NEAL: NERVOUS. SYSTEM IN SQUALUS ACANTHIAS. 203 
determine what is dorsal and what is ventral, it would follow from the 
evidence already stated by Platt (?91) that the anterior portion of the 
dorsal aorta in Squalus embryos comes to lie in part dorsal to the chorda, 
and therefore that this organ, commonly known as chorda dorsalis, could 
more correctly be named chorda ventralis. Kupffer’s argument thus 
leads to a reductio ad absurdum. 
According to Hoffmann (’96) the muscles innervated by the oculo- 
motorius have their origin from the posterior part (“ Fortsatz”) of the 
premandibular cavity. Because of the complicated development and 
the secondary subdivisions of this cavity, it is difficult to be certain ; 
yet it seems to me that, as in the case of the second and third cavities, 
the epithelium of both median and lateral walls participates in the pro- 
duction of the muscles formed from this cavity, viz. musc. obliquus 
inferior, and recti inferior, superior, and anterior. 
Before passing to a consideration of the nature of the “anterior 
cavities,” I wish to discuss, in connection with the preceding study of 
the morphology of the eye-muscle somites in Squalus, the evidence of 
the development of the eye muscles of Petromyzon which has been given 
by Hatschek (92) and Kupffer (94), and to determine in how far this 
brings us to an understanding of the morphology of the eye muscles in 
Vertebrates in general. The repeated confirmation of Marshall’s conclu- 
sion that the eye muscles in Selachii and Reptilia are derived from the 
epithelium of the first, second, and third cavities—van Wijhe (’82), 
Dohrn (’85), Orr (87), Kastschenko (788), Miss Platt (91), Oppel (92), 
Hoffmann (’96), and myself — seems sufficient to remove any doubt (so 
far as those groups of animals are concerned) which Kupffer (94) may 
have sought to throw upon that conclusion. In Amphibia, Birds, and 
Mammals, as is well known, the eye muscles are differentiated from the 
connective-tissue capsule surrounding the eye. Although the source of 
these cells is not known with certainty, there is no reason to doubt that, 
as in Selachii and Reptilia, they have their origin from the dorsal meso- 
derm. In direct contradiction to these facts, which hold true for higher 
Vertebrates, stand the conclusions of Hatschek and Kupffer, that in Cy- 
clostomes the eye muscles are splanchnic in their origin, i. e. derived from 
the mesoderm of the visceral arches. Let us examine the evidence given 
by them, in order to determine in how far it seems to warrant their con- 
clusions. Hatschek’s briefly summarized evidence has been stated on 
pages 192, 193, and needs no repetition, 
In sections of a 5 cm. Ammocates I find the relationship of the 
median posterior musculature of the eye capsule to the velar muscle, 
