24 
Fig. 1. 
Fig. 2. 
Fig. 3 
Fig. 4 
Fig. 5 
Fig. 6 
Fig. 7 
Fig. 8. 
Fig. 9 
Fig. 10 
ON THE STRUCTURE OF TRACHYPTERUS ARCTICUS. 
EXPLANATION OF THE PLATES. 
All the Figures are Natural Size. 
Prats I. 
Side view of the skull. 
The lower jaw, suspensorial, opercular, and hyoid apparatus, seen from within. 
. The cranium, from above. 
. The cranium, from behind. 
Puate II. 
. Longitudinal vertical section of the cranium. The supra-occipital and the frontal have been 
removed. 
. The ethmoid region, and vomer. 
. The branchial region, showing the arches on one side separated from their attachment below the 
cranium, and spread out horizontally. 
The bony elements of the branchial arches, laid out horizontally. 
. The right shoulder girdle and pectoral fin. 
_ A series of vertebre. The centra are numbered. Over the seventy-eighth are placed the 
corresponding interspinous bones and fin ray. 
