Or 
or 
Henry L. Bruner 
the ramus ophthalmicus V. From their origin the fibers of the muscle 
descend between the temporalis muscle, on one hand, and the cranial 
wall, eye muscles, and the vena jugularis interna, on the other. The 
posterior part of the muscle hes mediaa to the columella (epipterygoid) 
and is composed of almost vertical fibers. The anterior fibers extend 
downward and forward to a point lateral to the optic chiasma, where the 
muscle is continuous with the caudal part of the m. depressor palpebre 
inferioris. The fibers of the m. protrusor oculi terminate ventrally in a 
horizontal fascia which begins directly in front of the basisphenoid bone 
and extends forward under the vena jugularis interna and the sinus 
orbitalis. The anterior part of the fascia gives rise to the fibers of the 
m. depressor palpebre inferioris and is attached in the median line to 
the septum interorbitale. Posteriorly the fascia of opposite sides unite 
to form a continuous sheet (¢., Fig. 5, Plate I), which is free in the 
middle line, excepting an occasional band (?¢’.) which is attached to the 
cartilaginous basis cranil (compare also Fig. 4, Plate I). The pos- 
terior parts of the two protrusor muscles thus form practically a U- 
shaped digastric muscle with a middle fascia stretched below the two 
ven jugulares interne. 
The relations and function of this muscle are so pecuhar that I wish 
to call attention to some other forms in which the muscle is even more 
highly developed than in Lacerta. In Monitor niloticus (Fig. 2, Plate 
III; Fig. 1, Plate II) the protrusor muscle (m. p. 0.) arises by a well- 
developed tendon, the posterior part of the muscle is everywhere attached 
in the middle lne and the two muscles are entirely separate. The 
anterior fibers of the muscle extend far forward below the sinus orbitalis 
and terminate under the axis of the bulbus, in a fascia which hes in the 
floor of the sinus. 
In Anguis fragilis the m. protrusor oculi is also a strong muscle. It 
arises chiefly from the cranial wall dorsal to the proximal part of the 
ramus ophthalmicus V. The posterior part of the muscle extends down- 
ward to reach the ventral aspect of the vena jugularis interna, the an- 
terior fibers stretch forward and spread out fan-like on the floor of the 
sinus orbitalis. 
The posterior part of the m. protrusor oculi of Phrynosoma is shown 
in Fig. 1, Plate III. Here the muscle (m. p. 0.) is relatively short and 
stout. Its dorsal portion arises from a bony process which extends for- 
ward from the lateral part of the basisphenoid bone, its posterior fibers 
terminate in a fascia which is inserted, partly on the trabecula cranii. 
