536 CETACEA. 



but separated from each other by a groove, which can be detected in a similar 

 position as far back as the nineteenth caudal vertebra. 



The dorsal fin lies over the eighth lumbar and first caudal vertebrae, its apex 

 being between the spinous processes of these vertebrae. 



Ribs (Plate XLI, fig. 16) vary in number from ten to eleven. There are 

 one presternal and three mesosternal. The first two are thick and nearly cylin- 

 drical, whilst the third is slightly compressed from withotit inwards, a character 

 which becomes more intensified in the succeeding ribs, especially from the fourth 

 to the eighth, in which the shafts have considerable antero-posterior expansion, 

 though less marked in the remaining two. In the first, the part intervening 

 between the tubercle and angle is compressed from before backwards, but with 

 the tubercular portion much more strongly developed than in dolphins generally, 

 and the neck, instead of being merely a flattened prolongation of the shaft, is 

 narrow, compressed, and angular, with three surfaces, and diminishing in thick- 

 ness from the base of the tubercle to the head. The outer surface of the angle 

 is marked by a rough siu-face for muscular attachments. In the second rib, the 

 anterior becomes the external surface in the lower third, as the shaft is twisted 

 on itself, and the external surface between this and below the angle is almost ridge- 

 like, the posterior surface being round. From the angle to the head, the rib is 

 much antero-posteriorly compressed, and the outer aspect for an inch and a half 

 below the angle is produced outwards into a prominent curved muscular ridge 

 directed backwards and downwards, being continuous below with the rather sharp 

 external border of the rib, while above, it is jarolonged outwards and forwards 

 beyond the angle as a laminar triangular process. This ridge can be traced as far 

 back as the seventh rib, but gradually distally receding, its place in the eighth and 

 ninth ribs being taken by a flattened smooth sm^face on the posterior border, but it 

 re-appears in the ninth and tenth. The surfaces of the second rib are the same as in 

 the first. The neck is short, there being only 0-42 inch between the tubercular and 

 capitular surfaces. A well-marked process occurs on the lower border of the neck 

 immediately external to the head ; a rudiment of it may be detected in the first rib, 

 whereas it is strongly developed in the thnd, but almost lost in the f oiu'th rib. In the 

 third and succeeding ribs to the eighth, the shafts are externally flattened, but strong 

 and thick, the neck gradually diminishing in length till the tubercular portion and 

 head are merged in one in the sixth and following ribs. The angle is very well marked 

 in the third rib, as the triangular process is strongly developed, but in the following 

 ribs it forms a more and more obtuse angle with the shaft. The tenth has occasion- 

 ally a supplementary articular process on the posterior margin of the angle by 

 which it is in contact with the transverse process of the eleventh vertebra (PL XLI, 

 fig. 15) to which it is bound by strong ligamentary bands. An eleventh rib is occa- 

 sionally superadded, articulated to the eleventh and twelfth transverse process, and 

 sometimes applied to the rough surface on the posterior border or angle of the 

 tenth rib, which otherwise, so to speak, would have been itself applied to the 



