origin is from the lateral aspect of
the scapular spine; lateral aspect of the medial border posterior to
the spine; dorsal base of the posterior caritilaginous extension;
medial aspect of the lateral border to within 3 mm of the origin
of the M. triceps brachii, long head; and surfaces of the three facets
(Fig. 26). Insertion is by a thick tendon, a millimeter wide, onto
the dorsal aspect of the tip of the greater tuberosity of the hu-
merus.
The posteriorly elongate scapula in Desmodus positions the origin
of the infraspinatus relatively far posterior to the insertion. The
insertion on the dorsal aspect of the greater tuberosity also is dis-
placed well above the fulcrum at the center of the head. Thus this
muscle is the most powerful supinator of the brachium and no
doubt functions in the last part of the downstroke and first part
of the upstroke to raise the forearm and hand anteriorly to the
body. As this muscle is not situated to provide much abductive
force to the humerus, it is probably relatively important in the last
half of the downstroke in counteracting the pronating forces ap-
plied by the M. pectoralis, and helps position the wing into a lift-
generating configuration (Fig. 19).
Triceps Group
M. triceps brachii, caput lateralis (Fig. 43). — The origin is from a
strip a millimeter wide along the posterior surface of the humerus
beginning at the base of the lesser tuberosity and extending dor-
sally to the level of the top of the head. Insertion is by a large
sesamoid onto the olecranon process of the ulna.
M. triceps brachii, caput medialis (Fig. 43). — The origin extends
over 13 mm of the posterodorsal surface of the humerus beginning
2 mm lateral to the head. A second group of short fibers, assumed
to be part of this head, originates along the posterior aspect of the
distal half of the humerus and inserts into the common tendon to
the olecranon process of the ulna. Insertion is by a large sesamoid
onto the olecranon process of the ulna.
M. triceps brachii, caput longus (Fig. 43). — Origin is by two slips
from the two tubercles, 1.5 mm apart, posterior to the posterior
border of the glenoid fossa of the scapula. Insertion is by a large
sesamoid onto the olecranon process of the ulna.
Altenbach — Vampire Locomotor Morphology 91
A B
3^
^^^ 4%. jf-
E
f^^
-"^
^
m
I I I I I I I I I I I > I
ABCDEFGHIJKLMNOPQR
20 msec
Fig. 38. Electromyogram of right M. triceps brachii, long head, of Desmodus and
corresponding locomotor behavior. The contraction of the muscle occurs slightly
after the electrical event and is shown as a solid line above the electromyographic
recording. Corresponding locomotor stages and portions of the myogram are in-
dicated by the same letters.
92 Spec. Publ. Amer. Soc. Mamm. 6
An electromyographic record of the long head of the triceps
muscle during a jump into forward flight reveals a contraction that
begins during the inclination of the brachium and continues until
contact with the substrate is broken (Fig. 38B-G). After only a
short period of quiesence during the first of the coasting phase
(Fig. 38G-H) when contraction of the M. biceps brachii flexes and
begins supination of the forearm (Fig. 40G-H), contraction begins
to extend the forearm (Fig. 38H-I). The electromyogram shows
an increase in amplitude that probably represents greater strength
of contraction during the flick phase (Fig. 38I-K), where the fore-
arm is fully extended along with the digits to provide forward
thrust and to help position the wing for the first downstroke. The
contraction continues during the first half of the downstroke and
maintains the full extension of the arm (Fig. 38K-M). Past the level
of midbody, contraction ceases and the M. biceps brachii (Fig. 40L-
N) begins flexion of the forearm that continues through the first
third of the upstroke. Contraction of the triceps begins at about
the second third of the upstroke, stops for a few milliseconds, and
then continues during the flick phase and the first half of the next
downstroke (Fig. 380-R).
Although the electrodes were in the long head of the triceps,
one of the leads was near (and possibly may have contacted) the
posterodorsal aspect of the lateral head, and may have monitored
some of its electrical activity. Although the function of the three
heads may be slightly different, the nearly inseparable contact of
the bellies, the close approximation of the origin of the long, lat-
eral, and most of the medial head, and their common insertion on
the olecranon process, suggest that their action is functionally and
temporally quite similar. The long head may function to slightly
flex the brachium but, because the mechanical advantage is poor
for this movement, it could be easily counteracted by the scapular
musculature.
The large sesamoid in the insertional tendon is contoured to fit
closely the concavity on the posterior side of the distal articular
surface of the humerus and suggests that considerable tension is
applied by this muscle group. The jump is certainly the most de-
manding of the triceps, as it is the third largest muscle powering
the jump and since it must move the forearm through an arc of
about 140 degrees.
Altenbach — Vampire Locomotor Morphology 93
Extensor Group of the Forearm
M. extensor carpi radialis brevis (Figs. 46, 48). — The origin is by a
tough tendon on the medial edge of the dorsal epicondyle of the
humerus. Insertion is on a large tubercle on the anterodorsal base
of metacarpal III by a heavy tendon and onto the dorsolateral tip
of the trapezium by a rather elastic band of connective tissue.
By extending the third digit, this muscle extends the fifth digit
and aids the M. extensor carpi radialis longus in extending the re-
mainder of the hand-wing. A detailed discussion of both muscles
is included with the discussion of the M . extensor carpi radialis longus
below.
M. extensor carpi radialis longus (Figs. 46-48). — Origin is by a
heavy tendon on the medial aspect of the dorsal epicondyle of the
humerus. Insertion is onto the anterodorsal base of metacarpal II
and into a depression in the lateral base of metacarpal I by a heavy
tendon.
In Desmodus, as in other species of bats (Vaughan, 1959; Nor-
berg, 1970^), this muscle and the adjacent M. extensor carpi radialis
brevis are the largest muscles in the forearm. Although their origins
are displaced mediad to the center of rotation of the elbow joint,
the extremely large size of the bellies and the lack of a tough
connective tissue covering found in many other bats suggests that
these muscles are well suited to act independently of movements
at the elbow. Vaughan (1959) pointed out that in other species of
bats, such as Eumops perotis, Myotis velifer, and Macrotus waterhousii,
these muscles can act as relatively inelastic bands and automatically
extend the chiropatagium as the elbow is extended. This helps
concentrate the weight toward the body and eliminate weight in
the wing. The terrestrial propensity of Desmodus, and particularly
its jumping behavior, necessitate complete independence of move-
ments of the hand from movements of the rest of the arm, al-
though there appears to be a sacrifice of added weight in the wing.
The muscles are certainly stretched by extension of the elbow, but
the elastic components appear to absorb this movement and allow
the hand to remain folded against the forearm. This feature may
help explain the strong and mechanically advantageous insertion
of some of the flexors of the hand that have to hold the hand
flexed while the arm is fully extended, as in terrestrial feeding
94 Spec. Publ. Amer. Soc. Mamm. 6
■L
Fig. 39. Electromyogram of right M. extensor carpi radialis longus of Desmodus
and corresponding locomotor behavior. The contraction of the muscle occurs
slightly after the electrical event and is shown as a solid line above the electromy-
ographic recording. Corresponding locomotor stages and portions of the myogram
are indicated by the same letters.
Altenbach — Vampire Locomotor Morphology 95
posture or in the powered phase of the jump. This muscle begins
contraction during the powered phase of the jump and continues
until late in the first downstroke (Fig. 39, B to between I and J).
Shortly after the start of the coasting phase (Fig. 39E), partial ex-
tension of the digits is evident; however, I cannot fully explain the
early initiation of contraction. Perhaps co-contraction of antago-
nists tends to brace the carpus as the thrust of the pectoral limb
is directed against it and the thumb. The greater number of spikes
in the electromyogram indicate that the contraction during the
flick phase is stronger than that before it, suggesting that perhaps
the movement meets considerable resistance.
The muscle is quiescent in the last of the downstroke and first
half of the upstroke (Fig. 39I-K), but contracts during the last of
the flick phase and through the first half of the next downstroke
(Fig. 39, between K and L-N). The sequence of contraction is
essentially similar during the last of this cycle as in the one pre-
ceding it. Although no electromyographic data are available for
the M. extensor carpi radialis brevis, I assume its function is similar
to that of the M. extensor carpi radialis longus.
M. supinator (Fig. 46). — Origin is by a heavy tendon onto the
center of the dorsal (lateral) epicondyle of the humerus. Insertion
is over 10 mm of the anterior surface of the radius beginning 3
mm distal to its proximal articular surface.
As in other bats, this muscle originates by a tendon that contains
a sesamoid bone and is a flexor of the forearm. The muscle lacks
good mechanical advantage for this action. Thus it probably func-
tions mainly to brace and stabilize the elbow joints as strong su-
pinating forces, applied proximally to the humerus, raise the
flexed forearm as in the first half of the upstroke (Fig. 20). The
relatively large size of this muscle suggests the importance of this
function.
M. extensor poinds brevis (Fig. 48). — Origin is along 10 mm of the
interosseus surface of the ulna beginning 3 mm distal to the tip of
the olecranon process. Insertion is by a tendon heavily bound to
the anterodorsal aspect of the carpus and metacarpal I, which at-
taches on the dorsal aspect of the proximal base of the first phalanx
of digit I.
This muscle extends the thumb and, if resisted by the flexors of
the first metacarpal, extends the phalanges of the thumb. Desmodus
commonly rests much of its weight on the distal pad at the meta-
96 Spec. Publ. Amer. Soc. Mamm. 6
carpophalangeal junction of digit I during terrestrial locomotion
or when standing (Fig. 2), and this muscle is necessary in elevating
the claw during movements of the limb from this position. When
Desmodus is walking on a nervous or easily aroused host animal
prior to feeding, the claws may be elevated to minimize stimulation
of the skin of the host.
M. abductor pollicis longus (Fig. 49). — Origin is on 7 mm of the
interosseus surface of the ulna and along 16 mm of the interosseus
surface of the radius beginning at the medial contact of the radius
and ulna. Insertion is by a thick tendon on the anterior tip of the
scaphoid. The tendon divides proximal to the scaphoid and
another branch runs forward, inserts onto the ventromedial sesa-
moid on the distal tip of metacarpal I, and sends fibers into the
pad at the metacarpophalangeal joint of digit I.
The tendon, which inserts on digit I, probably is the remnant of
the M. abductor pollicis brevis, which has become tendinous and
shifted its origin from the scaphoid directly to the tendon of the
M. abductor pollicis longus. No doubt the elongation of the first digit
in Desmodus and its use in jumping have necessitated the reduction
of the M. abductor pollicis brevis to a tendon. The large and relatively
long belly of the M. abductor pollicis longus on the forearm is better
suited to provide power through a wide arc of movement than is
a shorter and much smaller muscle originating on the hand. By
becoming tendinous and shifting its origin directly to the tendon
of the M. abductor pollicis longus, the M. abductor pollicis brevis allows
more powerful movement of the thumb. Although no electromy-
ographic data are available, it is evident that the M. abductor pollicis
longus serves two important functions. Its contraction pulls the
scaphoid mediad over the lunar and thus puts tension on the M.
abductor digiti quinti (Fig. 49), which originates from the scaphoid,
and puts tension on the pisiform itself. As Vaughan (1959) noted,
this is important in bracing the fifth metacarpal and basal phalanx
of digit V against upward deflection during adduction of the wing.
