XIII 



PHYLUM CHORDATA 



501 



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

 (Mystaceti) sometimes not (Odontoceti). The lower jaw is remark- 

 able for the absence of an ascending ramus. 



The scapula in most of Cetacea is very broad and flat, expanded 

 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. 

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



Fio. 1081. Skull of Dolphin (Globiocepluilus), sagittal section, an. external nares ; 6/j. 

 basi-hyal ; BO. basi-occipital ; BS. basi-sphenoid ; cd. condyle of mandible ; cp. coronoid 

 process ; EO. ex-occipital ; Fr. frontal ; IP. inter-parietal ; ME. mesethmoid ; MX. maxilla : 

 Na. nasal ; Pa. parietal ; Per. periotic ; PL palatine ; P. MX. pre-maxilla ; pn. posterior nares ; 

 PS. presphenoid ; Pt. pterygoid ; sh. stylo-hyal ; SO. supra-occipital ; Sq. squamosal ; 

 th. thyro-hyal ; Vo. vomer. (After Flower.) 



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 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 is deposited. In the 

 toothed Whales the carpal bones are completely ossified, and are of 

 polygonal form : the phalanges are also ossified, with incomplete 



