538 CETACEA. 



ribs to the sternum having ever been separated, and the perfect sternum being quite 

 intact. It is significant that this sternum belongs to a skeleton with rib-like 

 processes attached to the superior process of the seventh cervical vertebra, and it 

 would thus appear that the presternum was involved in the same abnormality that 

 produced this imperfect rib. 



The first section of the mesosternum is about two-thirds of the length of the 

 presternum, is shortly oblong in form, and much dorso-ventrally compressed, with 

 concave but rounded lateral margins. It is perfectly flat internally, and very slightly 

 concave from side to side externally, but somewhat concave from before back- 

 wards. Its anterior and posterior extremities are rather deeply notched in the 

 middle Hne, the notch corresponding to the remains of a faint indication of the 

 original suture between the two portions of which it is composed. The right half is 

 considerably larger than the left. 



The second rib generally articulates between the presternum and first section of 

 the mesosternum, but in the youngest example before me, the attachment of the 

 second rib is behind the ossicle of the first segment of the mesosternum ; whereas 

 in the mother of this specimen it is in the normal position. The hinder angles of 

 the segment have each a hollow for the attachment of the third sternal rib. 

 The presternum and mesosternum are separated from each other in the young by a 

 considerable cartilaginous space, but they frequently unite even in adolescence. 

 The second segment of the mesosternum consists of two distinct ossicles separated 

 from each other and from the first section, in youth, by a wide cartilaginous inter- 

 val which afterwards disappears, the two ossicles becoming thoroughly amalgamat- 

 ed, and in adults they nearly equal the length of the first section. The fourth rib 

 is applied to the extremity of this ossicle. Only four ribs thus directly articulate 

 with the sternum as a whole. The xiphoid cartilage is rather large and Ungulate 

 in the young, but never presents any trace of ossification. 



Scapula (PL XLI, fig. 13). — This bone is fan-shaped and, as Cuvier re- 

 marks, " est beaucoup plus large qu'au dauphin." Its depth through its middle 

 (glenoid) is three-fifths of its greatest length. The postscapular fossa is absent, 

 the external surface being smooth and slightly convex. The suprascapular border 

 is long and forms nearly the half of an elongated oval, defining a nearly triangular 

 surface with the posterior border which is almost straight, the two meeting in a 

 point. The anterior margin is divided into two deep notches by the large acromion 

 which, in adults, developes a metacromial process directed upwards, the acromion 

 pointing reversely downwards. The capacity of the upper or supra-metacromial 

 notch is variable, even in the scapulae of the same individual, which is also the case 

 with the acromio-coracoid notch. The metacromial process is also variable in its 

 intensity in the same individual, but there is no trace of it in very young dol- 

 phins ; neither does the ossification of the coracoid show itself in early life. The 

 latter is a mere rudiment, being little more than a small pointed nodule rising about 

 half an inch above the glenoid articulation, which is more oval than round and 

 in this very different from Fontoporia. The outer surface is marked by a ridge run- 



