Split insertions of the oblique extraocular muscles in Carnivora.

IF 2.1
Keiko Meshida, Erica Miller, Todd Schmitt, Andrew Cartoceti, Edwin Gilland
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Abstract

This study examines the presence or absence of split insertions (i.e., bifurcated/bifid tendons) in the oblique extraocular muscles (O-EOMs) in various carnivoran and non-carnivoran mammals. The O-EOMs were dissected in 44 mammalian orbital specimens (20 families, 36 species). Split insertions were present in Carnivora species exclusively. Split insertions were found in both superior oblique (SO) and inferior oblique (IO) muscles in all 6 Felidae specimens examined. The SO tendons split after the trochlea and coursed anterior and posterior to the global layer of the superior rectus (SR) before inserting onto the sclera at the temporal edge of the SR. The IO bifurcated after running between global and orbital layers of the inferior rectus and inserted onto the sclera anterior and posterior to the lateral rectus global insertion. All 4 Canidae, 1 Hyaenidae, and 1 Viverridae specimens had bifid insertions only in the IO, except the red fox, which had both SO and IO split insertions as in Felidae. Of the 7 Mustelidae species, 3 in subfamily Mustelinae had bifid oblique insertions, while 3 species in Lutrinae and Gulolinae lacked them. Bifid insertions were absent in other carnivoran and all non-carnivoran species examined. The presence of split oblique insertions is thus most common in terrestrial carnivorans with highly developed forward vision (high degrees of orbital convergence and frontation, retinal area centralis, etc.). The split oblique insertions in Carnivora may contribute to both torsional (anterior insertions) and vertical (posterior insertions) eye movements. This would parallel oblique functions in humans, but with different anatomical means.

食肉目斜眼外肌的分裂插入。
本研究考察了在各种食肉动物和非食肉动物的斜眼外肌(O-EOMs)中是否存在分裂插入(即分叉/双裂肌腱)。共解剖了44个哺乳动物眼眶标本(20科36种)的O-EOMs。劈裂插入只存在于食肉目物种中。在所有6个被检查的Felidae标本中,在上斜肌(SO)和下斜肌(IO)中都发现了分裂插入。SO肌腱在滑车后分裂,沿上直肌(SR)的整体层前后走向,然后在SR的颞缘插入巩膜。IO在下直肌的整体层和眶层之间分叉,并在外侧直肌整体止点的前后插入巩膜。4只犬科、1只鬣狗科和1只Viverridae标本仅在IO中有双裂插入,但红狐标本与Felidae标本一样,在SO和IO中都有分裂插入。7种鼬科中,鼬亚科3种有斜插,鹭科和Gulolinae中3种没有斜插。在其他食肉动物和所有非食肉动物中没有双裂插入。因此,在前视高度发达的陆生食肉动物(高度的眼窝会聚和前视,视网膜中央区等)中,分裂斜嵌体的存在最为常见。肉食性目斜裂眼可能导致扭转眼(前眼)和垂直眼(后眼)的眼球运动。这与人类的斜肌功能相似,但具有不同的解剖学意义。
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