138 PROCEEDINGS OF THE NATIONAL MUSEUM vol. T:? 



and general form of the manus ; in hypaxial and sacrospinal muscu- 

 lature, the latter being largely instrumental in causing differences in 

 the processes of the vertebrae and in the conformation of the ilium ; 

 in the diversification of the hip muscles of Zaloph/m and their tend- 

 ency toward fusion in Phoca\ the astragalar extension in Phoca and 

 peculiarity of the flexor hallucis longus muscle; and of the flexi- 

 bility of the tarsal joint in Phoca. 



Differences which I consider might be attributed either to aquatic 

 adaptation of the two sorts shown, or to phylogenetic influences, con- 

 sist of the dissimilarities exhibited in the occipital musculature, 

 sternomastoid, cephalohumeral, humerotrapezius, rectus abdominis, 

 deltoid, the origin of the triceps longus and of adjoining muscles, the 

 presence of an episubcapularis in Zalophus only and of an abductor 

 digiti quinti longus in the Phoca only, the differences shown by the 

 humeral tuberosities, the palmaris longus, and the iliacus. 



Differences which may be laid chiefly to phylogenetic influences 

 rather than to aquatic adaptation consist of many of the details of 

 the skull, the presence of the complex division of the longus colli in 

 Zalophus only, and likely the absence in this genus of the quadratuc? 

 femoris, and of the presence in Zcdoplxfas only of the soleus. 



Resemblances of a quality which one might reasonably consider to 

 constitute evidence of close relationship comprise some features of 

 the triceps complex, similarity in the migration of attachments of 

 the brachial muscles, broadening of the antibrachial bones, resem- 

 blance shown by the deeper division of the biceps femoris, the occur- 

 rence of a hepatic venous sinus, and possibly of the details of tlie 

 tibial collateral ligament and plantaris tendon, and of the presence 

 of a superior division of the atlantoscapularis, although the latter 

 may likely be of little import. 



It has been mentioned that dissimilarities in the external car. 

 mode of swimming, and of terrestrial locomotion may be interpreted 

 as evidence that Phoca is the more highly adapted to aquatic life and 

 hence has diverged more from the fissiped type. In contrast to thi.s. 

 the thesis that Zalophus is the one that has traveled farther from the 

 typical terrestrial carnivore is supported by the greater tendency 

 toward " telescoping " of its skull, cartilagenous extensions of the 

 digits, the greater tendency toward flattening exhibited by the pedal 

 phalanges of this pinniped, and possibly by the development of the 

 nails. 



In scrutinizing the anatomical details encountered there occur 

 a number of questions which are not readily answered, as enumerated 

 below. To these the reader, if he be so minded, may add the query 

 as to why such arm muscles as the triceps and deltoid are so special- 

 ized or well developed in Phoca, This I am not including for the 

 reason that I am inclined to ascribe this condition to possible 



