Morphology of the basisphenoid pits and related structures of the bat Otomops martiensseni (Chiroptera : Molossidae)

Life Sciences Contributions 1 | O
Royal Ontario Museum

Morphology of the Basisphenoid
Pits and Related Structures

of the Bat Otomops martiensseni
(Chiroptera: Molossidae)

Dario Valdivieso
R. L. Peterson
J. R. Tamsitt

R C) M

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LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM
NUMBER 119

RL pErtRson. Morphology of the Basisphenoid
J. R. TAMSITT Pits and Related Structures
of the Bat Otomops martiensseni

(Chiroptera: Molossidae)

ROM

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DARIO VALDIVIESO is a Research Associate in the Department of Mammalogy, Royal Ontario
Museum.

R. L. PETERSON is Curator in the Department of Mammalogy, Royal Ontario Museum, and Professor in
the Department of Zoology, University of Toronto.

J. R. TAMSITT is Curator in the Department of Mammalogy, Royal Ontario Museum, and Associate
Professor in the Department of Zoology, University of Toronto.

Canadian Cataloguing in Publication Data
Valdivieso, Dario, 1936-

Morphology of the basisphenoid pits and related
structures of the bat Otomops martiensseni
(Chiroptera: Molossidae)

(Life sciences contributions; no. 119 ISSN 0384-8159)

Bibliography: p.

ISBN 0-88854-238-0 pa.

1. Bats — Anatomy. I. Peterson, Randolph L., 1920-
Il. Tamsitt, J.R., 1928- HI. Royal Ontario

Museum IVe title “Vs Sertes:

QL737.C54V35 599’ .4'0448 C79-0945 13-4

Publication date: 29 June 1979
ISBN 0-88854-238-0
ISSN 0384-8159

©The Royal Ontario Museum, 1979
100 Queen’s Park, Toronto, Canada MSS 2C6
PRINTED AND BOUND IN CANADA AT THE ALGER PRESS

Morphology of the Basisphenoid
Pits and Related Structures

of the Bat Otomops martiensseni
(Chiroptera: Molossidae)

Abstract

The morphology and histology of the basisphenoid pits were studied in
the bat Otomops martiensseni (Chiroptera: Molossidae). The pits are
deep and well-defined bony cavities located posteriorly in the nasal
pharynx. They are juxtaposed to the opening between the nasal and
laryngeal pharynges and anatomically communicate with the middle
ear through the auditory tube. Basisphenoid pits may function as
resonating chambers for sound waves emitted by the larynx, but
experimental research is needed to determine their importance in the
sonar system.

(basisphenoid pits; morphology and histology; Otomops martienssent;
Molossidae; Chiroptera)

Introduction

Literature concerning the anatomy of the ear of Chiroptera is considerable (Henson,
1961, 1970; Novick, 1977), but few works deal specifically with basisphenoid pits,
which are paired depressions in the basisphenoid bone anteromedial to the auditory
bullae that have been postulated to be associated with echolocation in certain bats
(Peterson, 1969). Basisphenoid pits are present in insectivorous bats of the families
Emballonuridae, Vespertilionidae, and Molossidae (G. S. Miller, 1907), but the
variation in size of pits is the greatest in molossid bats, a group which is
circumtropical in distribution (Walker, 1975) and in which echolocation is highly
developed (Griffin, 1958). Furthermore, after a preliminary review of many species
of free-tailed or mastiff bats of the family Molossidae by one of us (RLP), a general
correlation appears to exist between the development of the pits and the size and
complexity of the external ears. Such small, simple-eared bats as the flat-headed bats
of the genera Platymops and Sauromys have the least developed basisphenoid pits
(Peterson, 1965), and species with larger, complex external ears have the most
developed pits, as in the big-eared mastiff bats of the genus Otomops (Peterson,
1969).

We describe here the morphology, histology, and variation in size of the
basisphenoid pits in Otomops martiensseni (Matschie) of the family Molossidae.
Objectives are to describe the relationships of the pits to associated structures and to
attempt to correlate morphology with function in the sonar system.

