ORDER IV 



CETACEA 



81 



Succeeding the cervicals are 9-16 dorsal, 3-24 lumbar and 18-30 caudal 

 vertebrae. A sacrum is lacking. The upper arches and ossified epiphyses 

 of the trunk vertebrae are separated for a long time from the centrum and 

 are fused with the latter only in old age. The zygapophyses become more 

 or less vestigial. The diapophyses, on the other hand, are long and well 

 developed in the lumbar region. The ribs of Cetacea are distinguished from 

 those of other mammals by their loose union with the vertebral column 

 and sternum. The latter bone in baleen whales consists of a simple, broad, 

 shield-like piece, often concave anteriorly. In the Odontocetes there are two 

 to five bones, arranged in linear series. 



Fig. 109. 



Tursiops (Delphinus) tursio Fabr. sp. Atlantic Ocean. A, Superior aspect of skull. B, Lateral aspect of 

 the same. (After Cuvier) i/g. Pmx, Premaxilla ; Mx, maxilla ; ME, mesethmoid ; Na, nasals ; N, nares ; Fr, 

 frontal ; Pa, parietals ; Ju, zygomatic or jugal arch ; Sq, squamosal ; SO, supraoccipital ; co, condyle ; Exo, 

 exoccipital ; Md, mandible. 



The skull (Fig. 109) undergoes some very striking changes, due to the 

 mode of life, and consists of light, large -celled, thin bones. The brain- 

 cavity is remarkable on account of its extraordinary height, considerable 

 breadth, but extreme shortness. Since it becomes contracted above, the brain 

 has the shape of a foreshortened cone, with rounded contour. The very 

 strongly convoluted hemispheres of the cerebrum almost completely cover 

 the cerebellum. The olfactory lobes are either entirely lacking or only weakly 

 developed ; the nasal openings are destitute of turbinals and do not serve as 

 olfactory organs but entirely for breathing. With the exception of Zeiiglodon 

 the parietals do not meet in a sagittal suture, and are in contact in the medial 

 line only in the case of the baleen whales. But also among these the 

 extremely large supraoccipital overlies the parietals and interparietal and 



VOL. Ill G 