In addition, the M. abductor pollicis longus pulls the first metacarpal
ventrad and is important in terrestrial locomotion. In terrestrial
feeding postures, or in terrestrial locomotion with the body held
high above the substrate, this muscle shifts the weight from the
basal to the distal thumb pad thus elevating the bat higher. Con-
traction also aids in keeping the wing folded by flexing the fifth
digit through tension on the M. abductor digiti quinti. During the
Altenbach — Vampire Locomotor Morphology 97
last of the power phase of the jump, the M. abductor pollicis longus,
along with the M. flexor digitorus profundus and M. palmaris longus,
pull the thumb ventrad to provide the last upward thrust. In
addition, all of these muscles produce flexion of at least one digit
besides the first, thus helping to keep the remainder of the hand
folded.
M. extensor digiti quinti proprius (Fig. 48). — Origin is by a thin
tendon onto the distal edge of the dorsal (lateral) epicondyle of
the humerus. Insertion is onto the dorsal aspect of the proximal
tip of the second phalanx of digit V by a broad tendon.
At the point where this tendon meets the dorsal surface of the
fifth metacarpal, it is joined by a small tendon of the M. extensor
digitorum communis. This muscle deflects the phalanges of digit V
upward and tends to elevate the metacarpal slightly. The relative
size of the belly and the insertional tendon suggest this movement
is important. High-speed photographs of Desmodus in flight (Fig.
19) show that during the first half of the downstroke the phalanges
of digit V are deflected upward, thus shaping the distal plagio-
patagium and medial chiropatagium into a thrust-generating
structure similar to that of the distal chiropatagium. Contraction
of this muscle, combined with the passive forces from the air pres-
sure, would cause the upward deflection to be greater than that
from the air pressure alone and would shape that part of the wing
into a more efficient thrusting configuration. Simultaneous con-
traction of the M. abductor digiti quinti, M. opponens digiti quinti, and
M. abductor pollicis longus would overpower the M. extensor digiti
quinti proprius, flex the phalanges, depress the metacarpal, and sta-
bilize the phalanx against the metacarpal.
M. extensor digitorum communis (Figs. 46, 48). — Origin is by two
separate bellies with tendinous origin on the dorsal (lateral) epi-
condyle of the humerus and fleshy origin beginning 6 mm distal
to the proximal tip of the radius, and extending distad along the
dorsal surface of the radius for 14 mm. Insertion is through a
tendon to digit III, which runs along the dorsal aspect of the meta-
carpal and sends fibers to the proximal tips of the first and second
phalanges. The primary insertion of the tendon is on the postero-
dorsal aspect of the proximal tip of phalanx three. The tendon to
digit IV inserts on a tubercle on the dorsolateral aspect of phalanx
one, 2 mm distal to the proximal base.
The tendon to digit IV divides distal to the carpus and sends a
98 Spec. Publ. Amer. Soc. Mamm. 6
branch to the tendon of the M. extensor digiti quinti proprius at its
proximal contact with the metacarpal, thus it aids in dorsal deflec-
tion of the phalanges of digit V. The connections to digits III and
IV dorsally deflect the phalanges and slightly deflect the metacar-
pals. In the downstroke in forward flight (Fig. 19), the M. extensor
digitorum communis probably aids the force of the air stream in the
upward deflection of the phalanges to provide the propeller effect
and upturned configuration of the distal chiropatagium between
digits III and IV, which perhaps function to reduce tip vortices.
It also provides downward acceleration of air and lift production
in the last of the downstroke. More important, however, is the
function of this muscle in the flick phase of the upstroke. During
the first of the flick (Fig. 20N-P), when the forearm is extended,
the phalanges of digits III to V are deflected ventrally by the force
of the air and perhaps by contraction of the flexors of the digits.
As the flick nears completion, the phalanges are fully extended to
provide the last component of forward thrust and help to position
the wing for the downstroke. This movement appears to be par-
tially active and not simply the result of upward air pressure as
adduction begins.
M. extensor carpi ulnaris (Figs. 46-49). — Origin is from the deep
groove and adjacent ridge on the proximal 6 mm of the postero-
ventral surface of the ulna. Insertion is by a heavy tendon on the
tubercle on the dorsomedial aspect of metacarpal V, 2 mm distal
to its proximal tip.
This muscle is a powerful flexor of digit V and, because of lig-
aments that join the proximodorsal surfaces of metacarpals III and
V, the entire hand-wing. In the distantly related phyllostomatid
bat, Macrotus, this muscle inserts on metacarpal V but is an exten-
sor. In Eumops perotis and Myotis velifer (Vaughan, 1959), this mus-
cle inserts on metacarpal III and is a flexor. In Plecotus auritus
(Norberg, 1970^), the muscle inserts on metacarpal III and is an
extensor. The tendon is the thickest one to the hand, and the belly
is quite large. When the forearm is extended with the wing folded
as in terrestrial feeding postures or in parts of the climbing and
walking cycles (Figs. 2, 4, 6), the large M. extensor carpi radialis
longus and M. extensor carpi radialis brevis are stretched and apply
some passive, extensive forces to the hand. This muscle is no doubt
necessary to resist these forces and keep the wing folded. Inasmuch
as the radial extensors of Desmodus are not heavily invested in
Altenbach — Vampire Locomotor Morphology 99
connective tissue, they are probably rather elastic and thus do not
explain the need for the massive tendon of the M. extensor carpi
ulnaris. However, in landing on the ground, it is critical for the
wing to be quickly folded against the forearm to prevent injury to
the digits. It is also important for the wing to remain tightly folded
during terrestrial locomotion. The insertion seems well suited for
effecting such a rapid and powerful movement.
M. extensor indicis (Fig. 48). — Origin is on 14 mm of the postero-
dorsal surface of the radius to within about 4 mm of the distal
articular surface and on 9 mm of the interosseus surface of the
ulna, beginning about 8 mm distal to the proximal articulation of
the radius and ulna. Insertion is at several points. At the level of
the proximal carpus, the tendon gives rise to a sheet of tendon
that inserts on the anterodorsal carpus and dorsomedial aspect of
the proximal half of metacarpal I. Another colateral tendon arises
from the main tendon and runs to the dorsolateral aspect of the
distal third of metacarpal I. The main tendon inserts by way of a
sesamoid on a tubercle on the anterodorsal surface of metacarpal
II, 3 mm distal to its proximal base. At the level of the sesamoid,
small tendinous attachments run from the main tendon postero-
laterad to insert on the dorsal aspect of the bases of metacarpals
III and IV.
This muscle functions with the M. extensor carpi radialis longus
and M. extensor carpi radialis brevis to extend the hand-wing during
the coasting phase of the jump, and during the flick phase and
first half of the downstroke in forward flight. The attachments to
the dorsal aspect of the third and fourth metacarpals suggest it
also is important in bracing the hand against posterior and dorsal
air pressure during the flick phase of the upstroke, when the digits
are extended and the wing is strongly pronated and abducted. The
attachments to the first digit probably help raise it when the hand
is flexed by the M. extensor carpi ulnaris, as occurs in terrestrial
locomotion.
Pectoralis Group
M. subclavius (Figs. 44-45).— Origin is by a fleshy attachment to
the ventral aspect of the first costal cartilage adjacent to its attach-
ment to the manubrium and by tendinous attachment to the an-
terolateral border of the first costal cartilage. Insertion is on the
100 spec. Publ. Amer. Soc. Mamm. 6
posteroventral surface of the clavicle from its distal tip to within
2 mm of its articulation with the manubrium.
Because of the relatively free articulation of the clavicle and
scapula, this muscle is important in both jumping and flight. Con-
traction pulls the distal tip of the clavicle ventrad and slightly pos-
teriad, and can effectively brace the clavicle when co-contracting
with the M. clavotrapezius. Slight dominance of one or the other
could swing the clavicle dorsad or ventrad and still stabilize it as
a solid fulcrum for movements of the scapula and arm. High-speed
photographs of a jump show that the shoulder joint is depressed,
and although no direct evidence is available, this movement ap-
pears to be partly the result of depression of the tip of the clavicle
by this muscle. The electromyographic data for the M. clavotra-
pezius (Fig. 32) indicate contraction during all but the last of the
powered phase of the jump, but such contraction is necessary to
stabilize the clavicle and could be overpowered by the M. subclavius.
Seemingly the subclavius is not opposed by the clavotrapezius at
the last of the powered phase of the jump and probably depresses
the clavicle.
M. pectorahs. — This muscle appears to be divided into three ma-
jor bellies in Desmodus. However, I distinguish only between cla-
vicular and sternal portions, as the clavicular portion is widely sep-
arate from the remainder of muscle. As Vaughan (1959) described
for other species of bats, I have noted considerable individual vari-
ation in the degree of separation and arrangement of the non-
clavicular portion and consider it the posterior (sternal) division.
M. pectorahs, anterior (clavicular) division (Fig. 44). — Origin is on
the anteroventral aspect of the proximal base of the clavicle and
along the anterior and ventral aspect of the proximal half of its
shaft. Insertion is from the dorsal aspect of the medial tip of the
pectoral ridge, laterally for about 9 mm, superficial to the insertion
of the posterior (sternal) division of the M. pectorahs.
The clavicular M. pectorahs pulls the humerus craniad and ad-
ducts and pronates it slightly. This movement is not part of the
normal wingbeat cycle or of a jump, but occurs as the limb is
positioned prior to alighting on a horizontal surface (Fig. 23) and
in backward climbing (Fig. 6). In terrestrial locomotion, this muscle
probably functions along with the M. clavodeltoideus to swing the
humerus forward in the recovery stroke (Fig. 4). When cocontract-
ing with the sternal division of M. pectorahs, the clavicular division
Altenbach — Vampire Locomotor Morphology 101
can assist in adduction and pronation of the humerus and is prob-
ably responsible for much of the cranial inclination of the path of
the wing in the last half of the downstroke (Fig. 19).
M. pectoralis, posterior (sternal) division (Fig. 44). — Origin of one
belly is on the lateral aspect of the ventral arm of the manubrium,
the ventral aspect of the lateral arms to within 2 mm of their distal
tips, and the ventrolateral aspect of the posterior arm; that of the
other belly is on the ventral aspect of the body of the sternum to
within 2 mm of the posterior tip of xiphisternum and on a ten-
dinous raphe over the midline, beginning anteriorly on the tip of
the ventral arm of the manubrium and extending posterior to the
posterior tip of the body of the sternum. Insertion is onto the
ventral half of the anterior face of the proximal end of the pectoral
ridge and laterally for 10 mm along the anterior and ventral edge
of the pectoral ridge.
