SKULL AND VISCERAL SKELETON OF THE GREENLAND SHARK. 291 



foramen (Vg). From this point to its external orifice it pursues a course from within 

 outwards and backwards, and passes through the cranial wall external to and at a lower 

 level than the vagus canal. The canal in question is not continuous throughout, its 

 continuity being broken a short distance after its commencement, as it here opens into 

 the lower part of the vestibule of the ear. After a short interval, the canal is continued, 

 and passes to its outer opening (Figs. 1 and 4, Gp'). The first part of the canal is 

 narrow, the second is wide. In communicating with the vestibular part of the auditory 

 capsule, and consisting of a narrow and a wide part, the glosso-pharyngeal canal of 

 Lsemargus is similar to that of Centrophorus calceus, Acanthias, and the Eays. 



The Facial Canal. — This canal, which is short, commences just inside a depression 

 (Fig. 5, Af), which is common to part of the facial and the auditory nerve, and passes 

 transversely outwards, to open in the space under the band of cartilage, already men- 

 tioned, on the lateral aspect of the auditory region. 



The Orbital Region. 



This region lies between the auditory region behind, and the ethmoidal in front. 

 The post-orbital processes (Figs. 1, 3, and 4, Po), and the canals (Tr') for the trigeminal 

 and other nerves mark its posterior boundary, while the pre-orbital processes (Pr) and 

 ridges running downwards from them serve as its anterior limitation. A capacious 

 orbital cavity lies on either side of this region, and the supra-orbital crests, with their 

 post- and pre-orbital processes, stand boldly out from the skull. 



The dorsal portion of the orbital region (Fig. 1) forms the broadest part of the 

 skull, and presents on each side a concavity between the pre- and post-orbital processes. 

 Between the post-orbital processes there is a considerable median depression, in front 

 of which are two smaller depressions also occupying the mid-dorsal line. Internal 

 to each supra-orbital ridge there is a groove, the supra-orbital groove, continued for- 

 wards from a groove occupying a similar position in the auditory region, and on 

 the floor of this the supra-orbital foramina (&r) are situated. There are six or 

 seven of these foramina on each side, and one of the hindermost of them is always 

 larger than the others. In this respect Lsemargus agrees with Centrophorus calceus, 

 Galeus, and Mustelus. The supra-orbital grooves are deepest anteriorly, and in this 

 position each receives the upper opening of the pre-orbital canal (Pr"). Two 

 grooves, one of which runs along the inner and dorsal part of the nasal capsule, 

 while the other turns outwards and leads to the hinder part (em) of the ethmoidal canal, 

 commence at the point where the pre-orbital canal opens. 



The ventral aspect (Fig. 3) of this region of the skull presents a comparatively 

 narrow anterior and a broad posterior portion. The broad part forms the anterior 

 portion of the basilar plate (Bp) of the skull, and in front, on each side, it throws out a 

 shoulder-like process. In front of each shoulder is a concavity, the palato-basal 

 depression (Pd), for lodging the palato-basal process (PI. II. Fig. 1, Pp) of the palato- 



