352 Universitij of CalifoDiia Publications in Zoology [Vol.16 



sharply downward, forming the strong basal angle (h.a.. fig. 2). On 

 the anterior face of the basal angle there is a flattened articular surface 

 against which the orbital process of the upper jaw fits. Extending 

 from the margin of the cranium and below the preorbital process is 

 an antorbital process (a.pr.). This in Heptanchus maculatus serves 

 for the attachment of a slip of muscle which runs to the adductor 

 mandibulae. In the rays the antorbital process is connected with the 

 propterygium. 



The foramina perforating the walls of the brain-case differ con- 

 siderably from those figured by Gegenbaur (1872) for Heptanchus; 

 but they occupy essentially the same locations as those which he has 

 given for Hcxanchus (see his pi. 1, fig. 2). The first of these, between 

 the nasal capsules and the orbit, is the anterior opening of the orbito- 

 nasal canal {o.-n., my fig. 2). The posterior opening of this canal 

 {o.-n.') lies in the anterior part of the orbit. Above the latter is 

 a .smaller foramen for the anterior cerebral vein (f.a.c). Veutrally 

 and at the middle of the orbit is the large optic foramen (/. 77) 

 through which the second cranial nerve reaches the brain. Directly 

 above the optic is the ophthalmic for the superficial branch of the 

 seventh nerve (f.o.VII), while just posterior to the ophthalmic is 

 the smaller trochlear foramen (/. IV) through which the fourth cranial 

 nerve passes to the superior oblique mi:scle of the eye. Considerably 

 behind the optic and below and slightly back of the tip of the post- 

 orbital process is the enlarged orbital fissure (o. /.), through which 

 pass the fifth, sixth, and a part of the seventh cranial nerves. Below 

 and slightly posterior to the orbital fissure is the facial foramen 

 (/. VIP) for the hyomandibular branch of the seventh or facial nerve. 

 On a line between the facial and the optic foramina are. two 

 perforations, the nearer and more crescentic of which is for the 

 interorbital canal {i. o.) ; by means of this the orbital sinuses mediad 

 of the two eyes communicate. The other of these perforations 

 if.r.a.) is for the entrance of the ramus anastomoticus artery. Above 

 this is the .small opening (/". 777) for the exit of the third cranial 

 nerve to muscles of the eye. 



The visceral skeleton in Heptanchus is composed of a series of nine 

 pairs of cartilaginous arches which more or less completely surround 

 the buccal cavity and the pharynx. The first and largest of these 

 arches, the mandibular, is formed of the upper and lower jaws (pi. 28, 

 fig. 3 ) . This arch bears the teeth and has become the most highly 

 specialized of all the visceral arches. Its massive upper segment, the 



