290 ME PHILJP J. WHITE ON THE 



and inwards to a carotid canal (Ca'). The grooves may be bridged over with cartilage 

 in part of their extent. 



On the lateral surface of the auditory region, at its lower and hinder part, is the 

 depression (Fig. 4, j f) which forms an articular surface for the two heads of the 

 hyomandibular cartilage. The long axis of this depression is directed from above down- 

 wards and backwards, and for the most part it is distinctly demarcated from the 

 surrounding parts. It exhibits two surfaces, an upper and a lower, incompletely 

 separated from each other. The upper joint surface (j) is smaller than the lower (/), 

 and a small process, from which a distinct rim runs upwards and gradually fades away, 

 is situated at its lower and anterior part. The larger articular surface is deep compared 

 with the upper, and the basilar portion of the skull juts outwards under its lower part, 

 while at its upper and hinder part a stout process stands out from the skull, and over- 

 hangs it. 



In possessing a cranio-hyoid joint with two surfaces, the skull of Lsemargus agrees 

 with Zygaena. 



A pyramidal process (Figs. 1, 3, and 4, Ap) projects backwards from the auditory 

 region behind the cranio-hyoid joint. The lower surface of this process (Fig. 3) is 

 flattened, but its upper (Fig. 1) presents two grooved surfaces, an internal and an ex- 

 ternal, separated from each other by a ridge. The former of these leads up to the exit 

 foramen ( Vg') for the vagus, and the latter (Gp') to that for the glosso-pharyngeal nerve. 



A groove, the post-orbital groove (Fig. 4, Pg), begins above the smaller articular 

 surface of the cranio-hyoid joint, and is continued forwards and downwards to 

 terminate at the inter-orbital foramen (Io'), which lies a short distance below 

 the foramen (Tr'), for the trigeminal and other nerves. About the middle " of its 

 course, the groove is bridged over by a band of cartilage (x). The space beneath this 

 band, towards its fore part, is separated by a cartilaginous shelf into an upper and a 

 lower chamber, the former of which lodges, in the recent state, part of the orbital 

 sinus, while the latter contains part of the facial nerve, the palatine branch of which 

 escapes in front (PI), while another portion of the nerve passes from beneath the 

 band posteriorly. The lower part of the band may be perforated at several points for 

 the passage of nerves. A ridge extends from about the middle of this band at its 

 anterior part and forms the anterior and lower boundary of the post-orbital groove, and 

 the upper border of a groove which lies below it. This second groove leads to a deep 

 depression (y), at the bottom of which are two foramina. The hyoid artery rests in 

 this groove, and the foramina, which are the orifices of canals opening internally on the 

 lateral wall of the pituitary fossa, are for the branches of this artery. The band-like 

 arrangement covering the exit foramen of part of the facial is interesting, as in 

 Rhynchobatis, Trygon, Pristis, and Squatina a similar band covers the outer opening of 

 the facial canal. 



Glosso-pharyngeal Canal. — The inner opening (Fig. 5, Gp) of this canal is placed 

 at the lower and lateral part of the cranial cavity, in front of the pneumogastric 



