44 



elongated bone joined on to the lower end of the post-temporal, a clavicle, 27, which curves 

 forwards, and is shaped like a trough the cavity of which is posterior, the trough being 

 V-shaped in section. The clavicle is connected at its lower end, in the median ventral 

 line, with its fellow of the opposite side. 



The pectoral fin is supported by a flat basal plate attaclied within the upper part of 

 the trough of the clavicle ; this plate consists of two bones united by cartilage ; the 

 upper of these, 29, is the scapula ; the lower, 30, the coracoid. The pectoral fin-rays 

 are articulated to the posterior cartilaginous edge of this basal plate directly as the 

 caudal fin-rays to the fan-shaped terminal bone of the vertebral column. 



The pehic fin is similarly supported by a triangular single bone, 31, which is attached 

 to the lower end of the clavicle. It is usually called the pubic bone, thougli it is 

 probably homologous, not with any part of the pelvic arch of Elasmobranchs, but 

 with the basal cartilages of the pelvic fin in those forms. 



A flat bone in the median plane extends forwards from the junction of the clavicles 

 to the lower edge of the first basi-branchial. This bone, marked 28 in Fig. 3, has been 

 called the urohyal by Huxley, basi-branchiostegal by Parker, but has really nothing 

 to do either with the hyoid arch or the branchiostegal membrane ; it is better to call 

 it simply the iwjuhir bone. Posteriorly it sends off a pointed ventral process, while 

 the anterior three-fourths of it form a band of uniform width. 



