306 J. K. Thacher — Median avd Paired Fins. 



that the articulation (or failure of concrescence) of the metapterygium 

 and girdle has taken place farther aborad, and consequently a greater 

 number of rays devote their basal parts to the formation of the pelvic 

 girdle. Expectedly then, we find that the cartilage does in fact 

 spread around the branches of the next two nerves. Through the 

 foramina the ventral branches of these nerves pass, while the branches 

 to the dorsal side pass along to that side above the cartilage. 



The difference in respect to the relation between the cartilage and 

 the nerves in the pectoral and ventral limb is, that in the former the 

 cartilage thickens so as to include the branching place of the first 

 nerve or bundle of nerves, while in the pelvic limb, it is thinner and 

 merely transmits the ventral branch. In his Memoir on the Shoulder 

 Girdle, Gegenbaur has called attention to the two branching canals 

 or two pairs of openings in the shoulder girdle of the Batoidei. He 

 states that he has not observed whether the aborad one is traversed 

 by a nerve. I have examined this in the case of Raia erinaceus, and 

 found that both fore and after openings transmit nerves in the same 

 way. This is evidently what would be anticipated from what has 

 been herein said. We have here what we had in the ventral fin 

 (and girdle) of Eugoniphodxis ; a greater number of rays are devoted 

 to girdle building, and another bundle of nerves is included in the 

 spreading cartilage. 



The observations of Rolph on the innervation of Amphioxus^ are in 

 complete agreement with what would be required by the view here 

 advocated. He says " Der ventrale Ast verlauft herab bis in die 

 Seitenfalten. Beim Eintritt in dieselben theilt er sich in zwei Aeste, 

 deren einer {}%^ an der Aussenwand der Seitenfalte hinzieht; der 

 andere durchlaiift die Seitenfalte in querer Richtung, um in die 

 Bauchmuskulatur tiber zu treten, in der er sich nicht weiter verfolgen 

 lassen. Zuvor jedoch gibt er noch einen Zweig ab (^ig), welcher, n^ 

 parallel, an der inneren Wand der Seitenfalte verlauft." 



The manner of innervation, then, seems to me as totally inconsistent 

 with the Archipterygium theory as it is in thorough and telling har- 

 mony with the view which I have here presented. 



Addendum. 



Since the views expressed in the foregoing pages were complete in 

 my own mind six or eight months ago, I had looked for confirmation 

 of them in the brilliant investigations of Balfour on the development 



*Morph. Jahrb., Bd. ii, Hft. 1, p. 107, 1876. 



