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M Y D M E. 



The myodome (eye-muscle canal) of Scorpaena has the shape of a funnel, the body of which 

 is triangulär or semicircular in transverse section, while the tubulär portion is nearly circular in section. 

 The orbital opening of the canal is approximately an equilateral triangle with rounded corners, the 

 base of the triangle being presented dorsally and the triangle being bisected by the pedicle of the 

 basisphenoid. The opening is bounded ventrally by the body of the parasphenoid, laterally on either 

 side by the ascending process of the parasphenoid, and dorsally mainly by the body of the basi- 

 sphenoid though partly also by the prepituitary portions of the mesial processes of the proötics. At 

 the extreme dorso-lateral corner of the opening, is the internal jugular notch, that notch lying, as 

 already explained, between the basisphenoid and parasphenoid legs of the alisphenoid. From this 

 notch the internal jugular groove leads postero-laterally into the trigeminus opening of the trigemino- 

 facialis Chamber, the notch, groove and Chamber all being remnants of the upper lateral Chamber of 

 the myodome of Amia. 



Immediately internal to its orbital opening the myodome expands abruptly at its dorso-lateral 

 Corners, a pocket thus here being formed, on either side, which, as already stated, projects upward 

 and reaches the under surface of the thin floor of the trigemino-facialis Chamber. The myodome here 

 has its largest transverse section, and from here contracts rapidly to the hind edges of the proötics, 

 where the long and relatively small tube of the funnel begins. This tube lies wholly in the grooved 

 ventral surface of the basioccipital, the body of the funnel lying wholly between the proötics. Between 

 the ventral edges of these latter bones, and also between the ventral edges of the groove in the basi- 

 occipital, there is a long slit-like opening, the hypophysial fenestra. This fenestra extends the füll 

 length of the floor of the myodome but is closed, ventrally, by the parasphenoid, excepting at its 

 extreme hind end where the myodome opens onto the ventral surface of the skull. The roof of the 

 body of the myodome is formed in part by the basisphenoid, but mainly by the mesial processes 

 of the proötics, and it is perforated, in its anterior portion, by the median, pituitary opening of the 

 brain case. 



The pituitary opening is closed, in the recent state, by membrane, and, arising from this 

 membrane and extending forward to the hind edge of the pedicle of the basisphenoid, there is a vert- 

 ical band of tough fibrous tissue, attached by its dorsal edge to the ventral surface of the body of 

 the basisphenoid. The anterior end of this tissue gives origin, on either side, to the rectus inferior 

 muscle. The ventral edge of the band spreads, and is firmly attached to the dorsal edges of the recti 

 intemi muscles, those two muscles entering the myodome, on either side, ventral to the rectus in- 

 ferior, along the floor of the myodome and close against the pedicle of the basisphenoid. The attach- 

 ment of these recti interni to the ventral edge of the mid-vertical membrane seems to be the im- 

 portant origin of the muscles, for although they extend posteriorly considerably beyond the mem- 

 brane, approximately to the hind ends of the proötics, they are, in this part of their course, simply 

 attached to each other and to loose tissues in the myodome; the attachment of the muscles to each 

 other being strong. The rectus superior, on either side, enters the myodome near the dorsal end of 

 its orbital opening, there passing downward between the rectus inferior, mesially, and the rectus 

 externus laterally. Running downward and but slightly backward it passes lateral to the rectus 

 internus and has its origin on the dorsal surface of the parasphenoid. The rectus externus enters 

 the myodome along the lateral edge of its orbital opening, lying lateral to all the other muscles. 



