The study was carried out on 12 American Staffordshire Terriers (AST) each of
60 days&#8217; gestation. A morphological analysis of the extra-ocular muscles was
performed. The location of the rectus and oblique muscles and the retractor
bulbi muscle is described. The length and breadth of these muscles as well as of
their tendons, the distance between the final insertions of the tendons and the
corneal limbus and the line of insertions is also given

Janeczek, Maciej

Klećkowska, Joanna

Pospieszny, Norbert

Wojnar, Monika

English

Via Medica Journals

Folia Morphol. Vol. 62, No. 4, pp. 431–434Copyright © 2003 Via MedicaISSN 0015–5659www.fm.viamedica.plS H O R T  C O M M U N I C A T I O N431Address for correspondence: Prof. Norbert Pospieszny, Department Anatomy and Histology, Faculty of Veterinary Medicine, AgriculturalUniversity, ul. Kożuchowska 1/3, 51–631 Wrocław, Poland, tel: +48 71 320 57 48, e-mail: norpos@gen.ar.wroc.plMorphology of the extra-ocular muscles(musculi bulbi) of the American StaffordshireTerrier during the perinatal periodJoanna Klećkowska, Maciej Janeczek, Monika Wojnar, Norbert PospiesznyDepartment of Anatomy and Histology, Veterinary Faculty, Agricultural University, Wrocław, Poland[Received 28 May 2003; Revised 23 July 2003; Accepted 23 July 2003]The study was carried out on 12 American Staffordshire Terriers (AST) each of60 days’ gestation. A morphological analysis of the extra-ocular muscles wasperformed. The location of the rectus and oblique muscles and the retractorbulbi muscle is described. The length and breadth of these muscles as well as oftheir tendons, the distance between the final insertions of the tendons and thecorneal limbus and the line of insertions is also given.key words: dogs, American Staffordshire Terrier, eyeball, accessoryorgans of the eyeball, extra-ocular musclesINTRODUCTIONThe extra-ocular muscles are accessory organs ofthe eye (organa oculi accessoria) located betweenthe sclera and the wall of the orbit. They comprisethe dorsal (m. rectus dorsalis), ventral (m. rectus ven-tralis), lateral (m. rectus lateralis), medial rectus mus-cles (m. rectus medialis), the dorsal oblique (m. obliq-uus dorsalis) and ventral oblique muscles (m. obliq-uus ventralis) and the retractor bulbi muscle (m. re-tractor bulbi) [7]. Szekely [8] reported that ‘‘Threemuscles (medial rectus, inferior rectus and inferiorobliquus) derive from the prechordal mesoderm andthe other three muscles develop from the most ros-tral third of the medial paraxial mesoderm. The ex-ternal eye muscles and their neurons are not homol-ogous to any other striated muscle and motoneu-rons.’’ The development of the extra-ocular musclesin dogs has also been described by Aguirre et al. [1].Hifny and Misk [5] have provided a description ofthe morphology of the final insertions of the ten-dons of the extra-ocular muscles in domestic ani-mals, including dogs, in the postnatal period.In previous study we observed the extra-ocularmuscles in Persian cats in the perinatal period, giv-ing the morphometry of these muscles, the line ofthe final insertions of the tendons of the extra-ocu-lar muscles on the sclera, the location of the mus-cles and the distances between the final insertionsof the tendons of the muscles and the corneal lim-bus [unpublished data]The study was designed to perform a morpho-logical analysis of the extra-ocular muscles ofAmerican Staffordshire Terriers in the perinatalperiod.MATERIAL AND METHODSThe study was carried out on 12 dogs of the ASTbreed from 6 uteri and of 60 days’ gestation. Thefoetuses were preserved in 4% formaldehyde, inwhich they were kept for 12 months. For prepara-tion 0.5–1.5% acetic acid and 70% ethanol were usedto make the anatomical structures more recognis-able. The preparations were made with a magnify-ing glass (4.5×) and a stereoscopic microscope (6.5––22.5×). The measurements were taken with an elec-tronic slide calliper to the nearest 0.1 mm. For de-scriptive purposes NAV and NEV nomenclature servedas a reference book [7]. Data were statistically analy-432Folia Morphol., 2003, Vol. 62, No. 4sed using the Excel 2000 computer programme. Thedata and results are given in tables, figures and photo-graphs.RESULTSRecti musclesDorsal rectus. The dorsal rectus continues ros-trally over