494 



ANATOMY OF VERTEBEATES. 



abnormal. Where the trunk is lithe and subject to varied and 

 agile turns and bends, the number of pairs of free elongate pleur- 

 apophyses is small, and that of the vertebrae wanting them great; 

 thus the springing Cats, the swift-footed Dogs and Foxes, the 

 climbing Benturong, have 13 dorsal and 7 lumbar: the Viverrines 

 and Mustelines commonly show 14 dorsal and 6 lumbar; the 

 stifFer-trunked Hyaenas, Bears, and Seals have 15 dorsals and 

 5 lumbar : and mostly, where an exceptional excess occurs in any 

 of these groups in one series of vertebra3, it is balanced by as 

 exceptional a deficiency in the other series. 



B. Skull. — In the Harp Seal (^Phoca groenlandicd) the basi- 

 occipital is a thin plate, and shows a vacuity in front of the 

 foramen magnum : it early coalesces with the basisphenoid : the 

 paroccipital is small, subretroverted : the mastoid large, swollen, 

 not prominent. The frontal, fig. 338, ii, gives its larger proportion 

 to the orbital and olfactory chambers. In the latter the confluent 

 prefrontals and vomer form an extensive bony septum between 

 the meatuses which are blocked up anteriorly by the complex 

 turblnals. Both the tentorium and posterior part of the falx are 

 ossified. The shallow ' sella ' has overhanging posterior clinoid 

 processes. The petrosal is perforated by the entocarotid and 

 impressed by a deep transverse cerebellar fossa. The tympanic 

 forms a ' bulla.' The meatal portion of the tympanic is slightly 

 bent and directs the external auditory aperture obliquely forward 

 and upward. The squamosal has a small cranial plate, g, and a 



large thick zygomatic pro- 

 cess, 27, with rises at its 

 junction with the malar, 26, 

 to partially define the orbit 

 posteriorly. 



The seals, like other car- 

 nivora, have the orbit, e, 

 incomplete behind, and con- 

 tinuous with a large tem- 

 poral fossa ; the nasals, 15, 

 are short, and the nostril looks more or less upward, in refer- 

 ence to their common sojourn in water and the necessity of 

 rising to the surface to breathe. The condyle is the hindmost 

 part of the mandible. 



In the Grey Seal {Halichoerus griseus) the skull is remarkable 

 for the straightness of its upper contour and the sudden bending 

 down of the equally straight line formed by the deej:) and narrow 

 premaxillaries. There is a deep depression in the superoccipital. 



838 



Skull of a Seal {Plioca). 