The bellies of this massive muscle are the major adductors and
pronators of the humerus, and consequently of the arm and hand.
The origin over the manubrium, body, and xiphoid process of the
sternum makes this muscle effective in moving the humerus
through a variety of planes, as Vaughan (1959) pointed out for
other species. However, photographic evidence for Desmodus in
flight indicates that there is relatively little variability in the plane
through which the wing is adducted. The heavy wing loading in
this species (Hartman, 1963), combined with the proportionally
large meals that are consumed (Wimsatt, 1969), seem to have re-
sulted in relatively unvarying wingbeat patterns as opposed to hov-
ering, nectar-feeding species such as Leptonycteris sanborni (Alten-
bach, 1968).
Along with the M. serratus anterior, posterior division, the sternal
M. pectoralis adducts the humerus during the powered phase of
the jump. It is doubtful that the angle of the jump is controlled by
the M. pectoralis, as a jump, particularly when the bat has a full
stomach of blood, probably requires contraction of the entire mus-
cle. Variation in the rotation of the humerus during the jump is
likely under the control of the M. subscapularis, suprascapular
group, deltoid group, clavicular M. pectoralis, and M. latissimus
dorsi.
During the wingbeat cycle, the strong pronation of the arm and
hand, which orients the wing into a thrusting configuration during
the first half of the downstroke, is a result of contraction of the
102 Spec. Publ. Amer. Soc. Mamm. 6
Sternal division of M. pectoralis. There is perhaps more variability
in the function of this muscle during a wingbeat cycle than in a
jump. Greater contraction of specific parts of the muscle mass can
vary the degree of pronation and the plane of adduction of the
wing. As in a jump, the rotational stability is also controlled by the
supraspinatus, infraspinatus, subscapularis, deltoid group, clavic-
ular M. pectoralis, and M. latissimus dorsi.
In terrestrial locomotion, the sternal M. pectoralis probably sup-
ports most of the weight directed against the pectoral limbs. When
the bat is in elevated walking postures or standing in terrestrial
feeding posture with much of the weight probably supported by
the clavicle and posterior division of the M. serratus anterior, moving
the brachium is the task of the clavicular M. pectoralis, deltoid
group, and M. latissimus dorsi. Sudden movements from these pos-
tures would seemingly require the power of the sternal M. pecto-
ralis.
M. pectoralis abdominalis (Fig. 44). — Origin is on the abdominal
fascia beginning 2.5 mm lateral to the midline at the level of the
posterior tip of the xiphoid process and extending posterolaterad
for roughly 9 mm. Insertion is by a flat tendon, which attaches to
the medial 2 mm of the ventral aspect of the pectoral ridge pos-
terior to the insertion of the M. pectoralis.
As in other species, the M. pectoralis abdominalis is a rotator (pro-
nator) and flexor of the humerus. During the downstroke it can
increase pronation to form more of the medial wing into a thrust-
ing attitude or can oppose the supinating force exerted by the M.
biceps brachii. The pronation during the flick phase is probably
aided by this muscle along with the M. latissimus dorsi and M. teres
major.
In terrestrial locomotion, the power stroke of the pectoral limb
is probably aided by this muscle as it pronates and flexes the hu-
merus. The forearm is forced downward and posteriad by this
movement, thus driving the body forward.
Flexor Group of the Arm
M. coracobrachialis (Fig. 45). — Origin is on the dorsal third of the
anterior face of the coracoid process. Insertion is over about 4 mm
of the anteroventral surface of the humerus beginning approxi-
mately 1 1 mm lateral to the medial end of the pectoral ridge.
^^^J^J^
Altenbach — Vampire Locomotor Morphology 103
K y L M
L
-•JY«V**V1, r-
I I I I I I I I I I 1 1 I I I I I I I I I I I
A BCDE FGH I J KLMNOPQRSTUV
Fig. 40. Electromyogram of right M. biceps brachii, coracoid head, of Desmodus
and corresponding locomotor behavior. The contraction of the muscle occurs
slightly after the electrical event and is shown as a solid line above the electromy-
ographic recording. Corresponding locomotor stages and portions of the electro-
myogram are indicated by the same letters.
The M. coracobrachialis is a rather weak adductor and extensor
of the humerus. It probably aids in adduction of the wing and
exerts a stabilizing force to the brachium.
M. biceps brachii (Figs. 42, 44-47). — The origin of the coracoid
104 Spec. Publ. Amer. Soc. Mamm. 6
head is on the posterior and lateral aspect of the ventral three-
fourths of the tip of the coracoid process. The origin of the glenoid
head is by a tough tendon from the tubercle a millimeter anterior
to the glenoid fossa on the lateral aspect of the base of the coracoid
process. Insertion is by a heavy tendon that runs over the ridge on
the proximal end of the radius and attaches into the flexor fossa
on the posterior side of the radius.
As in other bats (Vaughan, 1959; Norberg, 19706), the bellies of
the biceps are flexors of the forearm and, because of the articu-
lation of the radius and humerus that allows only flexion and ex-
tension, supinators of the arm. Electromyographic data from a
jump into flight were recorded from electrodes in the coracoid
head, but probably are representative of the function of both
heads. There is little or no activity during the powered phase of
the jump (Fig. 40D-G) and the first contraction is a short burst
during the initial part of the coasting phase, which flexes the fore-
arm (Fig. 40G-H). Contraction again begins at the first of the
downstroke and continues until the beginning of the flick phase
of the upstroke (Fig. 40K-N). When opposed by contraction of the
M. triceps brachii, the biceps causes adduction of the arm and, as
Vaughan (1959) pointed out, provides rotational stability as it op-
poses the pronating forces applied by the M. pectoralis. When the
M. triceps brachii ceases contraction in the last half of the down-
stroke (Fig. 38), the biceps flexes and supinates the arm (Fig. 40L-
N). The function is similar in the next two cycles (Fig. 40O-V).
M. brachialis (Figs. 46-47). — Origin is over about 9 mm of the
anterior face of the humerus beginning 12 mm lateral to the distal
end of the pectoral ridge. Insertion is into the flexor fossa of the
radius in common with the tendon of the M. biceps brachii. This
muscle probably assists in the flexion and stabilization of the fore-
arm, as suggested in other species of bats (Vaughan, 1959, 1970c;
Norberg, 19706). No electromyographic data are available.
Flexor Group of the Forearm
M. flexor carpi ulnaris (Figs. 47, 49). — Origin is on the ventral
aspect of the ulna from its medial tip laterally for 5 mm and on
the adjacent M. palmaris longus about 4 mm distal to its origin.
Insertion is onto the posteromedial surface of the pisiform a third
of the distance to its ventral tip.
Altenbach — Vampire Locomotor Morphology 105
As in several other species of bats (Vaughan, 1959), this is a
flexor of the fifth metacarpal and thus the hand, because forces
applied to the pisiform are transmitted to the fifth metacarpal.
However, the belly is relatively small and the tendon is extremely
thin, indicating that the duty of flexion of the fifth metacarpal has
been taken over by other muscles such as the M. extensor carpi
ulnaris. As in Macrotus (Vaughan, 1959), the origin allows complete
independence of movement at the elbow and facilitates the ab-
duction of the extended hand-wing anterior to the body to provide
low drag on the upstroke.
M. palmaris longus (Figs. 47, 49). — Origin is by a heavy tendon
on the distal tip of the spinous process of the ventral (medial)
epicondyle of the humerus and from the ventral side of the prox-
imal 6 mm of the M. flexor digitorum profundus. Insertion is by an
aponeurosis onto the basal and distal thumb pads, on the ventral
sesamoids at the first metacarpophalangeal junction, on the ante-
rior face of metacarpal II, about 13 mm distal to its base, and on
the ventral aspect of the proximal few millimeters of metacarpals
III and V.
The relatively heavy attachments on the first digit and the rather
large belly of the palmaris longus in Desmodus suggest that this
muscle is important in ventral flexion of the thumb during the
jump and perhaps in terrestrial locomotion. The attachments on
the second and third metacarpals are suited to flex them toward
the radius and probably aid the M. flexor carpi radialis, M. flexor
carpi ulnaris, and M. extensor carpi ulnaris in keeping the wing tightly
folded during the jump and in terrestrial locomotion. When the
hand is fully extended in flight, the radial extensors of the hand
easily overpower this muscle, but it can function to ventrally brace
the second and third metacarpals against the force of the air stream
and help strengthen the leading edge of the wing. The attachment
to the fifth metacarpal probably serves a relatively passive bracing
function, as it is not suited to flex the metacarpal toward the radius.
The electromyographic data for the palmaris longus are not
ideal, because the bat did not fully extend the left wing during
most of the flight. However, the recorded activity of the muscle is
probably similar to that in normal locomotor activity. Sporadic con-
traction occurs during the step and partial hop before the bat
jumps into flight (Fig. 41A-G) and during the powered phase of
the jump (Fig. 41H-I). The flick phase does not seem typical (par-
106 Spec. Publ. Amer. Soc. Mamm. 6
B
fX?
^4#^ ^^ w^//
H
C D E
'4A.
F
%?
I I I I
Q R S T
Fig. 41. Electromyogram of right M. palmaris longus of Desmodus and corre-
sponding locomotor behavior. The contraction of the muscle occurs slightly after
the electrical event and is shown as a solid line above the electromyographic re-
cording. Corresponding locomotor stages and portions of the electromyogram are
indicated by the same letters.
Altenbach — Vampire Locomotor Morphology 107
clavotrapezius
occipito-pollicalis
omocervicalis
acromiotrapezius
spinodeltoideus
acromiodeltoideus
clavodeltoideus
triceps lateralis
triceps longus
teres major
latissimus dors
biceps brachii
spinotrapezius
rhomboideus
levator scapulae
serratus anterior, ant. div.
acromion proc.
supraspinatus
nfraspinatus
edial scapular
border
spinodeltoideus
serratus anterior,
post. div.
spinotrap. (cut)
lat. dor. (cut)
Fig. 42. Dorsal view of pectoral girdle musculature of Desmodus. Superficial
muscles (left of midline) and view with M. acromiotrapezius, M. spinotrapezius, M.
latissimus dorsi, and M. acromiodeltoideus removed (right of midline).
ticularly the movements of the right wing with the implanted elec-
trodes), but contraction occurs through this phase, perhaps to "fa-
vor" the wing and keep it partially flexed (Fig. 41L-N). Contraction
again occurs in the first half of the downstroke and ceases until the
middle of the upstroke, when a short burst occurs, perhaps to
partially flex the digits and "cock" them for extension in the flick
phase (Fig. 410-S). The contraction at the beginning of the flick
phase may be to resist the radial extensors and let their contraction
build up maximal tension before relaxation of the palmaris, and
perhaps other flexors, suddenly releases the hand. This could con-
tribute to a "snap" of the chiropatagium to provide considerable
thrust. The wing is more extended at this point and contraction
occurs during the entire downstroke.
