190 ALLEN: NEW ENGLAND WHALEBONE WHALES. 



corresponds to the tubercular articulation of other mammals, for the second articulation by 

 a stout rounded head between two neighboring segments of the spinal column is wholly lost. 

 Vestiges of this head or capitular portion appear in some of the anteriormost vertebrae (the 

 second and third in the Society's specimen) as short prolongations extending inward beyond 

 the tubercular surface of attachment. A second noteworthy peculiarity of the ribs is that 

 the first pair only are united to the sternum, and this union is ligamentous. The result of this 

 loose attachment is that the thoracic basket formed by the ribs must be capable of more or 

 less expansion, which is in correlation with the accordion-like plaiting of the throat. Possibly 

 this serves as an aid in expanding the cavernous bag of the great mouth so as to engulf as large 

 a quantity of water as may be, from which by closing the mouth and compressing the throat, 

 the food is strained out by the baleen. Possibly, also, an increased lung capacity is obtained 

 so that a longer stay under water may be made while the whale seeks its food. Yet, on the 

 other hand, the Sperm Whale which dives deeper and stays down for longer periods shows no 

 such adaptation, but has strong sternal ribs uniting the true ribs to the sternum. 



In the Finback, the anterior ribs are broadest, but increase in length and become nar- 

 rower and rounder in section. The sixth and seventh are the longest, and in the Society's 

 specimen (immature) are respectively 75 and 74.25 inches in length along the curve. 



The sternum is represented by the anterior segment only, the manubrium, for the seg- 

 ments which in most mammals follow this to form the breast bone, have quite disappeared 

 in the baleen whales. The outline of this bone in immature individuals is a trefoil, with two 

 broad anterior lobes and a narrow posterior part on either side of which come the first pair 

 of ribs. A deep median notch separates the two anterior wings and indicates the original 

 formation of the bone from two centers, one on each side. With age, the increasing ossifica- 

 tion usually closes this notch, though often leaving a small hole in the middle of the bone, 

 and the front end is developed into a median point, while at the same time the narrow poste- 

 rior portion is slightly lengthened, producing a somewhat cruciform bone. There is consid- 

 erable individual variation in the outline as well as variation due to age. Figures showing 

 the form of this bone in a number of specimens, are published by True (1904, pp. 140, 141, 

 figs. 8-31). 



The fore limb is developed in all whales, and its skeleton consists of the scapula, arm, 

 and hand bones as in other mammals, though these are much modified. The scapula is large, 

 fan-shaped, longer than high, with a broadly convex dorsal outline. This outline is not an 

 even curve, but is much flattened at the summit, and drops away suddenly at the posterior 

 third. The spinous process is low and feebly developed, and differs remarkably from its usual 

 condition among mammals in that it is very far forward, so as almost to coincide with the 

 anterior edge of the scapula. The acromion process given off at its base is large and projects 

 forward characteristically. The humerus is relatively very short and stout with large articular 



