292 MR PHILIP J. WHITE ON THE 



quadrate cartilage (ppt). The basal angle (Fig. 4, A) is not so marked in Lsemargus as 

 in the Notidanidse or in Scymnus, but seems rather to resemble that of Acanthias. 

 The narrower anterior basal portion of this region projects in the middle line, and forms 

 the hinder part of a keel (K) which runs under the ethmoidal region. The outer 

 openings (Co') of the carotid canals, which will subsequently be described, are placed 

 towards the anterior part of the basilar plate. A small mesial aperture (He), which is 

 the lower opening of a canal, evidently the hypophysis canal, is also found at the anterior 

 part of the basilar plate. 



The orbital cavity (Fig. 4). — Each cavity is overhung by a supra-orbital ridge with 

 its pre- and post-orbital processes. Its anterior boundary is formed by a cartilaginous 

 ridge, which, curving downwards from the pre-orbital process, gives rise to an 

 antorbital process (An) at the fore part of the orbit, and then curving backwards 

 from this point fades away as it approaches the palato-basal depression (Pd). Behind, 

 the orbital cavity has no distinct boundary as the auditory region merely slopes 

 forwards and inwards towards the orbital basin. A sort of floor is formed to the 

 orbital cavity behind by an outward projection of the basilar plate, but in front of this 

 the orbit is devoid of a floor. 



The post-orbital process. — This process (Figs. 1, 3, and 4, Po), which is of con- 

 siderable strength and size, is pyramidal in form, and has its apex directed outwards, 

 downwards, and backwards. One surface is directed upwards, a second downwards 

 and forwards, and a third downwards and backwards. The process resembles that found 

 in Acanthias. 



The pre-orbital process (Figs. 1, 3, and 4, Pr). — This process, which is not so pro- 

 minent as the post-orbital, is connected in front with the roof of the nasal capsule by a band 

 of cartilage (b) which roofs in the ethmoidal canal. The base of the process is pierced 

 by two canals, the upper and larger of which is the pre-orbital. The lower canal, which 

 is also found in Scyllium and Galeus, opens on the roof of the skull just in front of the 

 pre-orbital opening (Pr"). 



The palato-basal depressions (Figs. 3 and 4, Pol), the position of which has already 

 been indicated, are distinctly seen, one on each side of the inter-orbital septum. They have 

 a direction upwards and backwards, and a prominent ridge runs upwards from the 

 shoulders of the basilar plate and forms a hinder boundary for them. In. front of the 

 depressions there is a less pronounced ridge. 



Canal for the trigeminal and abducens nerves and the ophthalmic and buccal 

 branches of the facial. — This is a large canal, and its external orifice (Fig. 4, T/) is 

 situated at the back of the orbital cavity, considerably below the post-orbital process, 

 and its position in Lsemargus corresponds with that in Scymnus. The canal is short and 

 wide, and has a direction from within outwards and forwards. Its anterior wall is 

 less extensive than its posterior. 



Caned for the oculi-motor nerve. — This canal passes almost directly outward through 

 the cranial wall, and its outer opening (Fig. 4, Om') is placed a short distance in 