M. flexor carpi radialis (Figs. 47, 49). — Origin is on the postero-
ventral aspect of the proximal half of the belly of the M. pronator
teres. Insertion is on a large tubercle on the anteroventral base of
metacarpal II.
In phyllostomatids such as Macrotus, the insertion of this muscle
108 Spec. Publ. Amer. Soc. Mamm. 6
scapula
ledial head
triceps brachii
lateral head .
medial head
long head —
Fig. 43.
removed.
Ventral view of M. triceps brachii oi Desmodus: A, intact; B, medial head
is on the third metacarpal (Vaughan, 1959). The insertion on
metacarpal II in Desmodus permits the leading edge of the wing to
be actively flexed against the radius rather than passively flexed by
flexors of the third, fourth, or fifth digits. The position of the
insertion also reflects the need to rapidly fold the wing in an alight-
ing maneuver and to hold it firmly folded during terrestrial lo-
comotion, climbing, and jumping.
M. pronator teres (Fig. 47). — Origin is on the tip of the spinous
process of the ventral (medial) epicondyle of the humerus. Inser-
tion is on 10 mm of the ventral aspect of the radius beginning 8
mm distal to the tip of the spinous process.
As the humero-radial articulation allows little but flexion and
extension, this muscle acts as a weak flexor and a powerful ventral
brace of the radius. In terrestrial locomotion or alighting maneu-
vers, forces against the carpus are transferred to the humerus as
a strong supinating torque. The elbow must be strongly braced
against these forces without excessive connective tissue binding
that would reduce mobility. Co-contraction of the M. supinator also
stabilizes the radius against the humerus.
M. flexor digitorum profundus (Figs. 47, 49). — The origin includes
the ulna from 5 mm of its interosseus and ventral surface distal to
Altenbach — Vampire Locomotor Morphology 109
its contact with the radius; the tip of the spinous process of the
humerus; and a few fibers from the posterior surface of the radius
5 mm distal to the spinous process of the humerus. Insertion is as
follows: the tendon divides at the carpus into 1) a heavy tendon
that inserts on the middle of the ventral aspect of the first phalanx
of digit I (a tiny tendon diverges from this tendon and is the origin
for a small muscle inserting on the anterolateral aspect of the distal
tip of metacarpal I); 2) a tendon that runs over the pisiform and
inserts on the proximoventral tips of the first and second phalanges
of digit III; and 3) a tendon of origin for one belly on the M.
interossei that inserts on the posterior surface of metacarpal III, 10
mm distal to its proximal base.
This rather massive muscle supplies most of the ventral flexive
force to the thumb as it provides the last upward thrust in the
powered phase of the jump. The attachments to the metacarpal
and the two proximal phalanges of digit III flex the third digit
and help keep the wing tightly folded during the jump and in
terrestrial locomotion. Also, all of the forearm flexors of the
thumb, the M. flexor digitorum profundus, M. palmaris longus, and
the M. abductor pollicis longus have flexive attachments to at least
one of the other digits and help keep the chiropatagium folded
against the radius during ventral flexion of the thumb.
In flight, contraction of the flexor digitorum profundus would
ventrally brace the metacarpal and phalanges of the third digit and
could control depression of much of the leading edge of the wing
and the degree of upward deflection of the phalanges of digit III
by opposing the upward force of the air.
Extensors of the Manus
M. interosseus dorsale (Figs. 48-49). — Origin is on the posteroven-
tral surface of the base of metacarpal II. Insertion is by an apo-
neurosis on the antero ventral aspect of the tip of metacarpal III
and on the proximal half of the anteroventral surface of the first
phalanx of digit III.
It seems odd that this muscle should be absent in Macrotus and
Myotis (Vaughan, 1959) and present in Eumops (Vaughan, 1959),
Plecotus auritus (Norberg, 19706), and Desmodus. In Desmodus it
pulls the first phalanx of digit III anteroventrad and tightens the
chiropatagium between digits III and IV. It also braces the first
110 spec. Publ. Amer. Soc. Mamm. 6
occipito-pollicalis.
clavodeltoideus.
sternal pectoralis
biceps brachii
coracoid head
glenoid head
coraco-cutaneus
pectoralis abdom
clavicular pectoralis
subclavius
coracoid process
pectoral ridge
biceps brach.
coracoid head
glenoid head
serratus ant.
posterior div.
pect. abdom.
Fig. 44. Ventral view of pectoral girdle musculature of Desmodus. Superficial
muscles (left of midline) and view with M. pectoralis, sternal division, and M. clav-
odeltoideus removed (right of midline).
phalanx of digit III against upward deflection, and limits upward
deflection to phalanges two and three.
Flexor Group of the Manus
M. abductor pollicis brevis (Fig. 49). — See the account of M. ab-
ductor pollicis longus.
M. flexor pollicis brevis (Fig. 49). — Origin is by a long tendon from
the anteroventral tip of the lunar and from the ligament between
the anterolateral tip of the trapezium and the anterior base of
metacarpal II. Insertion is on the medial aspect of the distal tip of
metacarpal I and on the lateral aspect of the distal tip of metacar-
pal I.
The two bellies of this muscle are ventral flexors of metacarpal
I if contracting simultaneously and, if contracting singly, are ven-
trolateral or ventromedial flexors of the first metacarpal. As pow-
erful ventral flexion of the thumb is the function of the M. flexor
digitorum profundus, M. palmaris longus, and M. abductor pollicis lon-
gus, the flexor pollicis brevis probably is more important in moving
Altenbach — Vampire Locomotor Morphology 1 1 1
clavicle
subclavius
coracoid process
lesser tuberosity
serratus ant., ant.div.
subscapularis
biceps brachii
coracoid head
serratus ant.
post. div.
tendon of orig. for
glenoid biceps brach.
pectoral ridge
coracobrachialis
biceps brach
glenoid head
Fig. 45. Ventral view of deep pectoral girdle musculature of Desmodus. View
(left side) with M. pectoralis, sternal division, M. clavodeltoideus, M. pectoralis abdom-
inalis, M. pectoralis, clavicular division, removed and view (right side) with the above-
mentioned muscles and the M. subclavius and M. biceps brachii, coracoid head, re-
moved.
the thumb in delicate maneuvers during terrestrial locomotion or
climbing. In elevated walking or in a terrestrial feeding posture,
this muscle helps shift the weight from the basal pad of the thumb
to the distal pad at the metacarpophalangeal junction (Fig. 2C).
When the bat feeds from the neck or head of an animal, the
thumbs must be moved occasionally to give the claws purchase on
the skin or hair, and these muscles probably function in such move-
ments.
M. adductor pollicis (Figs. 48-49). — Origin is on the anteroventral
aspect of metacarpal II, 1.5 mm distal to the insertion of the M.
flexor carpi radialis and on the ventral aspect of metacarpal III distal
to its articulation with the carpus. Insertion is by an aponeurosis
on the dorsolateral aspect of the distal tip of metacarpal I and by
a tendon on the dorsal base of the second phalanx of digit I.
The more delicate ventrolateral movements of the thumb during
terrestrial locomotion, climbing, and perhaps feeding are powered
by this muscle and the lateral belly of the M. flexor pollicis brevis. If
the first metacarpal is braced by both bellies of the latter muscle,
112 Spec. Publ. Amer. Soc. Mamm. 6
propatagjalis proprius
e. d. q. p.
Fig. 46. Dorsal view of superficial musculature of the right forearm of Desmodus.
Abbreviations: e.c.r.b. , M. extensor carpi radialis brevis ; e.c.r.l., M. extensor carpi radialis
longus; sup., M. supinator; e.d.c, M. extensor digitorum communis; e.c.u., M. extensor
carpi ulnaris; e.p.b., M. extensor pollicis brevis; e.d.q.p., M. extensor digiti quinti proprius.
the M. adductor pollicis could elevate the terminal digit and claw,
and draw the entire digit ventrolaterad.
M. interossei (Fig. 49). — Individual muscles of this group are as
follows:
1) Origin is by a tendon on the ventral tip of the trapezium.
Insertion is on the posterior half of the ventral base of phalanx
one, digit III.
Along with the M. interosseus dorsale, this muscle stabilizes the
first phalanx of digit III against deflection upward by the force of
the air stream during adduction of the wing.
2) Origin is from the magnum and a tendon from the ventro-
lateral aspect of the base of metacarpal IV. Insertion is on the
ventrolateral aspect of the tip of metacarpal IV and on the ven-
trolateral aspect of the proximal tip of phalanx one.
This is a weak flexor of the first phalanx of digit IV and serves,
along with the third belly of this group of muscles, to brace the
Altenbach — Vampire Locomotor Morphology 1 13
f. d. p.
Fig. 47. Ventral view of superficial musculature of the right forearm of Des-
modus. Abbreviations: f.c.r., M. flexor carpi radialis; e.c.r.l., M. extensor carpi radialis
longus; p.t., M. pronator teres; f.d.p., M. flexor digitorum profundus; p.l., M. palmaris
longus; e.c.u., M. extensor carpi ulnaris; f.c.u., M. flexor carpi ulnaris.
fourth metacarpal against upward deflection during adduction of
the wing. It also assists in flexing the phalanges as the wing is
folded during an alighting maneuver or for terrestrial locomotion.
3) Origin is from the magnum and a small tendon from the
ventromedial aspect of the proximal base of metacarpal IV. Inser-
tion is on the ventral base of the first phalanx of digit IV by a
tendon.
This muscle works along with the second belly of this group,
and its function is essentially identical.
4) Origin is from a slip of the tendon of the M. flexor digitorum
profundus. Insertion is on the posteromedial surface of metacarpal
III 10 mm distad to its proximal tip.
When the M. flexor digitorum profundus contracts to ventrally flex
the thumb during a jump or in terrestrial locomotion, the origin
of this muscle is stretched, and the force, transmitted through the
belly, flexes the third digit against the radius. Contraction of this
belly of the M. interosseus under these conditions applies more force
114 Spec. Publ. Amer. Soc. Mamm. 6
e.c.r. I
Fig. 48. Dorsal view of the musculature and tendons of the right carpus of
Desmodus. All of the M. extensor indicis, except its major insertional tendon, is re-
moved. Abbreviations: e.c.r.l., M. extensor carpi radialis longus; e.c.r.b., M. extensor
carpi radialis brevis; e.i., M. extensor indicis (major tendon); e.p.b., M. extensor pollicis
brevis; e.c.u., M. extensor carpi ulnaris; e.d.q.p., M. extensor digiti quinti proprius; e.d.c,
M. extensor digitorum communis; i.d., M. interosseus dorsale; add. poll., M. adductor
pollicis; I-V, metacarpals I-V; 1, 2, phalanges of digit I.
and holds the third digit against the radius more firmly. When the
wing is extended during the wingbeat cycle, the elastic properties
of this muscle allow contraction of the M. flexor digitorum profundus
to ventrally brace the third metacarpal and first phalanx of digit
III but only apply minimal flexive force.
