ELASMOBRANCHS. 
1069 
low but broad, medially convex and laterally concave, 
are set one on each side of the foramen magnum, 
and a corresponding condyle, medially concave and 
laterally convex, is set on the front side of the con- 
fluent vertebral mass at the beginning of the spinal 
column (tig. 294, b). 
The temporal region surrounds the parts of the 
labyrinth, and frequently shows traces (elevations), 
even on the surface, of the position within the carti- 
lage of the labyrinthine canals (fig. 298, a. sc, psc, and 
On the outside of the lateral cranial walls there lie in 
this region the more or less marked articular cavities 
of the hyomandibular cartilage (km). Through the 
temporal region pass the foramina for the new us glos- 
sopharyngeus (fig. 298, C, gp), n. facialis (fig. 300, 
fa ), and, at the boundary between it and the orbital 
region, for the n. trigeminus ( tr ). 
The orbital region is furnished on each side in 
the most primitive forms with a posterior articular 
cavity for the palatine cartilage of the upper jaw (pa- 
ih ha 
Fig. 297. First dorsal fin with its skeletal parts and the subjacent part of the spinal column in an Asterospondyle (Hasse), a Porbeagle 
( Isurus cornubicus), 213 cm. long, from the North Sea. ] / 4 of the natural size. 
ra, radialia of the anterior margin; rb, basal radialia; fb, bunches of fibrils, partly inserted between the distal radialia; rmt, metapterygoid 
radialia, with their distal sections (rmt 2 — rintp ; Ig , vertical ligament of the dorsal fin, investing in its lower part (Igf the elastic ligament 
of the spinal column ( le ) — the last ligament is partly removed to show the roof of the spinal canal, composed partly of the interneural arches, 
partly of special supraspinal cartilages; in , interneural cartilages; ncc, neurapophyses ; c, vertebrae, complete, amphiccelous, with longitudinal 
lateral cavities and ribbed; monospondylous, each vertebra answering to only one neurapophysis ; ha, haemapophyses ; ih, interlnemal cartilages; 
the two last-mentioned cartilages together forming on each side of the spinal column a rim projecting outwards and downwards (answering 
to li in the preceding figure). 
hsc ) and the vestibule. On the upper side of the 
skull (tigs. 298 — 300) this region is usually depressed 
into a parietal cavity, where the two endolymphatic 
ducts or aqucediictas vestibuli (aqv) have their orifices. 
latoquadrate cartilage) on a postorbital process, and with 
an anterior articular cavity for the same cartilage at 
the bottom of the orbit, on an expansion of the cranial 
cartilage which has been called the basal disk, and which 
