510 H. W. NORRIS AND SALLY P. HUGHES 



the dilatator choanae of Siren and Amphiuma and the compressor 

 of the orbital gland in caecilians to be strictly homologous struc- 

 tures, and to be derived from a more primitive fundamental leva- 

 tor bulbi muscle, such as is found in many urodelans and anu- 

 rans. Such an homology seems to the writers highly plausible, in 

 spite of the fact that the innervation of the compressor muscle 

 in the caecilians is by a nerve that also innervates the temporal 

 and masseter muscles, derivatives of the primitive adductor 

 mandibulae muscle, while the levator bulbi muscle is by theory 

 derived from a primitive dorsal constrictor. 



It is not quite clear to us what the function of the preorbital 

 slip of the temporal muscle is when it is attached anteriorly to 

 the compressor of the orbital gland. It may possibly assist the 

 compressor muscle, but it more probably acts as a dilatator of 

 the gland. In Dermophis the muscle is innervated by a branch 

 that supplies the pterygoid as well as the masseter, temporal, and 

 compressor muscles: In Herpele and Caecilia, by a branch arising 

 from the base of the ramus mandibularis V near where the 

 branch to the pterygoid muscle is given off. Its posterior con- 

 nection with the tendon of the temporal muscle indicates that 

 it is but a part of that muscle. 



From this survey of the structures connected with the eyeball 

 it becomes clear that there is nothing anomalous in the structure 

 and relations of the ocular muscles and nerves in the caecilians 

 other than that which results from extreme degeneration of most 

 of the parts involved and the marked transformation which pro- 

 duces a- retractor tentaculi muscle. All parts and their inner- 

 vation can be directly homologized with structures and corre- 

 sponding innervation in the urodele amphibians. 



THE TRIGEMINAL NERVE 



1 . The roots and ganglia of the trigeminal nerve 



The distinctly double nature of the fifth nerve in the caecilians 

 was noticed by Wiedersheim and subsequent investigators. 

 Brauer and Marcus agree that the ophthalmicus profundus gang- 

 lion arises from a dorsolateral placode, and the maxillo-mandibu- 

 lar ganglion from the neural crest. 



