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J. Anat. (1987), 154, pp. 187-200
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The development of the orbital region of Caretta caretta
(Chelonia, Reptilia)
SHIGERU KURATANI
Department of Anatomy, University of the Ryukyus, 207, Uehara, Nishihara,
Okinawa, 903-01, Japan
(Accepted 16 December 1986)
INTRODUCTION
The orbitotemporal region of vertebrates is a highly modified part of the skull and
has been one of the most intriguing subjects of cranial morphology. Such study has
dealt primarily with the basic definition of the components of the neuro- and
splanchnocranium (Gaupp, 1900, 1902; de Beer, 1937; Goodrich, 1930; Portmann,
1976; Jollie, 1962; Romer & Persons, 1977; Starck, 1979 a). In particular, the morphological concept of the cavum epiptericum (Gaupp, 1902) was an innovation which
enabled later anatomists to homologise the complicated cranial base elements (Rice,
1920; Matthes, 1921; Presley & Steel, 1976). These works were mainly on the homology of the skeletal element itself (de Beer, 1926; Rieppel, 1976; Starck, 1979 a, b), but
the interrelationship with the eye muscles, which has often been implied by some
authors (Terry, 1917; de Beer, 1937), has never been extensively investigated.
The present paper is intended to give a precise description of the developing orbital
region in reptiles for the purpose of reconsidering the meaning of the orbital region of
the developing skull in the light of functional and comparative morphology. The
Caretta caretta embryos were used because it is a reptile from which it is easy to get
staged embryos.
MATERIALS AND METHODS
One hundred and twenty Caretta caretta, (Loggerhead turtle) embryos were
gathered in Shirahama, Wakayama, Japan in 1984. The eggs were taken from two
sites and were probably laid by two different females. Each embryo was staged from
the day when the maternal footprints were discovered for the first time. After
incubation, they were fixed either in Bouin's solution to make paraffin sections or 10 %
formalin to make whole stained specimens according to the method of Dingerkus &
Uhler (1974). The carapace length of each embryo was measured after fixation for
determining the stage of development (see Table 1). The sections were cut serially in
frontal, sagittal and horizontal planes and stained with Weigert's iron haematoxylin
and eosin or with Azan.The sections were projected on to a screen and traced to make
graphical reconstruction drawings for which the sagittal sections were mainly used.
OBSERVATIONS
General morphology of the orbital region
Figure 1 shows a lateral view of the orbital region of the Caretta embryo at a stage
where the developing skull is seemingly most appropriate for the general description
of the initial architecture of the orbital region of this animal.
7-2
188
SHIGERU KURATANI
Table 1. List of the sectioned embryos
Ser. no.
A-28e
A-29e
A-30e
A-32e
A-34e
A-36e
A-38e
B-16e
B-17e
B- 18e
B-26e
B-27e
B-32e
B-34e
B-36e
No.
Carapace length
(mm)
4
3
2
1
1
1
1
3
2
1
2
2
4
1
1
898
9.43
9 67
116
139
166
16 76
675
7 05
8 90
131
14 08
23 4
26-3
30-1
Stage
II
II
II
II
III
III
III
I
I
II
III
III
IV
IV
IV
The orbit of Caretta develops inferolateral to the developing forebrain as an extracranial space. The walls of the orbit are composed of six irregularly shaped cartilages,
each being a constituent of the neurocranium. The superior wall or roof of the orbit
is composed of the taenia marginalis, the anterior wall of the planum supraseptale and
the interorbital septum, the posterior wall of the pila metopica and the postorbital
cartilage or the later pila antotica. An important feature of the orbit at this stage is that
the pila metoptica protrudes prominently into the space of the orbit, and thereby
distinctively delineates the posterior portion, the cavum epiptericum.
At this stage, the formation of the inner wall of the orbit by these cartilages is not
yet completed; at the apex of the orbit, the primitive optic foramen remains wide open,
transmitting the optic nerve and the ophthalmic artery into the orbit. Near the base
of the orbit, the margin of the cartilage is more or less deeply indented. From these
cartilages originate the extrinsic eye muscles, i.e., the superior, posterior, inferior and
internal rectus muscles, and the superior and inferior oblique muscles.