Otomops martiensseni was chosen because the basisphenoid pits are the largest of
any molossid bat (Peterson, 1969). This species, which belongs to one of the most
distinctive genera of the family, is also characterized by large size (forearm length of
47 adults, 63—73 mm), exceptionally large external ears (length in 39 adults, 33-43
mm) that are conjoined on an extended snout, and by the absence of the tragus and
antitragus. O. martiensseni occurs in southern, central, and eastern Africa north to
Kenya (Meester and Setzer, 1971); southern Ethiopia (Largen et al., 1974); and the
Republic of Djibouti (Hill and Morris, 1971). Other taxa of Otomops occur in the
Malagasy Republic (O. madagascariensis), India (O. wroughtoni), Java (O.
formosus), and New Guinea (O. papuensis and O. secundus).

Materials and Methods

All specimens studied were from Kenya. Heads of nine preserved specimens of O.
martiensseni were dissected for studies of gross morphology. Seven heads were
sectioned, but only three were suitable for histological study. In addition,
basisphenoid pits were examined and measured in skulls of 47 adults. All specimens
examined are in the collections of the Department of Mammalogy, Royal Ontario
Museum. The nomenclature of osseous structures and organs follows M. E. Miller
(1962) and Henson (1970), and that of tissues follows di Fiore (1963).

Histological Methods

Techniques for preparation of osseous structures for histological study were those of
Luna (1968) with certain modifications. Specimens were fixed in Bouin’s or
preserved in formalin and stored in 65 per cent alcohol for one or more years. Before
processing, the tongue, the mandible, and the skin of the head were removed, and, if
fixed in formalin, the specimen was washed and placed in several changes of Bouin’s
for 2 weeks or longer. Heads were decalcified in 1 per cent nitric acid (in 80 per cent
ethanol) for 7 days, during which time the solution was changed daily. Specimens
were then washed for 4 hours in running tap water, dehydrated in 50, 70, 90, and 100
per cent ethanol for 24-hour periods, and then cleared for 4 hours in chloroform (one
change after 2 hours).

Conventional double-embedding procedures were not successful, and, after
experimentation, the following method was found to be effective. Entire heads were
placed in methyl benzoate in a vacuum oven maintained at 58°C for 24 hours. They
were then placed successively for 24-hour periods in 2, 4, and 6 per cent celloidin in
methy] benzoate and for 1 week in 8 per cent celloidin-methyl benzoate. Heads were
then transferred to pure benzene for 48 hours (one change at 24 hours), to a 1:1
solution of benzene-paraffin for 24 hours, and then placed in pure paraffin for 24
hours. Transverse and sagittal sections with tissues in situ were cut serially on a rotary
microtome at 15 wm, and staining was with Harris haematoxylin and eosin. Sections
were photographed through a Reichert Zetophan photomicroscope. When studying
the photomicrographs it should be kept in mind that the above procedure is a harsh
one and inevitably causes distortion. Measurements given (to 0.1 mm) therefore do
not necessarily reflect the sections’ true dimensions in life.

4

Measurements and Statistical Analyses of Cranial Characters

Measurements (in millimetres) were of the right side of the skull to avoid bias
attributable to asymmetry. Measurements were taken to the nearest 0.01 by a
bi-coordinate digitizer with a Wild M5 binocular stereomicroscope (Wild of Canada
Ltd., Mississauga, Ontario) adapted for an automatic Model PDP-8 Digitizing
System (designed by Ruscom Logics Ltd., Downsview, Ontario). Special details of a
system comparable to that used here and procedures for measurements were given by
Anderson (1972).

Characters measured were the length of basisphenoid pits (greatest straight-line
distance between the anterior and posterior margins of the pit measured on its long
axis), width of the pits (greatest straight-line distance between the medial and lateral
margins of the pit), and width of the septum between the basisphenoid pits
(straight-line distance at the midpoint between the lateral margins of the septum).

Specimens were sorted by sex for statistical analyses. Mean and standard error
were calculated for each character, and differences between the sexes were examined
using Student’s t-tests (Sokal and Rohlf, 1969).