M. abductor digiti quinti (Fig. 49). — Origin is by a tendon from
the posterior tip of the scaphoid. Insertion is by a broad aponeu-
rosis on the ventromedial aspect of the distal tip of metacarpal V
and on the ventromedial base of phalanx one.
This muscle is large in Desmodus and is situated to brace the fifth
metacarpal against the force of the airstream during adduction of
the wing and ventrally flex the first phalanx of digit V. In Macrotus
(Vaughan, 1959), this muscle is quite tendinous and acts as an
inelastic brace; however, the relatively large, fleshy belly suggests
its function is more variable in Desmodus. Relaxation during the
first half of the downstroke allows the upward deflection of the
phalanges (Fig. 19), which provides thrust from the middle of the
wing. Contraction ventrally flexes the phalanges and shapes this
Altenbach — Vampire Locomotor Morphology 1 15
palm. long.
Fig. 49. Ventral view of the musculature and tendons of the right carpus of
Desmodus: A, view of the insertion of the M. palmaris longus; B, view of the anatomy
with the palmaris removed. Abbreviations: f.c.u., M. flexor carpi ulnaris; abd. p.l.,
M. abductor pollicis longus (and perhaps brevis); int. (1-4), bellies of Mm. interossei;
f.c.r., M. flexor carpi radialis; f.p.b., M. flexor pollicis brevis; f.d.p, M. flexor digitorum
profundus; add. poll., M. adductor pollicis; abd. d.q., M. abductor digiti quinti; o.d.q.,
M. opponens digiti quinti; e.c.u., M. extensor carpi ulnaris; II-V, metacarpals of digits
II-V (metacarpal I not visible); 1, 2, phalanges of digit I.
part of the wing into a cambered surface suited for production of
lift. This function is probably aided by contraction of the M. ab-
ductor pollicis longus, which displaces the origin proximally.
M. opponens digiti quinti (Fig. 49). — Origin is by a tendon on a
tubercle of the posteroventral aspect of the pisiform adjacent to its
articulation with metacarpal V. Insertion is by an aponeurosis on
the ventrolateral aspect of the tip of metacarpal V.
The tendons of this muscle and the M. abductor digiti quinti fuse
distally, thus their function is essentially the same. However, be-
cause the opponens digiti quinti originates on the pisiform, it is
not affected by contraction of the M. abductor pollicis longus and
can flex the phalanges of the fifth digit, even if the abductor is
relaxed. Co-contraction of all three can powerfully flex the pha-
langes and overpower the M. extensor digiti quinti proprius to hold
the fifth digit at a high and rigid camber.
DISCUSSION
Terrestrial Locomotor Behavior
j-^ESMODUS rotundus is the most terrestrially oriented of bats; its
-Ly agility in quadrupedal locomotion far surpasses that of other
species and even that of many small rodents and carnivores. As
several authors have described (Beebe, 1927; Price, 1950; Ditmars
and Greenhall, 1935, 1936; Dalquest, 1955; Wimsatt, 1959), it runs
along horizontal or vertical surfaces with ease and executes sudden
evasive maneuvers that make it difficult to capture. This terrestrial
facility is closely involved with feeding behavior, as no other bat
except Desmodus (and perhaps the other sanguivorous bats, Diaemus
and Diphylla) shows such agility in terrestrial locomotion. Obser-
vations of Desmodus scrambling over the backs and necks of host
animals prior to feeding (or to avoid movements of the host animal
to brush them off), and running or hopping about on the ground
while feeding, illustrate the adaptive value of this effective terres-
trial locomotion. Although several other species of bats easily move
about on the ground and occasionally catch food to alight prior to
catching the food, Desmodus, and perhaps to a lesser extent the
other two sanguivorous bats, are the only chiropterans that have
become so specialized in feeding as quadrupeds.
According to Vaughan (1959, 1970^, 1970^), bats probably
evolved as crevice dwellers and thus, initially, were adapted for
terrestrial locomotion in confined spaces. Even in bats such as Eu-
mops perotis, Myotis velifer (Vaughan, 1959), Antrozous pallidus (Burt,
1934), Nyctalus noctula (Anonymous, 1969), Rhinolophus ferrume-
quinum (Southern, 1964), and Eptesicus fuscus (Altenbach, 1968),
which readily move about in quadrupedal fashion on the ground
or other surfaces, the limbs are directed more or less lateral to the
body, which is typically held quite close to the surface. The power
strokes are directed posterolaterally by flexion and slight pronation
of the brachii, extension of the elbows, and by posterior swings of
the laterally extended pelvic limbs. These types of movements are
necessary in a crevice or in confined roosts, but are inefficient,
inasmuch as the weight is supported on laterally directed limbs.
The large M. pectoralis is well suited to support much of the weight,
116
Altenbach — Vampire Locomotor Morphology 1 17
but the muscles that move the limbs have to work against the forces
that maintain posture.
As described in the section on locomotion, Desmodus inclines the
body and holds it well above a horizontal surface when walking or
running. The shanks are directed almost vertically, the brachii are
directed relatively posterolaterally, and the forearms are partially
flexed and directed anteroventrally and slightly laterally. The net
result of this posture is that the contact of the limbs with the surface
is shifted nearer the body and more below it, requiring less effort
to maintain the posture. Thus greater muscular effort can be de-
voted to moving the limbs, resulting in more rapid and complex
movements. Posteroventral thrusts with both pectoral and pelvic
limbs produce a hopping gait that rapidly carries the bat over the
ground and allows chasing of host animals.
The orientation of the hind limbs makes them well suited to
pulling, thus the bats typically climb backwards. The pectoral limbs
incline the body away from the surface and aid climbing by for-
ward thrusts. With the body in a climbing position, the pectoral
limbs are able to thrust the bat outward into flight or laterally in
an avoidance reaction. There are few records of predators feeding
upon bats in roosts, thus the agility on vertical surfaces in roosts
appears to be a secondary advantage of locomotor mechanisms
evolved for terrestrial feeding.
Desmodus regularly consumes a large volume of blood, often as
much as 100 per cent of its body weight, in a single feeding period
(Wimsatt, 1969). This, and the habit of feeding from the ground
or moving about on the ground between feeding periods, require
the ability to launch into flight from the ground when heavily
loaded. Host species, such as large ungulates, often are found in
the open and some distance from trees or rock outcrops on which
the bats could climb and from which they could drop into flight.
Many other species of bats require a drop from a roost to build
the air speed necessary for flight. Bats other than Desmodus that
can fly from the ground, such as some nectar feeding species {Lep-
tonycteris, Glossophaga) and lightly-loaded insectivorous taxa {Antro-
zous, Myotis, Plecotus), push off from the surface with partially or
fully extended wings and begin flight with a lift-generating wing-
beat cycle.
The ability to shift the pectoral limbs almost directly under the
118 Spec. Publ. Amer. Soc. Mamm. 6
body and several other anatomical modifications allow Desmodus to
achieve flight from the ground by a powerful jump, which carries
it, even when fully gorged on blood, high enough above the surface
to initiate a high-amplitude wingbeat cycle. The jump is effected
by a powerful adduction of the brachii, extension of the elbows,
and ventral flexion of the thumbs. The extreme elongation of the
thumbs, which are proportionally longer than in any other bat,
provides a long lever arm for this flexive movement that adds the
final upward momentum during the jump. The pelvic limbs supply
little of the upward thrust, as they function primarily to shift the
center of gravity over the powerful pectoral limbs. The jumping
behavior also plays an important role in avoiding being stepped on
by a large host animal and perhaps avoiding terrestrial predators.
Although jumps into flight are directed primarily forward and
upward, a direction that allows maximal thrust from the pectoral
limbs, avoidance jumps can occur in any direction. Both avoidance
jumps and jumps into flight are powered by the pectoral limbs,
while the hind limbs shift the weight into the line of the jump.
Alighting maneuvers on a horizontal surface are essentially the
reverse of the movements used in a jump into flight. Contact with
the substrate is made first with the thumbs. The downward mo-
mentum is slowed by muscular resistance to hyperextension of the
thumbs, flexion of the elbows, and abduction of the brachii. The
movement effectively breaks the force of the landing and is prob-
ably advantageous for alighting softly on or near a host animal.
Rodney Honeycutt, Ira Greenbaum, and Robert Baker (personal
communication) speculate that because obligate blood feeding ap-
pears in mammals only in the genera Desmodus, Diphylla, and Diae-
mus, these bats probably evolved from a common ancestor that was
already a sanguivore. I cannot speculate about the evolutionary
development of sanguivory in bats, but I feel that Desmodus is cer-
tainly the most derived, from a locomotor morphological stand-
point, of the Desmodontinae. The morphological modifications of
the limbs and girdles reflect selective pressures somewhat different
than those expected to have acted on a bat that typically parasitizes
large domestic animals of man.
The habit of feeding on large ungulates from the ground, and
the ability to feed from relatively active terrestrial rodents, suggest
that perhaps the bats initially fed on small terrestrial mammals or
other vertebrates and that the facility for terrestrial locomotion
Alteyibach — Vampire Locomotor Morphology 1 19
developed in response to this mode of feeding. Seemingly, if the
bats had fed initially on large ungulates, they could have readily
fed from the back or neck and the ability to run on the ground
would not have been necessary. With only a small thrust of the
limbs, the bats could have dropped off the back or neck into flight.
Thus, the complex energy-demanding jump would not have been
necessary. Probably the mechanisms of the jump evolved as a
means to rapidly negotiate rough terrain in pursuit of a small
mammal or other vertebrate, rather than to avoid movements of
larger animals. Elongation of the thumbs, no doubt, facilitated
rapid locomotion and permitted increasingly longer hops. Tran-
sition from a long hop to flight by initiation of the wingbeat cycle
does not seem a great step. Once developed, the jumping behavior
probably allowed larger meals to be taken in a single feeding pe-
riod and perhaps permitted feeding on the limbs of larger animals,
as it facilitated avoidance maneuvers.
Flight and Aerodynamic Considerations
Investigators of bat locomotor morphology have characterized
bats as relatively derived or underived on the basis of the degree
of anatomical and behavioral modification contributing to efficient
flight. In most species characterized by efficient flight, sometimes
described as relatively derived, there are anatomical features of
the pectoral limbs and girdles that automatically move distal parts
of the wings when more medial parts are moved. These features
also limit the planes of movement possible for the wings, but per-
mit great mechanical advantage for muscles to power the move-
ments and allow concentration of muscle mass nearer the center
of gravity. Such species can fly rapidly over relatively long distances
with minimal energy expenditure and are well suited for long feed-
ing periods in flight or for migration.
