VIII PECTORAL AND PELVIC GIRDLES 239 
fins, in some of the Lower Devonian Acanthodei (e.g. Climatius), 
may be regarded in that light. 
The Pectoral and Pelvie Girdles.—The pectoral girdle is more 
primitive in Cladoselache and Pleuracanthus than in any other 
Elasmobranch. In the former (Fig. 145, A) it may be doubted 
if the girdle has passed beyond the basipterygial stage, and 
although a definite girdle is present in the latter genus (Fig. 
250) its lateral 
halves retain their 
primitive distinct- 
ness. Existing 
Elasmobranchs, in- 
cluding the Holo- 
cephali, have a 
pectoral girdle in 
ene form of a 
dorsally incomplete 
hoop of cartilage 
imbedded in the 
muscles of the 
body-wall, close 
behind the last 
branchial arch (Fig. 
fae): The-upper * ar 
or dorsal portion 
of each half is the 
scapula, and the 
SS = 
See 
\ \ 
VV \\ 
Fig. 141.—The right half of the pectoral girdle and the fin 
ais of an Elasmobranch (Chiloscyllium). d.7, Dermal horny 
ventral is the cora- fibres ; meso, mesopterygium ; mefa, metapterygium : 
cold. Between pect, pectoral girdle ; pro, propterygium. (From Parker 
: and Haswell.) 
these two portions 
of the girdle, and defining their limits, there are articular surfaces 
for the basal cartilages of the pectoral fin. 
Cladoselache (Fig. 145, B) had no pelvic girdle, nor does it 
appear that this primitive Elasmobranch had acquired even 
a basipterygium. Plewracanthus, on the contrary, had a pair of 
pelvic rudiments distinct from well-developed basipterygia. In 
other Elasmobranchs there is a distinct girdle, formed by the 
median union of primitively distinct lateral rudiments, consisting 
of a simple transverse bar of cartilage, imbedded in the ventral 
abdominal wall, just in front of the cloacal aperture, and having 
