SUMMARY AND CONCLUSION. 



Before drawing this memoir to a close, it may be convenient that I shoukl briefly 

 summarise the leading peculiarities of the Penguins as compared with other birds, and 

 direct attention to the principal facts contained in the foregoing pages. 



From what has gone before it appears that the Spheniscidse constitute an exceedingly 

 well-defined group of birds, every member of which is characterised by the following 

 skeletal features. 



In respect of the axial skeleton, the cranium is truly schizognathous, and is chiefly 

 remarkable for the great development of the transverse temporal crest, which separates 

 the occipital from the temporal region of the skull. This crest, developed to some extent 

 in all the members of the group Spheniscidse, is more pronounced in certain genera 

 than in others, being more strongly marked in S])heniscus than in either Eudyptes or in 

 Aptenod)jtes, and more so in the former than in the latter genus. 



The vertebral column of every member of the group is characterised (a) by the 

 presence in the cervical region of well-developed sigmoidal curves, which are more 

 pronounced than in other birds, and are doubtless correlated with the peculiarly erect 

 attitude of the Penguins when on land ; (&) by the opisthoccelous character of the dorsal 

 vertebrae, a character which, judging from the frequency of its occurrence in the two 

 groups, is more truly reptilian than avian ; (c) by the mobility of the dorsal vertebrae 

 upon one another, and the absence, even in the adult, of that complete anchylosis between 

 the dorsal and lumbo-sacral vertebrae on the one hand, and of the latter with the pelvic 

 bones on the other, which obtains in the majority of birds. 



In respect of the appendicular skeleton, we find the bones of the wing in the Sphenis- 

 cidae modified in accordance with the alteration of function of that organ, and its 

 conversion from an instrument of aerial to one of aquatic progression. These modi- 

 fications are manifested in the enormous size of the scapula, which thus afi'ords attachment 

 to the powerful muscles of the shoulder joint, that is, to those muscles which act upon 

 the wing as a whole ; in the great strength of the coracoid bone, which in Spheniscus and 

 in Eudyptes is perforated by a foramen for the transmission of the nerve to the pectoralis 

 medius muscle ; in the lateral compression of all the bones of the wing, a character 

 which obtains among certain other diving birds, but which only reaches its maximum in 



(ZOOL. CHALL. EXP. — PART XVIII. — 1883.) S 30 



