/ 



196 ON THE MORPHOLOGICAL CONSTITUTION OF 



points, regarding which we cannot at present be said to possess 

 any. First, the development of the cyclostomes, but more 

 especially of branchiostoma ; secondly, the mode in which the 

 trunk sclerotomes increase in number and become arranged in 

 groups ; thirdly, the mode in which the same changes proceed 

 in the cranium ; fourthly, the determination of the series of 

 cephalic nervous centres, with their corresponding nerves 

 (neurotomes), more especially in the medulla oblongata, with 

 the causes which determine the grouping and order in which 

 the cerebral nerves pass through the walls of the cranium. 



If there appear to be no sufficient developmental grounds 

 for making a distinction between the branchial arches of the 

 amphibian and fish, as belonging to a splanchno-skeleton, and 

 the hyoidean and mandibular as referable to the neuro- or 

 endo-skeleton, it becomes important to determine the signifi- 

 cation of the sclerous elements of the larynx, trachea, and 

 bronchial tubes. Without presuming to anticipate the minute 

 observation of the development of the parts themselves neces- 

 sary for the solution of a question of this kind, I would venture 

 to suggest that the proper cartilages of the larynx are de- 

 veloped from the inferior or mesial extremities of certain of 

 the visceral laminse ; and that the cartilages of the trachea 

 and bronchial tubes are a pair of highly-developed actinapo- 

 physeal systems, referable to one of the posterior visceral 

 arches. 



Post-stomal Neuractinapophyscs. — In addition to the audi- 

 tory capsules, I recognise as post-stomal neuractinapophyses 

 more particularly those ossicles attached to the post-frontals, 

 mastoids, and external occipitals of fishes. Those attached to 

 the post-frontals may enter into the formation of the infra- 

 ocular bony arch. Those, again, which are developed' on the 

 temporal and occipital sclerotomes are modified so as to 

 co-operate in the cranial suspension of the scapular girdle. 



In conclusion, Goethe was the first to indicate the inter- 



