192 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ventral to the dorsal aorta.* The vessel which Dohrn (’88) called the 
carotis, and which he stated lay ventral to the connecting stalk of the 
first cavity, if comparable at all, is comparable only to the carotis ven- 
tralis of Amniota.? 
The chief arguments concerning the nature of the 2d (mandibular) 
cavity have already been given in connection with the general question 
of the pre-otic mesodermal segments, and it is therefore not necessary to 
repeat them here. The evidence of a continuous lumen between this 
cavity and the alimentary canal stated by Miss Platt (?91*) has been 
interpreted by her as favoring the view that the cavity is formed as an 
outgrowth from the dorsal wall of the alimentary canal, similar to the 
mesodermal pouches in Amphioxus. Kupffer (94), however, regards it 
as evidence in favor of his view, that these cavities are abortive visceral 
pouches. It is necessary, finally, to recapitulate a point in evidence 
which has only an indirect bearing on the question of the somatic value 
of the Ist, 2d, and 3d cavities, but which concerns vitally the morphol- 
ogy of the eye muscles (derived in Selachii from these cavities). It 
has been stated by Hatschek (92) and Kupffer (92-96) for Ammo- 
cotes (Petromyzon Planeri). Their results tend to show that the eye 
muscles of that low Vertebrate are, with the possible exception of the 
muse. rectus posterior (externus), derived from splanchnic and not from 
somatic mesoderm. According to Hatschek (92), the muse. obliquus 
superior appears as a differentiated portion of the muscles of the velum, 
which correspond with the musc. adductores mandibule. His evidence 
«pp. 149, 150) is as follows: “ Vom vorderen inneren Rande dieses Mus- 
kels [velar muscle] dringt nämlich ein Muskelfaserbündel dorsal in das 
Bindegewebe ein und zicht seitlich am Trabekel vorbei zwischen dem 
ersten und zweiten Trigeminusganglion hindurch bis in die Nähe des 
Auges, wo es im Bindegewebe zugespitzt endet. Von da beginnt — 
wie ein zweiter Muskelbauch — mit seinem zugespitzten hinteren Ende 
der muse, obliquus superior und zieht, wieder anschwellend, in gleicher 
Richtung weiter zum Auge. Die histologische Uebereinstimmung beider 
1 Kupffer’s statement applies to that cavity in Ammocates which has been 
homologized, in my opinion correctly, by most investigators (Balfour, Dohrn, 
Shipley ’87, Kupffer) with the premandibular cavity of Selachii. 
2 In my opinion those writers who have quoted Balfour ('81) and Marshall (' 81) 
as holding that the connecting stalk of the premandibular (1st) cavity is ventral 
have misunderstood them. They both spoke of the two lateral parts of this cavity 
as prolonged ventralwards to meet below the base of the forebrain. They give no 
proof that the stalk is morphologically ventral, and in my opinion speak of it as 
ventral only with reference to the wall of the brain. 
