204 bulletin: museum of comparative zoology. 



which is the probable homologue of the muse, adductor mandibulse of 

 Selachii, to be those stated by Hatschek. Whether iu this muscle 

 group we have to do with the muse, obliquus superior, I am not able to 

 state, since its iuuervatiou still remains uncertain to rae.^ I know, how- 

 ever, that it is not innervated by the oculomotorius. Its fibres, more- 

 over, are not continuous with those of the velar muscle at this stage of 

 development, if indeed they are at any stage. Hatschek's chief evi- 

 dence that this muscle is derived from the velar muscle apparently 

 consists in their histological resemblance, which he states is complete. 

 At the stage studied by me this is certainly untrue. For I find that 

 while the velar muscle is composed of large fibres, at least 7/a in diam- 

 eter, the fibres of the muscle in question are iu their widest part not 

 over 3/A in diameter, and also that, while the fibres of the former show 

 well marked longitudinal and cross striations, those of the latter show 

 these very faintly. ^Moreover, the nuclei of the former are for the most 

 part round or oval, while those of the latter are exceedingly elongated. 

 It is of course possible that Hatscliek bases his statements on the exam- 

 ination of the histological conditions in embryos of a different stage of 

 development. But even if we grant that the muse, obliquus superior in 

 Cyclostomes is, as in the Selachii, derived from the dorsal part of the 

 musculature of the mandibular arch, this evidence no more warrants the 

 conclusion that the muscle is splanchnic in origin in the former group 

 than in the latter. Of its dorsal origin and somatic nature in the latter 

 group, proof has been given above- 

 Even more theoretical than his conclusions concerning the origin of 

 the muse, obliquus superior appears Hatschek's inference that the eye 

 muscles innervated by the oculomotorius are derived from the con- 

 strictors of the visceral arches, a conclusion which he draws apparently 

 by the method of exclusion. It does not seem to have occurred to him 

 that these muscles may have had their origin from the connective-tissue 

 capsule of the eye, the cells of which are in my opinion derived from the 

 dorsal mesoderm in this region, which in early stages becomes disinte- 

 grated and surrounds the eye vesicle. Kupffer ('94) thinks that the 

 more difficult part of the task of tracing the development of the eye 

 musculature in Ammocoetes is accomplished when he has followed the 

 growth of muscle cells from the so called " Trabekular " and the mandib- 

 ular arches until they come into close relation with the eye capsule in 



1 That Hatschek ('92) incorrectly identified the nnise. rectus posterior, has been 

 shown by M. Fiirbringer ('97) from the study of its innervation, a matter to which 

 Hatschek seems to have paid no attention. 



