160 SKELETONS OF THE SEAL AND WALRUS. 



element ma}^ be, and often is, present, but short and fixed, 

 in both cervical, lumbar, sacral, and caudal vertebrae; in 

 some mammals, e. g. monotremes, the pleurapophysis may 

 remain unanchjlosed in some of the neck-vertebras, but 

 it is short, like a transverse process; and the so-called 

 "perforated transverse process" in all mammals consists 

 of the diapophysis, parapophysis, and pleurapophysis; 

 the hole being the interval between those parts; in the 

 lumbar vertebrae the pleurapophysis is short, and con- 

 fluent or connate with the diapophysis. 



Eeturning to the skeleton of the walrus, we find that 

 nine pairs of ribs directly join the sternum, which con- 

 sists of eight bones. The transverse processes of the last 

 cervical are imperforate, consisting of the diapophysis 

 only. The neural arches of the middle dorsal vertebrae 

 are without spines and very narrow, leaving wide unpro- 

 tected intervals of the neural canal. The bones of the 

 neck are modified to allow of great extent and freedom 

 of inflection. The perforated transverse processes of the 

 third to the sixth cervicals inclusive are remarkable for 

 the distinctness of their constituent parts. Inferior ridges 

 and tuberous processes, called " hypapophyses," are de- 

 veloped from some dorsal and lumbar vertebras. These 

 processes indicate the great development of the anterior 

 vertebral muscles, e.g. the "longi colli" and "psore," and 

 relate to the important share which the vertebrae and 

 muscles of the trunk take in the locomotion of the sea- 

 tribe, especially when on dry land, where they may be 

 called " gastropods," in respect of their peculiar mode of 

 progression. The walrus alone seems to have the power 

 of supporting itself on the fore fins, so as to raise the 

 belly from the ground. There is no trace of clavicle in 

 any seal. The upper part of the sca])ula exceeds the 



