426 



studying the relations of the pre-spiracular cartilage, not only in the 

 dogfish but in many other species of Selachians, my attention became 

 directed to other spiracular structures, such as the spiracular caeca 

 and the possible remnants of the lower portion of the hyoid cleft, and 

 a few remarks on these are subjoined. 



In. an original figure by Marshall i) of the skull of Scyllium 

 canicula, there is shown a ligament, described in the accompany- 

 ing text as follows: "the pre-spiracular ligament is a strong fibrous 

 band in which is a small nodule of cartilage, and which runs from 

 the anterior border of the auditory capsule to the distal end of the 

 hyomandibular cartilage, where it blends with the hgaments connecting 

 the hyomandibular cartilage with the upper and lower jaws, close to 

 the angle of the mouth." 



Many other instances might be given of modern books on zoology 

 containing similar statements and figures, but this will suffice for the 

 present criticism. 



Dissection of the head of the dogfish shows that the ligament 

 in question is situated behind the spiracle and has no connection 

 whatever with the pre-spiracular cartilage. Its upper end (see fig. 1 si.) 

 is inserted into the cartilage of the auditory capsule immediately above 

 the anterior extremity of the post-orbital groove, in which runs the 

 vein connecting the orbital and anterior cardinal blood sinuses. Its 

 lower extremity is inserted partly on the palatoquadrate cartilage at 

 its extreme posterior end, and partly on the outer surface of the lower 

 end of the hyomandibular. The hyoidean branch of the seventh nerve, 

 passing out backwards from the orbit, runs below the upper extremity 

 of the ligament, and below the anterior end of the post-orbital groove ; 

 it then curls round between the hinder edge of the ligament and the 

 hyomandibular cartilage, and passes down immediately below the skin, 

 behind the external aperture of the spiracle. 



Lying internal or ventral to the hyomandibular, there is a second 

 ligament (fig. 1 il), whose lower extremity is attached to the postero- 

 internal edge of the lower half of the hyomandibular, and partly also 

 to the upper end of the ceratohyal. Its whose upper end is firmly 

 bound to a lateral projection at the base of the skull, below and 

 behind the foramen for the fifth nerve. This ligament is also post- 

 spiracular in position, and is not shown in Marshall's figure. 



The ligaments binding the jaws of Elasmobranchs to the hyoman- 



1) Practical Zoology, Marshall and Huest, 4tb Ed. 1895, Fig. 45. 



