328 CHORDATA. 
to the facets are the three dasa/ elements of the fin, called 
the propterygium, mesopterygium and metapterygium, the 
first and last extending forwards and backwards. Each 
bears on its outer border a row of numerous fiz-rays which 
are jointed. 
The posterior elements are the pelvic girdle and pelvic fin. 
The girdle consists of a ventral pudic dar at each end of 
which is a small dorsal z/iac process, an anterior prepubic 
Process and a pair of acetabular facets. To the posterior of 
Fig. 234.—DorsaL Vizw oF PELVIC GIRDLE AND FINS OF THE 
SKATE. (4d nat.) 
Pubic Bar. | Prepubic Process. 
First Fin-ray. 
Iliac Process. Second and Third 
in-rays. 
Metapterygium. 
Distal Joint of \ 
Basipterygium. 
these is articulated the metapterygium, bearing a number of 
Jin-rays. To the anterior facet is attached the thickened 
first fin-ray. 
In its complete adaptation to an aquatic habitat, with gills 
or gill-slits, its paired fins with fin-rays, its two-chambered 
respiratory heart, and its sensory ampull, the skate is a type 
of its class Pisces. 
In its cartilaginous skeleton, its placoid scales, heterocercal 
tail, spiral intestine and cloaca, the form of its urogenital 
organs and its embryonic development, it is typical of the 
order Elasmobranchit. 
_ Its dorso-ventrally compressed body and reduced dorsal 
fin are typical of the Bazoidel, a group comprising the rays: 
and skates. Minor features determine its family and genus. 
