Rabl, Metamerism of the Vertebrate Head. 



151 



In 1882 he published the following table : 



Segment. Nerve. 

 I Olfactory 



f Oculo-motor 

 \ Trochlearis 



3 Trigeminal 



f Facial 

 ^ \ Abducent 



5 Glossopharj'ngeal 



6 Vagus 1st branch 



7 Vagus 2d branch 



8 Vagus 3d branch 



9 Vagus 4th branch 



10 Vagus 5th branch 



1 1 Vagus 6th branch 



Visceral cleft. 

 Olfactory 



Lachrymal 



Buccal 



Spiracular 



1st branchial 



Visceral arch. 



ry 



I Maxilla 



V Mandibular 

 I Hyoid 



I 1st branchial 

 2d branchial -^ 



'■ 2d branchial 

 3d branchial % 



V 3d branchial 



4th branchial 



5th branchial 

 6th branchial 

 7th branchial 



|- 4th branchial 



V Sth branchial 



V 6th branchial 



Van Wijhe about the same time published investigations on 

 the selachian head. 



Nine mesoderm segments were identified, three of which lie 

 cephalad of the ear capsule. The several somites subdivide 

 into a myotom and sclerotom but vary greatly in subsequent 

 modifications. From the walls of the first myotom are formed 

 those eye-muscles which are innervated from the oculomotor 

 while the muscle supplied by the trochlearis ( oblig. sup.) is 

 formed from the walls of the second myotom and the rectus ex- 

 ternus from the third myotom. The fourth and fifth myotoms 

 disappear. 



Each nerve to a visceral arch originates as a dorsal root 

 and divides into a ramus dorsalis and a ramus ventralis, both of 

 which may possess a ganglion. The ramus ventralis forms two 

 principal branches, the ramus posttrematicus and ramus 

 pharyngeus, which latter forms a ramus praetrematicus. 



Alborn ( in his work — Ueber die Segmentation des 

 Wirbeithier Korpers, 1884.) concludes that mesomerism (seg- 

 mentation of mesoderm ) stands in no necessary connection 

 with branchiomerism (segmentation of entoderm, i.e. gill clefts.) 

 In so far as the distribution of nerves is influenced by the latter 



