XIII 



PHYLUM CHORDATA 



533 



long, narrow bones, bound but a very small part of the oral border 

 of the upper jaw. The nasals (Na.) are very small. The tym- 

 panic bone is very large, and is sometimes fused with the 

 periotic (Mystacoceti) sometimes not (Odontoceti). The lower 

 iaw is remarkable for the absence of an ascending ramus. 



The scapula in most of the Cetacea is very broad and flat, ex- 

 panded into the shape of an open fan. The spine is usually situated 

 close to the anterior border, sometimes coalescent with it. The 

 acromion is curved and flat, the coracoid also compressed and parallel 

 with the acromion. In some, both acromion and coracoid are absent. 



Fr 



FIG. 1150. Skull of Dolphin (Globiocephalue'), sagittal section, a. angle of mandible ; an. 

 external nares ; AS. alisphenoid ; bh. basihyal ; BO. basioccipital ; BS. basisphenoid ; cd. 

 condyle of mandible; cp. coronoid process; Ex.0, exoccipital ; Fr. frontal; IP. inter- 

 pariotal ; ME. mesethmoid ; MX. maxilla ; Na. nasal ; Pa. parietal ; Per. periotic ; PI. pala- 

 tine ; P. MX. premaxilla ; pn. posterior nares ; PS. presphenoid ; Pt. "pterygoid " ; sh. stylo- 

 hyal ; -SO. supraoccipital ; Sq. squamosal ; th. thyro-hyal ; Vo. vomer. (After Flower.) 



There is never any trace of a clavicle. The humerus is short and 

 very stout ; the head freely movable in the glenoid cavity ; the distal 

 articulating surfaces are flat and oblique, meeting at an angle. The 

 proximal ends of the radius and ulna are so firmly united with the 

 humerus as to allow of very little movement ; at the distal end 

 there are no synovial membranes. The manus is extremely modified. 

 There are no synovial joints ; the carpus is in some (Whale-bone 

 Whales) almost entirely cartilaginous, as also are the metacarpals 

 and phalanges the cartilages being coalescent or separated by 

 intervals of fibrous tissue : in some of the carpal elements bone 