Specimens Examined

Specimens studied are adults unless indicated otherwise. Those sectioned were two
males and a female from Mount Suswa, Kedong Valley, Rift Valley (01° 10’ S, 36°
20’ E). In addition, four males and a female from Mount Suswa, Kedong Valley, Rift
Valley; one juvenile male and two females from Lake Naivasha, Rift Valley (01° 10’
S, 36° 21’ E); and a female from Koboko, Ithundu Caves (02° 12’ S, 37° 43’ E) were
dissected for studies of gross morphology.

Measurements of the basisphenoid pits were taken in 47 skulls from the following
localities: two males and three females, Ithundu Caves; 11 males and seven females
from 19 km W Makindu (02° 18’ S, 38° 00’ E); six males and 11 females from Mount
Suswa, Kedong Valley, Rift Valley; and seven females from Lake Baringo, Kampi
ya Moto (00""I 1S; 35°52”"B).

Abbreviations Used in the Figures

AT auditory tube NPH nasal pharynx

BS basisphenoid bone OAT orifice of auditory tube

BSP basisphenoid pit OC oral cavity

E epiglottis OLPH opening of laryngeal pharynx
ES esophagus SBSP mesial septum separating

by larynx basisphenoid pits

LPH laryngeal pharynx SP soft palate

M malleus SSE stratified squamous epithelium
ME middle ear cavity TB tympanic bone

MF mandibular fossa ™ tympanic membrane

NP nasal passage TT tensor tympani muscle

Results

In crania of O. martiensseni the basisphenoid pits are large (about 3.0 mm long and
1.5 mm wide) and deep with overhanging edges which are pronounced posteriorly
and posterolaterally. They are divided by a septum which is broad anteriorly but
becomes narrow as it tapers posteriorly (Fig. 1). The pits are deep posteriorly
(1.5-1.6 mm) and become shallow (1.0—1.2 mm) towards the anterior margins
(Fig. 2). The large tympanic bone, which is elongated and projects forward to touch
the pterygoid bone anteromedially, covers the posterolateral margin of each pit and
terminates as a broad, lobular structure (Fig. 1). In a transverse plane the pits are
located about midway between the foramina ovale and the mandibular fossae.

When the pharyngeal region of O. martiensseni is studied macroscopically (Figs.
2, 3), the basisphenoid pits are partially covered by the soft palate and are located
immediately dorsal to the opening of the laryngeal pharynx (Figs. 3A-C, 4A). This
opening, which is 1.5 mm wide and 2.0 mm long, is dorsal to the epiglottis of the
larynx and proximal to the opening of the esophagus (Fig. 4B). The folds of the
epiglottis (Fig. 4C) are shaped to fit into the lips of the opening of the laryngeal
pharynx (Figs. 3B, C), and the two structures are juxtaposed (Figs. 2, 3c). Moreover,
the opening of the nasal pharynx is continuous with the cavities of the basisphenoid
pits.

The basisphenoid pits are cancellous, bony cavities (Figs. 5A-D, 6A-D). The ground
substance of the bone is deeply stained by eosin, and immediately internal to it is a
layer of loose connective tissue containing large adipose cells 28 to 30 wm in
diameter with eccentrically placed nuclei. Cells in this layer are irregular in shape,
and also present are many lymphocytes and numerous, larger polymophonuclear
leucocytes. This layer is highly vascularized, and throughout it numerous small blood
vessels occur, some of which are capillaries. Others are venules surrounded by a
condensation of connective tissue, and some are arterioles with smooth muscle fibres
surrounding the endothelium which forms a wall equal in thickness to that of the
lumen. This layer, which varies in thickness from 40 to 50 wm, is thickest at the
posterior and anterior ends of the pits, dorsal and proximal to the mesial septum, and
immediately dorsal to areas where the osseous edges project medially from the lateral
walls of the pits.

Internal to this layer is a layer of numerous cartilage cells as well as many elastic
fibres. This stratum varies in thickness from 25 to 40 4m and also contains numerous
mucous glands and lymphatic nodules.

