Hi 

Here are some articles regarding morphometry and development of the extraocular muscles, and one book chapter as well

In the early stage, the orbital muscle separates the orbital content from the surrounding loose spaces to maintain conditions adequate for the development of orbital fat and other connective tissues . Orbital development is dependent on interactions between the eye, neural crest, and developing extra ocular muscles “extrinsic muscles” . The extrinsic muscles of the eye develop from mesenchymal condensations in the future embryonic orbital region, and can be identified as individual muscles by the 6th week; the origin of these muscles remains a matter of some controversy; the mesenchyme in this area gives rise to three preotic condensations, each supplied by its own cranial nerve, these may have been anterior axial mesodermal somites continuous with those of the trunk, but separated from the latter by the expanding vertebrate braincase; these muscle primordia migrate from their points of origin at the orbital apex, forward to their sites of insertion on the globe .