BOM SN DRE Lae OF THE GNATHOSTOME FISHES 587: 
it, and he apparently shows it also in a figure (pl. 11, fig. 3) said 
to be of Mustelus (but probably Galeus?). The superior liga- 
ment is also described and figured by him, without being so named, 
in both Mustelus and Galeus, but in these two fishes only. 
Whether or not either of these two ligaments were found by him in 
other selachians can not be definitely told from the descriptions. 
Gegenbaur does not mention the relations of the superior ligament 
to the vena jugularis, but he makes the evident mistake of saying 
(l. ¢., p. 168) that the nervus hyomandibularis facialis passes 
through the slit-like space between the ligament and the hyoman- 
dibula and then continues onward, close against the cranium 
(dicht am Schidel), to the posterior surface of the hyomandi- 
bula. Gadow (’88) describes and figures one or both of the liga- 
ments in Heptanchus, Oxyrhina and Sphyrna, but the figures 
and descriptions are of little value excepting in that they indicate 
that the ligaments are both generally found in the Selachii. 
In embryos of Mustelus laevis I found, in 1901, both of these 
postspiracular ligaments, the superior ligament being in part at- 
tached, ventrally, to the dorsal edges of two diverticula of the 
spiracular canal, and I now find both of these ligaments in an 
adult specimen of this fish, the attachment to the spiracular canal 
not being, relatively, so markedly developed as in embryos. In 
Chlamydoselachus I find the inferior ligament strongly devel- 
oped, while the superior ligament is represented by connective 
tissue strands which have their origin, partly on the postero-ven- 
tral surface of the postorbital process of the neurocranium, dorsal 
to the vena jugularis, and partly on the projecting anterior cor- 
ner of the dorsal end of the hyomandibula and hence morpho- 
logically ventral to the vena jugularis. Running postero-ven- 
trally, these two separate strands of tissue are apparently both 
attached wholly to the dorsal edge of the spiracular canal, but 
as the posterior wall of this canal is in part closely applied against 
and attached to the hyomandibula by intervening connective 
tissue, the two strands are doubtless continuous with this tissue 
and hence attached also to the hyomandibula. The superior 
postspiracular ligament of my embryos of Mustelus is thus here 
apparently in process of differentiation. In Heptanchus I find 