The most internal layer of the pits is thin (10-20 wm) and is also the most well
defined of those layers lining the pits. It consists of a pseudostratified, ciliated,
columnar epithelium. The nuclei of these cells are large (8-12 wm) and touch the
basal membrane. In regions of the basisphenoid pits where the osseous portion of the
edges terminates ventromedially and is continuous with the soft palate, columnar
epithelium lines the pits but is covered externally by a layer of dense connective tissue
(10-15 wm wide). In the soft palate this dense connective tissue replaces the loose
connective tissue that lines the osseous portions of the pits. In the region of the
auditory tube, as it passes through the soft palate and opens into the lumen of the pits
(Figs. 6B, C), the mucosa lining the auditory tube is separated from the lining of the
pits by a thick (0.4-0.5 mm) layer of loose connective tissue, lymphatic nodules, and
numerous mucous glands.

6

palatine
spine

presphenoid pterygoid
hamulus mandibular
fossa

basisphenoid basisphenoid

septum pit
basicochlear
fissure
tympanic
bulla tympanic
bone
5 mm

Fig. 1 Ventral view of skull of Otomops martiensseni ROM 41923, adult female.

The osseous portion of the mesial septum of the pits is covered by a
pseudostratified, ciliated, columnar epithelium continuous with that which lines the
pits. In the pharyngeal region, however, the ventral part of the septum is covered by a
thin layer (40-45 um) of striated muscle, external to which are loose connective
tissue, hyaline cartilage, and mixed glands. In the region of the orifice of the auditory
tube, the ventral tip of the septum bears mostly glandular tissue, and anteriorly, as the
ventral portion of the septum expands and the pits diminish in size, the osseous
component predominates and bears only a few glands distally.

basisphenoid

eptum j ;
een septu ede clas

passage

nasal
septum

nostril

i esophagus
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pharynx

nasal ventricle
pharynx of larynx

epiglottis

soft
tongue palate

k 5 mm 1

Fig. 2 Parasagittal section of the head of Otomops martiensseni ROM 45945, adult male.

The large middle ear or tympanic cavity is lined with a membrane consisting of a
thin layer (25-40 wm wide) of connective tissue covered with simple cuboidal
epithelium. Epithelial cells are cuboidal or columnar, with nuclei in two or more
rows, and cilia are widely distributed in all areas of the cavity. Small mucous glands
are infrequently present, and capillaries are numerous in the connective tissue.

The large tensor tympani muscle, the only middle ear muscle studied, originates on
the ventral surface of the ventrolateral edge of the basisphenoid pit immediately
posterior to the pharynx and then passes ventrally to the ventrolateral edge of the pit
(Figs. 5B-D), where it reaches maximum size (2.0 mm wide and 1.5 mm thick).
Posteriorly the muscle decreases in size, passes ventrolaterally to the cochlear wall
(Fig. 5A), and crosses the cavity of the middle ear before inserting on the malleus.

The auditory or Eustachian tube is large (2 mm long and 4 mm wide at its greatest
diameter) and anteriorly fills most of the space of the tympanic bone (Figs. 6A-C). It
is almost completely surrounded by the tympanic bone throughout most of its distance
and is partially surrounded by cartilage in the pharyngeal region. The lining consists
of fibrillar connective tissue, external to which is ciliated, columnar epithelium

Fig. 3. Transverse sections through the pharyngeal region of Otomops martiensseni ROM 41912, adult
female.
A Entire head showing relationship of nasal pharynx, laryngeal pharynx, and basisphenoid bone.
B Section slightly posterior to that in A, showing basisphenoid pits and opening of laryngeal
pharynx.
Cc Section slightly posterior to that in B, enlarged and in greater detail to illustrate juxtaposition of
basisphenoid pits to epiglottis and larynx.

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(20-40 um wide) which becomes stratified in the region of the pharynx. Glands are
absent in the posterior osseous region, and the lining adheres closely to the
surrounding bone. In the cartilaginous part towards the pharynx, the lining or mucosa
becomes thicker dorsally (50-70 4m wide) and contains many mixed glands. Cilia
are randomly dispersed but occur throughout the tube. Lymphocytes are numerous in
the surrounding connective tissue, and nodules are formed in the region proximal to
the orifice of the tube.

