458 J. FRANK DANIEL 
cranium. ‘This, in figure 6, has béen removed so as to show the 
proximal end of the hyomandibula. The superior post-spiracular 
ligament (s.p-s.l.) of Ridewood ’96; (see also W. K. Parker ’79), 
arising in the postero-ventral angle of the socket and anterior 
to the auditory capsule, attaches itself to the distal third of 
the hyomandibula. Further, the hyomandibula is bound to 
the ceratohyoid by a hyomandibulo-hyoid ligament (l.hm-h, 
fig. 6) which arises on the side of the distal end of the hyoman- 
dibula and passes over to the anterior and inner face of the 
ceratohyal segment, extending thence to its distal third. 
A series of ligaments may next be described which are effective 
in swinging the first or mandibular arch, all but one of which 
connect this arch directly to the second. That one, however, 
indirectly and in part, attaches the first arch to the cranium. 
Those binding the first arch to the second directly and appearing 
externally are three in number. The first of these is a dorsal — 
ligament (l.hm-q., fig. 6) which passes from the upper part of 
the hyal surface of the quadrate posteriorly to the medial and 
anterior part of the hyomandibula. This ligament is doubtless 
that part of the superior post-spiracular ligament which Ride- 
wood (’96, p. 427) described for Scyllium as attaching on the 
quadrate. In Heterodontus francisci, however, its attachment 
is on the hyomandibula, few of its fibers being continuous with 
the superior post-spiracular ligament. I have therefore called 
it by a separate name, the ligamentum hyomandibulo-quad- 
ratum (1.hm-q.). 
At the joint there is a complex median ligament (l.m., figs. 
6 and 7) which passes from the inner side of the quadrato- 
mandibular joint externally, principally, to the cerato-hyoid 
cartilage. The quadrate part of this ligament (l.m., fig. 7), 
however, arising under the large ligament which joins the man- 
dible to the quadrate (l.g-m.7.), runs upward and _ posteriorly 
to attach to the hyomandibula, mediad of and slightly distal to 
the attachment of the ligamentum hyomandibulo-quadratum. 
All of those fibers of the median ligament which arise from the 
joint and from the mandible (l.m., fig. 7) are attached to the 
ceratohyoid. 
