fi76 



PROF. G. B. HOWES ON THE PECTORAL 



[Dec. 2, 



(also synovial) upon the excavated anterior border of the meso- 

 pterygium (ms.). 



The posterior plate {np.) is, for the most part, in well-defined 

 articulation, by means of an efficient synovial capsule, with the 

 postero-lateral moiety (" glenoid commissure " of Parker ') of the 



ms. 



Fiff. 3. 



Fig. 1. Horizontal section- through the left pectoral fin of Ptcroplatca hl- 



ruiido, (^ . 

 Pig. 2. A similar section of the corresponding fin of a second specimen (alsoc? ), 



older than fig. 1. 

 Fig. 3. A similar section of the corresponding fin of a Myliobatis aquila. 



All natural size. 



Eeferences. — g.s., shoulder-girdle ; /as., mesopterygium ; int., nietapterygium ; 



wjJ., neopterjgium ; 2}p- i^rojiterygium. 



The black areas denote synovial cavities. 



^ Eay Soc. Monograph on Sboulder-girdle and Sternum, p. 8. 



■■^ I have found from experience that sections, such as those here figured, give 

 more satisfactory results than do mere macerated preparations. In the 

 latter, as in ordinary dio.sections, the presence of occasional superficial 

 furrows, at the points of fusion of rajs or segments or of the disposition of 

 nerves, tendons, &c., and the appearances produced by the remains or cut edges 

 of inter-muscular septa, are apt to be seriously misleading. 



Haswell speaks (Proc. Linn. Soc. N. S. W. vol. ix. part. i. p. 35) of the 

 proptei-ygium of Trygon jMstinaca as having in articulation with its distal 

 extremity " a stout ray with which are connected a number of fin-rays." 

 Gegenbaur makes no mention of this, and, as I have looked for it carefully, but 

 in vain, in the five individuals of the species which I have dissected, I think it 

 pi'obable that Haswell may have been misled in the manner indicated, or that his 

 " stout ray " was but a fusion of rays such as may occur at any point in any fin. 



