136 Mr. W. K. Parker on the Structure [Dee. 16, 



At a still later period the nerve given off from the ganglion unites with 

 the anterior nerve-root. 



The development of the anterior nerve-roots is far simpler than that of 

 the posterior. 



Some little time after the appearance of the posterior roots there spring, 

 on each side, from the ventral corner of the spinal cord, a series of conical 

 outgrowths. These correspond in number with the muscle-plates, and are 

 the rudiments of the anterior roots of the spinal nerves. 



These outgrowths are not vertically below the posterior roots, a feature 

 which remains permanent in the adult. 



The points of attachment of the anterior roots undergo no change of 

 position like those of the posterior roots ; and after they have attained a 

 considerable size they unite with the latter. 



The author has also observed that the posterior roots of some and pro- 

 bably of all the cranial nerves develop in the same way as the posterior 

 roots of the spinal nerves, and points out the bearing of this upon the 

 morphological relations between the spinal and cranial nerves. 



The remainder of the paper consists of a series of speculations upon 

 the bearing of the above-mentioned facts upon various physiological and 

 morphological problems. These, for the most part, do not admit of being 

 abstracted. 



One point the author mentions is the probable homology of the commis- 

 sure he has detected uniting the dorsal ends of the posterior nerve-roots 

 with the commissure he has described in a previous paper ("A preliminary 

 Account of the Development of the Elasmobranch Fishes," Quart. Journ. 

 of Micros. Science, October 1874, plate 15. fig. 14), which at first unites all 

 the branches of the vagus nerve, and which is subsequently represented by 

 their common junction before uniting with the medulla oblongata. 



II. " On the Structure and Development of the Skull in the 

 Batrachia."— Part II. By W. K. Parker, F.B.S. Received 



October 28, 1875. 



(Abstract.) 



In the present communication I wish to correct, as much as possible, 

 what now seems to be erroneous in my former account of the Batrachian 

 skull (that of the frog, Phil. Trans. 1871), and also to describe and 

 illustrate the stages in the skulls of three kinds of toads. 



Happily for me, Professor Huxley took up this subject at the begin- 

 ning of last year; and I had frequent opportunities of working, as 

 well as for discussion, with him. 



It was soon made plain to me that in my former account of the 

 behaviour of the visceral arches I had been wrong in describing the 

 hyoid arch of the third stage as composed of an upper and a lower 

 piece. 