the eyeball, along with the levator of theupper eyelid (m. levator palpebrae superioris). It runsover the ligament of the dorsal oblique to attach tothe sclera. The tendon of the dorsal rectus is longand its insertion line is broad and oblique (Fig. 1).The dorsal rectus was the longest muscle of all theextra-ocular recti (Table 1).Ventral rectus. The ventral rectus passes rostrallyunderneath the eyeball, its tendon being hidden un-der the muscle belly of the ventral oblique. It is inter-posed between the lateral and medial recti (Fig. 2).The tendon is long with a broad straight insertionline (Fig. 1). The tendon of the ventral rectus wasthe furthest of all the extra-ocular recti tendons fromthe corneal limbus (Table 1).Medial rectus. The medial rectus runs medially tothe eyeball between the dorsal and ventral recti (Fig. 2).The muscle has a long tendon and the tendon inser-tion line is broad and convex (Fig. 1 and Table 1).Lateral rectus. The lateral rectus passes laterallyto the eyeball between the dorsal and ventral recti (Fig. 2).The tendon is long and its insertion line is broad andTable 1. Morphometry of the rectus muscles of the American Staffordshire TerrierLength of the Length of the Width of the Distance insertionmuscle [mm] tendon [mm] tendon [mm]  — cornea limbus [mm]Lateral rectus X 7.47 2.06 2.27 2.50SD 1.00 0.69 0.34 0.64Medial rectus X 8.00 2.04 3.37 2.83SD 0.80 0.61 0.31 0.37Dorsal rectus X 8.14 2.01 2.95 3.05SD 1.00 0.67 0.29 0.24Ventral rectus X 7.46 2.13 3.66 3.44SD 0.90 0.68 0.37 0.63X — mean, SD — standard deviationFigure 2. Extra-ocular muscles of the dog. The right eye; A — thirdeyelid, B — cornea, 1 — ventral oblique, 2 — lateral rectus,3 — medial rectus, 4 — ventral rectus, 5a — retractor of eyeball(ventrolateral funicle), 5b — retractor of eyeball (ventromedialfunicle).CSDRLRMRVRFigure 1. The rectus muscles position with respect to the eye-ball. The left eye; C — cornea, S — sclera, DR — dorsal rectus,VR — ventral rectus, LR — lateral rectus, MR — medial rectus.433Joanna Klećkowska et al., Morphology of the extra-ocular musclesoblique (Fig. 1). The lateral rectus tendon was theclosest of all the extra-ocular recti to the corneal lim-bus (Table 1).Oblique musclesDorsal oblique. The dorsal oblique derives fromthe margin of the dorsomedial optic canal and con-tinues inside the periorbit between the dorsal andmedial recti. In the upper part of the orbit it formsa thin tendon that passes through a trochlea andbeneath the final tendon of the dorsal rectus. It thengoes across the eyeball and under the final tendonof the lateral rectus. The dorsal oblique has a nar-row tendon insertion line and the longest tendon ofall the extra-ocular muscles. The tendon of the dor-sal oblique is entirely underneath the tendon of thelateral rectus (Fig. 3). The dorsal oblique was the long-est and narrowest muscle of all the extra-ocular rec-tus and oblique muscles (Table 2).Ventral oblique. The ventral oblique tendon orig-inates from the muscular fossa (fossa muscularis) of thelacrimal bone (os lacrimale), follows ventrally throughthe ventral rectus, ascends dorsally the temporal areaof the eyeball and ends on the sclera close to the lateralrectus (Fig. 4). The tendon insertion line of the ventraloblique is broad. In dogs this tendon is divided into twosections: one faces the front of the tendon of the lateralrectus and the other is partly hidden beneath it (Fig. 3).The ventral oblique was the shortest muscle of all theextra-ocular muscles (Table 2).Retractor bulbi muscleThe retractor bulbi muscle comprises four separateflat muscular funiculi: the dorsolateral, dorsomedial,ventrolateral and ventromedial. The funiculi lie amongthe extra-ocular recti. The final insertion of each funic-ulus is on the sclera at varying distances from the cor-neal limbus (Fig. 4). The retractor bulbi muscle had theCSDLVLVMDMFigure 4. The retractor bulbi muscle position with respect to theeyeball. The left eye; C — cornea, S — sclera, DM — funiculusdorsomedial, DL — funiculus dorsolateral, VM — funiculus ven-tromedial, VL — funiculus ventrolateral.CSLRVODOFigure 3. The oblique muscles position with respect to the eye-ball. The left eye; C — cornea, S — sclera, LR — lateral rectus,VO — ventral oblique, DO — dorsal oblique.Table 2. Morphometry