The ophthalmic nerve (V1) traverses the orbit anteriorly, passing inferior to the
superior rectus muscle, crossing over the ophthalmic artery and the optic nerve, and
finally, after having passed between the superior oblique and the inferior rectus
muscles, leaves the orbit to enter the nasal region. The major veins, the supraorbital
and the infraorbital, are also observed to traverse the orbit posteriorly. The supraorbital vein runs inferior to the superior oblique and superior to the superior rectus
muscle, while the infraorbital passes first across both the superior and inferior surface
of the inferior oblique muscle, and then inferior to the internal and inferior rectus
Fig. 1 (a-b). (a) A somewhat simplified reconstruction of the Caretta chondrocranium with
neighbouring extracranial structures, viewed from the lateral side. Some parts of the visceral skeleton
and the posterior part of the chondrocranium, including the otic capsule, are not shown. The
proximal heads of three rectus muscles, superior, inferior, and posterior are situated in this cavum.
(b) the chondrocranium of the same embryo. The extracranial space lateral to the pila metoptica and
the postorbital cartilage is called the cavum epiptericum, the posterior portion of the orbit. The
anterior portion of the inner wall of the cavum epiptericum, the pila metoptica forms the posterior
margin of the optic nerve foramen.
Abbreviations for all Figures are on p. 200.
Orbital development in Caretta caretta
1(a)
1(b)
189
190
SHIGERU KURATANI
muscles. Both these veins thus enter the cavum epiptericum and unite to give rise to
the anterior cardinal vein. The prominent pila metoptica (the anterior reflection of the
flexured cranial wall), and pile antotica (the posterior reflection), are arranged at an
acute angle to each other, resulting in the formation of a flexured wall with a deep
hollow extracranial space called, as mentioned above, the cavum epiptericum (Fig.
l,a,b). The flexured wall is pierced by the foramina for the cranial nerves, the
ophthalmic artery, and for the hypophysial vein. The postorbital cartilage, which
represents the posterior moiety of the flexured wall, is marked in its lower half by a
deep indentation for the trigeminal ganglion.
Contained in the cavum epiptericum are the proximal parts of the posterior,
superior, and inferior rectus muscles, the ophthalmic artery, the anterior cardinal vein
with its tributaries (the supraorbital, infraorbital and the hypophysial veins), the
large trigeminal ganglion with the proximal part of the ophthalmic nerve, and the
cranial nerves (Fig. 1 a).
Development of the orbital region
Stage I, 7 mm carapace length (Fig. 2 a, b)
This is the earliest embryo employed in this study. The anterior portion of the orbit
is not yet formed; it is merely bordered posteriorly by the pila metoptica and inferiorly
by a pair of trabecular cartilages which are portions of the cranial base. The taenia
marginalis, planum supraseptale, and interorbital septum are not formed yet, and
neither is the primitive optic foramen. Posteriorly the postorbital cartilage is developing. At this stage, the pila metoptica is observed to be a complex which consists of the
supratrabecular cartilage and its four processes, superior, middle, antero-inferior, and
postero-inferior. The anteromedial process is not yet formed (see below). The supratrabecular portion located superior to the ophthalmic artery is the principal, and in
fact, the most densely condensed part of the pila metoptica. The superior process unites
with the postorbital cartilage superior to the foramen for the oculomotor nerve. This
process extends upwards to become continuous with the primordium of the taenia
marginalis and gives rise to the superior rectus muscle. The middle process extends
between the oculomotor nerve and the hypophysial vein posteriorly to unite with the
postorbital cartilage. The postero-inferior process lies just medial to the posterior
rectus muscle uniting the supratrabecular cartilage with the polar cartilage. The
antero-inferior process also unites the supratrabecular cartilage with the cranial base,
and the inferior rectus muscle originates from this cartilage.
The later pila antotica, or the postorbital cartilage, on the other hand, develops as
a thick vertical cartilage wall traversing the cranial cavity. This cartilage is penetrated
by the trochlear nerve where the superolateral portion of this cartilage makes the
summit of the flexure. The abducens nerve penetrates the cranial base at the base of
the postorbital cartilage, or at the junction of the latter and the parachordal cartilage.
The nerve runs anteriorly for a short distance to innervate the posterior rectus muscle
anlage. The proximal head of this muscle anlage is attached to the inferolateral part
of the anterior surface of the postorbital cartilage. The oculomotor nerve passes down
along the anterior surface of the latter cartilage making the groove on it for the
proximal part of its course. Having penetrated the cranial wall, it innervates the
superior rectus, grazing the ophthalmic artery from behind and ending in the belly of
the inferior rectus muscle.
