STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 797 



the haemal processes appear to be about to give rise to the 

 haemal arches of the tail. 



This peculiar state of things led Gotte, and subsequently one 

 of us, to deny for Elasmobranchs all homology between the ribs 

 and any part of the haemal arches of the tail ; but in view of the 

 explanation just suggested, this denial was perhaps too hasty. 



FIG. 2. 



r.p - 



. . . V. etuis. 



Transverse section through the ventral part of the notochord, and adjoining structures 

 of an advanced Scyllium embryo at the root of the tail. 



Vb., cartilaginous sheath of the notochord; ka., haemal process; r.p., process to 

 which the rib is articulated ; m.el., membrana elastica externa ; ck., notochord ; 

 ao., aorta; V.cau., caudal vein. 



We are the more inclined to take this view because the re- 

 searches of Gotte appear to shew that an occurrence, in many- 

 respects analogous, has taken place in some Teleostei. 



In Teleostei, Johannes Muller, and following him Gegenbaur, 

 do not admit that the haemal arches of the tail are in any part 

 formed by the ribs. Gegenbaur (Elements of Comp. Anat., trans- 

 lation, p. 431) says, "In the Teleostei, the costiferous transverse 

 processes" (what we have called the haemal processes) "gradually 