of the oblique muscles of the American Staffordshire TerrierLength of the Length of the Width of the Width of themuscle [mm]  tendon [mm] muscle [mm]  tendon [mm]Dorsal oblique X 8.79 3.48 1.64 1.35SD 0.89 0.75 0.21 0.08Ventral oblique X 7.44 2.85 3.06 3.03SD 0.74 0.90 0.48 0.28X — mean, SD — standard deviation434Folia Morphol., 2003, Vol. 62, No. 4longest funiculi of all the extra-ocular muscles and thefuniculi tendons were the closest of all the extra-ocu-lar recti to the corneal limbus (Table 3).DISCUSSIONThe morphology and development of the extra-ocular muscles is inherently connected with the de-velopment of the head and its evolution in Vertebra-ta. The examinations proving that the extra-ocularmuscles originate from the prechordal and paraxialmesoderm show their unique nature [8]. It is consid-ered that the origin and development of the extra-ocular muscles as well as the propius lingual musclesmay play a considerable role in tracing the evolutionand the development of the head in Vertebrata. Theaccessible literature lacks information on the morphol-ogy of the extra-ocular muscles in dogs in the perina-tal period. The course of the extra-ocular muscles inadult dogs has been described in the studies by Evans[3], Nickel et al. [6], Frewein and Vollmerhaus [4] andDyce et al. [2]. The morphology of the tendons of theextra-ocular muscles in various species of domesticanimals, including dogs, in the postnatal period wasexamined by Hifny and Misk [5]. They described theline of the final insertions of the tendons of the extra-ocular muscles and the tendon morphometry of dogs.Their studies comprised dogs whose breed, sex andage were not specified. Our studies have been car-ried out on specimens of one breed and from thesame gestational period.A comparison of the present results with thoseby Hifny and Misk [5] has shown no differences inthe lines of the final insertions of the extra-ocularmuscles. Differences did emerge, however, in thetendon morphometry of the examined muscles andin the distances between the final insertions of themuscle tendons and the corneal limbus.CONCLUSIONSThe present study on the morphology of the ex-tra-ocular muscles reveals the following:1. The dog’s sex, weight and length did not affectthe muscle morphometry in this period of perinatal life.2. The retractor bulbi muscle was closer to thecorneal limbus than the extra-ocular recti.3. The course of the line of the final insertions ofthe tendons on the sclera varied.REFERENCES1. Aguirre GD, Rubin LF, Bistner SI (1972) Developmentof the canine eye. Am J Vet Res, 12, 33: 2399–2414.2. Dyce KM, Sack WO, Wensing CJG (1996) Textbook ofveterinary anatomy. 2 Ed., WB Saunders Company.3. Evans HH (1993) Millers anatomy of the dog. 3 Ed.,WB Saunders Company.4. Frewein J, Vollmerhaus B (1994) Anatomie von Hundund Katze. Balckwell Wissentschafts-Verlag, Berlin.5. Hifny A, Misk NA (1982) A comparative study of thesurgical anatomy of the Tendons of insertions of theextrinsic muscles of the eyeball in different domesticanimals. Anat Histol Embryol, 11: 19–26.6. Nickel R, Schummer A, Seiferle E (1999) Lehrbuch derAnatomie der Haustiere. Band II, Parey Buch Verlag.7. Nomina Anatomica Veterinaria (NAV), Nomina Embryo-logica Veterinaria (NEV) (1994) New Jork, Ithaca, Zurich.8. Szekely G (1994) Comparative anatomy of cranial nervemotor nuclei: with a comment on evolution of the cran-iofacial region. Europ J Morph, 32, 2–4: 217–224.Table 3. Morphometry of the retractor bulbi muscle of the American Staffordshire TerrierLength of the Length of the Width of the Distance insertionmuscle [mm] tendon [mm] tendon [mm]  — cornea limbus [mm]Dorsomedial funiculus X 9.58 2.11 2.37 1.82SD 0.95 0.35 0.51 0.44Dorsolateral funiculus X 9.80 2.06 2.71 1.96SD 0.52 0.22 0.41 0.21Ventromedial funiculus X 9.30 2.01 2.97 1.86SD 0.98 0.24 0.50 0.30Ventrolateral funiculus X 9.46 2.76 2.76 1.82SD 0.88 0.34 0.40 0.37X — mean, SD — standard deviation

Morphology of the extra-ocular muscles (musculi bulbi) of the American Staffordshire Terrier during the perinatal period

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Morphology of the extra-ocular muscles (musculi bulbi) of the American Staffordshire Terrier during the perinatal period

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