Species with inefficient flight, often characterized as underived,
are better suited to feeding on nectar or fruits, or feeding and
maneuvering in a cluttered environment, and necessarily lack the
anatomical features that restrict planes of movement and provide
automatic movements of more distal parts of the wings. The great-
er variability of movements permits slow, intricate, or hovering
flight or terrestrial locomotion necessary for feeding.
It is important to note that the morphological features of the
120 Spec. Publ. Amer. Soc. Mamm. 6
limb and girdle that permit either highly efficient flight (or flexible,
relatively inefficient flight) may be equally derived and probably
reflect considerable evolutionary modification. Desmodus is certain-
ly an example of a morphologically derived bat that has specialized
in the tremendous variability and amplitude of movements that
are necessary for flight, rapid terrestrial locomotion, and also for
jumping, which effects the transition between flight and terrestrial
locomotion.
The momentum imparted by the jump is sufficient to carry the
body approximately 20 to 30 cm above the ground, giving
the bat time to unfold and position the wings for the first down-
stroke. However, both forward and upward velocity rapidly de-
crease during this coasting phase. Desmodus derives forward thrust
from unfolding the wings, which is similar to a movement in the
last half of the upstroke in Desmodus and in certain other phyllo-
stomatid (Altenbach, 1968), vespertilionid, and rhinolophid bats
(Eisentraut, 1936), and which Norberg (1970(7) termed the flick
phase. In this movement the digits and forearm are extended and
the entire arm is powerfully abducted and pronated. The dorsal
surface of the wing is directed posteriorly and dorsally against the
air stream, thus providing a component of forward thrust to rein-
force the forward momentum of the bat prior to initiation of the
wingbeat cycle. Several muscles power this flick; thus it can gen-
erate more thrust than can abduction of the wing alone.
The wingbeat cycle of Desmodus is peculiar because it shows both
the high amplitude downstroke typical of many vespertilionid bats
and the extended wing, low drag upstroke, and flick typical of the
phyllostomatid nectar-feeders to which Desmodus is closely related
(Forman et al., 1968). The same morphological features of the
shoulder girdle that permit the limbs to be directed ventral to the
body in terrestrial locomotion and in the jump allow a downstroke
of high amplitude. Although the flick, prior to the first downstroke
after a jump, supplies some increase in forward speed, the air
speed and upward velocity are low at the start of the downstroke;
thus maximal thrust and lift are necessary to initiate forward flight.
As in other bats (Eisentraut, 1936; Vaughan, 1959, 1970c?; Alten-
bach, 1968; Norberg, 1970a), the force of the air as the wing is
adducted deflects the phalanges of digit IV upward, thus making
the portion of the wing adjacent to digit IV a thrusting surface.
However, the arm is strongly pronated to orient the leading edge
Altenbach — Vampire Locomutur Morphology 121
of the wing well below the trailing edge, forming all but the prox-
imal third of the plagiopatagium and the chiropatagium, nearly 80
per cent of the wing area, into a thrusting structure. This contrasts
sharply with published estimates that only 20 per cent of the wing
area is configured to provide thrust in other bats. Photographs
taken several wingbeats after initiation of flight indicate that the
phalanges of the fifth digit also are deflected upward to increase
this thrusting effect. The distal portion of the chiropatagium often
is not fully unfolded during the first, and occasionally the second
or third, downstroke; yet motion pictures indicate rapid accelera-
tion during this period. Obviously, thrust is being produced by the
more medial parts of the wing and not by just the propeller effect
of the distal chiropatagium as is typically described for bat flight.
During the downstroke, both the upward and forward velocity of
the body increases, apparently the result of downward and back-
ward acceleration of air produced by the adduction of the wings.
Eisentraut (1936) stated that upward drive is produced by the ad-
duction of the wings in the downstroke but more recent discussions
of bat flight (Vaughan, 1959, 1966, 1970^, 1970^) suggest lift is
only produced by air flow over a cambered surface. In Desmodus,
as in any bat, the latter is perhaps the case in more rapid forward
flight. However, at least in Desmodus, much of the lift in the initial
flight following a jump and in the slow accelerating flight that
follows, is the result of acceleration of air ventrally during adduc-
tion of the wings.
An upward deflection of the distal two phalanges of digit III
during the downstroke perhaps reduces the formation of tip vor-
tices and, during the last half of the stroke, provides additional
lift. Adduction of the wings continues slightly anteriorly in the last
half of the downstroke and the tips occasionally meet below the
body. The high amplitude of the stroke permits production of
continuous air acceleration and thus thrust and lift production for
a relatively long period.
As in some nectar-feeding species of phyllostomatids, the down-
stroke gives way to the upstroke by a gradual change of direction
and position of the wing. Drag is minimized by raising the wings
anterior to the body, while they are fully extended, and with the
plane oriented vertically. A pronounced flick, similar to that de-
scribed by Eisentraut (1936) and Norberg (1970a) in other species,
completes the upstroke and provides additional thrust. The flick
122 Spec. Publ. Amer. Soc. Mamm. 6
can occur only in bats with great freedom of movement of the arm
and hand. In species that have evolved more efficient, high-speed
flight, anatomical modifications of the pectoral limb allow more
automatic extension and flexion of the hand and centralization of
weight and do not permit this type of upstroke and flick. There
is little doubt that this movement produces forward thrust in Des-
modus, as Eisentraut (1936) believed it does in several other species.
The most conclusive evidence is the rapid acceleration during this
movement prior to the first upstroke following a jump. Although
of greater amplitude, the initial flick is similar to that observed in
subsequent wingbeats of slow forward flight. There is only slight
flexion of the digits toward the forearm during the first half of the
upstroke in slow forward flight, thus extension of the digits plays
a lesser role in flight than it does in the initial flick.
Although no high-speed photographic data are available on rap-
id flight, the flick is certainly more important in slow flight than
in rapid flight. During the flick, thrust is derived by a posterior
swing of the more distal portions of the wing against the air. Ob-
viously, as the forward speed of the bat increases, the thrust from
the flick decreases. The high thrust required during the initial
flight following a jump is probably not so vital at high cruising
speeds and the upstroke is basically a recovery stroke. There is
almost certainly a modification of the wingbeat cycle during rapid
forward flight, but it remains for high-speed photographs to illus-
trate it. Perhaps the amplitude of the downstroke is less and the
stroke begins at a lower angle above horizontal (and continues
quite deep), as in some molossid bats, which are best suited for this
type of flight (Vaughan, 1959, 1966, 1970^). Inasmuch as Desmodus
is anatomically suited for the upstroke with the wing positioned
anterior to the body and its plane oriented vertically, this portion
of the stroke may remain relatively unchanged, and a pronounced
flick may occur. However, it may be more passive than in initial
flight after a jump or in slow forward flight.
Desmodus has a heavy wing loading (4.8 cmVg), as do molossids
such as Molossus bondae (4.0 cmVg), and phyllostomatids such as
Phyllostomus hastatus (3.4 cm^/g), and Artibeus jamaicensis (4.5 cmV
g) — Hartman, (1963). However, its aspect ratio is low (2.66) as
compared to Molossus bondae (3.6) and Phyllostomus hastatus (3.48).
Struhsaker's data (1966), calculated by slightly different methods,
place Desmodus (4.9) and Leptonycteris sanborni (4.6) below Molossus
Altenbach — Vampire Locomotor Morphology 123
nigricans (5.9) and Tadarida brasiliensis (6.7), and above several
species varying from 4.13 {Myotis velifer) to 2.44 {Antrozous pallidus) .
These data illustrate that Desmodus is somewhat unique in having
both a heavy wing loading and a low aspect ratio. Other investi-
gators have associated high aspect ratio and high wing loading with
relatively high-speed, unmaneuverable direct flight, such as that
of many molossid bats. Many of the species with low aspect ratio
wings, such as Antrozous pallidus, Myotis lucifugus, and Pipistrellus
hesperus are lightly loaded and have delicate, even hovering, flight.
Although Leptonycteris is less heavily loaded than is Desmodus,
Struhsaker (1961) found its loading more comparable to Desmodus
than to the other bats he investigated. The flight of these two bats,
however, is quite different. In slow and hovering flight, Leptonyc-
teris gains high lift from a medial and anterior swing of the forearm
and hand produced by a flexion of the elbow in the last half of the
downstroke (Altenbach, 1968). This movement supplies lift with-
out movement of the body through the air stream. The length of
the hand compared to that of the arm is relatively greater in Lep-
tonycteris than in Desmodus (Findley et al., 1972) and reflects the
role of the hand in lift production. Desmodus exhibits no such mod-
ification of the wingbeat cycle, and the relatively shorter and small-
er hand-wing probably reflects evolutionary compromises for both
flight and terrestrial locomotion. Desmodus appears to utilize a high
amplitude downstroke to provide maximal thrust and lift during
the wingbeat cycles following a jump. As thrust is certainly pro-
duced during the downstroke by much of the plagiopatagium in
addition to the chiropatagium, a large chiropatagium is not nec-
essary for thrust production. Elongation of the wings would be
disadvantageous, because the jump carries the bat less than 0.3 m
above the ground and contact of the wings with the ground at the
bottom of a deep stroke would certainly reduce acceleration. The
short hand can be folded quickly in an alighting maneuver to pre-
vent damage to the rather delicate digits and, when folded, is not
bulky enough to hamper quick movements necessary in the rapid
terrestrial locomotion typical of this bat.
The need for a relatively long limb in quadrupedal locomotion
and particularly for jumping probably prevents reduction in the
length of the antebrachium and brachium. Thus, to maintain a
wing of the proportions necessary for production of high thrust
and lift, and, at the same time to keep its length minimal and
124 Spec. Publ. Amer. Soc. Mamm. 6
provide a long limb for quadrupedal locomotion and jumping, the
relative length of the hand is reduced.
Since flight serves primarily to move the vampire bat relatively
short distances between roosting and feeding areas, there is no
need of anatomical modification for highly efficient flight, typical
of species that feed in flight or cover long distances in feeding and
migration. Great freedom of movement of the limbs, however, is
necessary in the terrestrial feeding behavior of this bat and espe-
cially for the transition from terrestrial locomotion to flight. Thus
speciahzation of the appendicular anatomy has been toward ex-
treme variability and amplitude as well as independence of move-
ment. Features that allow maximal muscular mass to power high
energy demanding movements have permitted development of
jumping behavior for transition between terrestrial and aerial
modes of locomotion. Some of these same features also permit
extremely high thrust and lift production necessary to sustain
flight after a jump and while carrying a heavy load of blood.
