European Journal of Anatomy

Official Journal of The Spanish Society of Anatomy
Cover Volume 16 - Number 1
Eur J Anat, 16 (1): 49-58 (2012)

Early fetal development of the medial canthal ligament and Hornerâ??s muscle: a histological study

Hajime Osanai1, Hiroshi Abe2, Jose F. RodrĂ­guez-VĂĄzquez3, GenMurakami4, Mineko Fujimiya5, Hiroshi Ohguro1

1Department of Ophthalmology, Sapporo Medical University, Sapporo, Japan 2Department of Anatomy, Akita University School of Medicine, Akita, Japan 3Department of Anatomy and Embryology II, Faculty of Medicine, Complutense University, Madrid, Spain 4Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, Iwamizawa, Japan 5Department of Anatomy, Sapporo Medical University, Sapporo, Japan

ABSTRACT Hornerâ??s muscle is a well known structure that accelerates lacrimal drainage. However, the fetal topographical relationship between this muscle and the medial canthal ligament (MCL) seems to differ from the adult morphology because a fetal connective tissue band toward the eyelids has never been demonstrated.We examined horizontal and frontal sections of 15 specimens (20-30 weeks of gestation) from the large collection of human fetuses stored at the Complutense University in Madrid (Spain). Frontal sections demonstrated the orbicularis oculi muscle inserting to a raphe-like structure along the horizontal parts of the lacrimal canaliculi. In horizontal sections, the raphe-like structure corresponded to a fibrous tissue mass sandwiched by the superior and inferior lacrimal canaliculi. The tendons of Hornerâ??s muscle were divided into 1) the so-called â??reflection tendonâ? that included the typical myotendineous junction at the insertion into the maxilla, and 2) the so-called â??direct tendonâ? in the roof of the lacrimal sac. However, Hornerâ??s muscle did not insert into the canaliculi, but was simply attached to, or embedded in, the fibrous sheath around them. Notably, none of these connective tissue structures was attached to the tarsi. Hornerâ??s muscle and its tendon might contribute to formation of the bony attachment of the future MCL, but the main part of the MCL most likely originates from the raphe-like structure. The connection between the MCL and the tarsi seems to be established after birth due to the growth of connective tissue along the lacrimal canaliculi. Although congenital entropion is a rare condition among Westerners, the present study demonstrated that the tarsus is unlikely to be fixed at a late stage in Western fetuses.

Keywords: Hornerâ??s muscle, Orbicularis oculi muscle, Mial canthal ligament, Medial palpebral ligament, Lacrimal canaliculus, Human fetus

European Journal of anatomy
ISSN 2340-311X (Online)