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MB. E. PHELPS ALLIS, JUjSV, ON 



subdermal fascia. The posterior upp§r labial lies internal and 

 aboral to the anterior one and is closely attached to the musculus 

 levator labii superioris, the tendon of that muscle passing ventral 

 to the ligament related to the anterior labial and having its 

 insertion on the ventro-lateral antorbital process. 



In a specimen that I have of Mustelus, probably vulgaris, there 

 are two upper labials, and they are strikingly similar to those 

 shown by Gegenbaur in a figure (1872, fig. 3, pi. 11) said, in the 

 explanations of the plates, to be of Mustelus, but referred to in 

 the text as of Galeus. In this figure the jaws are furnished with 

 sharp pointed teeth; and Marshall and Spencer (1881) and 

 Hide wood (1895) have each independently called attention to 

 the fact that, because of these teeth, the figure is probably 

 of Galeus, as it is said by Gegenbaur to be in his text. But, 

 curiously enough, in this figure with sharp teeth, and hence 

 probably of Galeus, there are two upper labials similar to those 

 1 find in my specimen of Mustelus, identified by the presence of 

 pavement teeth, .while in the figure said by Gegenbaur (I. c. 

 fig. 2, pi. 12) to be of Galeus, but furnished with pavement 

 teeth and hence probably of JShi&telus, there is but one labial. 

 Gegenbaur furthermore says (/. c. p. 214) that both Meckel and 

 J. Miiller also found but one upper labial in Mustelus ; but 

 K. Fiirbringer (1903) has since found two of them in Mustelus 

 equestris. If these labials do not vary in different specimens 

 or species of Mustelus, it is thus probable that Gegenbaur, in 

 his figures above referred to, interchanged either the labials 

 or the teeth, as well as the names, of the two fishes. 



But, whatever the error in these two figures of Gegenbaur's 

 may be, in my specimen, which has pavement teeth, there are 

 two upper labial cartilages, and they both lie in the maxillary 

 portion of the labial fold. The anterior labial is about twice as 

 long and much stouter than the posterior one, and lies external 

 and oral to it, as does the anterior labial in Chlamycloselachus . 

 Its hind end lies but slightly anterior to the hind end of the 

 posterior upper labial and is attached to that labial, but not 

 to the mandibular one, by ligamentous tissues. The anterior 

 half, approximately, of the anterior labial lies internal to the 

 ventral edge of the musculus levator labii superioris, in a pocket 

 formed in the tough connective tissues that cover the external 

 surface of the palatoquaclrate. The labial is freely movable 

 in this pocket, and its anterior end lies directly upon the palato- 

 quadrate, in a scarcely perceptible depression in that cartilage, 

 but is in no way attached either to it or to the chondrocranium. 

 The walls of the pocket are differentiations of a dermal or 

 subdermal fascia which is somewhat ligamentous in character, 

 and which extends antero-mesially and is attached to the 

 posterior surface of the nasal capsule ; this fascia doubtless 

 representing the one from which the ligament attached to this 

 labial in Chlamydoselachus is developed. 



The posterior upper labial of Mustelus is bound by ligamentous 



