EEPOET ON THE SPHENISCID^. 11 



junction with the cerato-branchial elements, present a cartilaginous portion which is 

 never completely ossified. 



The Vertebral Column. 



The vertebral column of the adult Eudyptes cJirysocome from Tristan d'Acunha, 

 consists of forty-two vertebrae, of which thirteen are cervical, nine dorsal, twelve lumbo- 

 sacral, and eight coccygeal. 



Cervical Vertebrce} 



The cervical vertebrae, as defined below, are thirteen in number in every species of 

 Penguin which I have examined. 



The atlas presents the form characteristic of birds in general, and consists of a simple 

 bony ring which is divided into two segments, a dorsal and a ventral, by means of a 

 transverse bar of bone. In the Penguins the transverse ligament is converted into an 

 osseous bar which intervenes between the neural and articular portions of the bone. The 

 cup-shaped cavity for the reception of the occipital condyle is perforated, the perforation 

 being filled up by the apex of the odontoid process of the axis, which thus enters into the 

 formation of the articulation between the occipital bone and the atlas. The dorsal arch 

 of the atlas is quite complete, and is destitute of a spinous process. Its extremities are 

 prolonged backwards in the form of two small osseous cornua. 



The odontoid process of the axis resembles that of birds in general. 



The bodies of the other cervical vertebrae in Eudyptes chrysocome from Tristan 

 d'Acunha, have the usual form, their extremities being provided with the saddle-shaped 

 articular surfaces met with in other birds. The lower surfaces of the second, third, tenth, 

 eleventh, and twelfth cervical vertebrae are provided with well-developed hypapophyses. 

 These processes are absent in the other cervical vertebrae, with the exception of the 

 thirteenth, in which, however, the hypapophysis is reduced to a mere nodular I'udiment. 

 In the case of the second and third vertebrae, the hypapophyses present the form of sharp 

 bony spines, while in the tenth, eleventh, and twelfth they are broad and laterally com- 

 pressed plates of bone. 



The lower (ventral) surfaces of the bodies of the cervical vertebrae are longitudinally 

 grooved for the accommodation of the two carotid arteries. These are not, however, 

 contained in a complete bony canal as in many birds, inasmuch as the bony nodules of 

 opposite sides which arise from the cervical ribs, do not unite with one another across 

 the middle line in the Penguins. 



The carotid arteries come into contact with the vertebral column at the ninth, and 



1 Under the term " cervical " I include those vertebrs, and those only, which, lying pre-axiad of the thorax, are 

 destitute of moveable ribs. Adopting Huxley's definition (" Anatomy of Vertebrates," p. 277), the cervical segment of the 

 column includes two additional vertebrae, which, however, I regard as appertaining to the dorsal series along with 

 which they will be described. 