Orbital development in Caretta caretta
191
2(a)
soy~~~~~i
2(b)
Fig. 2(a-b). (a) Stage I Caretta embryo. Lateral view of the orbitotemporal region of the
chondrocranium, along with other structures, seen from the lateral side. The posterior part of the
chondrocranium is not shown. Note the low position of the optic nerve. (b) Chondrocranium of the
same embryo. The pila metoptica is composed of the supratrabecular cartilage and neighbouring
processes.
192
SHIGERU KURATANI
Stage II, 9 mm carapace length (Fig. 3 a, b)
In Stage II, the planum supraseptale, the interorbital septum and the taenia
marginalis develop and constitute the superior and the posterior walls of the orbit;
they simultaneously form the superior and the anterior boundaries of the primitive
optic foramen respectively, thereby completing the formation of the foramen.
The superior process of the pila metoptica expands to the front of and above the
oculomotor nerve to unite with the newly formed taenia marginalis, thus forming the
superior margin of the primitive optic foramen. The superior rectus is attached to the
posterior end of this cartilage.
The lateral edge of the postorbital cartilage now lies medial to the abducens foramen
and this cartilage itself is not perforated by the latter nerve.
The anterior continuation of the taenia marginalis, i.e. the planum supraseptale,
which develops dorsal to the interorbital septum, serves as the roof of the orbit, and
simultaneously bounds the primitive optic foramen superiorly. This planum gives
origin to the superior oblique muscle. In the cavum epiptericum, the anlage of the
posterior rectus and retractor bulbi muscles are observed to be separated from each
other. The anlage of the former muscle is attached to the postero-inferior process and
the latter to the basal part of the postorbital cartilage. The inner rectus muscle is found
to develop from the anteromedial portion of the inferior rectus muscle which is not yet
attached to any part of the chondrocranium (Fig. 1 a).
Stage III. 15 mm carapace length (Fig. 4a, b)
In Stage III, rather drastic morphological changes occur, especially in the region of
the pila metoptica with its processes and in the pila antotica. The most characteristic
change is that the postero-inferior process degenerates. This results in the fusion of the
foramina for the hypophysial vein and for the ophthalmic artery, and simultaneously,
the posterior rectus muscle loses its central portion of origin, and bridges between the
posterior part of the supratrabecular cartilage and the cranial base. The antero-inferior
process is also beginning to fade, causing the primitive optic foramen to fuse with the
foramen of the ophthalmic artery. Some of the whole stained embryos have lost this
process prior to the formation of the anteromedial process (see below), so that the
inferior tip of the pila metoptica looks as if it is hanging in the middle of the orbit. The
supratrabecular portion of the pila metoptica is beginning to develop an anteromedial
process passing medially towards its counterpart and anteriorly to the posterior
process of the interorbital septum, i.e., the cartilago hypochiasmatica.
The superior process of the pila metoptica expands further anteriorly, rendering the
cavum epiptericum still shallower. The middle process is also beginning to be reduced
to form a large foramen, the fenestra metoptica, through which the oculomotor nerve
and the hypophysial vein pass out of the cranial cavity into the cavum epiptericum.
The trochlear nerve passes through the foramen in the taenia marginalis. The superior
and inferior oblique muscles and the inner rectus muscle originate from the interorbital
septum.
The medial portion of the postorbital cartilage is beginning to be resorbed, but the
superior and lateral edges of this cartilage remain. The latter is now to be called pila
antotica. Simultaneously, the pila antotica has also moved a little posterolaterally
toward the abducens nerve foramen, thus making the expansion of the cavum
epiptericum less distinctive. By this stage, the pilae metoptica and antotica no longer
make an acute angle. The separation of both pilae and the obliteration of the cavum
epiptericum proceed still further in the following stage.
Orbital development in Caretta caretta
193
3(a)
jos
3(b)
Fig. 3 (a-b). (a) Partly reconstructed drawing of Stage II chondrocranium along with other structures.
The taenia marginalis is indicated by broken lines. The inferior rectus is attached to the anteroinferior process and the posterior rectus to the postero-inferior process. The taenia marginalis and
planum supraseptale are developing encircling the optic foramen. (b) Chondrocranium of the same
embryo.
