SOME PARTS OF THE SKELETON OF FISHES 285. 
abranchiate Vertebrata, and the Mammalia, present a series of well- 
marked gradations in the mode in which the ramus of the mandible 
is attached to the skull. In the fish it is separated by the os 
articulare, the quadratum, and the temporo symplectic. In the 
Amphibia the latter becomes less distinct. In the abranchiate Ovz- 
para it disappears, but the ramus of the mandible is still separated 
from the skull by the articulare and quadratum. In the Mamaadlia,. 
finally, these are converted into the malleus and incus respectively, 
and the ramus comes into direct contact with the squamosal element 
of the skull. 
DESCRIPTION OF PLATE III. [PLatE 28]. 
Fig. 1. The tail of a young fish, 5-16th of an inch long. 
Fig. 2. The tail of a young fish, 7-16th of an inch long. 
Fig. 3. The tail of a half-grown specimen. 
Fig. 4. The tail of a full-grown Gasterosteus. 
The two last figures are drawn in their proper relative proportions, while figs. 1 and 2 
are on a much larger scale than figs. 3 and 4. 
The letters have the same signification throughout. 
a. Centrum of the last distinct vertebra. 
. Urostyle. 
. Notochord. 
. Neural arch of the last distinct vertebra. 
Interior arch of the same vertebra. 
. Inter-hemal cartilage or bone of the last ordinary vertebra. 
. Anterior hypural apophysis. 
Posterior hypural apophysis. 
. Principal caudal fin-rays. 
Interneural cartilage or bone of last ordinary vertebra. 
. Anterior epiural apophysis. 
. Posterior epiural apophysis. 
. Superior accessory fin-rays. 
b. Inferior accessory fin-rays. 
Nerney FRO S 
= 
es 3 & 
2s 