The orifice of the auditory tube (70-80 4m wide) opens through the soft palate into
the basisphenoid pit in the pharyngeal region (Fig. 6C). As the auditory tube narrows
(50-60 4m wide) towards the orifice, the tube has two diverticula and is surrounded
by hyaline cartilage, which unites laterally with the osseous portion of the lateral rim
of the pit. In this region the auditory tube is lined with stratified, columnar epithelium
(20-25 um wide). The orifice, which opens into the lumen of the pit proximal to the
most medial projection of the osseous edge of the pits (Fig. 6C), is not surrounded by
cartilage but by loose connective tissue, glandular tissue, blood vessels, and striated
muscle. At the juncture of the orifice with the lumen of the pit, the epithelium
changes from stratified columnar to the pseudostratified, ciliated, columnar
epithelium that characteristically lines the pits.

The walls of the larynx are cartilages bound together by two thick connective tissue
membranes, and the lining of the cavity is a mucous membrane. The M.
cricothyroideus forms the bulk of the muscle surrounding the laryngeal cartilages.
The epiglottis is a cartilaginous plate (Figs. 3B, 4C), and the perichondrium of this
structure 1s continuous with the lamina propria of the mucous membrane and with a
layer of stratified, squamous epithelium. The shape of the pharynx is conical (Fig.
6c). The nasal pharynx is lined with columnar, ciliated epithelium, and the laryngeal
or oral pharynx is lined by stratified, squamous, nonkeratinizing epithelium. The
pharyngeal epithelium lies on a thick, connective tissue membrane with many elastic
fibres and less numerous collagenous fibres. Internally, a thick layer of striated
muscle with several mixed glands and a fibrous layer connects the pharynx (Figs. 6C,
D) with adjacent structures.

Dimensions of the basisphenoid pits in 19 male and 28 female O. martiensseni did
not differ significantly. Means and standard errors of the length of the pit of males
and females were, respectively, 2.89 + 0.047 and 2.86 + 0.048 (P: = > 0.05 ns),
and those of the width were, respectively, 1.54 + 0.023 and 1.52 + 0.019 (P: = 0.84
ns). Width of the mesial septum separating the pits, however, was significantly
smaller (P: = < 0.03) in females (0.63 + 0.010) than in males (0.65 + 0.011). In
both sexes, however, the position of the pits was identical, that is, centred at a level
slightly posterior to the most anterior projections of the mandibular fossae (Fig. 1).

Discussion

Except for an increase in surface area due to the presence of basisphenoid pits, the
histological pattern of tissues in the pharyngeal region of Otomops martiensseni is not
unlike that of other mammals. Nonetheless, the presence of basisphenoid pits in this
and other species of Microchiroptera is unique, and such related structures as the

10

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auditory tube and middle ear correspondingly differ from those structures in most
other Microchiroptera, which have been characterized as being similar to those of
such mammals as marsupials, insectivores, and some rodents (Henson, 1970). In
Microchiroptera lacking basisphenoid pits, the air-filled, middle ear cavity
communicates directly with the pharynx via the auditory tube, but in O. martiensseni
the auditory tube communicates with the pharynx via the lumen of the basisphenoid
pits. Although emphasis has been placed on the morphology of the middle ear of bats
by most researchers (see Henson, 1961, 1970), to our knowledge the connection of
the middle ear cavity and the lumen of the basisphenoid pit by the auditory tube has
not been previously documented. |

Although Henson (1961) stated that the auditory tube in bats does not appear to be
markedly different from that of other mammals, the tube is exceptionally large in O.
martiensseni, and indeed is so in all bats that have been adequately studied (A. Pye,
pers. comm.). In O. martiensseni it occupies most of the anterior space of the
tympanic bone. Moreover, diverticula of the auditory tube were observed in O.
martiensseni. These diverticula have been documented previously by Pye and
Hinchcliffe (1968) in the phyllostomatid bat Chiroderma villosum and by Hinchcliffe
and Pye (1969) in six other species of Microchiroptera.

In O. martiensseni the tympanic bone encloses most of the middle ear cavity and
the posterior part of the auditory tube. It is large and terminates anteriorly in a lobular
structure (as in Tadarida; Wassif, 1948) rather than in the styliform process that is
characteristic of other Microchiroptera (Henson, 1970). The tensor tympani muscle,
the mass of which correlates with body size, is well developed in Microchiroptera
(Henson, 1970). The large size of this muscle in O. martiensseni is therefore not
exceptional considering its function in preventing a significant amount of the pulse
sound pressure from reaching the cochlea by contraction of this and the stapedius
muscle (Henson, 1965).