194
SHIGERU KURATANI
4(a)
4(b)
~~~~~~~~of
VA~~~~~amp.:-
\. 1-
Fig. 4(a-b). (a) The orbitotemporal region of a Stage III chondrocranium with the extracranial
structures. Note that the posterior rectus bridges the posterior corner of the supratrabecular cartilage
and the cranial base. (b) Chondrocranium of the same embryo. Note that the postero-inferior process
has degenerated and the anteromedial process is beginning to develop. The middle process is also
beginning to disappear.
Orbital development in Caretta caretta
195
Stage IV. 35 mm carapace length (Fig. 5 a, b)
The chondrocranium of the Stage IV embryo shows the more or less fully developed
features of the Chelonian orbit as is described in the literature (in general: Kamal &
Bellairs, 1980; Dermochelys: Nick, 1912; Chelonia: Fuchs, 1915; Emys: Kunkel, 1912;
Chelydra: Rieppel, 1976). Specifically, the formation of the subiculum infundibuli and
the cartilago hypochiasmatica are shown in these forms.
The anteromedial process of the former stage, the subiculum infundibuli, has united
with its counterpart on the opposite side, and united anteriorly with the cartilago
hypochiasmatica which has developed as the projection of the posterior edge of the
interorbital septum. This fusion occurs inferior to the optic chiasma in the midline,
causing an elevation of the inferior margin of the secondary optic foramen. As a result,
the level at which the optic nerve passes through this foramen has moved superiorly
as compared to the Stage III position. The antero-inferior process has totally disappeared (Figs. 4b, 5), and the inferior rectus muscle is now attached to the subiculum
infundibuli but remains orientated as much downwards as before. As a result, the
former ophthalmic artery foramen has become confluent with the inferior portion of
the primitive optic foramen. In this connection, it should be mentioned that the
ophthalmic artery, which at earlier stages passed through the ophthalmic foramen, has
disappeared by this stage. Thus, the newly formed optic foramen is now encircled
posterolaterally by new cartilages and comes to be called the secondary optic foramen.
The inner rectus, on the other hand, has moved still farther superocaudally up to the
anterior edge of the secondary optic foramen. Thus, the proximal heads of the four
rectus muscles, superior, posterior, inferior, and the inner rectus muscles are gathered
around the secondary optic foramen as close to each other as before.
The pila metoptica thus has no original cartilage part that connects directly with the
cranial base. The middle process has completely disappeared, leaving a more enlarged
foramen, the fenestra metoptica, which, as mentioned above, is confluent with the
former ophthalmic artery foramen and the space just beneath the cartilago hypochiasmatica. On the other hand, the superior process has moved more obliquely and
anteriorly to border the superior edge of the secondary optic foramen. This process
now lies in a transverse plane so that it does not serve as the laterally reflected wall of
the cavum epiptericum but appears to be a part of the lateral wall of the neurocranium.
The basal portion of the pila antotica has moved still further laterocaudally to end
close to the abducens nerve foramen. Its superior end, which is fused with the posterior
portion of the taenia marginalis, also bends caudally. The retractor bulbi muscle
continues to be attached solely to the pila metoptica as before.
DISCUSSION
In the above descriptions, it has become clear that the pila metoptica changes its
form during development (Fig. 6). The two main factors or changes which seem to be
involved in the configuration of this structure are the formation of the expanded
interorbital septum and the rearrangement of the extrinsic eye muscles. These changes
also result in the apparent obliteration of the cavum epiptericum. In the following
discussion, the configuration and deformation of the pila metoptica will be illustrated
first and then the two factors which are correlated with the cartilage development in
the orbitotemporal region will be dealt with.
Configuration and deformation of the pila metoptica
The pila metoptica is comprised of the main part called the supratrabecular cartilage
(de Beer, 1937; the cartilago suprapolaris: Goldschmidt, 1972), and the peripheral
196
5(a)
SHIGERU KURATANI
5(b)
los
'.:.- ., '. :'.
ch
.'- :'
Fig. 5 (a-b). (a) Graphically reconstructed illustration of a Stage IV Caretta embryo. Lateral view of
the orbitotemporal region of the chondrocranium along with other structures. The subiculum
infundibuli is fused with the cartilago hypochiasmatica, elevating the optic nerve. The antero-inferior
process is lost. The ophthalmic artery has degenerated as well. The middle process has vanished,
leaving the fenestra metoptica. (b) The chondrocranium of the same embryo. Note that the cavum
epiptericum no longer exists as a separate space.