In effect, Desmodus has specialized in variability to feed as a ter-
restrial vertebrate and yet retain the advantages of a flying verte-
brate. Thus, this bat has reduced competition with other bats for
food resources, yet has retained the advantage of mobility and
ability to use secluded roosts that are inaccessible to most preda-
tors.
Anatomical Considerations
Perhaps the most striking osteological feature of the pectoral
girdle is the nature of articulation of the clavicle and scapula, which
allows the scapula to rock freely about its long axis. In other species
of bats such as Plecotus auritus (Norberg, 1970^), Eumops perotis and
Myotis velifer (Vaughan, 1959), and Eptesicus fuscus (Altenbach,
1968), the clavicle is boiind distally to both the acromion process
and the base of the coracoid process. This feature stabilizes the
pectoral girdle and gives the muscles that rock the scapula and the
wing, when the humerus and scapula are locked dorsally or ven-
trally, great mechanical advantage. However, the amplitude and
variability of movements of the wing are greatly restricted. Thus,
efficiency is gained at the expense of flexibility of movement. In
phyllostomatids such as Leptonycteris sanborni (Altenbach, 1968) and
Macrotus luaterhousii (Vaughan, 1959), the articulation of the scap-
Altenbach — Vampire Locomotor Morphology 125
ula and clavicle is similar to that of Desmodus, but the arrangement
in Desmodus allows much greater freedom of movement.
The relatively small angle through which the humerus can be
adducted or abducted relative to the scapula is surprising, consid-
ering the great amplitude of the movement of the brachium during
terrestrial locomotion, jumping, and flight, but suggests that some
of the muscles that insert on the scapula (M. serratus anterior, tra-
pezius group, and M. rhomb oideus) are important in moving the
arm. The spinous process of the ventral (median) epicondyle of
the humerus has no distal projection typical of many fast-flying
molossid, vespertilionid, and mormoopid bats; thus, muscles orig-
inating from it are not affected by movements at the elbow.
The ulna is strongly fused to the radius distally and rigidly ar-
ticulated with it proximally. The elevated carriage of the body in
terrestrial locomotion and jumping in this bat directs forces against
the long axis of the forearm, thus bracing is needed. In addition,
the relative independence of the hand from movement at the el-
bow requires more muscle mass in the forearm, and the rigid ulna
supplies a solid structure for the origin of such muscle. Investment
of the distal end of the radius with deep grooves and ridges for
confinement of insertional tendons of forearm muscles reflects the
large forces involved during terrestrial locomotion and jumping.
The carpus is not highly specialized except, as in other bats, to
limit the movements of all but digit I to a single plane, thus bracing
the hand-wing against the forces of the air stream in flight. How-
ever, digit I is greatly elongated, almost 30 per cent the length of
the forearm, and the articulation of the first metacarpal and tra-
pezium allows considerable freedom of movement. The articula-
tion is bound by ligaments ventrally and the articular surfaces slope
away dorsally from the ventral binding, allowing the thumb to be
oriented laterally when the forearm is directed perpendicularly
against a surface. The thumb thereby functions in maintaining
balance when the body is elevated in terrestrial locomotion, and
can be flexed powerfully from this position to supply the last up-
ward thrust in a jump and to provide thrust in rapid terrestrial
lomotion.
The metacarpophalangeal joints of digits IV and V and the first
interphalangeal joint of digit III permit considerable upward de-
flection of the phalangeal elements distal to them, thus enabling
the posterior part of the chiropatagium and distal part of the pla-
126 Spec. Publ. Amer. Soc. Mamm. 6
giopatagium to supply high thrust during the downstroke. This
appears unique among bats as, in others, only the phalanges of
digit IV deflect upward to provide the propeller effect described
by Vaughan (1959) and Eisentraut (1936).
The myology of the pectoral girdle and limb was described in
detail earlier and only the outstanding features, unique to Desmo-
dus, will be discussed here.
The M. clavotrapezius is large and its complete separation from
the M. acromiotrapezius and its heavy origin reflect importance in
bracing and moving the clavicle. In bats that have the clavicle
bound in two points to the scapula, the division between these
muscles is obscure and their function nearly identical, inasmuch
as rotational forces applied to the scapula are transferred directly
to the clavicle. The antagonist of the M. clavotrapezius, the M. suh-
clavius, also is large, and together these muscles stabilize the clavicle
and probably lower and raise it during jumping and flight. The
remainder of the trapezius group functions much as in other bats
to stabilize the scapula and rock it about its long axis.
Electromyographic data indicate the deltoid group, at least the
acromio- and spinodeltoids, functions to stabilize the dorsal scap-
ulohumeral articulation during the powered phase of the jump
and much of the downstroke in forward flight. This indicates, in-
directly, that the posterior division of the M. serratus anterior aids
the M. pectoralis in adducting the humerus through nearly the
entire jump and much of the downstroke. Vaughan (1959) sug-
gested that in other bats, particularly those having the scapula and
clavicle bound in two places, the posterior division of the serratus
only stops the upstroke and initiates the downstroke, the remain-
der of the downstroke being powered by the M. pectoralis and M.
subscapularis as they adduct the humerus using the scapula as a
fulcrum. In Desmodus, the two largest pectoral muscles, the M.
pectoralis and the posterior division of M. serratus anterior, are pos-
sibly responsible for nearly all of the brachial adduction in a jump
and for much of the brachial adduction in flight.
The M. clavodeltoideus is situated to extend the humerus, and its
size and complete separation from the clavicular M. pectoralis sug-
gest importance of this movement, which produces a power stroke
in backward climbing and in positioning the pectoral limbs for
alighting on a horizontal surface.
The pronators of the arm, the M. latissimus dorsi, M. pectoralis
Altenbach — Vampire Locomotor Morphology 127
abdominalis, M. teres major, M. subscapularis, and the posteriormost
fibers of the sternal M. pectoralis play an important role in the flick
phase of the upstroke. Pronation of the arms after initial abduction
of the wings in a vertical orientation anterior to the body swings
the distal half of the wings posteriorly against the air and provides
forward thrust. Although Eisentraut (1936) described the flick and
believed it produced thrust in several species of bats, recent in-
vestigators have implied the entire upstroke is entirely a recovery
stroke and provides no thrust. Indeed, in the molossids and many
vespertilionids, particularly those with features that limit freedom
of movement of the wings and provide highly efficient flight, the
flick is nearly impossible and the upstroke is a recovery stroke.
However, in rhinolophids, a few vespertilionids (Eisentraut, 1936;
Norberg, 1970(7), and many phyllostomatids, including Desmodus,
the flick is important in providing thrust, as the relatively large
size of the muscles involved and the good mechanical advantage
for the movements they power, suggest. In addition to the above-
mentioned muscles the three heads of the M. triceps brachii extend
the elbow to aid this movement, and the two largest forearm mus-
cles, the M. extensor carpi radialis longus and M. extensor carpi radialis
brevis, along with the M. extensor indicis, powerfully extend the chi-
ropatagium. The relatively small acromio- and spinodeltoids are
certainly not large enough to power a thrust-producing upstroke,
but they are well suited to raise the wing anteriorly to the body by
supination of the humerus and thus elevate the flexed forearm.
This type of upstroke seems quite typical of most phyllostomatids,
rhinolophids, some vespertilionids, and certainly Desmodus. It re-
duces drag initially and positions the wing for the flick, in contrast
to the case in the molossids and mormoopids where the upstroke
is a recovery stroke and the entire movement is essentially wasted
effort.
The M. biceps brachii is adapted to provide a strong, supinating
force to the arm and to flex the forearm as in other species. It
probably aids somewhat in the downstroke, even though the hu-
merus is dorsally locked with the scapular border. However, its
main function is very likely control of rotational stability of the
arm and flexion of the forearm at the first of the upstroke.
The importance of the thumb in Desmodus is evidenced by the
size of the tendons and bellies of the muscles that ventrally flex it.
The M. flexor digitorum profundus, the M. palmaris longus, and the
128 Spec. Piibl. Amer. Soc. Mamm. 6
M. abductor pollicis longus all have large tendons running to the
ventral aspect of the first digit. In other bats, the M. abductor pollicis
longus inserts on the scaphoid, and, in at least one species, Plecotus
auritis, the M. abductor pollicis brevis originates there and inserts on
the first digit. In Desmodus, the latter muscle has become tendinous
and originates directly on the tendon of the former, thus permit-
ting a longer and larger forearm muscle to power the flexion of
the thumb. The muscles of the hand, M. abductor pollicis and M.
flexor pollicis brevis, which insert ventrally on the thumb, are well
suited to move the thumb to give the claw purchase in such ma-
neuvers as climbing or walking. All of the above-mentioned fore-
arm flexors of the thumb have at least one flexive attachment to
digits II through V. Thus, as they flex the thumb in a jump or in
terrestrial locomotion, they also aid in keeping the digits flexed
toward the forearm and flex the phalanges. The major flexor of
the hand wing, the M. extensor carpi ulnaris, inserts on the medial
base of metacarpal V where it has great mechanical advantage.
The insertional tendon is massive and suggests the importance of
this muscle in holding digit V and, because of ligamentous attach-
ments between the metacarpals of digits III and V, the rest of the
hand-wing against the forearm, and in rapidly folding the hand-
wing during an alighting maneuver. The other major flexor of the
hand, the M. flexor carpi ulnaris, inserts on the pisiform as in other
species, but is small and probably only weakly assists M. extensor
carpi ulnaris. M. flexor carpi radialis is best suited to ventrally brace
the second metacarpal, and thus the leading edge of the hand-
wing. This is important when the leading edge of the wing is ori-
ented below the trailing edge for high thrust production in the
downstroke.
Because of the capacity for upward deflection of the phalanges
of digits IV and V and all but the basal phalanx of digit III, and
the capacity to vary greatly the degree of pronation or supination
of the arm, Desmodus can vary greatly the angle of attack, camber,
and degree of thrusting configuration of the wing. M. extensor dig-
itorum communis is well suited to actively deflect the phalanges of
digits III and IV, and the M. extensor digiti quinti proprius is suited
to deflect the phalanges of digit V. The upward deflection of the
phalanges of digit V is evident only during about the first half of
the downstroke, whereas that of digits III and IV persists to the
end of the downstroke. Thus it is critical that there be independent
Altenhach — Vampire Locomotor Morphology 129
control of digit V. As M. abductor digiti quinti originates on the
scaphoid in Desmodus, flexion of the phalanges of digit V is partially
under control of the M. abductor pollicis longus, which inserts on
the scaphoid and first digit. Along with the M. opponens digiti quinti,
these muscles can ventrally flex the phalanges of digit V to elimi-
nate the thrusting contour of the wing in that region and transform
it into a more cambered lift-generating surface. During a jump or
in terrestrial locomotion, the M. abductor pollicis longus can keep
the phalanges of the fifth digit flexed as it flexes the thumb by
pulling the origin of the M. abductor digiti quinti.
