456 DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 
inspiration takes place, the dilatatores narium act sharply and drag the alar fibro-carti- 
lages with a jerk outwards, producing a wide oval orifice to each nasal opening. ‘Then, as 
respiration becomes easier, the nares assume the appearance delineated in fig. 5, Pl. LIL. 
After a time, or when reentering the water, a quick sudden closure of the nostrils is 
effected by muscular action, when the alar fibro-cartilages and their appendices are 
thrown inwards and upwards, effectually obliterating the outer nasal openings, which 
are reduced, as depicted in fig. 4, an, Pl. LII., to two obtuse angular slits. Whilst the 
above is the more pronounced mode of action, yet, under quieter conditions, these steps 
of dilatation and closure occur more gradually, though the process is similar to what 
has been described. 
Finally, the mystacal bristles are characteristically affected by all motor changes of 
the muzzle. Usually they lie adpressed or overriding each other with an inward curve ; 
but under other circumstances, as in feeding, they move en masse, and form a natural 
screen or sieve, whilst the creature by a succession of sucks and gulps strains its soft 
molluscan food. Besides simultaneous movement of the bristles, due to the inherent 
force of the great naso-labial group of muscles, each bristle individually possesses a 
certain amount of special motor power by reason of a pencil of muscular fibres at its 
root. These fibrille are developments equivalent to the cutaneous muscles met with in 
the skin of Birds, Hedgehog, &c. In the Walrus (see fig. 27, m, Pl. LV.) they are 
interwoven with a plexiform arrangement of fleshy fibres which cross between and bind 
the roots of the bristles together; this matrix communicates deeply with the massive 
naso-labial group of muscles; and by a consentaneous action the movements above 
spoken of are produced. 
Essentially similar structures are found throughout the Carnivora, and extra deye- 
lopment of the structures passes by a gradation throughout the Seals to its maximum 
in the Morse. 
In the Eared Seals (Ofaria) there are virtually no recognizable inherent muscles of 
the pinna, though there are a few faint fibres which might be classed with these; but I 
am rather inclined to consider them homologues of the so-called auricular group of 
human anatomy. My reason for this opinion is founded on the fact that in the Walrus, 
though strictly speaking earless, there are three well-defined and, indeed, comparatively 
large, fleshy bundles, whose situation and origin partially agree with the auricular 
muscles. Professor Humphry’ has arrived at the same determination with regard to 
the fasciculi present in the Seal, where, however, an attollens and attrahens are very 
rudimentary indeed as compared with those of Trichechus. 
The first, attollens (atl, fig. 26, Pl. LV.), or superior auricular, is a long narrow band 
which arises upon the surface of the occipito-frontalis and temporal muscles, and, 
directed obliquely downwards and forwards, ends in a pointed manner on the upper 
1 Journ. of Anat. and Physiol. 2nd Ser. No. 2, May 1868, p. 296, “On the Myology of Orycteropus capensis 
and Phoca communis.” 