In Otomops and other Microchiroptera orientation sounds are produced by the
larynx (Griffin, 1958; Novick and Griffin, 1961). Ossification and fusion of
cartilages have occurred, and the intrinsic muscles are well developed, especially the
M. cricothyroideus, which applies tension to the vibrating membranes (Novick and
Griffin, 1961). Moreover, the pinnae of some bats of the Molossidae are highly
modified to receive high frequency signals (Henson, 1965). In O. martiensseni the
external ear is exceptionally large, but unlike some other species of the family, in
which the tragus is small or absent and the antiragus large (e.g., some species of
Eumops and Tadarida), it lacks both structures. Although functions of the tragus and

Fig. 5 Representative photomicrographs (posterior to anterior) from 15 wm serial sections through the
posterior region of the basisphenoid pits of Otomops martiensseni ROM 66258, adult male.
Haematoxylin-eosin stain. Distance of each section from the posterior end of the basisphenoid pits,
expressed as a percentage of postero-anterior length (where 100 per cent is the most posterior): A
100 per cent, B 98 per cent, C 93 per cent, and D 86 per cent.

A Most posterior region of the basisphenoid pits (BSP). The posterior wall of the right pit
contains loose connective tissue.

B_ Section slightly anterior to that of A. Proximity of basisphenoid pits (BSP) to middle ear cavity
(ME) and tensor tympani muscle (TT) are illustrated.

Cc Increase in size of basisphenoid pits (BSP) and of tensor tympani muscle (TT).

D Increase in size of basisphenoid pits (BSP) and reduction in size of tensor tympani muscle (TT)
and of middle ear cavity (ME).

14

antitragus have been suggested (Henson, 1970), none has been substantiated. In
Otomops the mobile lateral margin of the ear may be depressed, so that the ear
becomes a funnel, and this change in position may be analogous in function to the
tragus and antitragus. Alternately, the lateral margin of the external ear may act as a
flap or a valve to close the meatus when intense sounds are presented to the ear, as in
Mormoops (Wever and Vernon, 1961).

Correlated with the extreme development of the external ear in O. martiensseni is
the large size of the middle ear, auditory tube, and tympanic bones; the last are thin
and occupy much of the posteroventral part of the skull. The cochlea of this species is
large relative to body size (Pye, 1973). Moreover, the basisphenoid pits are deep and
well defined, and the close proximity of the opening of the laryngeal pharynx and the
epiglottis may be significant, in that sound waves emitted from the larynx could be
resonated in the pits before emission through the mouth cavity (or possibly through
the nasal passages, although evidence from other molossids indicates oral emission;
Gould, 1970).

Various aspects of echolocation in bats have been reviewed by Novick (1973,
1977), Simmons et al. (1975), and others. Most research has been based on studies of
Microchiroptera other than bats of the family Molossidae. No experimental research
has been conducted with bats of the genus Oromops (Pye, 1973), and only a few
species of Tadarida and Molossus have been studied (Griffin and Novick, 1955;
Henson, 1965, 1967; Pye, 1966), so that any interpretation of sonar mechanisms in
O. martiensseni would be speculative, as bats of the Microchiroptera differ from
family to family and even from species to species (Simmons, 1969). Moreover, the
molossid bats studied to date appear to be flexible in their echolocating behaviour
(Sales and Pye, 1974).

Although there is no experimental evidence, the possibility exists that basisphenoid
pits may function as resonating chambers. Further research is needed to correlate the
echolocating behaviour in Otomops and other molossid bats with peculiarities of
structural design.

Fig. 6 Representative photomicrographs (posterior to anterior) from 15 wm serial sections through middle
and anterior regions of the basisphenoid pits of Otomops martiensseni ROM 66258, adult male.
Haematoxylin-eosin stain. Distance of each section from the posterior end of the basisphenoid pits,
expressed as a percentage of postero-anterior length (where 100 per cent is the most posterior): A 69
per cent, B 58 per cent, C 46 per cent, and D 12 per cent.

A Midregion of basisphenoid pits. Proximity of basisphenoid pits (BSP) and auditory tube (AT)
are illustrated.

