Royal Physical Society. 389 



The transverse process of the second vertebra is greatly de- 

 veloped. It lies horizontally at its origin, but as it passes 

 outwards it alters its plane, and describes a curve, with the 

 convexity forwards, and its anterior margin turned downwards. 

 It is adapted to the anterior extremity of the swimming bladder, 

 and is connected by a ligament with the ex-occipital bone. 

 Bilharz considers it as a part superadded to the second ver- 

 tebra, and calls it by the name given to it by Miiller, the 

 spring process (springfederfortsatz), and describes as the 

 transverse process that of the third. From the dorsal surface 

 of the spring process a cylindrical secondary process, the 

 stem process of Bilharz, pass inwards ; and its inner ex- 

 tremity is so nearly in contact with the neural arch that it 

 presses against it when the spring process is pressed upwards. 



Professor Miiller was the first to mention the spring process, 

 and its connection with the swimming-bladder, both in Mal- 

 apterurus and other fishes.* A strong slip of the dorsal 

 muscle connects the anterior surface of the process with the 

 occiput ; and by its contraction Miiller considers that the 

 process is drawn forwards, and that so the air in the swimming- 

 bladder is rarified ; and that, when the contraction ceases, 

 the process springs back into its place by its elasticity. The 

 stem process, by abutting against the neural arch, will pre- 

 vent too great a displacement of the spring process. 



Immediately behind the transverse process of the second 

 vertebra lies that of the third, shorter and broad, lying in the 

 horizontal plane, so that the swimming-bladder, in expanding, 

 will press it upwards. The transverse process of the fourth 

 vertebra is a simple stiliform process, rather shorter than that 

 of the third. Its neural arch is prolonged into a rudimentary 

 spine, and a round foramen, closed by a membrane, is left 

 between it and the neural arch in front. In M. electri- 

 cus, Bilharz represents this foramen as nearly completed by 

 the latter arch, and a separate bone fitted into the remaining 

 interval, and overlying the two following spines. This bone 

 he calls the spine of the second vertebra. It does not exist 



* Miiller's " Archiv," 1842, p. 319. He states that the Silurians in which 

 he has observed this apparatus have a narrow branchial fissure, — viz., the ge- 

 nera Auchenipterus, Synodontis, Doras> Malapterurus, and Euanimus. 



