256 
DES. A. CAETE AND A. MACALISTEE ON THE 
culs-de-sac were thus formed, which seemed as though they were rudimentary puncta ; 
each of these extended to the depth of nearly a line, and was protected superiorly by a 
similar fold of mucous membrane. 
The muscles of the orbit were ten in number*. 
The superior rectus arose by two heads, one from the common tendinous sheath of the 
optic nerve, or ligament of Zinn ; the second head had its origin from the superior margin 
of the optic foramen ; these origins soon united and passed forwards to be inserted into 
the sclerotic coat, about If inch posterior to the edge of the cornea. This muscle was 
crossed superficially by the frontal branch of the ophthalmic division of the fifth nerve, 
and its tendon was split by the following muscle. 
The superior oblique, which arose from the ligament of Zinn, ran forwards to a point 
about 3 inches behind the cornea, where the direction of its fibres was changed by 
passing through an opening formed by the splitting of the tendon of the superior rectus. 
From this pulley-like contrivance, which was lined by a small synovial bursa, the fibres 
of the superior oblique took a direction backwards, outwards, and slightly downwards, 
and were inserted tendinous into the sclerotic immediately in front of the insertion of 
the choanoid muscle. 
The internal rectus arose from the inner side of the optic foramen ; its fibres ran for- 
wards on the posterior or external side of the globe of the eye to be inserted into the 
sclerotic about 1 inch behind the cornea. 
The external rectus arose from the outer side of the optic foramen ; its fibres ran for- 
wards on the posterior or external side of the eyeball to be inserted into the sclerotic 
about 1 inch behind the cornea. 
The inferior rectus had its origin, like the preceding, from the border of the optic 
foramen, and in addition from the ligament of Zinn ; its fibres passed forwards and out- 
wards, and in a manner precisely similar to the superior rectus. This muscle was perfo- 
rated by the fibres of the inferior oblique ; its tendon formed by the reunion of the sepa- 
rated fasciculi was inserted into the sclerotic at about 1^ inch below and behind the 
cornea. 
The inferior oblique was a short curved muscle ; it arose from the inferior and ante- 
rior angle of the orbit ; its fibres passed backwards and upwards, and having wound 
through the pulley-like contrivance formed for it in the inferior rectus, before referred 
to, was inserted into the posterior and inferior portion of the sclerotic. 
The choanoid muscle was distinctly quadripartite, having its origin from the sheath of 
the optic nerve, and being inserted, as in other mammals, into the posterior aspect of the 
sclerotic coat. 
The nerves seen in the dissection of the orbit were the third, which supplied the supe- 
rior, inferior, and internal recti, the inferior oblique, and the choanoid ; the fourth, 
which was distributed to the superior oblique ; the sixth to the external rectus ; and the 
fifth to the soft parts of the orbit. 
* The levator palpebrce superioris was absent. 