Orbital development in Caretta caretta
197
tm
Fig. 6. Diagramatic illustration of the changing orbital region of the Caretta chondrocranium. The
lines representing the contours of the developing chondrocranium are superimposed, assuming that
the distance between the optic nerve and the cephalic flexure does not change during development.
Note that the position of the optic nerve moves higher with the development of the interorbital
septum and the pila metoptica shifts anteriorly during development. The pila antotica or postorbital
cartilage also moves posteriorly. Black arrows indicate the movement of the cartilage elements and
the large arrows indicate the shift of the proximal heads of the superior, inferior and the posterior
rectus muscles respectively.
processes around it, i.e. the superior, anteromedial (chondrifies later), antero-inferior,
postero-inferior and the middle processes. These processes have had little mention in
the literature and are provisionally named as shown above in the present study. The
cartilages are all chondrifications of the primary cranial wall and the changing pila
metoptica is to be illustrated through the chondrification and the degeneration of these
subdivisions as follows.
The supratrabecular cartilage is at first almost independently chondrified and is seen
as the posterior portion of the subiculum infundibuli in the fully formed chondrocranium (Fig. 6). The postero-inferior process serves as the posterior edge of the
ophthalmic artery foramen connecting the supratrabecular cartilage and the cranial
base, and is the first to regress. The antero-inferior process is another element which
connects the supratrabecular cartilage with the cranial base. This forms the anterior
edge of the ophthalmic artery foramen. By the regression of this cartilage, the pila
metoptica loses its original connections to the skull base. The middle process dis-
198
SHIGERU KURATANI
appears next and the pilae metoptica and antotica become separated completely
leaving the fenestra metoptica between them. Around the time the last two processses
degenerate, the anteromedial process grows from the supratrabecular cartilage, and
finally fuses with the cartilago hypochiasmatica. This fusion results in the formation
of the posterior edge of the secondary optic foramen. In the course of these changes,
the superior process also moves gradually forward and the pila metoptica as a whole
looks as if it has shifted anteriorly, moving over the ophthalmic artery.
A similar shift of the pila also seems to take place in other reptilian embryos that
have some of the above cartilage elements (Kamal & Bellairs, 1980; Kunkel, 1911,
1912). All through the above stages of modification, the pila metoptica is always found
between cranial nerves II and III, and it can be so-called wherever it is situated,
although it consists of different elements at each stage of development. This seems
never to have been mentioned in the literature but is important because this change
does not appear to occur in other vertebrates such as placental mammals which also
have a cartilage called the pila metoptica (de Beer, 1926, 1937; Presley & Steel, 1976;
Starck, 1979 a, b; Jarvik, 1980). The homology of the pila metoptica, especially in
relation to the ophthalmic artery, needs further study.
Arrangement of the eye muscles
As mentioned above, the proximal heads of the rectus muscles in Caretta have a
tendency to gather around the optic chiasma during development (Figs. 5 a, 6), and
these movements seem to be correlated with the anterior shift and the deformation of
the pila metoptica as well as with the formation of the cartilago hypochiasmatica and
the subiculum infundibuli. The postero-inferior process disappears with the movement
of the posterior rectus muscle, and the antero-inferior process disappears with the
upward movement of the inferior rectus muscle which finally attaches to the
anteromedial process. The rostral movement of the superior process is related to the
superior rectus muscle which also reaches to the posterior edge of the secondary optic
foramen.
This final condition of the eye muscle appears in many lower vertebrates and is
regarded as the basic arrangement of the muscles, i.e. the rectus muscles are attached
to the interorbital septum around the optic foramen and the obliquus muscles to the
planum antorbitale or the reptilian planum supraseptale (Corning, 1900; Goodrich,
1930). However, in those forms which have an extensively chondrified cranium, the
muscle migrations probably do not affect the apparent development of the chondrocranium, even if such migrations exist.
