522 



Vertebrata. 



tinguishable : tlie entire vertebral column, with the exception of 

 the cervical region, is very flexible, the intervertebral discs thick. 

 The jaws are much elongated; the jugal in the Odontoceti is very- 

 thin ; the nasal very short, often rudimentary (best developed in 

 the Mystacoceti) . The scapula without a spine; clavicles absent. 

 As was mentioned above, the bones of the fore limb are immovably 

 connected ; there are four or five fingers ; it is interesting to note 

 that soine of these have more than three joints. There is 

 a vestigial pelvis in the form of two bones, one on each side, which 

 are neither connected with each other nor with the vertebral column : 

 in some of the Mystacoceti rudiments of the hind limb, the femur 

 and tibia, are also present, but embedded in the muscle. Lachrymal 

 glands and ducts are absent, but the Harderian gland is present, 

 and, indeed, well developed, the secretion having a fatty consistency. 

 The nasal cavities are a pair of tubes, oblique in the Mysta- 

 coceti, almost perpendicular in the Odontoceti; in the Mystacoceti, 

 rudimentary turbinals and small olfactory nerves are present ; in the 

 Odontoceti the turbinals are wanting, whilst olfactory nerves may or 

 may not be present. In the Odontoceti the teeth are usually very 

 numerous, generally homodont and conical ; there is no replacement. 

 The Mystacoceti have teeth in the embryonic condition (similar in 

 form to those of the Odontoceti), but they are small and are never 



out. The baleen or 

 whalebone in the 

 mouths of these Whales, 

 consists of two longi- 

 tudinal rows of strong 

 transverse folds of skiu 

 depending perpendi- 

 cularly from the palate, 

 and covered with a well- 

 developed horny layer 

 which constitutes the 

 chief mass. The whale- 

 bone, therefore, is a 

 stiff three-cornered plate 

 of horn, which is, for the 

 most part, solid, but 

 has a cavity at the base, 

 wherein is the soft part, 

 consisting of connective 

 tissue and mucous mem- 

 brane. The whalebone 

 has three edges : a shorter, dorsal one, connected with the palate ; 

 an outer, smooth, straight one ; and an inner, oblique edge, which 

 is the longest of the three, and much frayed out; in the inner 



Fig. 419. Diagrammatic tramsyerse section of the 

 anterior portion of the head of a Balaenopterid. 

 b cartilage, corresponding to the nasal septum of other 

 Mammalia ; ia whalebone, / grooves of the skin, i pre- 

 maxilla, m maxiUa, tu tongue, u mandible, v vomer. — 

 After Yves Delage. 



