3g8 H. B. POLt.ARD, 



this animal with the Selachii and with the Urodela it has seemed well 

 to commence with the muscular system. From the accounts of pre- 

 vious writers — L. Agassiz, J. Mülleu, Traquaiu and van Wijiie — 

 the osteology is sufficiently well - known to justify this course while 

 the muscular system, not hitherto treated, shows more clearly than 

 any other the connection between the Selachii, whose myology has 

 been so well described by Vetter, on the one hand and the Urodela 

 on the other. 



At the end of each section of this paper will be found a sum- 

 mary which will, I trust, make manifest the bearing of the observations 

 preceding. 



Muscular System. 



Constrictor arcuum visceralium (oberiiächliche 

 Ringmusculatur). 

 Belonging to this system may be distinguished: 



Levator maxillae superioris and protractor hyomandibularis. 

 Retractor hyomandibularis and opercularis with a small muscle 



at the angle of the jaw. 

 Intermaxillaris anterior. 

 Intermaxillaris posterior with mantle muscle. 

 Interarcuales ventrales. 

 Levatores arcuum. 

 On removing the preoperculum and the spiracular ossicles the 

 Protractor hyomandibularis and Levator maxillae superioris are imme- 

 diately seen (fig. 2). The former takes its origin from the postfrontal, 

 that is the fused sphenotic and dermal postfrontal. It runs backwards 

 and almost horizontally, and is inserted on the hyomandibular and 

 operculum where the two articulate. At about the middle of its course 

 a slip of muscle passes upwards and is inserted on the spiracular 

 ossicles which thus, as stated by Johannes Miiller, can be closed 

 at will. 



The Levator maxillae superioris almost forms a continuous sheet 

 with the Protr. hyom. It arises from the sphenotic and passes down- 

 wards and backwards spreading out in the form of a fan. Its attach- 

 ment is to the upper edge of the (dermal) metapterygoid though some 

 of its most anterior fibres pass on to the true quadrate and also a 

 tendon passes to the angle of the hyomandibular. 



Hy the contraction of these two muscles the operculum is pulled 

 outwards and the gill cavity expanded, the angle of the jaw is raised 



