A Topographical Anatomical Description of the Orbit of the Alpaca, Vicugna pacos

To describe the gross anatomy of the orbita in Huacaya alpacas, identify species-specific features, and provide comparative anatomical information relevant to clinical ophthalmic practice.

Nine heads from postmortem donated Huacaya alpacas were used.

Two skulls were evaluated to characterize the orbita, and six additional heads were analyzed using gross dissection and saw sectioning.

The orbita is completely enclosed by bone and protects the mm. bulbi and associated nn. craniales. The mm. bulbi originate mainly around the can. opticus and for. orbitorotundum, except for the m. obliquus ventralis, that arises from the os lacrimale. Orbital nerves include the n. opticus, the ocular motor nerves (n. oculomotorius, n. trochlearis, n. abducens), as well as the n. ophthalmicus and n. maxillaris. With the exception of the m. obliquus dorsalis, m. rectus lateralis, and the lateral part of the m. retractor bulbi, all mm. bulbi are innervated by the n. oculomotorius. These exceptions are innervated by the n. trochlearis and n. abducens, respectively.

The macroscopic anatomy of the orbita in Huacaya alpacas largely corresponds to that of domestic animals. However, novel details were identified, including bifurcation of the n. trochlearis near the m. obliquus dorsalis and fine connecting branches of the n. ophthalmicus to adjacent structures. These features warrant further study to support veterinary care and improve understanding of alpaca orbital anatomy.