B Opening of lumen of basisphenoid pits (BSP) with nasal pharynx (NPH) and laryngeal pharynx
(LPH).

C Opening of orifice of the auditory tube (OAT) into lumen of basisphenoid pits (BSP). Section
demonstrates union of lumen of pits with pharynx and proximity of epiglottis (E) and larynx
(i);

D Reduction in size of basisphenoid pits (BSP) anteriorly. Only the pit on the right
communicates with the nasal passage (NP), which is separated from the oral cavity (OC) by
the soft palate (SP).

15

Acknowledgements

We thank Mrs. Sophie Poray, Mr. Brian Herbert, and Mr. Anker Odum for
illustrations; Mr. Cary Gilmour for laboratory assistance; Mr. James Borack and Mr.
Leighton Warren for the photographs; Ms. Judy Eger and Mr. David Nagorsen for
critical comments; and Mrs. Denise Machalski and Ms. Nancy Grepe for clerical and
other assistance. We particularly thank Dr. Ade Pye for her helpful suggestions and
criticisms of a previous draft of the manuscript. Acknowledgement is made for the
use of facilities of the Laboratory of Analytical Systematics housed in the ROM and
financed by a grant from the National Research Council of Canada to the Department
of Zoology, University of Toronto.

This research represents part of a comprehensive bat research programme which is
the result of the financial support to the second author from the National Research
Council of Canada (Operating Grant A2385) and from the Royal Ontario Museum.

16

Summary

The paired basisphenoid pits of Otomops martiensseni are large and deep, with
overhanging edges which are pronounced posteriorly and posterolaterally. They are
divided by a septum which is broad anteriorly but becomes narrow as it tapers
posteriorly. The pits are deep posteriorly but become shallow towards the anterior
margins. In a transverse plane the pits are located approximately midway between the
foramen ovale and the mandibular fossa.

Histologically the basisphenoid pits are of cancellous bone; the ground substance is
highly vascularized and is surrounded by a membrane of loose connective tissue. The
arrangement and constitution of the tissues that line the pits internally do not differ
from the normal mammalian histological pattern for the pharyngeal region.

The basisphenoid pits are partially covered by the soft palate and are located
immediately dorsal to the opening of the larynx. The folds of the epiglottis are shaped
to fit into the lips of the opening of the laryngeal pharynx, and the two structures are
juxtaposed. The close proximity of the opening of the laryngeal pharynx and the
epiglottis to the pits may be significant, in that sound waves emitted from the larynx
could be resonated in the cavities of the pits before emission through the oral cavity.
The pits communicate with the middle ear by way of the opening of the auditory tube.

Sommaire

Les fosses basisphénoidaux d’Otomops martiensseni sont grosses et profondes avec
des bords proéminents postérieurement et postérieurelatéralement. Elles sont separées
par un septum qui est ample dans sa part antérieure mais qui est rétréci dans sa part
postérieure. Les fosses sont profondes dans sa part postérieure et plus peu profondes
dans sa part antérieure. Dans un plan latéral, les fosses sont localisées a mi-chemin
entre le foramen ovale et la fosse mandibulaire.

Histologiquement, les fosses basisphénoidaux sont osseuses et tres vascularisées,
et elles sont enturées par une membrane de tissu conjonctif. L’arrangement et la
constitution des structures contigués a les fosses basisphénoidaux presentent le patron
histologique normal de la région pharyngienne des mammiferes.

Les fosses sont couvertes partiellement par le voile du palais et elles sont localisées
en direction dorsale immédiate a |’ouverture du pharynx laryngien.

Cette ouverture est localisée dorsalement a l’épiglotte du larynx. La configuration
des plis de l’épiglotte est modelée par s’ajustent a les levres de |’ouverture du pharynx
laryngien et ces deux structures sont juxtaposées.

Anatomiquement, les fosses se communiquent avec |’oreille moyenne par le canal
auditif.

La proximité si marquée de |’ouverture du pharynx laryngien et de l’épiglotte avec
les fosses peut tre ainsi significative parce que des ondes du son émises par le larynx
peuvent étre resonnées dans les cavités des fosses basisphénoidaux avant |’émission
du son par la cavité buccale.

17

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