30 COMPARATIVE ANATOMY. 



to the point of junction between the zygomatic, the maxil- 

 lary, and the post-frontal bones. Chevron bones are lateral 

 appendages to cervical vertebrae, and represent the transverse 

 processes of the corresponding bones in Mammalia. Bodies 

 of vertebra articulate by double concave, or ball-and-socket 

 joint. Bones without epiphyses, generally solid; hollow in 

 Dinosauria. Carapax and plastron portions of skeleton of 

 Chelonia are modified vertebral segments. Inferior maxil- 

 lary bone possesses five distinct centres dental, angular, 

 opercular, articular, and two smaller pieces seen upon the 

 inner surface. Bones of skull commonly united by perma- 

 nent suture, excepting in Ophidia and majority of Chelonia, 

 where they are early consolidated. 



Aves. Articulation of skull as in Reptilia. Articulations 

 of cervical vertebrae allowing free motion; but those of dor- 

 sal and lumbar vertebrae are immovable. Ribs also fixed; 

 conspicuous posterior processes. Sternum of a variety of 

 shapes, generally conspicuously keeled for origin of great 

 muscles of flight (pectorales). Size of coccyx determined by 

 that of tail feathers; long reptilian extension in Archceopteryx 

 bones generally hollow; air is admitted, during respira- 

 tion, into all skeletons as a rule, excepting terminal portions 

 of extremities. In Hirundo (swallow), and Trochilus (hum- 

 ming-bird), the bones are solid. Bones of skull unite by 

 early obliteration of sutures, excepting Sfruthio (ostrich). 



Mammalia. Articulation with spine, by two condyles 

 made up on either side by union between single basi-occipital 

 and the two ex-occipital bones. Intermaxillary bones unite 

 with superior maxillary in man, but remain separate in lower 

 mammals. Spheno-parietal suture tolerably constant in car- 

 nivorous, as temporo-frontal suture is in other types; num- 

 ber of cervical vertebrae seven, apparent exception in Brady- 

 pus (sloth) ; anterior tubercles of the transverse process of cervi- 

 cal vertebrae, and the transverse processes of the lumbar verte- 

 brae, rudimentary ribs (pleurapophyses). Exo-skeleton (?) in 

 Edentata. Inferior maxillary bone probably composed of 

 the number of centres seen in lower animals. Often com- 

 posed of two halves connected by cartilage at symphysis 



