ANATOMY OF HETERODONTUS: ENDOSKELETON A471 
perforates the girdle between these two projections. Above the 
articular process (a.pt.) and on the scapula is the postscapular 
projection to which the heavy lateral musculature attaches. Be- 
tween the anterior projection and the mid-line there is a deep 
concavity on the coracoid from which the arcuales communis 
muscles arise. 
b. The pelvic girdle (fig. 13) consists of a flattened bar— 
slightly cupped up in the middle and expanded at the ends. The 
right and left halves of this are firmly fused together. Three 
foramina perforate the pelvic girdle near each end (f.pl.); . 
through the median one the iliac artery passes, and through the 
other two, nerves. At the termini of the girdle are the articular 
processes for the right and left fins. Each articular surface 
consists of two protuberances (a.pl.) which fit into lus cel 
of the fin skeleton proper. 
* 2. The skeleton of the fins 
a. The paired fins. 1. The skeleton of the pectorals (fig. 26) 
is made up of a group of large basal cartilages from which radiate 
numerous rows of radialia. The basal cartilages in the pectoral 
of Heterodontus francisci are unlike those previously described 
for the adult of Heterodontus philippi. In the former there are 
three pieces, pro- meso- and metapterygium, the first (the 
propterygium) being absent in the adult of the latter species. 
(Mivart ’79, p. 449; Huxley ’76, p. 50; and Gegenbaur ’65, II, 
pl. 9, fig. 3; see also Howes ’87, pl. 3.) 
This propterygial basal (pr-p.) in Heterodontus francisci is 
a clearly marked cartilage, quadrilateral in shape and somewhat 
elongated. It is followed by a series of four radialia, the first of 
which is large and plate-like. Contiguous to this plate-like 
radial is a hexagonal plate, a part of which evidently belongs to 
the first radial of the mesopterygium. 
The, mesopterygium (ms-p.) is a stout cartilage, from the 
enlarged distal end of which five rows of rounder radials radiate. 
The most proximal segment of the first row of radialia joins 
distally the hexagonal plate of the propterygium just described. 