The large M. extensor carpi radialis longus and M. extensor carpi
radialis brevis originate medial to the center of the elbow joint and
thus are stretched slightly by extension of the elbow. However,
they are not invested in a tough connective tissue sheath of deep
fascia, as is the case in many molossids and vespertilionids, and do
not automatically extend the digits when the elbow is extended.
When the flexors of the hand-wing relax, particularly if the elbow
is partially or fully extended, these muscles can powerfully and
rapidly extend the fingers.
SUMMARY
THE mechanisms of terrestrial locomotion, jumping behavior,
and flight of the common vampire bat, Desmodus rotundus,
were analyzed with high-speed photographs and electromy-
ographs, and were correlated with osteological and myological fea-
tures of the pectoral girdle and limbs. Great freedom of movement
at the articulation of the scapula and clavicle, and independence
of movement in the arm and hand, allow the pectoral limbs to be
positioned below the body for efficient, rapid, and extremely agile
terrestrial locomotion. These same anatomical modifications, cou-
pled with specialization at the shoulder joint, enable the two largest
muscles in the bat, the M. pectoralis and the posterior division of
the M. serratus anterior, to power a deep adduction of the arms to
effect a jump into flight. Extreme elongation and development of
powerful associated flexor musculature permit the thumbs to pro-
vide an additional upward thrust in the jump. The jump is vital to
achieve flight after taking a blood meal from a prey animal on the
ground. The anatomical features of the pectoral girdle and limb
130 Spec. Piibl. Amer. Soc. Mamm. 6
that facilitate both the jump and the remarkable terrestrial loco-
motion are the most spectacular anatomical modifications in this
bat. They suggest Desmodus became evolutionarily specialized for
feeding terrestrially from small active prey animals. Feeding from
the backs or necks of large prey species seemingly would not have
necessitated the development of such rapid and agile hopping lo-
comotion. More important is that this manner of feeding would
not necessitate the extreme modification of the limbs and girdles
to execute the jump into flight so characteristic of this bat. The
habit of feeding from backs and necks of the large domestic ani-
mals of man is probably an opportunistic utilization of a relatively
new and more abundant food source.
During the downstroke of the initial flight following a jump, up
to 80 per cent of the area of the wings is configured to provide
thrust. The same large muscles of the pectoral girdle that provide
adductive power in jumping are able to power at least the first half
of a deep downstroke that initially supplies high thrust and sub-
sequently supplies both lift and thrust vital to initiation of forward
flight. The upstrokes in initial flight occur ahead of the body and
are terminated in a pronounced flick that provides additional
thrust and positions the wing for a subsequent downstroke. The
first few wingbeats following a jump into flight illustrate that thrust
and lift production are the result of the acceleration of air back-
ward and downward by movement of the wings. The amplitude
and directionality of the wingbeat, and the velocity and configu-
ration of the wings during the wingbeat cycle, determine the mag-
nitude and direction of the air acceleration. Thus a downstroke
could produce almost pure lift or pure thrust depending upon
how it was directed and the configuration of the wings. This view
contrasts with interpretations of bat flight, which suggest that lift
is produced by differential velocity of airflow over opposite sides
of the cambered plagiopatagium and that thrust is produced ex-
clusively by the distal chiropatagium. In many of the flights re-
corded in this study, the distal part of the chiropatagium, the por-
tion often said to be the prime producer of thrust, remained folded
as the bat rapidly accelerated. Thrust was obviously being pro-
duced by more medial portions of the wing.
Among many evolutionary compromises seen in the vampire bat
are the relative shortening of the hand and the retention of a large
muscle mass distally in the wing to control the hand movements.
Altenbach — Vampire Locomotor Morphology 131
A relatively long hand would be advantageous for lift and thrust
production, but would be difficult to quickly fold and unfold in
transition to and from terrestrial locomotion, and would be likely
to strike the ground on a high amplitude downstroke in the initial
flight following a jump. It also would be advantageous to have
more muscle mass concentrated near the center of gravity and to
have movements in the hand more automatic, as in certain other
bats, but the need for independent movement in the hand has
necessitated retention of considerable muscle mass distally. The
tight folding of the digits during extension of the arm during a
jump, and the extended orientation of the digits as the arm is
flexed during the first half of the upstroke, are good examples of
this independence of movement.
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INDEX
(page numbers in italic type denote illustrations)
Aerodynamics {see Locomotion,
flight)
Anatomy {see Myology, Osteology)
Climbing {see Locomotion, climbing)
Electromyograph
ofM. acromiodeltoideus, 85,86, 87
of M. biceps brachii, 103, 104
of M. clavotrapezius, 76, 78
of M. extensor carpi radialis longus,
94, 95
of M. latissimus dorsi, 82, 83-84
of M. palmaris longus, 105, 106,
107
of M. spinodeltoideus, 87,88, 89
of M. spinotrapezius, 77, 78-79
of M. triceps brachii, 91, 92
Electromyography
interpretation of, 72, 73
techniques of, 6, 7-8, 10
Flight {see Locomotion, flight, initial
flight)
Hanging {see Locomotion, hanging)
Hopping {see Locomotion, hopping)
Jump {see Locomotion, jump)
Locomotion
alighting
adaptive significance of, 51,
118
on horizontal surface, 49, 50,
51, 118
on vertical surface, 51-52
similarity to jump, 51
climbing
ascending, i 6, 17, 18, 117
descending, 18
flight
aerodynamics
aspect ratio, 122-123
relative hand length, 123
wing loading, 122
aerodynamic requirements,
42-43
anatomical specialization for,
124-129
downstroke, 42, 43, 46, 47, 48,
49
lift and thrust generation
during, 43-44
wing configuration during,
42, 43-44, 46-49
efficiency of, 119-120
rapid, 122
upstroke and flick, 44, 45, 46,
47, 48, 49
lift and thrust generation
during, 45-46, 49
hanging, 11, 12
transition to flight from, 12,
29,50
hopping, 14,75, 17, 117
evolution of, 119
initial flight
acceleration during, 120-121
aerodynamic requirements of,
120-121
anatomical specialization for,
125-129
coasting and initial flick
acceleration during, 33, 121
duration of movement, 31,
38
wing movement during, 31,
32, 33, 37, 120
first downstroke, 33-35, 120-
122
135
136 Spec. Publ. Amer. Soc. Mamm. 6
acceleration during, 35,
120-121
lift and thrust generation
during, 34, 35, 120-121
flick (see upstroke and flick)
flight path during, 31
into steep flight path, 39, 40
thrust production during,
120-121
turn during, 39, 40, 41
upstroke and flick, 35-39,
120-122
acceleration during, 38
wing configuration during,
120-121
jump
adaptive significance of, 21-22,
117
anatomical specialization for,
58, 59-60, 125-129
backward, 27, 28
evolution of, 119
in other bats, 1 17
into flight
anterolaterally, 27
coasting phase, 20, 21, 22,
25-26, 118
from vertical surface, 29, 30
from walking gait, 29
prejump posture, 22, 23
thrusting phase, 20, 21, 22,
23-25, 118
variation in, 22-23
standing, 9, 10-11
terrestrial {see also climbing, hop-
ping, walking)
agility during, 117
anatomical specialization for,
58, 59-60, 125-129
evolution of, 118-119
in other bats, 1 16
significance of limb position,
117
walking, 12-13, 14, 117
Myology
M. abductor digiti quinti, 114, 115
M. abductor pollicis brevis, 95-97,
115
M. abductor pollicis longus, 96-97,
115
M. acromiodeltoideus, 85-86, 107
M. acromiotrapezius, 78, 107
M. adductor pollicis, 111-112,77-^,
775
M. biceps brachii, 103-104, 107,
110, 111, 112, 113
M. brachialis, 104, 772, 775
M. clavotrapezius, 75-78, 707
M. clavodeltoideus, 84-85, 107,
110
M. coracobrachialis, 102-103, 77 7
M. coraco-cutaneous, 75, 110
M. extensor carpi radialis brevis, 93,
772, 77^
M. extensor carpi radialis longus,
93, 95,112, 113, 114
M. extensor carpi ulnaris, 98-99,
772, 775, 77-^, 775
M. extensor digitorum communis,
97-98, 772, 77^
M. extensor digiti quinti proprius,
97,112, 114
M. extensor indicis, 99, 77-7
M. extensor pollicis brevis, 95-96,
772, 114
M. flexor carpi radialis, 107-108,
775, 775
M. flexor carpi ulnaris, 104-105,
775, 775
M. flexor digitorum profundus, 108-
109,775, 775
M. flexor pollicis brevis, 110-111,
775
M. infraspinatus, 90, 707
Mm. interossei, 112-114, 775
M. interosseus dorsale, 109-110,
77^, 775
M. latissimus dorsi, 83-84, 107
Altenbach — Vampire Locomotor Morphology 137
M. levator scapulae, 79, 107
M. occipito-pollicalis, 73-74, 107,
110
M. omocervicalis, 83, 107
M. opponens digiti quinti, 115
M. palmaris longus, 105-107, 7i3,
115
M. pectoralis, 100-102, 770
M. pectoralis abdominalis, 102, 7 70
M. pronator teres, 108, 7 75
M. propatagialis proprius, 74-75,
772
M. rhomboideus, 81, 83, 7C7
M. serratus anterior, anterior divi-
sion, 79,107, 111
M. serratus anterior, posterior divi-
sion, 50, 81,107, 110, 111
M. spinodeltoideus, 87, 89, 707
M. spinotrapezius, 78-79, 707
M. subclavius, 99-100, 1 10, 1 1 1
M. subscapularis, 84, 77 7
M. supinator, 95, 772
M. supraspinatus, 89-90, 707
M. teres major, 84, 707
M. teres minor, 89
M. triceps brachii, 90-92, 705
Osteology
cervical vertebrae, 53
clavicle, 59-60
articulation with scapula, 59-
60
digit I, 66, 67, 68
digit II, 66, 67, 69
digit III, 66, 67, 69-70
digits IV-V, 66, 67, 70-71
humerus, 60, 67, 62-64
articulation with radius and
ulna, 64
articulation with scapula, 58,
62
lumbar vertebrae, 54-55
manus, 66, 67 , 68
radius and ulna, 63, 64-66
ribs, 56
sacral vertebrae, 55
scapula, 56, 57, 59, 80
articulation with clavicle, 58,
59-60, 80
articulation with humerus, 58,
62,80
orientation, 58, 59-60, 80
sternum, 54, 55-56
thoraic vertebrae, 53-54
ulna {see radius and ulna)
Photographic techniques
electromyographic, 6, 7-8
motion picture, 6, 7
still, 5, 7
Positional terminology, 52, 53
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