454 J. FRANK DANIEL 
foramen for the vagus (f.X). Below the vagus are three smaller 
foramina (two in fig. 5) through which the spino-occipital nerves 
of the ventral root type pass. Finally between the posterior end 
of the cranial notochord and the ventral margin of the occipital 
crest is the large foramen magnum (f.m.). 
At the posterior end of the cranium (fig. 4) ventral to the fora- 
men magnum is the cranial notochord, at the sides of which 
are the occipital condyles (0.cd.) by which the spinal column is 
joined to the cranium. At the side of and slightly above each 
‘condyle is the large foramen for the vagus nerve (f.X); above 
this are two smaller foramina through which a spino-muscularis 
artery (f.s-m.) perforates the cartilage without entering the 
brain case. These, I take it, are the foramina which Haswell 
(’84, p. 93) describes for Crossorhinus as ‘‘a pair of small aper- 
tures of unknown function.” Still further laterally is the 
opening for the glossopharyngeal or ninth cranial nerve (f.JX). 
At the lower angles of the posterior part of the cranium are the 
post- and superior articular processes (po.hm. and s.hm.) by 
which the hyomandibular suspensorium is fixed to the cranium. 
A view of the rostral region (fig. 1 and text fig. A) explains the 
structures there involved. It is noted that the pointed anterior 
end bifurcates into dorso-lateral halves which, near the middle 
line, bend downward and fuse with the median ventral trabecular 
piece. These, in Heterodontus francisci, were they compared 
with a form in which the rostral cartilages compose a well- 
marked framework, as for example Pseudotriacis microdon 
(Jaquet ’05), would show but slightly their rostral nature. A 
comparison with another type is instructive in this respect. 
In Crossorhinus (Orectolobis) Haswell (’84) figures a cranium 
(6 of text fig. A) in which he describes paired pieces (rst.) as being 
prolongations of the ventral floor. From the condition present 
in the heterodont sharks it would seem not improbable that 
they are in fact projections from the dorsal and the lateral 
walls rather than from the floor. If such be true the likeness 
between Crossorhinus and Heterodontus in this regard is strik- 
ing, for a union of the median rostral piece (rst.) with the olfactory 
wing (ol.wg.) above and of the olfactory wing and the basitra- 
