A Contribution to tlic Anatomy of Siren Incertina. 673 



Immediately behind these lie two small accessory lobes. The 

 lateral lobes are slightly connected with the medial one by connective 

 tissue, within which the glandular structure may also be continuous, 

 while the accessory lobes are completely separated from the main 

 mass. The medial lobe lies between the anterior ends of the two 

 cerato - hyoidei externi. The lateral lobes follow the inner border of 

 the same muscles, being partially covered by them. The two accessory 

 lobes lie imbedded in the subcutaneous connective tissue, resting upon 

 the main muscular mass of the trunk. Upon the ventral surface of 

 the lateral lobes Ues the hypoglossal nerve, which supplies in this 

 position the genio-hyoideus. 



In one specimen I found that the medial lobe failed completely, 

 and that the two accessory lobes were connected with the lateral ones, 



V. Cranial nerves. 



The majority of the cranial nerves have already been so com- 

 pletely and exactly described, that it would be superfluous to attempt 

 a complete description here. I have selected for description, therefore, 

 only those parts where previous investigation either fails or is not 

 in accord with my results. For the rest, the reader is referred to 

 the summary in Bronn, or to the original work of Fischer, also to 

 the diagrammatic plate here given. Nearly every statement given here 

 I have repeatedly verified by means of the examination of serial 

 sections, a method which, it must be remembered, was not in the 

 hands of the earlier investigators of this subject. 



Trigeminus (figs. 9, red). 



This important nerve takes its origin from the Gasserian ganglion 

 ((r) which lies in the cranial cavity partly behind the alisphenoid 

 cartilage and partly behind the petrosal bone and auditory capsule; 

 Ijeing blended posteriorly with the most anterior portion of the facialis 

 ganglion, from which it receives a few elements. 



The nerve passes through the alisphenoid at its thickest portion 

 by three trunks, the most superior of which divides again almost im- 

 mediately after its exit, thus making four main trunks. This pecu- 

 liarity, before noticed in Siredon alone of all the Urodelans, is a fish- 

 characteristic, and its occurrence among these two low Amphibians is 

 perhaps a matter of considerable significance. 



These four stem, as they leave the ganglion, pass into the same 

 opening in the cranial wall , but the lowest branch , Ramus ophtha!- 



