THE SPINAL NERVES. 79 



discussions the reader is referred to Kupffer's excellent 

 digest ('96) and to Fiirbringer's great monograph ('97). 



It should be noted that neither of these works clears up 

 the problems connected with the pre-hyal ventral muscu- 

 lature of teleostomes and that in regard to another impor- 

 tant moot question they are absolutely contradictory, viz., 

 the morphology of the hypoglossus region of the cyclo- 

 stomes. In the case of Petromyzon Kupffer describes the 

 ventral musculature of the head as innervated from the 

 vagus and not from the "hypoglossus" or first spinals, as 

 in most other vertebrates. He thought that the ventral 

 musculature of Petromyzon is of dermal origin and that it 

 is not derived from the lateral muscle plates, as is the 

 case with the "hypoglossus musculature" of other verte- 

 brates. This would explain the innervation from the 

 vagus instead of the first spinals and there would be no 

 true hypoglossus in Petromyzon, for the corresponding 

 musculature is wanting. 



Subsequenty Neal ('97), working under Kupffer's direc- 

 tion, has re-opened the question, and he finds that the 

 ventral musculature of the head is developed in Petromy- 

 zon in exactly the same way as in other vertebrates and 

 is homologous throughout the series. He therefore con- 

 cludes that the r. recurrens vagi of Petromyzon is homolo- 

 gous with the hypoglossus of higher vertebrates, while 

 the so called hypoglossus of the older writers on Petromy- 

 zon is composed of true spinal nerves. 



Fiirbringer, however, comes to a quite different con- 

 clusion. He finds ('97, p. 597), both in Ammocoetes and 

 in adult Petromyzon, that the r. recurrens vagi is im- 

 properly named, for it contains no vagus fibres v^^hatever; 

 it is rather a r. recurrens spinalis, only secondarily bound 

 up with vagus fibres and clearly separable from them. 

 Petromyzon, therefore, conforms to all of the other verte- 

 brates, of which Fiirbringer has studied types of every 

 class, in that the hypoglossus musculature is innervated 

 by the spinals and the spinals only, the vagus never 

 participating. Alcock ('98, p. 150) fully confirms 