Growth of the interorbital septum, elevation of the optic chiasma and the modification
of the cavum epiptericum
is
classified
as being of the tropibasic type in which the trabecular
The reptilian skull
cartilage narrows into a broad, vertical interorbital septum (de Beer, 1937; Starck,
1980). The formation of the latter cartilage results in the inward invasion of the
extracranial space (the orbit) and consequently, modification of the inner wall of the
cavum epiptericum. The narrowing begins from the anterior tip of the trabecular and
continues posteriorly whereby the anterior half of the cranial flexure, i.e., the pila
metoptica and a part of the taenia marginalis, is obliged to lie longitudinally. In doing
so, the superior process of the pila metoptica moves forward with the proximal head
of the superior rectus, and in the fully formed chondrocranium, the anterior half of the
flexure does not surround the cavum epiptericum any longer but continues cranially
to become a part of the planum supraseptale. The original cephalic flexure is now to
Orbital development in Caretta caretta
199
be observed merely as a faint midway curvature of the taenia marginalis (Fig.
5a,b).
The dwindling of the cavum in reptilian chondrocranium development might be
thus associated with the formation of a broad interorbital septum, which may be an
adaptation to the relative growth of the large eyeball. Such a condition is repeated in
the avian chondrocranium which has a similar extensive interorbital septum (de Beer,
1937; Starck, 1979a). Curiously enough, the reflection of the flexure is reserved in
mammalian skulls as the meningeal membrane covering the trigeminal ganglion
anteriorly as a part of the tentorium cerebelli (Presley & Steel, 1976). This may be due
to the smaller size of the eyeball and the low grade of deformation in the orbital
region.
SUMMARY
In the development of the orbital region of the Caretta chondrocranium, the
rearrangement of the several eye muscles seems to be correlated with the apparent
anterior shift of the neurocranial element, the pila metoptica. The pila consists of the
main part, the supratrabecular cartilage, and five processes, the superior, middle,
anteromedial, antero-inferior and the postero-inferior. The superior process forms the
attachment of the superior rectus muscle and, together with the muscle, moves
anteriorly during development. In the course of the anterosuperior shift of the inferior
rectus muscle, the antero-inferior process degenerates and the anteromedial process is
newly formed. The postero-inferior process gives origin to the posterior rectus muscle
and regresses as a result of the upward shift of the muscle. All these changes are the
result of the secondary arrangement of the eye muscles gathered around the secondary
optic foramen which has been newly formed through the pila metoptica deformation.
The elevation of the optic nerve which is brought about through the formation of the
interorbital septum, is another factor that brings about the above changes. Because of
these changes, the anterior part of the cranial flexure, the pila metoptica, lies in a
longitudinal plane and consequently it, as well as the cavum epiptericum, is obliterated
and a large antero-inferiorly opening extracranial space, the orbit of the reptile, is
produced.
I am most grateful to Mr. H. Tanase of Seto Marine Biological Laboratory,
Kyoto University, for his help during the search for turtle eggs on Shirahama sea
shore, to Dr. M. Tasumi of the Department of Zoology, Kyoto University for providing me with the ideal environment to carry out this study and to Professor Dr.
S. Tanaka for his critical reading of the manuscript.
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Abbreviations for Figures
aip, antero-inferior process of the pila
metoptica;
amp, anteromedial process of the pila
metoptica;
btr, basitrabecular process;
ch, cartilago hypochiasmatica;
fin, fenestra metoptica;
gc, ganglion ciliaris;
gt, ganglion trigemini;
hv, hypophysial vein;
ic, internal carotid artery;
ios, interorbital septum;
iov, infraorbital vein;
mp, middle process of the pila metoptica;
na, nasal capsule;
oa, ophthalmic artery;
of, primitive optic foramen;
oi, m. obliquus inferior;
os, m. obliquus superior;
pa, pila antotica;
pc, parachordal cartilage,
pip, postero-inferior process of the pila
metoptica;
PM, pila metoptica;
po, postorbital cartilage;
pq, palatoquadrate cartilage;
pss, planum supraseptale;
ret, m. retractor bulbi;
rinf, m. rectus inferior;
rint, m. rectus interior;
rp, m. rectus posterior;
rs, m. rectus superior;
si, subiculum infundibuli;
sof, secondary optic foramen;
sov, supraorbital vein;
sp, superior process of the pila metoptica;
st, supratrabecular cartilage;
tr, trabecula cranii;
tc, trabecula communis;
tm, taenia marginalis;
vca, vena cardinalis anterior;
II-VII, cranial nerves.